TY - JOUR
AU - Purohit, Hemant J
AB - Abstract In view of the realization that fossil fuels reserves are limited, various options of generating energy are being explored. Biological methods for producing fuels such as ethanol, diesel, hydrogen (H2), methane, etc. have the potential to provide a sustainable energy system for the society. Biological H2 production appears to be the most promising as it is non-polluting and can be produced from water and biological wastes. The major limiting factors are low yields, lack of industrially robust organisms, and high cost of feed. Actually, H2 yields are lower than theoretically possible yields of 4 mol/mol of glucose because of the associated fermentation products such as lactic acid, propionic acid and ethanol. The efficiency of energy production can be improved by screening microbial diversity and easily fermentable feed materials. Biowastes can serve as feed for H2 production through a set of microbial consortia: (1) hydrolytic bacteria, (2) H2 producers (dark fermentative and photosynthetic). The efficiency of the bioconversion process may be enhanced further by the production of value added chemicals such as polydroxyalkanoate and anaerobic digestion. Discovery of enormous microbial diversity and sequencing of a wide range of organisms may enable us to realize genetic variability, identify organisms with natural ability to acquire and transmit genes. Such organisms can be exploited through genome shuffling for transgenic expression and efficient generation of clean fuel and other diverse biotechnological applications. JIMB 2008: BioEnergy-Special issue Introduction Environmental pollution, global warming, limited fossil fuel reserves, and ever increasing quantities of wastes are a set of issues on the top of organizational and societal agenda [55]. These issues have resulted in renewing our interest in the generation of cleaner energy. The presently available energy sources are thermonuclear energy, nuclear breeders, solar energy, wind energy, hydropower, geothermal energy, ocean currents, tides and waves [181]. Except for fossil fuels, all other forms of energy sources cannot be used directly as fuel. These must be converted to fuel form even for generating electricity [11, 181]. Parallel to these physical and chemical sources, there has been a growing interest in bioenergy: fuels from Fisher–Tropsch synthesis, bio-ethanol, fatty acid (m)ethyl esters, bio-methanol, acetic acid, bio-hydrogen (H2), and methane (CH4) [23, 29, 48]. The questions arise on the selection of raw materials and bio-fuels which may provide the necessary quantum of bioenergy for a sustainable society. In spite of 50 years of efforts world wide, the solution(s) seem to be far from achieved. Ethanol and CH4 produced through anaerobic digestion are among the best known microbial products and have been extensively studied [44]. Bio-ethanol can be produced from wheat, sugar-beet, corn, straw and wood [47]. Cellulose, the major raw material for bio-ethanol production is insoluble in most solvents and has a low accessibility to acid and enzymatic hydrolysis. Hemi-cellulose (pentose sugar) is largely soluble in alkali and more easily hydrolyzed. Sucrose and starch with the aid of invertase and amylase lead to ethanol production [33, 138]. Ligno-cellulose in spite of being the most abundant biological material however, is limited by the delignification step. Bio-diesel via trans-esterification of vegetable oil has over twice the price of petroleum diesel due to cost of feed stock. Most of the bio-diesel is produced from soybean oil, methanol and an alkaline catalyst. The high value of edible oils as food products is a major challenge to make bio-diesel production cost-effective. Alternatively, one may use beef tallow, pork lard, yellow grease [28] and restaurant waste as feed stock but the free fatty acids present in them cannot be converted to bio-diesel using an alkaline catalyst [16, 31]. The global scenario for bio-fuel reflects that a 5% displacement of gasoline requires about 5–8% of available cropland to produce ethanol whereas displacement of diesel to the same extent requires about 13–15% of the available cropland [60]. Displacement of available cropland for bio-ethanol and bio-diesel production may appear lucrative for producing bioenergy; however, this may turn out to be counterproductive especially from the point of view of developing nations, where food has obvious precedence over fuel. Search for efficient cellulases and use of non-edible oil for production of these bio-fuels is likely to make it economical and sustainable. Potential candidates which may compete as a fuel for the post fossil fuel era are synthetic gasoline, methanol, ethanol and H2. Electric energy can be used as an alternative as its extremely clean in end use and can be produced from all primary energy sources [46]. For selecting a fuel for the future, the following criteria must be considered: (a) transportation—fuel must be convenient to transport; (b) versatility—must convert with ease to other forms of energy at the user end; (c) utilization efficiency—must be high; (d) environmental compatibility—must not have adverse effect on environment; (e) safety—must be safe to use; (f) economics—must be inexpensive [181]. On comparing all the candidates—fuel oil, methanol, ethanol, H2 and CH4–H2 stands out as the best possible fuel [182]. The main driving force for investigating the production of H2 instead of CH4 is the higher economic value of H2, owing to its wider range of applications in the chemical industry [81]. Among the various unique characteristics are its maximum energy conversion possibilities for a given application. On combustion it gives water and a very small amount of NOx [11]. H2 has the best motivity factor of unity, has a maximum energy per unit weight (122 kJ/g) [181] and is easy to collect, store and transport [78, 181]. H2 has been suggested as a fuel which would eliminate most air pollution problems such as acid rain, health affects, property damage, etc. However, many complications still persist before H2 can be accepted. One of the reasons for the delayed acceptance of H2 has been the difficulty of production on a cost effective basis [55, 99]. Just like any other process or technology which is yet to be developed, evaluated and established on commercial scale, there are other associated drawbacks here as well. It is in the incipient stage and the struggle to produce it in large quantities overshadows our attempts and worries to devise mechanisms to develop a safe storage system. Efforts are however, being made in the areas of electrochemical power generation devices (fuel cells) with very promising developments [143]. We will leave these issues here itself and proceed on our journey of biological H2 production. Reviews have appeared virtually on all aspects of biological H2 production: photosynthetic and non-photosynthetic; H2 producing microbes; simple and complex organic matters including bio-wastes as feed; conditions affecting H2 production; alternative fuels such as bio-ethanol, bio-diesel, bio-oil etc. [1, 35, 47, 82, 83, 110, 125, 142, 148, 215]. A perusal reveals that individuals have dealt with the problem in their own way. There is thus a need to consolidate the solutions and take a holistic approach to: (1) identify and select (a) the microbes(s) with high H2 producing abilities from a range of substrates (pure sugars and complex organic matter); (b) the type of feed(s) which are easily biodegradable and available in large quantities (biological wastes or specially grown plants); (c) hydrolytic bacteria and their associates (enhancers and augmenters); (2) select physiological conditions promoting growth of H2-producers and suppressing H2-quenchers; (3) maintain the population of H2-producers optimal for H2-production and suppressing alternative metabolic routes (ethanol, lactic acid, etc.); (4) look for those microbes which can produce value added products without affecting H2-yields (such as polyhydroxybutyrate (PHB) production and industrially important enzymes, etc.). In light of this information, it may be desirable to develop consortia of microbes and feed for optimal and economically feasible H2 production. Since food is constantly required and waste is constantly produced, biowaste may be good feed material. The debate of non-photosynthetic versus photosynthetic H2 production [24, 99] seems to converge on a consensus of employing the two in a sequential or combined dark-photofermentation manner [72]. Sequential dark and photo-fermentation is rather a new approach in biological H2 production. A few attempts made in this direction support the view that higher H2 production yields can be obtained when two systems are combined [196, 199]. Further optimization of the system to provide optimum media composition and environmental conditions for the two microbial components of the process is necessary [41, 97, 196, 198, 199]. Hydrogen production H2 does not exist naturally in earth’s crust in uncombined state. There is a need to produce H2. It can be produced from fossil fuels and biomass [26] via coal gasification, steam reforming and partial oxidation of oil [8, 173]. Although the processes involve renewable sources and involve expensive techniques, these are still practiced due to the “abundant” availability of low cost coal from water (thermal and thermo-chemical processes) or electrolysis and photolysis. A significant portion of biomass sources like straw and wood is poorly degradable and cannot be converted to biofuels by microorganisms [49]. Biomass gasification is well established technique for H2 production whereas flash pyrolysis is still developing [30]. Biomass gasification is a form of pyrolysis, which takes place at high temperature and produce a mixture of gases containing 6–6.5% H2 [13, 116]. Thermo-chemical processes involve gasification followed by reforming of Syngas (H2 + CO) (CO: 28–36%; H2: 22–32%; CO2: 21–30%; CH4: 8–11%; C2H2: 2–4%) [115]; or fast pyrolysis followed by reforming of the carbohydrate fraction of bio-oil (CH4 + CO2) [27, 36]. Reformed gas through water–gas shift results in H2, which can be purified by pressure swing adsorption technique. The gasification of waste biomass to produce synthesis gas (or syngas) could offer a solution to this problem, as microorganisms that convert CO and H2 (the essential components of syngas) to multicarbon compounds are available [49]. Owing to the heavy utilization of fossil and non-fossil fuels and many problems involved, it is difficult to predict the fate of these H2 production processes [35]. The major drawbacks of the conventional methods are high temperatures of >850 °C [72] (i.e., high energy consumption per ton of H2 produced [160] and not always environmentally benign and/or fossil fuel processing [118, 127]) and difficulties in handling a relatively un-reactive fuel as a solid and in removing a large amount of ash. In addition, pure oxygen (O2) is consumed for the process [8]. The capital cost of other cell components in water electrolysis, are highly prohibitive (80% of the operating cost of H2 is due to electricity) [72]. Biological hydrogen production Researchers have been investigating H2 production with anaerobic bacteria since the 1980’s, but most of the relevant research used pure bacterial strains as biocatalysts [19]. Production of gases in the human intestine is well known. Evidences of explosive mixture of intestinal gases were reported during electro-surgery and during colonic polyplectomy [55]. Large amount of H2 is produced as a byproduct of colonic fermentation of dietary fiber and un-adsorbed carbohydrates [100, 144, 150]. Other evidences of H2 production from carbohydrates like fructans obtained from Jerusalem artichokes have been reported from human being [150]. Intake of foods like beans, raisins, bananas, fruit juices was found to increase H2 production [55]. Some chemotrophic H2 producing bacteria are symbionts on humans and animals. H2 producing microbes belonging to Enterobacteriaceae were isolated from sewage treatment plants [19, 109]. H2 evolution from lake sediments has also been observed [45]. Even the organisms living in deep sea vents where the sun never shines ultimately depend on the oxygen expelled by photosynthetic surface life and on the H2 given off by the fermentation of photosynthetically produced organic matter [210]. Physiology of hydrogen production Hydrogen metabolism is basically H2 ↔ 2H+ + 2e− [187]. Ionization of H2 results in H2 uptake whereas reverse reaction leads to H2 evolution. Ionization of H2 is perhaps more common and can be found in many biochemical pathways, where ionized H2 and electrons are carried through electron carries transport system (ETS) by NAD and various cytochromes, eventually combining the O2 to form water and H2. H2 ions are utilized by aerobic organisms to make adenosine triphosphates (ATPs) through ETS. H2 evolution per se does not confer any advantage to microbes. However, in the absence of an external e− acceptor (O2), where the supply of energy is limited, some anaerobes have adapted to use inorganic compounds such as sulfates and nitrates as their terminal oxidants. Hence, for the complete degradation of complex organic matter in nature, H2 serves as the terminal e− acceptor for sulphate reducers, nitrate reducers and methanogens [44, 45]. Thus H2 evolution is obligatory for some members of the microbial community. This natural phenomenon can be exploited for efficient biodegradation. In contrast, photosynthetic organisms, where the energy supply and reducing power can accumulate and be in excess in relation to the overall metabolic scheme, H2 evolution is strictly for the elimination of excess electrons. H2 is produced during microbial growth, through a set of complex biochemical reactions. Many enzymes are involved, which catalyze these reactions. Glucose is a key compound in microbial metabolism. Metabolism of glucose generates energy and intermediates like pyruvate. In general, for every mol of ATP (energy molecule) synthesized 1 mol of protons is formed and 1 mol of H2 is evolved as result of substrate dehydrogenation. Fermentative bacteria oxidize pyruvate and formate with the help of hydrogenase and formic dehydrogenlyase enzyme. Strict anaerobes have hydrogenase enzymes while facultative and heterotrophic anaerobes have complex soluble hydrogenase enzymes [169]. Photosynthetic bacteria which have the ability to fix atmospheric nitrogen (N2) have enzyme nitrogenase, which evolves H2 by an energy dependent process [209]. Whereas in aerobic N2 fixing bacteria the H2 evolved may be recycled by an enzymes uptake hydrogenase, which counteracts the inefficient use of energy in the N2 fixing process [170]. In particular, hydrogenases are widespread in prokaryotic and lower eukaryotic organisms, although they diverge in their protein structure and in the type of electron carrier they use (e.g. ferredoxins, rubredoxins and quinones etc.) [154]. Fermentation reactions can produce many different end products such as H2, acetate, ethanol and others. The H2–acetate couple produces more ATP per mol of substrate than alcohols such as ethanol and butanol and is energetically “preferred” bacterial fermentation product for a sugar [106]. Acetic acid production $$ {\text{C}}_{6} {\text{H}}_{{12}} {\text{O}}_{{\text{6}}} + {\text{2H}}_{{\text{2}}} \to 2{\text{CH}}_{3} {\text{COOH}} + 2{\text{CO}}_{2} + 4{\text{H}}_{2} $$ 1 Butyric acid production $$ {\text{C}}_{6} {\text{H}}_{{12}} {\text{O}}_{6} \to {\text{CH}}_{3} {\text{CH}}_{2} {\text{CH}}_{2} {\text{COOH}} + 2{\text{CO}}_{2} + 2{\text{H}}_{2} $$ 2 What does not favor H2 production? Lactic acid production, which may take place via three different pathways [44] Homofermentative pathway $$ {\text{C}}_{6} {\text{H}}_{{12}} {\text{O}}_{6} \to 2{\text{CH}}_{3} {\text{CHOHCOOH}} $$ 3 Heterofermentative pathway $$ {\text{C}}_{6} {\text{H}}_{{12}} {\text{O}}_{6} \to {\text{CH}}_{3} {\text{CHOHCOOH}} + {\text{CH}}_{3} {\text{CH}}_{2} {\text{OH}} + {\text{CO}}_{2} $$ 4 Bifidum pathway $$ 2{\text{C}}_{6} {\text{H}}_{{12}} {\text{O}}_{6} \to 2{\text{CH}}_{3} {\text{CHOHCOOH}} + 3{\text{CH}}_{3} {\text{COOH}} $$ 5 Ethanol production: [44] $$ {\text{C}}_{6} {\text{H}}_{{12}} {\text{O}}_{6} \to 2{\text{CH}}_{3} {\text{CH}}_{2} {\text{OH}} + 2{\text{CO}}_{2} $$ 6 Acetic acid production without H2 production: [23, 44] $$ {\text{C}}_{6} {\text{H}}_{{12}} {\text{O}}_{6} \to 3{\text{CH}}_{3} {\text{COOH}} $$ 7 Acetic acid production and H2 consumers: [23, 44] $$ 4{\text{H}}_{2} + 2{\text{CO}}_{2} \to {\text{CH}}_{3} {\text{COOH}} + 2{\text{H}}_{2} {\text{O}} $$ 8 Maximum H2 yield from fermentative H2 production is 4 mol/mol glucose (H2 productivity, HP: 33%), which can be achieved when only volatile fatty acids (VFAs) are produced and no microbial growth occurs [2]. When butyric acid is produced 2 mol H2/mol glucose (HP: 17%) is produced and when ethanol is produced zero mol H2/mol glucose (HP: 0%) is produced. H2 production from sewage sludge was most efficient when butyric acid production was predominant and propionic acid was a minor component of VFAs [19]. Higher propionic acid was a signal of inefficient H2 fermentation. Current H2 productivities are in the range of 10–20%, which is equivalent to 1.17 to 2.34 mol H2/mol glucose [2, 10, 107]. Under mesophilic conditions at a hydraulic retention time (HRT) of 4–6 h, butyric acid and acetic acid were high. At longer HRT, d-l-lactic acid accumulated and at 6 h of HRT, ethanol was produced. Under these conditions, propionic acid and isobutyric acid were not detected [44]. A continuous-flow stirred tank reactor (CSTR) at thermophilic conditions produced 5–10-fold higher H2 and lower biomass and ethanol [208]. Incidentally, in another study, H2-producing anaerobic sequencing batch reactor (ASBR) had a higher H2 production rate, compared with that produced using CSTRs. This study suggested that the H2-producing ASBR is a promising bio-system for prolonged and stable H2 production particularly if enriched H2-producing bacterial populations are achieved [22]. Biodiversity of hydrogen producing microbes and their associates In nature, microbial communities grow on a wide range of substrates. This co-operation results in a stable, self-regulatory and sustainable system that convert complex organic matter content into a wide range of intermediates, with the final production of CH4 and CO2 (Fig. 1). In fact, what is needed is a group of hydrolytic microbes, which will solublize the insoluble complex components (carbohydrates, fats and proteins) of the organic matter. Here we may also look for those microbes, which may act as stimulants or enhancers for the hydrolytic bacteria and consequently for H2 producers as well. These solublized intermediates then act as feed for H2 producers, which may be photosynthetic or non-photosynthetic and may operate singly or as consortia (of similar types) or as mixed cultures. Since H2 production alone cannot account for more than 33% of the energy present in the organic matter [2], we may also need to look for those organisms which may have the ability to utilize the partially digested feed for producing PHB and CH4. It will ensure better utility and complete degradation. Fig. 1 Open in new tabDownload slide Strategy for efficient degradation of biological wastes It will be necessary to evaluate the type of feed suitable for H2 production. Although a wide range of pure sugars, complex carbohydrates and biological waste have been employed as feed for microbial H2 production, the issue of the “best” source is still open. In fact, the process has some major limitations such as physiological conditions such as repression by nitrate, sulfate and fumarate [169], acetone [205], molecular nitrogen [90] and accumulation of H2 causes feed back inhibition [64] and high partial pressure of H2 inhibits microbial growth [95]. The phenomenon is more prominent when anaerobic degradation of organic compounds like ethanol, fatty acids, etc., is related to H2 evolution [169]. The presence of H2 quenchers is also an additional limitation. In nature, low partial pressure of H2 is maintained by the presence of H2 consumers. Such an association of H2-producers (Table 1) and H2-consumers (Table 2), also known as syntrophic association or inter species H2-transfer is observed in many ecosystems [204]. In such mixed populations, H2 is produced by Ruminococcus sp., Selenomonas ruminantium, Clostridium cellobioparum, Citrobacter freundii, Acetobacterium woodii, Trichomonas brockii and Syntrophomonas wolfei [169] (Table 1). Biodiversity of hydrogen producers Archaea Methanobacterium Methanococcus Methanosarcina Methylotrophs Pyrococcus Thermococcus Actinobacteria Mycobacterium Cyanobacteria Anabaena Aphanocapsa Calothrix Gloeobacter Gloeocapsa Halobacterium Lyngbya Mastidocladus Microcyctis Nostoc Oscillatoria Phormidium Spirulina Synechococcus Synechocystis Firmicutes Acetobacterium Bacillus Butyrivibrio Caldicellulosiruptor Clostridium Eubacterium Frankia Peptostreptococcus Ruminococcus Sarcina Selenomonas Streptococcus Thermobacteroides Veillonella Bacteroidetes/Chlorobi Acetomicrobium Bacteroides Chlorobium Pelodictyon Thermotogae Thermotoga Fusobacteria Fusobacterium Proteobacteria Alpha Azospirillum Rhizobium Rhodobacter Rhodomicrobium Rhodopseudomonas Rhodospirillum Proteobacteria Beta Alcaligenes Rubrivivax Proteobacteria Delta Desulfovibrio Syntrophobacter Proteobacteria Epsilon Campylobacter Proteobacteria Gamma Aeromonas Azomonas Azotobacter Chromatium Citrobacter Enterobacter Escherichia Hafnia Klebsiella Pseudomonas Salmonella Serratia Thiocapsa Thermotogales Thermotoga Eukarya Ciliophora Dasytricha Parabasalidea Trichomonas Viridiplantae, Chlorophyta Ankistrodesmus Chlamydomonas Chlorella Chrondrus Codium Corallina Kirchneriella Porphyridium Scenedesmus Archaea Methanobacterium Methanococcus Methanosarcina Methylotrophs Pyrococcus Thermococcus Actinobacteria Mycobacterium Cyanobacteria Anabaena Aphanocapsa Calothrix Gloeobacter Gloeocapsa Halobacterium Lyngbya Mastidocladus Microcyctis Nostoc Oscillatoria Phormidium Spirulina Synechococcus Synechocystis Firmicutes Acetobacterium Bacillus Butyrivibrio Caldicellulosiruptor Clostridium Eubacterium Frankia Peptostreptococcus Ruminococcus Sarcina Selenomonas Streptococcus Thermobacteroides Veillonella Bacteroidetes/Chlorobi Acetomicrobium Bacteroides Chlorobium Pelodictyon Thermotogae Thermotoga Fusobacteria Fusobacterium Proteobacteria Alpha Azospirillum Rhizobium Rhodobacter Rhodomicrobium Rhodopseudomonas Rhodospirillum Proteobacteria Beta Alcaligenes Rubrivivax Proteobacteria Delta Desulfovibrio Syntrophobacter Proteobacteria Epsilon Campylobacter Proteobacteria Gamma Aeromonas Azomonas Azotobacter Chromatium Citrobacter Enterobacter Escherichia Hafnia Klebsiella Pseudomonas Salmonella Serratia Thiocapsa Thermotogales Thermotoga Eukarya Ciliophora Dasytricha Parabasalidea Trichomonas Viridiplantae, Chlorophyta Ankistrodesmus Chlamydomonas Chlorella Chrondrus Codium Corallina Kirchneriella Porphyridium Scenedesmus [5, 17, 55, 72, 82, 83, 91, 148, 169, 188] Open in new tab Biodiversity of hydrogen producers Archaea Methanobacterium Methanococcus Methanosarcina Methylotrophs Pyrococcus Thermococcus Actinobacteria Mycobacterium Cyanobacteria Anabaena Aphanocapsa Calothrix Gloeobacter Gloeocapsa Halobacterium Lyngbya Mastidocladus Microcyctis Nostoc Oscillatoria Phormidium Spirulina Synechococcus Synechocystis Firmicutes Acetobacterium Bacillus Butyrivibrio Caldicellulosiruptor Clostridium Eubacterium Frankia Peptostreptococcus Ruminococcus Sarcina Selenomonas Streptococcus Thermobacteroides Veillonella Bacteroidetes/Chlorobi Acetomicrobium Bacteroides Chlorobium Pelodictyon Thermotogae Thermotoga Fusobacteria Fusobacterium Proteobacteria Alpha Azospirillum Rhizobium Rhodobacter Rhodomicrobium Rhodopseudomonas Rhodospirillum Proteobacteria Beta Alcaligenes Rubrivivax Proteobacteria Delta Desulfovibrio Syntrophobacter Proteobacteria Epsilon Campylobacter Proteobacteria Gamma Aeromonas Azomonas Azotobacter Chromatium Citrobacter Enterobacter Escherichia Hafnia Klebsiella Pseudomonas Salmonella Serratia Thiocapsa Thermotogales Thermotoga Eukarya Ciliophora Dasytricha Parabasalidea Trichomonas Viridiplantae, Chlorophyta Ankistrodesmus Chlamydomonas Chlorella Chrondrus Codium Corallina Kirchneriella Porphyridium Scenedesmus Archaea Methanobacterium Methanococcus Methanosarcina Methylotrophs Pyrococcus Thermococcus Actinobacteria Mycobacterium Cyanobacteria Anabaena Aphanocapsa Calothrix Gloeobacter Gloeocapsa Halobacterium Lyngbya Mastidocladus Microcyctis Nostoc Oscillatoria Phormidium Spirulina Synechococcus Synechocystis Firmicutes Acetobacterium Bacillus Butyrivibrio Caldicellulosiruptor Clostridium Eubacterium Frankia Peptostreptococcus Ruminococcus Sarcina Selenomonas Streptococcus Thermobacteroides Veillonella Bacteroidetes/Chlorobi Acetomicrobium Bacteroides Chlorobium Pelodictyon Thermotogae Thermotoga Fusobacteria Fusobacterium Proteobacteria Alpha Azospirillum Rhizobium Rhodobacter Rhodomicrobium Rhodopseudomonas Rhodospirillum Proteobacteria Beta Alcaligenes Rubrivivax Proteobacteria Delta Desulfovibrio Syntrophobacter Proteobacteria Epsilon Campylobacter Proteobacteria Gamma Aeromonas Azomonas Azotobacter Chromatium Citrobacter Enterobacter Escherichia Hafnia Klebsiella Pseudomonas Salmonella Serratia Thiocapsa Thermotogales Thermotoga Eukarya Ciliophora Dasytricha Parabasalidea Trichomonas Viridiplantae, Chlorophyta Ankistrodesmus Chlamydomonas Chlorella Chrondrus Codium Corallina Kirchneriella Porphyridium Scenedesmus [5, 17, 55, 72, 82, 83, 91, 148, 169, 188] Open in new tab Biodiversity of hydrogen metabolizers Archaea Archaeoglobus fulgidus Methanopyrus kandleri Methanothermus fervidus Pyrodictum brockii Aquificales Aquifex aeolicus Aquifex pyrophilus Calderobacterium hydrogenophilum Hydrogenobacter thermophilus Cyanobacteria Aphanothece halophytico Prochlorothrix hollandica Westiellopsis prolifica Firmicutes Rhodococcus opacus Streptomyces thermoautotrophicus Proteobacteria Alpha Acetobacter flavidum Bradyrhizobium japonicum Paracoccus denitrificans Proteobacteria Beta Acidovorax facilis Ralstonia eutrophus Rhodocyclus gelatinosus Thiobacillus plumbophilus Proteobacteria Delta Desulfomicrobium baculatus Proteobacteria Epsilon Helicobacter pylori Wolinella succinogenes Proteobacteria Gamma Pseudomonas carboxydovorans Eukarya, Ciliophora Nyctotherus ovalis Archaea Archaeoglobus fulgidus Methanopyrus kandleri Methanothermus fervidus Pyrodictum brockii Aquificales Aquifex aeolicus Aquifex pyrophilus Calderobacterium hydrogenophilum Hydrogenobacter thermophilus Cyanobacteria Aphanothece halophytico Prochlorothrix hollandica Westiellopsis prolifica Firmicutes Rhodococcus opacus Streptomyces thermoautotrophicus Proteobacteria Alpha Acetobacter flavidum Bradyrhizobium japonicum Paracoccus denitrificans Proteobacteria Beta Acidovorax facilis Ralstonia eutrophus Rhodocyclus gelatinosus Thiobacillus plumbophilus Proteobacteria Delta Desulfomicrobium baculatus Proteobacteria Epsilon Helicobacter pylori Wolinella succinogenes Proteobacteria Gamma Pseudomonas carboxydovorans Eukarya, Ciliophora Nyctotherus ovalis [82, 83, 148] Open in new tab Biodiversity of hydrogen metabolizers Archaea Archaeoglobus fulgidus Methanopyrus kandleri Methanothermus fervidus Pyrodictum brockii Aquificales Aquifex aeolicus Aquifex pyrophilus Calderobacterium hydrogenophilum Hydrogenobacter thermophilus Cyanobacteria Aphanothece halophytico Prochlorothrix hollandica Westiellopsis prolifica Firmicutes Rhodococcus opacus Streptomyces thermoautotrophicus Proteobacteria Alpha Acetobacter flavidum Bradyrhizobium japonicum Paracoccus denitrificans Proteobacteria Beta Acidovorax facilis Ralstonia eutrophus Rhodocyclus gelatinosus Thiobacillus plumbophilus Proteobacteria Delta Desulfomicrobium baculatus Proteobacteria Epsilon Helicobacter pylori Wolinella succinogenes Proteobacteria Gamma Pseudomonas carboxydovorans Eukarya, Ciliophora Nyctotherus ovalis Archaea Archaeoglobus fulgidus Methanopyrus kandleri Methanothermus fervidus Pyrodictum brockii Aquificales Aquifex aeolicus Aquifex pyrophilus Calderobacterium hydrogenophilum Hydrogenobacter thermophilus Cyanobacteria Aphanothece halophytico Prochlorothrix hollandica Westiellopsis prolifica Firmicutes Rhodococcus opacus Streptomyces thermoautotrophicus Proteobacteria Alpha Acetobacter flavidum Bradyrhizobium japonicum Paracoccus denitrificans Proteobacteria Beta Acidovorax facilis Ralstonia eutrophus Rhodocyclus gelatinosus Thiobacillus plumbophilus Proteobacteria Delta Desulfomicrobium baculatus Proteobacteria Epsilon Helicobacter pylori Wolinella succinogenes Proteobacteria Gamma Pseudomonas carboxydovorans Eukarya, Ciliophora Nyctotherus ovalis [82, 83, 148] Open in new tab Biological hydrogen producers Unicellular algae like Scenedesmus, Chlamydomonas and Chlorella are capable of liberating H2 in the presence of light. It involves the transfer of reductant from oxidative carbon metabolism through the photosynthetic ETS to release H2. The other mechanism involves the photo-oxidation of water and electron transport. Algae can also metabolise glucose for liberating H2 (Table 1). In photosynthetic bacteria, H2 evolution occurs when N2 gas is absent, ATP from phosphorylation and reductant from acetate, succinate, fumarate or malate oxidation are in excess. H2 evolution is achieved through oxidative decarboxylation of pyruvate via an adaptive H2-producing enzyme system [203]. Although extensive reviews of algae and photosynthetic microorganisms have been published, their usage for H2 production has been limited. The prerequisite for the use of the most plentiful resources—light and water, is the adaptation of the algae to an anaerobic atmosphere. Unfortunately, H2 production by this process is quite ineffective since the simultaneously produced O2 inhibits the hydrogenase enzymes involved in H2 production [191]. Possible photosynthetic organisms require solar collectors and engineering analysis has suggested that solar generators would be too costly [55]. Use of non-photosynthetic bacteria to produce H2 will eliminate the need for solar collectors. Chemotrophic H2 producers include several bacteria such as Ruminococcus albus, R. flavefaciens, S. ruminantium, Megasphaera elsdensii, etc. [188] (Table 1). Certain Trichomonades and other anaerobic protozoa are also known to produce H2 [148]. H2 production through dark fermentation has been observed in C. freundii [109], Enterobacter, Escherichia and Hafnia [72]. H2 evloution was associated with formate degradation through soluble hydrogenase in Bacteroides clostridiiformis, Eubacterium limosum, Fusobacterium necrophorum and R. flavefaciens and through non-soluble hydrogenase in the case of R. albus [55]. S. ruminantium grown with Methanobacillus omelianskii evolved H2 through reduced NADH formed during degradation of glucose, glycerol or lactate [55]. Another approach receiving attention involves a coupled system of halobacteria and marine cyanobacteria [134]. Strict anaerobes need reducing agents such as argon, nitrogen, hydrogen gas, l-cystine-HCl to remove trace amounts of oxygen present in the medium. This is an expensive way to tackle the problem of oxygen. Therefore, utilization of Enterobacter aerogenes along with Clostridium instead of expensive chemical reducing agents was suggested to be effective in H2 production by dark fermentation [197, 198]. Non-endospore forming H2-producers are enteric bacteria such as Enterobacter spp. [124] or/and Citrobacter sp. [129]. H2 production has been recorded at 3.9 mol/mol glucose by Enterobacter cloaceae DM11 [113], which is extremely high considering the enteric bacteria, which usually produce <1 mol H2/mol glucose [126]. E. cloaceae IIT BY08 produced 6 mol H2/mol sucrose, the highest among all carbon sources tested [91]. Although Clostridium spp. are among the most widely studied H2-producers and Bacillus the least studied [64, 84, 157], Bacillus may be a better choice as H2 producer (Discussed in later section). Clostridium saccharolyticus, a mesophile is among the best H2 producers with the potential to yield 3.0 l/l/h, which is equivalent to 121 mmol H2/(l × h) [99]. Bioaugmenters, inducers and stimulators The cost of a biomass-derived fuel depends critically on the yield of sugar conversion to the final products, in particular the pentose sugars (constituting 5–30% of the total carbohydrates) from hydrolysis of hemicellulose. It is for such reasons that much attention has been focused on the engineering of strains to use all sugars released from biomass hydrolysis [161]. Important plant polysaccharides such as cellulose, arabino-xylans, resistant starch, glucans (1,3–1,4-β glucans) components of plant cell walls and endosperm of cereals (barley, rye, sorghum, rice and wheat) constitute a significant proportion of biological wastes. Bacteria are known for hydrolyzing these bio-molecules by excreting (1) lichenases: Clostridium acetobutylicum; C. thermocellum, Bacillus spp., Bacillus macerens, B. circulans, B. brevis, R. flavefaciens; (2) lumiarinases: Rhodothermus marinus; C. thermocellum, Thermotoga neopolitana, T. maritima; (3) lichenin, 1,3-1,4-β glucan (β glucanases): Clostridium spp., Bacteriodes sp. [184]. Bacillus pumilus expresses a wide range of hydrolytic enzyme activities such as xylanase, amylase, phytase and pectinase. The multi-component enzymatic secretion by B. pumilus leads to extensive and rapid solublization, degradation and breakdown of complex ligno-cellulosic components present in wheat bran. It enhances availability and accessibility of tightly bound lignin complexes and phenolics like ferulic acid, veratric acid and nutrient N for laccase biosynthesis from Gonoderma sp. [156]. Lignocellulosic biomass has long been recognized as a potential sustainable source of mixed sugars for fermentation to biofuels and other biomaterials [52]. At present, purified hydrolytic enzymes are still too expensive and not as potent with real pretreated lignocellulosic feedstock. Nature’s most efficient systems to biodegrade lignocellulose are mixed cultures in insect and mammalian guts that have evolved with the host [3]. For the hydrolytic step, laccase has emerged as one of the most sought after enzymes and is being used successfully to delignify wood tissues [1, 157]. Lignin mineralization and solublization can help in the release of cellulose from ligno-cellulosic wastes reportedly available in large quantities [88] by Aneurinibacillus, Azotobacter, Bacillus sp., Bacillus megaterium, Paenibacillus sp., Serratia marcescens [18, 121, 135]. Sinorhizobium fredii [54] produces carboxymethyl cellulase (CM-cellulase EC 3.2.1.4) and polygalacturonase (pectinase EC 3.2.1.15) for cleaving glycosidic bonds in plant cell wall polymers. Another ezymatic activity at the solublization stage, which has gained importance, is a specific protease (keratinase) [131] because of the use of feathers as feed for H2 production [7]. Keratinolytic activity has been observed in Bacillus sp., B. licheniformis K-508, Streptomyces sp., Thermoactinomyces sp., Vibrio sp., [7, 112], Aspergillus sp., Alternaria radicina, Trichorus spiralis, Stachybotrys atra, Onygene spp., Absidia spp., Trichophyton mentegrophytes, T. rubrum, T. sallinae, [41]; Microsporum canis, M. gypseum [186], Streptomyces pectum, S. albus, S. thermoviolaceus, S. fradiae, Bacillus spp., Fervidobacterium pennovorans, B. licheniformis PWD-1 and Bacillus sp. FK46 [164]. The addition of metabolic analogues like amino-acids and their analogues and vitamins have been reported to stimulate the production of enzymes, DL- serine resulted in 3.8 fold increase in polygalacturonase production by Bacillus sp. [156]. Stimulation in pectinolytic enzyme synthesis by Sclerotinia sclerotiorum occurred by the addition of histidine, glutamate, alanine, asparagine, aspartate, glutamine, arginine and proline to the fermentation media [156]. Addition of DL-norleucine, L-leucine, DL-isoleucine; L-lysine monoHCl and DL-B-phenylalanine resulted in 2.78 fold increase in pectinase production by Streptomyces sp. [9]. Biotin, riboflavin and pyridoxine HCl induced laccase production from Cyathus bulleri [32]. Vitamins (pyridoxine HCl), L-ascorbic acid, thiamine HCl, nicotinic acid, riboflavin and biotin stimulated laccase production from Gonoderma sp. [156]. Microbial treatment systems for the degradation of organic matter need an optimal microbial community and property to enhance the desired output [120]. The importance of bioaugmentation in degradation processes by introducing microbes in the system can be illustrated by the following examples. The efficiency of the 2–4-DCP degrading mixed culture in an activated sludge was enhanced [139] by Comamonas testosterone, which had an ability to degrade 3-chloro-aniline [12]. Similarly, a resin acid-degrading bacterium, Zoogloea resiniphila HdhA-35 was exploited to counteract pH stress in an aerated lagoon treating pulp and paper mill effluent [202]. Inducers enhance enzyme activity either by expression of the major subtilisin type enzymes in feather degradation, which has been reported as feed for H2 producers [112], by surfactants known to stimulate bacterial enzyme production [146] or by myo-inositol as a carbon source induces CM-cellulase [54]. Hydrogen production from organic substrates Cellulose is a major component of carbon fixed by plants. Microbes with ability to degrade cellulose to H2 are of great importance e.g., C. cellbioparum, S. ruminantium, R. flavefaciens, etc. [101, 174, 188, 204]. Other H2 producers utilize hemicelluloses, starch, sucrose and other complex carbohydrates [40, 51, 103, 106, 178, 205]. All organic substrates are not directly degraded to H2 and involve some intermediates. Several other organic compounds [204, 205] including fatty acids [205] may be degraded by anaerobic microbes to produce H2. Facultative anaerobic bacterium Klebsiella pneumoniae and Azospirillum brazilense [5, 17] produce H2 during N2 assimilation, where hydrogenase and nitrogenase play important roles. Many chemotrophs produce H2 by using different carbohydrates [169, 204, 205]. H2 production from simple molecules like glucose [149, 203], xylose [51, 165], maltose [149] and lactose [84] follow pyruvate route. This metabolic pathway is followed in Clostridium spp. and several other anaerobes: T. brockii [205], Peptococcus anaerobium, E. limosum, M. elsdenii, Sarcina maxima, S. ventriculi, R. albus, Veillonella alcalescens, etc [169]. In addition to H2 producing bacteria, some protozoa also have the ability to oxidize pyruvate. Theoretically, the maximum H2 production (mol/mol of substrate) varies from 4.0 from glucose, potato starch and cellulose, 2.0 from lactate and 8.0 from sucrose. However, the reported conversion efficiencies of Clostridium intermedius varies up to 38% from glucose, while that of Clostridium butyricum varies up to 55% from sucrose and that of Clostridium sp. up to 59% from xylose [14, 74, 166]. Cellulose conversion efficiencies of 18% was observed under certain conditions [105]. Highest H2 yield obtained from glucose is around 2.0 to 2.4 mol/mol [39, 72, 122, 176]. Chen and Lin [21] reported 4.52 mol H2/mol sucrose and up to 6.0 mol H2/mol sucrose have been reported with E. cloaceae [91]. Hydrogen production from biowastes In addition to the pure organic substrates, biowastes rich in carbohydrates have also proved to be potential sources of H2. Fermentation of raw starch of corn, potato and cassava peel results in H2 generation [15]. On a very small scale, sugarcane, corn pulp and paper waste [149, 177], cheese whey [151, 153], lactic acid factory waste [168] and dairy waste water [180] have also been employed for H2 generation. H2 generation by mixed microbial cultures, pure Bacillus subtilis and B. licheniformis strains from damaged wheat grains [64, 158] and pea-shells [65] have also proved to be potential raw materials. H2 constituted 30–65% of the total biogas produced, which is equivalent to 50 to 80 L H2/ kg total solids. H2 production at the rate of 555 ml/g starch waste is among the highest production observed with sugar factory waste water, bean curd manufacturing waste, food waste and sucrose rich waste water (Table 3). Certain microbes such as Rhodobacter sphaeroides have been successfully used in production of H2 from fruit and vegetables waste [87, 117] and have also been tested on sewage with positive results [19, 98, 189]. The efficiency of H2 production varies with the type of waste employed as feed. The process is currently still at the laboratory stage, and work needs to be done on increasing cost efficiency and application. H2 from biomass has the potential to compete with H2 produced by other methods such as from natural gas, which includes catalytic conversion of hydrocarbons, electrochemical or photochemical water splitting [1]. In fact, H2 generation from sweet sorghum, wheat grains, pea-shells followed by anaerobic digestion of the remaining biomass [4, 65, 158] is a step towards enhancing the efficiency of biological H2 production. Microbial conversion of biological wastes in to hydrogen Substrate . H2 yield (ml/g substrate) . References . Bean curd manufacturing waste, food waste, sucrose rich waste water, sugar factory waste water, starchy waste 300–555 [57, 58, 72, 101, 104, 119] Noodle manufacturing waste water, potato starch, pulped sugar beet, rice winery waste water, wheat bran 200–300 [58, 101] Cabbage, carbohydrate rich high solid organic waste, carrot, chicken skin, dairy wastewater, egg, fat, filtered leachate of waste bio-solids, fruit and vegetable waste, keratin waste, lean meat, molasses, municipal waste, rice bran, sewage, sweet sorghum, wheat grains, wheat starch <200 [4, 7, 19, 41, 57, 64, 66, 72, 87, 98, 117, 158, 180, 189, 206] Substrate . H2 yield (ml/g substrate) . References . Bean curd manufacturing waste, food waste, sucrose rich waste water, sugar factory waste water, starchy waste 300–555 [57, 58, 72, 101, 104, 119] Noodle manufacturing waste water, potato starch, pulped sugar beet, rice winery waste water, wheat bran 200–300 [58, 101] Cabbage, carbohydrate rich high solid organic waste, carrot, chicken skin, dairy wastewater, egg, fat, filtered leachate of waste bio-solids, fruit and vegetable waste, keratin waste, lean meat, molasses, municipal waste, rice bran, sewage, sweet sorghum, wheat grains, wheat starch <200 [4, 7, 19, 41, 57, 64, 66, 72, 87, 98, 117, 158, 180, 189, 206] Open in new tab Microbial conversion of biological wastes in to hydrogen Substrate . H2 yield (ml/g substrate) . References . Bean curd manufacturing waste, food waste, sucrose rich waste water, sugar factory waste water, starchy waste 300–555 [57, 58, 72, 101, 104, 119] Noodle manufacturing waste water, potato starch, pulped sugar beet, rice winery waste water, wheat bran 200–300 [58, 101] Cabbage, carbohydrate rich high solid organic waste, carrot, chicken skin, dairy wastewater, egg, fat, filtered leachate of waste bio-solids, fruit and vegetable waste, keratin waste, lean meat, molasses, municipal waste, rice bran, sewage, sweet sorghum, wheat grains, wheat starch <200 [4, 7, 19, 41, 57, 64, 66, 72, 87, 98, 117, 158, 180, 189, 206] Substrate . H2 yield (ml/g substrate) . References . Bean curd manufacturing waste, food waste, sucrose rich waste water, sugar factory waste water, starchy waste 300–555 [57, 58, 72, 101, 104, 119] Noodle manufacturing waste water, potato starch, pulped sugar beet, rice winery waste water, wheat bran 200–300 [58, 101] Cabbage, carbohydrate rich high solid organic waste, carrot, chicken skin, dairy wastewater, egg, fat, filtered leachate of waste bio-solids, fruit and vegetable waste, keratin waste, lean meat, molasses, municipal waste, rice bran, sewage, sweet sorghum, wheat grains, wheat starch <200 [4, 7, 19, 41, 57, 64, 66, 72, 87, 98, 117, 158, 180, 189, 206] Open in new tab Conditions affecting biological hydrogen production Critical factors in biological H2 production are organic concentration, pH, nutrients, partial pressure of H2, stirring, H2 quenchers (Table 2), etc. [77, 128, 130, 160]. Among the various culture conditions which influence H2 production are: pH, temperature, feed concentration, bacterial population, retention period, etc. [24, 84, 99, 102, 118]. Maximum H2 production occurs over a pH range of 5.5 to 6.5. One of the most important factors influencing biological H2 production is temperature. However, mesophilic range of 30–37 °C continues to be optimal for this process [84]. A few attempts of H2 production in the thermophilic range have also been reported [192]. At high carbohydrate concentration, a metabolic shift occurs from H2 to alcohols [119, 130]. The impact of organic loading rate on H2 yield varies. An improvement in H2 yield was observed at lower organic loading rates of sucrose, glucose and rice winery waste water. On the other hand, similar improvement was also recorded at higher organic loading rates of sucrose, glucose and citric acid waste waters [86]. Sparging the bioreactor with N2 has been reported to increase H2 yield [57, 58, 79, 118]. Currently the reasons for increased H2 production during sparging are not very clear. Sparging was assumed to decrease the dissolved H2 concentration to alter the activity of H2 production enzymes [85]. Pyruvate : Ferredoxin oxido-reductase (PFOR) can function at H2 concentration observed in fermentative H2 system. NADH : Ferredoxin oxido-reductase (NFOR) can only function for dissolved H2 < 0.5 μM (<60 Pa) [2]. Therefore, higher H2 is possible by decreasing H2 for NFOR. In their study, the dissolved H2 could be decreased only at 485 μM (i.e., 103 times higher). It appears that impractically high sparging rates would be needed to decrease dissolved H2 in to the NFOR regulatory zone [85]. Mandal et al. [113] observed double the H2 yield during batch culture of E. cloaceae DM11. The H2 yield during vacuum operation was 3.9 mol/mol glucose. However, Kraemer and Bagley [86] concluded that no meaningful relationship exists between sparging rates and H2 yield. Incidentally, CO2 sparging drastically decreased microbial diversity in a continuous mixed culture [85]. It may thus serve as a warning sign because such conditions may even have an adverse effect on growth and activity of H2 producing microbes. Immobilized whole cell technique leads to high reaction rates and thus represents an efficient approach [171] to biocatalysis for carrying out several biochemical reactions including H2 production [89, 133, 140, 155, 190, 195, 207] and CH4 production [66]. Most of the solid matrices used for the immobilization of the whole cells are synthetic polymers or inorganic materials. These systems include polyurethane, polyvinyl alcohol, agar gel or porous glass beads, calcium alginate, polyacryl amide gel, k-carageenan or cellulose, banana leaves, wood chips, activated charcoal, baked bricks or clay [6, 89, 110, 155, 195]. Use of immobilized whole cells compared to free floating cells increases the mean cell residence time in the reactor. Studies to improve H2 yields through immobilization have resulted in up to 1.7 fold increase [80, 93, 189]. A four-fold increase in H2 production by immobilizing B. licheniformis on brick dust has resulted in a H2 yield of 1.5 mol/mol glucose in batch culture [89]. Lignocellulosic agricultural waste materials such as rice hull, sugarcane bagasse, wheat straw [130], pea-shells [65], banana leaves [66] and coconut coir [92] are regarded as abundant, inexpensive and readily available natural sources. Many countries have imposed regulations to restrict field burning of these wastes in response to restrictions on carbon emission due to global warming [132]. In the past, these waste have been sent to landfills, but in recent years their disposal has become a problem, due to increasing cost of transportation and scarcity of landfill sites for quick disposal [65]. These are potential support materials for retaining large populations of H2 producers within the reactor. In fact, it has been possible to increase H2 yield up to 2.36 mol/mol glucose by immobilizing Bacillus strains on these ligno-cellulosic wastes [69]. Another factor which greatly influences the H2 generation from biowastes is the presence of H2 quenchers (Table 2) among the mixed microbial populations, primarily sulfate reducers, nitrate reducers and methanogens. In such scenarios, there is thus little or no net evolution of H2. Different techniques employed to suppress methanogenic activity include heating the waste [129], using specific and non specific inhibitors such as 2-bromoethene sulfonate (BES) or acetylene [159, 160, 177], using microbial and enzymatic pretreatments [158], or low pH and high temperature combinations [20, 122, 129]. Product formation by microflora depends upon dominant populations and selective enrichment of certain microbes can be achieved by inoculations with pure cultures. Increase in H2 yields at low N2 content has also been recorded [122]. It seems that although H2 production can be initiated, for continuous production we may need to further standardize the culture conditions, such as changes in retention time, feed composition, pH, etc. In search of potential “wonder” bug(s) for hydrogen production In spite of a large number of reports on H2 producing microbes, the bioconversion of biological material in to H2 has been observed to operate at very low efficiencies. The top-rated challenges and technical barriers include no known microorganism capable of naturally producing more than 4 moles of H2 per mole of glucose, the metabolic pathways have not been thoroughly identified and the reaction is energetically unfavorable. The biomass feed stocks are too costly and there is thus a need to develop low cost methods for growing, harvesting, transporting and pre-treating energy crops and or biomass waste products [214]. In the absence of a robust, industrially capable organism, the platform for research to genetically alter the metabolic pathways of the existing microbes is open. As microbiologist and biotechnologists, we need to carefully screen microbial diversity [136] from samples representing a vast diversity of environments, ranging from “normal” environments such as soil, sea water and sediments to extreme environments [108]. The search for a robust H2 producer(s) begins with an important organism, capable of fermenting multiple sugars as feed, withstand adverse environmental conditions, compete with naturally occurring microflora, tolerate “toxic” compounds, produce compounds of economic importance and grow aerobically, even under fermentative conditions, preferably independent of light, etc. Among the potential candidates as “wonder” bug(s) for H2 production are the facultative anaerobes such as Aeromonas, Alcaligenes, Bacillus, Campylobacter, Citrobacter, Escherichia, Enterobacter, Klebsiella, Salmonella, Serratia, Streptococcus, Thermotoga and aerobic chemotrophs such as Azospirillum, Azotobacter, Mycobacterium, Pseudomonas and Rhizobium. The key microbial groups in the diverse consortia of anaerobic fermenters and those related to the hydrolysis and acidogenic fermentation of the organic matter are Clostridia and Enterobacteriaceae, since they generate H2 from carbohydrates and other organic substrates. At present the top contenders as the future H2 producers among the non-photosynthetic organisms are Clostridium, Enterobacter and Bacillus [84, 125]. On the other hand, among the photo-biological H2 producers are R. sphaeroides, Rhodobium marinum and V. fluvialis [76]. Facultative anaerobes such as E. aerogenes [167] and obligate anaerobes such as Clostridium spp. [40] are known to convert sucrose to H2 at the rate of 1.25 and 2.2 mol/mol hexose, respectively. Lay et al., [96] studied the feasibility of H2 production from organic fraction of municipal solid waste by Clostridium and could evolve 180 ml H2/g volatile solids. In cow dung cellulose is the most abundant carbohydrate and the amounts of soluble carbohydrates and starch are negligible. Clostridium cellulosi decomposes cellulose with the production of H2, CO2, acetate and ethanol as fermentation products [201], which may be the reason for low H2 production from cow waste by C. thermocellum [200]. In a mixed microbial population in H2 producing granular sludge, at least 65% of the species belonged to Clostridium. Since most Clostridium spp. cannot tolerate O2, addition of a reducing agent such as cysteine to the medium is common practice [166]. Facultative anaerobes may therefore promote H2 production by obligate anaerobes, by consuming any traces of O2 in a reactor. For example, E. aerogenes and C. butyricum growing on starch yielded 2 mol/ mol glucose without any reducing agent [197]. The exchange of roles between Clostridium and Bacillus as H2 producers was observed in an innovative approach to enrich mixed microbial populations of H2 producers. Here heat pre-treatment and changes in HRT have shown that spore forming bacteria such as Clostridium tetanomorphum are predominant in the initial stages (up to day 15) and Bacillus laveolaticus as dominant bacteria there after in H2 producing bioreactors [163]. In another study, increase in H2 production at reduced HRT was linked to a shift in bacterial population from Clostridium sp. and Bacillus (most closely related to B. racemilacticus and B. myxolacticus) to predominantly Clostridium sp. [62, 175]. These studies suggested that the shift in microbial population has been probably due to the presence of homo-acetogens at longer HRT and acidogens at shorter HRT. Such studies may provide clues as to why Bacillus spp. have not been reported widely among the H2 producers. A comparison of the H2 producing potentials of Clostridium, Enterobacter and Bacillus from a wide range of studies reveal the following: Clostridium sp., C. butyricum and C. paraputrificum have been shown to yield 1.3 to 2.5 mol H2/mol sugar [38, 50, 74, 165, 195]. E. aerogenes and E. cloacae have been largely studied for H2 production from glucose, sucrose and molasses. Here, H2 yields varied from 0.6 to 3.8 mol/mol sugar [111, 127, 167] and Bacillus coagulans, B. licheniformis and B. subtilis have been shown to evolve 1.5 to 2.36 mol H2/mol glucose [69, 84, 91]. B. licheniformis and B. subtilis could also generate H2 from damaged wheat grains at the rate of 45 to 64 L/ kg Total solids [64, 158]. Among the most recent developments is the proposal to run the two systems in sequence or in combination. A mixed culture of Clostridium sp. and Bacillus sp. yielded 1.52 mol H2/mol sucrose [163]. Here the mechanism in operation is the utilization of carbohydrates or carbohydrate rich wastes for dark fermentation and fatty acids for photosynthetic process. In a co-culture of C. butyricum and Rhodobacter sp. higher H2 yields of 4.5 mol/mol glucose were observed in comparison to single dark fermentation (1.9 mol/mol glucose) and sequential two step fermentation of starch yielding 3.7 mol/mol glucose [196]. Similarly, higher H2 yields from different substrates were reported by co-cultures of R. marinum and V. fluvialis compared to R. marinum alone [61]. In yet another combination of Lactobacillus amylovous and R. marinum, higher H2 yield was linked to lower production rate [75]. A mixed culture of E. aerogenes and R. sphaeroides resulted in the evolution of 3.15 mol H2/mol glucose [84]. Genomics in aid of hydrogen production In order to overcome the metabolic barriers by manipulating electron flux, a single host organism for transgenic expression of H2 pathways is necessary. With the advent of recent advances through microbial genome projects, a large amount of genetic and metabolic information has been made available in public domains [212, 213]. Genomic data mining approach has been exploited for searching novel H2 producers [68]. Sequence analysis and pathway alignment of H2 metabolism glyoxalate and dicarboxylate metabolic pathways (formate dehydrogenase and hydrogenase) in 176 sequenced genomes [213] has led to the identification of potential H2 producers such as Wolinella succinogenes, Desulfitobacterium dehalogenans, Burkholderia fungorum and Novosphingopbium aromaticiviorans, etc. In the past decade, very few new H2-producing organisms have been reported (e.g. Caldicellulosiruptor saccharolyticus, Gloeocapsa alpicola, Rubrivivax gelatinosus and Thermotoga elfii), and there has been little significant improvement in the H2 yields, which ranges up to 3.3 mol/mol of glucose [114, 172, 179]. In view of these facts, this genomic approach has revealed certain interesting potential H2 producers. These novel H2 producers [68] show unique characteristics such as (1) degradation of industrial wastewaters (perchlorates), remediation of contaminated soil and ground water, (2) bioremediation by dehalogenation of chlorinated phenols, ethenes, polychlorinated biphenyls (PCBs), (3) beneficial plant root colonizers, role in global C-cycle and (4) degradation of aromatic hydrocarbons including toluene, p-cresol, xylene, naphthalene, etc. They have ability to grow in a wide range of environments including soil, fresh waters, and marine life. These bacteria thus not only have the potential to produce H2, but are also known to utilize wastes as feed. This data mining approach can be further extended to detect robust organisms, which are not presently categorized among the H2 producers because of absence of gene(s) crucial for the H2 metabolic pathway to be fully functional. Such an approach has been recently suggested for the detection of “non” producers of polyhydroxyalkanoates and antibiotics [70, 71] and possible shuffling of genomes for transforming them to producers [70]. Comparative genomics of sequenced genomes of Bacillus revealed that it possesses genes for α, β, and γ subunits of formate dehydrogenase, but genes for the large and small subunits of hydrogenase could not be detected. Hence, it was categorized among “non”-producers. However, a review of published literature reveals that Bacillus can produce H2, [64, 84, 158], which may imply that another hydrogenase might be operative. Incidentally, there are no reports available in public domain on the enzymes involved in H2 production in Bacillus. There are two separate pathways operative in Clostridium and Escherichia. In Clostridium, the genes for Pryuvate Fd/Flavodoxin oxidoreductase [EC.1.2.7.1] and H2 Fd/Flavodoxin oxidoreductase [EC.1.2.7.2] are involved in H2 production. In Escherichia, Pryuvate formate lyase, PFL [EC 2.3.1.54], Formate dehydrogenase Fdh-α, Fdh-β, Fhh-γ [EC 1.2.1.2] and Hydrogenase (Large and small subunits) [EC 1.18.99.1] are responsible for H2 evolution. Incidentally, Pyruvate Fd/ Flavodoxin oxidoreductase is highly expressed in C. acetobutylicum and C. perfringens and is missing in the genomes of B. subtilis and B. halodurans [73]. On the other hand, Pryuvate Formate lyase is not highly expressed in C. acetobutylicum and again is missing in two Bacillus genomes, B. subtilis and B. halodurans. It is however among the prominently expressed genes in enteric proteobacteria and not in other prokaryotes. In such a scenario Bacillus apparently uses Pyruvate dehydrogenase complex (pdh ABCD) [63], which is highly expressed in B. subtilis and B. halodurans and is missing in C. acetobutylicum and C. perfringens [73]. It provides clues that Bacillus and Clostridial H2 production systems are under different metabolic controls. The complete pathway of H2 production in Bacillus needs to be elucidated before resorting to genome shuffling approaches can be exploited. Bacillus can be considered as a strong contender for the future biological H2 producer because of its unique features. Bacillus represents microbes of high economic, medical and biodefense importance, production of bio-pesticides [53] and biofuels such as H2 [64, 158], commercial enzymes and probiotics. Among the 175 different Bacillus species, a majority of isolates are represented by Bacillus anthracis, B. cereus, B. thuringiensis, B. subtilis, B. licheniformis, B. pumilus, B. megaterium, B. sphaericus, B. clausii and B. halodurans [211]. Because of these divergent characteristics of economic importance and intra species diversity, 11 closely related Bacillus are among the 29 Bacillales sequenced so far [213].The very basis of the complete nucleotide sequencing of B. licheniformis type strain (ATCC 14580) genome was its enormous economic importance [147]. Two gene clusters involved in cellulose degradation and utilization have been reported from B. licheniformis which may enable it to utilize biowaste rich in cellulose into cellobiose and ultimately glucose to produce H2 [147]. Among the various strains of Bacillus isolated in our laboratory, Bacillus sp. and B. licheniformis have been shown to produce H2 [64, 158]. These two Bacillus strains have the capacity to ferment glucose, maltose, fructose, dextrose, sucrose, mannose, etc. Unlike most other bacilli, which are predominantly aerobic, B. licheniformis is a facultative anaerobe with a saprophytic lifestyle, which may allow it to grow in additional ecological niches. B. licheniformis is known for its numerous commercial and agricultural uses primarily because of its extracellular products which include several proteases, α-amylase, penicillinase, pentosanase, cycloglucosyltransferase, β-mannanase and several pectinolytic enzymes important for degradation of polysaccharides, proteins, lipids and other nutrients. The proteases are used in the detergent industry, for dehairing and bating of leather [34, 37], and degradation of feather [7, 112], where as amylases from B. licheniformis can hydrolyse starch, hence used for desizing textiles and sizing of paper [34], and oil recovery [25, 123]. The ability to transform into an endospore, enhances it ability to survive under unfavourable conditions and even compete with other microbes [162]. In metal contaminated waste-waters, the use of metal (Ni) resistant microorganisms such as Bacillus sp. can reduce bio-available metal concentrations via sequestration and may foster enhanced biodegradation [152]. Bacillus strains are also bestowed with an ability to even mitigate the affects of fungal pathogens on maize, grasses and vegetable crops [141]. In brief, Bacillus has many features which favour it as an organism of choice for H2 production. Being a spore former, it can survive under unfavourable conditions and even compete with other microbes. It has a large number of enzymatic activities such as lipase, amylase, protease, urease, cellulose, etc for hydrolyzing cellulose and biological wastes in to simpler soluble compounds. It can produce laccase, which is important for de-lignification of ligno-cellulosic bio-wastes Its ability to produce poly galacturonase is stimulated by addition of amino-acids. Bacillus has unique advantage over other microbes, being non- photosynthetic, does not require light for H2 production. It is capable of converting wastes such as damaged wheat grains, pea-shells, starch, etc. to H2. Its ability to produce H2 could be enhanced up to 2.36 mol/mol glucose by immobilization on ligno-cellulosic wastes. The role of Bacillus in improving the efficiency of degradation process can be gauged by its ability to produce large number of industrially important products including PHA. Bacillus spores are being used as human and animal probiotics, which do not pose any environmental health hazard. In agriculture it holds importance due to its denitrification property. Conclusion The economics of biological H2 production process is quite low at present. To realize the goal of efficient H2 production, the importance of diverse microbial communities in mineralization of organic matter (biological matter/wastes) occurring in natural ecosystems [185] need not be re-emphasized [145]. Microbial and functional diversity are to be harnessed, including those for bioproducts like volatile fatty acids and bioplastics, CH4, etc. [2, 56, 86, 145]. Although photosynthetic organisms such as Rhodopseudomonas, Rhodospirillum and Rhodobacter have been shown to produce H2 and PHB, [59, 98, 183, 193] non-photosynthetic organisms such as Bacillus strains have been shown to produce H2 and PHB albeit in independent studies [84, 94, 158, 194] and more recently even in a single organism [137]. In yet another novel approach, mining of sequenced genomes has revealed certain organisms with potential to produce these two products and have ability to grow on industrial waste waters [67]. For biological H2 and energy production to become an economically feasible commercial activity, an integrated approach would require the participation of specialists from each aspect of this multi-step process and application of knowledge acquired from diverse areas. Future energy systems require money and energy to build. We may all agree that there are finite supplies of both. Hard decisions must be made about the path forward and must be followed by a sustained and focused effort [173]. The integration of agroenergy crops and biorefinery manufacturing technologies offers the potential for the development of sustainable biopower and biomaterials that will lead to a new manufacturing paradigm [139]. Acknowledgments We are thankful to Prof. S. K. Brahmachari, Director, Institute of Genomics and Integrative Biology, CSIR, Dr. S. Devotta, Director, National Environmental Engineering Research Institute, CSIR and CSIR Task Force project for providing the necessary funds, facilities and moral support. References 1. Alcalde M , Ferrer M, Plou FJ, Ballesteros A Environmental biocatalysis: from remediation with enzymes to novel green processes Trends Biotechnol 2006 24 281 287 10.1016/j.tibtech.2006.04.002 Google Scholar Crossref Search ADS PubMed WorldCat 2. Angenent LT , Karim K, Al-Dahhan MH, Wrenn BA, Domíguez-Espinosa R Production of bioenergy and biochemicals from industrial and agricultural wastewater Trends Biotechnol 2004 22 477 485 10.1016/j.tibtech.2004.07.001 Google Scholar Crossref Search ADS PubMed WorldCat 3. Angenent LT Energy biotechnology: beyond the general lignocellulose-to-ethanol pathway Curr Opin Biotechnol 2007 18 191 192 10.1016/j.copbio.2007.05.003 Google Scholar Crossref Search ADS WorldCat 4. Antonopoulou G, Gavala HN, Siadas IV, Angelopoulos K, Lyberatos G (2007) Biofuels generation from sweet sorghum: fermentative hydrogen production and anaerobic digestion of the remaining biomass. Bioresour Technol. doi:10.1016/j.biortech.2006/.11.048 5. Ashby GA , Dilworth MJ, Thorneley RN Klebsiella pneumoniae nitrogenase. Inhibition of hydrogen evolution by ethylene and the reduction of ethylene to ethane Biochem J 1987 247 547 554 1148448 10.1042/bj2470547 Google Scholar Crossref Search ADS PubMed WorldCat 6. Bagai R , Madamwar D Long-term photo-evolution of hydrogen in a packed bed reactor containing a combination of Phormidium valderianum, Halobacterium halobium, and Escherichia coli immobilized in polyvinyl alcohol Int J Hydrogen Energy 1999 24 311 317 10.1016/S0360-3199(98)00053-6 Google Scholar Crossref Search ADS WorldCat 7. Bálint B , Bagi Z, Tóth A, Rákhely G, Perei K, Kovács KL Utilization of keratin-containing biowaste to produce biohydrogen Appl Microbiol Biotechnol 2005 69 404 410 10.1007/s00253-005-1993-3 Google Scholar Crossref Search ADS PubMed WorldCat 8. Balthasar W Hydrogen production and technology: today, tomorrow and beyond Int J Hydrogen Energy 1984 9 649 668 10.1016/0360-3199(84)90263-5 Google Scholar Crossref Search ADS WorldCat 9. Beg QK , Bhushan B, Kapoor M, Hoondal GS Effect of amino acids on production of xylanase and pectinase from Streptomyces sp. QG-11–3 World J Microbiol Biotechnol 2000 16 211 213 10.1023/A:1008979512413 Google Scholar Crossref Search ADS WorldCat 10. Beneman JR Hydrogen biotechnology: progress and prospects Nat Biotechnol 1996 14 1101 1103 10.1038/nbt0996-1101 Google Scholar Crossref Search ADS PubMed WorldCat 11. Bicelli PL Hydrogen: a clean energy source Int J Hydrogen Energy 1986 11 555 562 10.1016/0360-3199(86)90121-7 Google Scholar Crossref Search ADS WorldCat 12. Boon N , Top EM, Verstraete W, Siciliano SD Bioaugmentation as a tool to protect the structure and function of an activated sludge microbial community against a 3-chloroaniline shock load Appl Environ Microbiol 2003 69 1511 1520 150069 10.1128/AEM.69.3.1511-1520.2003 Google Scholar Crossref Search ADS PubMed WorldCat 13. Bridgwater AV Renewable fuels and chemicals by thermal processing of biomass Chem Eng J 2003 91 87 102 10.1016/S1385-8947(02)00142-0 Google Scholar Crossref Search ADS WorldCat 14. Brosseau JD , Zajic JE Hydrogen gas production with Citrobacter intermedius and Clostridium pasteurianum J Chem Tech Biotechnol 1982 32 496 10.1002/jctb.5030320310 Google Scholar Crossref Search ADS WorldCat 15. Buranakarl L , Ito K, Izaki K, Takahashi H Purification and characterization of a raw starch-digestive amylase from non-sulfur purple photosynthetic bacterium Enzyme Microb Technol 1988 10 173 179 10.1016/0141-0229(88)90084-1 Google Scholar Crossref Search ADS WorldCat 16. Canakci M , Van Gerpen J Biodiesel production from oils and fats with high free fatty acids Trans ASAE 2001 44 1429 1436 10.13031/2013.7010 Google Scholar Crossref Search ADS WorldCat 17. Chan YK , Nelson LM, Knowles R Hydrogen metabolism of Azospirillum brasilense in nitrogen-free medium Can J Microbiol 1980 26 1126 1131 10.1139/m80-186 Google Scholar Crossref Search ADS PubMed WorldCat 18. Chandra R , Raj A, Purohit HJ, Kapley A Characterisation and optimization of three potential aerobic bacterial strains for kraft lignin degradation from pulp paper waste Chemosphere 2007 67 839 846 10.1016/j.chemosphere.2006.10.011 Google Scholar Crossref Search ADS PubMed WorldCat 19. Chang JS , Lee KS, Lin PJ Biohydrogen production with fixed bed bioreactors Int J Hydrogen Energy 2002 27 1167 1174 10.1016/S0360-3199(02)00130-1 Google Scholar Crossref Search ADS WorldCat 20. Chen CC , Lin CY, Lin MC Acid-base enrichment enhances anaerobic hydrogen process Appl Micro Biotechnol 2002 58 224 228 10.1007/s002530100814 Google Scholar Crossref Search ADS WorldCat 21. Chen CC , Lin CY Using sucrose as a substrate in an anaerobic hydrogen producing reactor Adv Environ Res 2003 7 695 699 10.1016/S1093-0191(02)00035-7 Google Scholar Crossref Search ADS WorldCat 22. Cheong D-Y , Hansen CL, Stevens DK Production of bio-hydrogen by mesophilic anaerobic fermentation in an acid-phase sequencing batch reactor Biotechnol Bioeng 2007 96 421 432 10.1002/bit.21221 Google Scholar Crossref Search ADS PubMed WorldCat 23. Christensen CH , Jørgensen B, Rass-Hansen J, Egeblad K, Madsen R, Klitgaard SK, Hansen SM, Hansen MR, Andersen HC, Riisager A Formation of acetic acid by aqueous-phase oxidation of ethanol with air in the presence of a heterogeneous gold catalyst Angew Chem Int Ed 2006 45 4648 4651 10.1002/anie.200601180 Google Scholar Crossref Search ADS WorldCat 24. Das D , Verziroglu TN Hydrogen production by biological processes: A survey of literature Int J Hydrogen Energy 2001 26 13 28 10.1016/S0360-3199(00)00058-6 Google Scholar Crossref Search ADS WorldCat 25. De Clerck E , De Vos P Genotypic diversity among Bacillus licheniformis strains from various sources FEMS Microbiol Lett 2006 231 91 98 10.1016/S0378-1097(03)00935-2 Google Scholar Crossref Search ADS WorldCat 26. De Luchi MA Hydrogen vehicles: an evaluation of fuel storage, performance, safety, environmental impacts, and cost Int J Hydrogen Energy 1989 14 81 130 10.1016/0360-3199(89)90001-3 Google Scholar Crossref Search ADS WorldCat 27. Demirbas A , Arin G An overview of biomass pyrolysis Energy Sources 2002 5 471 482 10.1080/00908310252889979 Google Scholar Crossref Search ADS WorldCat 28. Demirbas A Biodiesel fuels from vegetable oils via catalytic and non-catalytic supercritical alcohol transesterifications and other methods: a survey Energy Convers Manage 2003 44 2093 2109 10.1016/S0196-8904(02)00234-0 Google Scholar Crossref Search ADS WorldCat 29. Demirbas A Bioenergy, global warming, and environmental impacts Energy Sources 2004 26 225 236 10.1080/00908310490256581 Google Scholar Crossref Search ADS WorldCat 30. Demirbas A Biodiesel production from vegetable oils via catalytic and non-catalytic supercritical methanol transesterification methods Prog Energy Combus Sci 2005 31 466 487 10.1016/j.pecs.2005.09.001 Google Scholar Crossref Search ADS WorldCat 31. Demirbas A Progress and recent trends in biofuels Prog Energy Combus Sci 2007 33 1 18 10.1016/j.pecs.2006.06.001 Google Scholar Crossref Search ADS WorldCat 32. Dhawan S , Kuhad RC Effect of aminoacids and vitamins on laccase production bt the bird’s nest fungus Cyathus biulleri Bioresour Technol 2002 84 35 38 10.1016/S0960-8524(02)00026-3 Google Scholar Crossref Search ADS PubMed WorldCat 33. Du W , Xu Y, Liu D, Zeng J Comparative study on lipase catalyzed transformation of soybean oil for biodiesel production with different acyl acceptors J Mol Catal B Enzymat 2004 30 125 129 10.1016/j.molcatb.2004.04.004 Google Scholar Crossref Search ADS WorldCat 34. Erickson RJ Schlesinger D Industrial applications of the bacilli: a review and prospectus Microbiology 1976 Washington American Society for Microbiology 406 419 Google Scholar Google Preview OpenURL Placeholder Text WorldCat COPAC 35. Esper B , Badura A, Rögner M Photosynthesis as a power supply for (bio-)hydrogen production Trends Plant Sci 2006 11 543 549 10.1016/j.tplants.2006.09.001 Google Scholar Crossref Search ADS PubMed WorldCat 36. European Commission, (EC) (2004) Promoting biofuels in Europe. Bruxelles, Belgium: European Commission, Directorate-General for Energy and Transport. B-1049. Available from: http://europa.eu.int/comm/dgs/energy_transport/index_en.html 37. Eveleigh DE The microbial production of industrial chemicals Sci Am 1981 245 155 178 10.1038/scientificamerican0981-154 Google Scholar Crossref Search ADS WorldCat 38. Evvyernie D , Yamazaki S, Morimoto K, Karita S, Kimura T, Sakka K, Ohmiya K Identification and characterization of Clostridium paraputricum M-21, a chitinolytic, mesophilic and hydrogen producing bacterium J Biosci Bioeng 2000 89 596 601 10.1016/S1389-1723(00)80063-8 Google Scholar Crossref Search ADS PubMed WorldCat 39. Fang HHP , Liu H Effect of pH on hydrogen production from glucose by mixed culture Bioresour Technol 2002 82 87 93 10.1016/S0960-8524(01)00110-9 Google Scholar Crossref Search ADS PubMed WorldCat 40. Fang HHP , Liu H, Zhang T Characterisation of a hydrogen-producing granular sludge Biotechnol Bioeng 2002 78 44 52 10.1002/bit.10174 Google Scholar Crossref Search ADS PubMed WorldCat 41. Fascetti E , D’Addario E, Todini O, Robertiello A Photosynthetic hydrogen evolution with volatile organic acid derived from the fermentation of source selected municipal wastes Int J Hydrogen Energy 1998 23 753 760 10.1016/S0360-3199(97)00123-7 Google Scholar Crossref Search ADS WorldCat 42. Friedrich J , Gradisar H, Mandin D, Chaumont JP Screening fungi for synthesis of keratinolytic enzymes Lett Appl Microbiol 1999 28 127 130 10.1046/j.1365-2672.1999.00485.x Google Scholar Crossref Search ADS WorldCat 43. Gavala HN , Skiadas IV, Ahring BK Biological hydrogen production in suspended and attached growth anaerobic reactor systems Int J Hydrogen Energy 2006 31 1164 1175 10.1016/j.ijhydene.2005.09.009 Google Scholar Crossref Search ADS WorldCat 44. Gest H , Kamen M Photoproduction of molecular hydrogen by Rhodospirillum rubrum Science 1949 109 558 10.1126/science.109.2840.558 Google Scholar Crossref Search ADS PubMed WorldCat 45. Goodwin S , Conrad R, Zeikus JG Influence of pH on microbial hydrogen, metabolism in diverse sedimentary ecosystems Appl Environ Microbiol 1988 54 590 593 202500 Google Scholar Crossref Search ADS PubMed WorldCat 46. Gregory DP , Pangborn JB Hydrogen Energy Ann Rev Energy 1976 1 279 309 10.1146/annurev.eg.01.110176.001431 Google Scholar Crossref Search ADS WorldCat 47. Hahn-Hägerdal B , Galbe M, Gorwa-Grauslund MF, Lidén G, Zacchi G Bio-ethanol – the fuel of tomorrow from the residues of today Trends Biotechnol 2006 24 549 556 10.1016/j.tibtech.2006.10.004 Google Scholar Crossref Search ADS PubMed WorldCat 48. Hansen AC , Zhang Q, Lyne PWL Ethanol–diesel fuel blends—a review Bioresour Technol 2005 96 277 285 10.1016/j.biortech.2004.04.007 Google Scholar Crossref Search ADS PubMed WorldCat 49. Henstra AM , Sipma J, Rinzema A, Stams AJM Microbiology of synthesis gas fermentation for biofuel production Curr Opin Biotechnol 2007 18 200 206 10.1016/j.copbio.2007.03.008 Google Scholar Crossref Search ADS PubMed WorldCat 50. Heyndrickx M , Vansteenbeeck A, De Vos P, De Ley J Hydrogen gas production from continuous fermentation of glucose in a minimal medium with Clostridium butyricum LMG 1213t1 Syst Appl Microbiol 1986 8 239 244 10.1016/S0723-2020(86)80087-X Google Scholar Crossref Search ADS WorldCat 51. Heyndrickx M , De Vos P, De Ley J Fermentation of d-xylose by Clostridium butyricum LMG 1213t sub(1) in chemostats Enzyme Microb Technol 1991 13 893 897 10.1016/0141-0229(91)90105-J Google Scholar Crossref Search ADS WorldCat 52. Himmel ME , Ding S-Y, Johnson DK, Adney WS, Nimlos MR, Brady JW, Foust TD Biomass recalcitrance: engineering plants and enzymes for biofuels production Science 2007 315 804 807 10.1126/science.1137016 Google Scholar Crossref Search ADS PubMed WorldCat 53. Hofte H , Whiteley HR Insecticidal crystal proteins of Bacillus thuringiensis Microbiol Rev 1989 53 242 255 372730 Google Scholar Crossref Search ADS PubMed WorldCat 54. Hu CY , Lin LP Characterization and purification of hydrolytic enzymes in Sinorhizobium fredii CCRC15769 World J Microbiol Biotechnol 2003 19 515 522 10.1023/A:1025122714976 Google Scholar Crossref Search ADS WorldCat 55. Huang SD , Secor CK, Ascione R, Zweig RM Hydrogen production by non-photosynthetic bacteria Int J Hydrogen Energy 1985 10 227 231 10.1016/0360-3199(85)90092-8 Google Scholar Crossref Search ADS WorldCat 56. Huang T-Y , Duan K-J, Huang S-Y, Chen CW Production of polyhydroxyalkanoates from inexpensive extruded rice bran and starch by Haloferax mediterranei J Ind Microbiol Biotechnol 2006 33 701 706 10.1007/s10295-006-0098-z Google Scholar Crossref Search ADS PubMed WorldCat 57. Hussy I , Hawkes FR, Dinsdale R, Hawkes DL Continuous fermentative hydrogen production from a wheat starch co-product by mixed microflora Biotechnol Bioeng 2003 84 619 626 10.1002/bit.10785 Google Scholar Crossref Search ADS PubMed WorldCat 58. Hussy I , Hawkes FR, Dinsdale R, Hawkes DL Continuous fermentative hydrogen production from sucrose and sugarbeet Int J Hydrogen Energy 2005 30 471 483 10.1016/j.ijhydene.2004.04.003 Google Scholar Crossref Search ADS WorldCat 59. Hustede E , Steinbuchel A, Schlegel HG Relationship between the photoproduction of hydrogen and the accumulation of PHB in non-sulphur purple bacteria Appl Microbiol Biotechnol 1993 39 87 93 10.1007/BF00166854 Google Scholar Crossref Search ADS WorldCat 60. IEA (International Energy Agency) (2004) Biofuels for transport: a international perspective. 9, rue de la Fe´ de´ ration, 75739 Paris, cedex 15, France (available from: http://www.iea.org) 61. Ike A , Murakawa T, Kawaguchi H, Hirata K, Miyamoto K Photoproduction of hydrogen from raw starch using a halophilic bacterial community J Biosci Bioeng 1999 88 72 77 10.1016/S1389-1723(99)80179-0 Google Scholar Crossref Search ADS PubMed WorldCat 62. Iyer P , Bruns MA, Zhang H, Ginkel SV, Logan BE H2-producing bacterial communities from a heat-treated soil inoculum Appl Microbiol Biotechnol 2004 66 166 173 10.1007/s00253-004-1666-7 Google Scholar Crossref Search ADS PubMed WorldCat 63. Jung HL , Bowden SJ, Cooper A, Perham RN Thermodynamic analysis of the binding of component enzymes in the assembly of the pyruvate dehydrogenase multienzyme complex of Bacillus stearothermophilus Protein Sci 2002 11 1091 1100 2373555 10.1110/ps.4970102 Google Scholar Crossref Search ADS PubMed WorldCat 64. Kalia VC , Jain SR, Kumar A, Joshi AP Fermentation of biowaste to hydrogen by Bacillus licheniformis World J Microbiol Biotechnol 1994 10 224 227 10.1007/BF00360893 Google Scholar Crossref Search ADS PubMed WorldCat 65. Kalia VC , Joshi AP Conversion of waste biomass (pea-shell) into hydrogen and methane through anaerobic digestion Bioresour Technol 1995 53 165 168 10.1016/0960-8524(95)00077-R Google Scholar Crossref Search ADS WorldCat 66. Kalia VC, Anand V, Kumar A, Joshi AP (1997) Efficient biomethanation of plant materials by immobilized bacteria. In: Proceedings of R’97 congress (recovery, recycling, re-integration) Geneva, Switzerland Feb 4–7 ’97 I:200–205 67. Kalia VC , Chauhan A, Bhattacharyya G, Rashmi H Genomic databases yield novel bioplastic producers. Nat Biotechnol 2003 21 845 846 10.1038/nbt0803-845 Google Scholar Crossref Search ADS PubMed WorldCat 68. Kalia VC , Lal S, Ghai R, Mandal M, Chauhan A Mining genomic databases to identify novel hydrogen producers Trends Biotechnol 2003 21 152 156 10.1016/S0167-7799(03)00028-3 Google Scholar Crossref Search ADS PubMed WorldCat 69. Kalia VC, Lal S (2006) A process for enhanced biological hydrogen and methane production by fermentative hydrogen producers and methanogens immobilized on lignocellulosic wastes. Patent application No. 152NF2006 (Indian) 70. Kalia VC , Lal S, Cheema S Insight in to the phylogeny of polyhydroxyalkanoate biosynthesis: horizontal gene transfer Gene 2007 389 19 26 10.1016/j.gene.2006.09.010 Google Scholar Crossref Search ADS PubMed WorldCat 71. Kalia VC , Rani A, Lal S, Cheema S, Raut CP Combing databases reveals potential antibiotic producers Expert Opin Drug Discov 2007 2 211 224 10.1517/17460441.2.2.211 Google Scholar Crossref Search ADS PubMed WorldCat 72. Kapdan IK , Kargi F Bio-hydrogen production from waste materials Enzyme Microb Technol 2006 38 569 582 10.1016/j.enzmictec.2005.09.015 Google Scholar Crossref Search ADS WorldCat 73. Karlin S , Theriot J, Mrázek J Comparative analysis of gene expression among low G + C gram-positive genomes Proc Natl Acad Sci 2004 101 6182 6187 395943 10.1073/pnas.0401504101 Google Scholar Crossref Search ADS PubMed WorldCat 74. Kataoka N , Miya A, Kiriyama K Studies on hydrogen production by continuous culture system of hydrogen-producing anaerobic bacteria Water Sci Technol 1997 36 41 47 10.1016/S0273-1223(97)00505-2 Google Scholar Crossref Search ADS WorldCat 75. Kawaguchi H , Hashimoto K, Hirata K, Miyamoto K H2 production from algal biomass by mixed culture of Rhodobium marinum A-501 and Lactobacillus amylovorus J Biosci Bioeng 2001 91 277 282 10.1016/S1389-1723(01)80134-1 Google Scholar Crossref Search ADS PubMed WorldCat 76. Keenan TM , Nakas JP, Tanenbaum SW Polyhydroxyalkanoate copolymers from forest biomass J Ind Microbiol Biotechnol 2006 33 616 626 10.1007/s10295-006-0131-2 Google Scholar Crossref Search ADS PubMed WorldCat 77. Khanal SK , Chen WH, Li L, Sung S Biological hydrogen production: effects of pH and intermediate products Int J Hydrogen Energy 2004 29 1123 1131 Google Scholar OpenURL Placeholder Text WorldCat 78. Khoshoo TN (1991) In: Khoshoo TN (ed) Environmental concerns and strategies. Ashish Publishing House, New Delhi, pp 255–372 79. Kim DH , Han SK, Kim SH, Shin HS Effect of gas sparging on continuous fermentative hydrogen production Int J Hydrogen Energy 2006 31 2158 2169 10.1016/j.ijhydene.2006.02.012 Google Scholar Crossref Search ADS WorldCat 80. Kim JO , Kim YH, Ryu JY, Song BK, Kim IH, Yeom SH Immobilization methods for continuous hydrogen gas production biofilm formation versus granulation Process Biochem 2005 40 1331 1337 10.1016/j.procbio.2004.06.008 Google Scholar Crossref Search ADS WorldCat 81. Kleerebezem R , van Loosdrecht MCM Mixed culture biotechnology for bioenergy production Curr Opin Biotechnol 2007 18 207 212 10.1016/j.copbio.2007.05.001 Google Scholar Crossref Search ADS PubMed WorldCat 82. Kondratieva EN , Gogotov IN Production of molecular hydrogen in microorganisms Adv Biochem Eng Biotech 1983 28 139 191 Google Scholar OpenURL Placeholder Text WorldCat 83. Kosaric N, Lyng RD (1988) Microbial production of hydrogen. In: (Rehm HJ, Reed G (eds) A comprehensive treatise in 8 volumes. vol 6b, pp101–134 Vett. Verlegsgesell-shaft mbh, Weinheim, FRG 84. Kotay SM , Das D Microbial hydrogen production with Bacillus coagulans IIT-BT S1 isolated from anaerobic sewage sludge Bioresour Technol 2007 98 1183 1190 10.1016/j.biortech.2006.05.009 Google Scholar Crossref Search ADS PubMed WorldCat 85. Kraemer JT , Bagley DM Supersaturation of dissolved H2 and CO2 during fermentative hydrogen production with N2 sparging Biotechnol Lett 2006 28 1485 1491 10.1007/s10529-006-9114-7 Google Scholar Crossref Search ADS PubMed WorldCat 86. Kraemer JT , Bagley DM Improving the yield from fermentative hydrogen production Biotechnol Lett 2007 29 685 695 10.1007/s10529-006-9299-9 Google Scholar Crossref Search ADS PubMed WorldCat 87. Kruse O , Rupprecht J, Mussgnug JH, Dismukes GC, Hankamer B Photosynthesis: a blueprint for solar energy capture and biohydrogen production technologies Photochem Photobiol Sci 2005 4 957 970 10.1039/b506923h Google Scholar Crossref Search ADS PubMed WorldCat 88. Kuhad RC , Singh A Lignocellulose biotechnology: current and future prospects Crit Rev Biotechnol 1993 13 151 172 10.3109/07388559309040630 Google Scholar Crossref Search ADS WorldCat 89. Kumar A , Jain SR, Sharma CB, Joshi AP, Kalia VC Increased hydrogen production by immobilized microorganisms World J Microbiol Biotechnol 1995 11 156 159 10.1007/BF00704638 Google Scholar Crossref Search ADS PubMed WorldCat 90. Kumar A , Jain SR, Kalia VC, Joshi AP Effect of some physiological factors on nitrogenase activity and nitrogenase mediated hydrogen evolution by mixed microbial culture Biochem Mol Biol Int 1998 45 245 253 Google Scholar PubMed OpenURL Placeholder Text WorldCat 91. Kumar N , Das D Enhancement of hydrogen production by Enterobacter cloacae IIT-BT 08 Process Biochem 2000 35 589 593 10.1016/S0032-9592(99)00109-0 Google Scholar Crossref Search ADS WorldCat 92. Kumar N , Das D Continuous hydrogen production by immobilized Enterobacter cloacae IIT-BT 08 using lignocellulosic materials as solid matrices Enzyme Microbiol Technol 2001 29 280 287 10.1016/S0141-0229(01)00394-5 Google Scholar Crossref Search ADS WorldCat 93. Kumar N, Roy N, Mishra J, Mukherjee L, Das D (2003) Scanning electron microscopy of immobilized whole cells: A case study on the hydrogen production using immobilized Enterobacter cloacae IIT-BT 08. Science, Technol. Education microscopy: an overview, pp 352–362 94. Labuzek S , Radecka I Biosynthesis of PHB tercopolymer by Bacillus cereus UW85 J Appl Microbiol 2001 90 353 357 10.1046/j.1365-2672.2001.01253.x Google Scholar Crossref Search ADS PubMed WorldCat 95. Lamed R , Zeikus JG Ethanol production by thermophilic bacteria: relationship between fermentation product yields of and catabolic enzyme activities in Clostridium thermocellum and Thermoanaerobium brockii J Bacteriol 1980 144 569 578 294704 Google Scholar Crossref Search ADS PubMed WorldCat 96. Lay JJ , Lee YJ, Noike T Feasibility of biological hydrogen production from organic fraction of municipal solid waste Water Res 1999 33 2579 2586 10.1016/S0043-1354(98)00483-7 Google Scholar Crossref Search ADS WorldCat 97. Lee CM , Chen PC, Wang CC, Tung YC Photohydrogen production using purple non-sulfur bacteria with hydrogen fermentation reactor effluent Int J Hydrogen Energy 2002 27 1309 1313 10.1016/S0360-3199(02)00102-7 Google Scholar Crossref Search ADS WorldCat 98. Lee KS , Lo YS, Lo YC, Lin PJ, Chang JS H2 production with anaerobic sludge using activated-carbon supported packed bed bioreactors Biotechnol Lett 2003 25 133 138 10.1023/A:1021915318179 Google Scholar Crossref Search ADS PubMed WorldCat 99. Levin DB , Pitt L, Love M Biohydrogen production: prospects and limitations to practical application Int J Hydrogen Energy 2004 29 173 185 10.1016/S0360-3199(03)00094-6 Google Scholar Crossref Search ADS WorldCat 100. Levine AS , Tallman JR, Grace MK, Parker SA, Billington CJ, Levitt MD Effect of breakfast cereals on short-term food intake Am J Clin Nutr 1989 50 1303 1307 Google Scholar Crossref Search ADS PubMed WorldCat 101. Li CL , Fang HHP Fermentative hydrogen production from wastewater and solid wastes by mixed cultures Crit Rev Environ Sci Technol 2007 37 1 39 10.1080/10643380600729071 Google Scholar Crossref Search ADS WorldCat 102. Lin CY , Lay CH A nutrient formulation for fermentative hydrogen production using sewage sludge mciroflora Int J Hydrogen Energy 2005 30 285 292 10.1016/j.ijhydene.2004.03.002 Google Scholar Crossref Search ADS WorldCat 103. Liu GZ , Shen JQ Effects of culture and medium conditions on hydrogen production from starch using anaerobic bacteria J Biosci Bioeng 2004 98 251 256 10.1016/S1389-1723(04)00277-4 Google Scholar Crossref Search ADS PubMed WorldCat 104. Liu H , Fang HHP Hydrogen production from wastewater by acidogenic granular sludge Water Sci Technol 2002 47 153 158 Google Scholar Crossref Search ADS WorldCat 105. Liu H , Zhang T, Fang HPP Thermophilic H2 production from cellulose containing wastewater Biotechnol Lett 2003 25 365 369 10.1023/A:1022341113774 Google Scholar Crossref Search ADS PubMed WorldCat 106. Logan BE , Oh SE, Kim IS, van Ginkel S Biological hydrogen production measured in batch anaerobic respirometers Environ Sci Technol 2002 36 2530 2535 10.1021/es015783i Google Scholar Crossref Search ADS PubMed WorldCat 107. Logan BE Extracting hydrogen and electricity from renewable resources Environ Sci Technol 2004 38 160A 167A 10.1021/es040468s Google Scholar Crossref Search ADS PubMed WorldCat 108. Lozupone CA , Knight R Global patterns in bacterial diversity Proc Natl Acad Sci USA 2007 104 27 11436 11440 2040916 10.1073/pnas.0611525104 Google Scholar Crossref Search ADS PubMed WorldCat 109. Lutgen H , Gottschalk G Cell and ATP yields of Citrobacter freundii growing with fumarate and H2 or formate in continuous culture J Gen Microbiol 1982 128 1915 Google Scholar PubMed OpenURL Placeholder Text WorldCat 110. Madamwar D , Garg N, Shah V Cyanobacterial hydrogen production World J Microbiol Biotechnol 2000 16 757 767 10.1023/A:1008919200103 Google Scholar Crossref Search ADS WorldCat 111. Mahyudin AR , Furutani Y, Nakashimada Y, Kakizono T, Nishio N Enhanced hydrogen production in altered mixed acid fermentation of glucose by Enterobacter aerogenes J Ferment Bioeng 1997 83 358 363 10.1016/S0922-338X(97)80142-0 Google Scholar Crossref Search ADS WorldCat 112. Manczinger L , Rozs M, Vágvölgyi C, Kevei F Isolation and characterization of a new keratinolytic Bacillus licheniformis strain World J Microbiol Biotechnol 2003 19 35 39 10.1023/A:1022576826372 Google Scholar Crossref Search ADS WorldCat 113. Mandal B , Nath K, Das D Improvement of biohydrogen production under decreased partial pressure of H2 by Enterobacter cloacae Biotechnol Lett 2006 28 831 835 10.1007/s10529-006-9008-8 Google Scholar Crossref Search ADS PubMed WorldCat 114. Maness PC , Weaver PF Hydrogen production from a carbon-monoxide oxidation pathway in Rubrivivax gelatinosus Int J Hydrogen Energy 2002 27 1407 1411 10.1016/S0360-3199(02)00107-6 Google Scholar Crossref Search ADS WorldCat 115. Maschio G , Lucchesi A, Stoppato G Production of syngas from biomass Bioresour Technol 1994 48 119 126 10.1016/0960-8524(94)90198-8 Google Scholar Crossref Search ADS WorldCat 116. Mc Kendry P Energy production from biomass (part 1): overview of biomass Bioresour Technol 2002 83 37 46 10.1016/S0960-8524(01)00118-3 Google Scholar Crossref Search ADS PubMed WorldCat 117. Mertens R , Liese A Biotechnological applications of hydrogenases Curr Opin Biotechnol 2004 15 343 348 10.1016/j.copbio.2004.06.010 Google Scholar Crossref Search ADS PubMed WorldCat 118. Mizuno O , Dinsdale R, Hawkes FR, Hawkes DL, Noike T Enhancement of hydrogen production from glucose by nitrogen gas sparging Bioresour Technol 2000 73 59 65 10.1016/S0960-8524(99)00130-3 Google Scholar Crossref Search ADS WorldCat 119. Mizuno O , Ohara T, Shinya M, Noike T Characteristics of hydrogen production from bean curd manufacturing waste by anaerobic microflora Water Sci Technol 2000 42 345 50 Google Scholar Crossref Search ADS WorldCat 120. Moharikar A , Purohit HJ, Kumar R Microbial population dynamics at effluent treatment plants J Environ Monit 2005 7 552 558 10.1039/b406576j Google Scholar Crossref Search ADS PubMed WorldCat 121. Morii H , Nakamiya K, Kinoshita S Isolation of lignin-decoloursing bacterium J Ferment Bioeng 1995 80 296 299 10.1016/0922-338X(95)90835-N Google Scholar Crossref Search ADS WorldCat 122. Morimoto M , Atsuko M, Atif AAY, Ngan MA, Fakhru’l-Razi A, Iyuke SE, Bakir AM Biological production of hydrogen from glucose by natural anaerobic microflora Int J Hydrogen Energy 2004 29 709 713 10.1016/j.ijhydene.2003.09.009 Google Scholar Crossref Search ADS WorldCat 123. Mukherjee S , Das P, Sen R Towards commercial production of microbial surfactants Trends Biotechnol 2006 24 509 515 10.1016/j.tibtech.2006.09.005 Google Scholar Crossref Search ADS PubMed WorldCat 124. Nakashimada Y , Rachman MA, Kakizono T, Nishio N Hydrogen production of Enterobacter aerogenes altered by extracellular and intracellular redox state Int J Hydrogen Energy 2002 27 1399 1405 10.1016/S0360-3199(02)00128-3 Google Scholar Crossref Search ADS WorldCat 125. Nandi R , Sengupta R Microbial production of hydrogen: an overview Crit Rev Microbiol 1998 24 61 84 10.1080/10408419891294181 Google Scholar Crossref Search ADS PubMed WorldCat 126. Nashio N , Nakashimada Y High rate production of hydrogen / methane from various substrates and wastes Recent Prog Biochem Biomed Eng Japan I 2004 90 63 87 10.1007/b94192 Google Scholar Crossref Search ADS WorldCat 127. Nath N , Das D Improvement for fermentative hydrogen production: various approaches Appl Microbiol Biotechnol 2004 65 520 529 10.1007/s00253-004-1644-0 Google Scholar Crossref Search ADS PubMed WorldCat 128. Noike T , Mizuno O Hydrogen fermentation of organic municipal wastes Water Sci Technol 2000 42 155 162 Google Scholar Crossref Search ADS WorldCat 129. Oh YK , Seol EH, Kim JR, Park S Fermentative biohydrogen production by a new chemohetreotrophic bacterium Citrobacter sp. Y19 Int J Hydrogen Energy 2003 28 1353 1359 10.1016/S0360-3199(03)00024-7 Google Scholar Crossref Search ADS WorldCat 130. Okamoto M , Miyahara T, Mizuno O, Noike T Biological hydrogen potential of materials characteristic of the organic fraction of municipal solid wastes Water Sci Technol 2000 41 25 32 Google Scholar Crossref Search ADS PubMed WorldCat 131. Onifade AA , Al-Sane NA, Al-Mussallam AA, Al-Zarbam S Potentials for biotechnological applications of keratin-degrading microorganisms and their enzymes for nutritional improvement of feathers and other keratins as livestock feed resources Bioresour Technol 1998 66 1 11 10.1016/S0960-8524(98)00033-9 Google Scholar Crossref Search ADS WorldCat 132. Orlando US , Baes AU, Nishijima W, Okada M A new procedure to produce lignocellulosic anion exchangers from agricultural waste materials Bioresour Technol 2002 83 195 198 10.1016/S0960-8524(01)00220-6 Google Scholar Crossref Search ADS PubMed WorldCat 133. Pandey A , Pandey A, Srivastava P, Pandey A Using reverse micelles as microreactor for hydrogen production by coupled systems of Nostoc/R. palustris and Anabaena/R. palustris World J Microbiol Biotechnol 2007 23 269 274 10.1007/s11274-006-9224-3 Google Scholar Crossref Search ADS WorldCat 134. Patel S , Madamwar D Photohydrogen production from a coupled system of Halobacterium halobium and Phormidium valderianum Int J Hydrogen Energy 1994 19 733 738 10.1016/0360-3199(94)90236-4 Google Scholar Crossref Search ADS WorldCat 135. Perestelo F , Falcon MA, Carnicero A, Rodriguez A, de la Fuente G Limited degradation of industrial, synthetic and natural lignins by Serratia marcescens Biotechnol Lett 1994 16 299 302 10.1007/BF00134629 Google Scholar Crossref Search ADS WorldCat 136. Pontes DS , Lima-Bittencourt CI, Chartone-Souza E, Nascimento AMA Molecular approaches: advantages and artifacts in assessing bacterial diversity J Ind Microbiol Biotechnol 2007 34 463 473 10.1007/s10295-007-0219-3 Google Scholar Crossref Search ADS PubMed WorldCat 137. Porwal S, Kumar T, Lal S, Rani A, Kumar S, Cheema S, Purohit HJ, Sharma R, Patel SKS, Kalia VC (2007) Hydrogen and polyhydroxybutyrate producing abilities of microbes from diverse habitats by dark fermentative process. Bioresour Technol. doi:10.1016/j.biortech.2007.11.011 138. Puppan D Environmental evaluation of biofuels Period Polytech Ser Soc Man Sci 2002 10 95 116 Google Scholar OpenURL Placeholder Text WorldCat 139. Quan X , Shi H, Liu H, Lv P, Qian Y Enhancement of 2,4-dichlorophenol degradation in conventional activated sludge systems bioaugmented with mixed special culture Water Res 2004 38 245 253 10.1016/j.watres.2003.09.003 Google Scholar Crossref Search ADS PubMed WorldCat 140. Rachman MA , Nkashimada Y, Kakizono T, Nishio N Hydrogen production with high yield and high evolution rate by self-flocculated cells of Enterobacter aerogenes in a packed-bed reactor Appl Microbiol Biotechnol 1998 49 450 454 10.1007/s002530051197 Google Scholar Crossref Search ADS WorldCat 141. Ragauskas AJ , Williams CK, Davison BH, Britovsek G, Cairney J, Eckert CA, Frederick WJ Jr, Hallett JP, Leak DJ, Liotta CL, Mielenz JR, Murphy R, Templer R, Tschaplinski T The path forward for biofuels and biomaterials Science 2006 311 484 489 10.1126/science.1114736 Google Scholar Crossref Search ADS PubMed WorldCat 142. Raizada N , Sonakya V, Anand V, Kalia VC Waste management and production of future fuels J Sci Ind Res 2002 61 184 207 Google Scholar OpenURL Placeholder Text WorldCat 143. Ramachandran R , Menon RK An overview of industrial uses of hydrogen Int J Hydrogen Energy 1998 23 593 598 10.1016/S0360-3199(97)00112-2 Google Scholar Crossref Search ADS WorldCat 144. Raskin J Intestinal gas Geriatrics 1980 38 77 Google Scholar OpenURL Placeholder Text WorldCat 145. Reddy CSK , Ghai R, Rashmi H, Kalia VC Polyhydroxyalkanoates: an overview. Bioresour Technol 2003 87 137 146 10.1016/S0960-8524(02)00212-2 Google Scholar Crossref Search ADS PubMed WorldCat 146. Reddy RM , Reddy PG, Seenayya G Enhanced production of thermostable β-amylase and pullulanase in the presence of surfactants by Clostridium thermosulfurogenes SV2 Process Biochem 1999 34 87 92 10.1016/S0032-9592(98)00073-9 Google Scholar Crossref Search ADS WorldCat 147. Rey MW, Ramaiya P, Nelson BA, Brody-Karpin SD, Zaretsky EJ, Tang M, Lopez de Leon A, Xiang H, Gusti V, Clausen G, Olsen PB, Rasmussen MD, Andersen JT, Jørgensen PL, Larsen TS, Sorokin A, Bolotin A, Lapidus A, Galleron N, Ehrlich SD, Berka RM (2004) Complete genome sequence of the industrial bacterium Bacillus licheniformis and comparisons with closely related Bacillus species. Genome Biol 4, 5:r77. doi:10.1186/gb-2004-5-10-r77 148. Robson R (2001) Biodiversity of hydrogenases. In: Cammack R, Robson R, Frey M (eds) Hydrogen as a fuel: learning from nature. Taylor and Francis, London (http://www.kcl.ac.uk/ip/richardcammack/H2/hbook1.html) 149. Roychowdhury S , Cox D, Levandowsky M Production of hydrogen by microbial fermentation Int J Hydrogen Energy 1988 13 407 410 10.1016/0360-3199(88)90126-7 Google Scholar Crossref Search ADS WorldCat 150. Rumessen JJ , Bode S, Hamberg O, Gudmand-Hoyer E Fructans of Jerusalem artichokes: intestinal transport, absorption, fermentation, and influence on blood glucose, insulin, and C-peptide responses in healthy subjects Am J Clin Nutr 1990 52 675 681 Google Scholar Crossref Search ADS PubMed WorldCat 151. Salih FM Improvement of hydrogen photoproduction from E. coli pre-treated cheese whey Int J Hydrogen Energy 1989 19 807 812 Google Scholar OpenURL Placeholder Text WorldCat 152. Sandrin TO , Maier RM Impacts of metals on the biodegradation of pollutants Environ Health Persp 2003 111 1093 1101 10.1289/ehp.5840 Google Scholar Crossref Search ADS WorldCat 153. Sasikala K , Ramana CV, Rao PR Photoproduction of hydrogen from the waste water of a distillery by Rhodobacter sphaeroides O.U. 001 Int J Hydrogen Energy 1992 17 23 27 10.1016/0360-3199(92)90217-K Google Scholar Crossref Search ADS WorldCat 154. Scow KM , Hicks KA Natural attenuation and enhanced bioremediation of organic contaminants in ground water Curr Opin Biotechnol 2005 16 246 253 10.1016/j.copbio.2005.03.009 Google Scholar Crossref Search ADS PubMed WorldCat 155. Seon YH , Lee CG, Park DH, Hwang KY, Joe YI Hydrogen production by immobilized cells in nozzle loop bioreactor Biotechnol Lett 1983 15 1275 1280 10.1007/BF00130311 Google Scholar Crossref Search ADS WorldCat 156. Sharma KK , Kapoor M, Kuhad RC In vivo enzymatic digestion, in vitro xylanase digestion, metabolic analogues, surfactants and polyethylene glycol ameliorate laccase production from Gonoderma sp. kk-02 Lett Appl Microbiol 2005 41 24 31 10.1111/j.1472-765X.2005.01721.x Google Scholar Crossref Search ADS PubMed WorldCat 157. Shin HS , Youn JH, Kim SH Hydrogen production from food waste in anaerobic mesophilic and thermophilic acidogenesis Int J Hydrogen Energy 2004 29 1355 1363 10.1016/j.ijhydene.2003.09.011 Google Scholar Crossref Search ADS WorldCat 158. Sonakya V , Raizada N, Kalia VC Microbial and enzymatic improvement of anaerobic digestion of waste biomass Biotechnol Lett 2001 23 1463 1466 10.1023/A:1011664912970 Google Scholar Crossref Search ADS WorldCat 159. Sparling R , Daniels L The specificity of growth inhibition of methanogenic bacteria by bromoethane sulfonate Can J Microbiol 1987 33 1132 1136 10.1139/m87-199 Google Scholar Crossref Search ADS WorldCat 160. Sparling R , Risbey D, Poggi-Varaldo HM Hydrogen production from inhibited anaerobic composters Int J Hydrogen Energy 1997 22 563 566 10.1016/S0360-3199(96)00137-1 Google Scholar Crossref Search ADS WorldCat 161. Stephanopoulos G Challenges in engineering microbes for biofuels production Science 2007 315 801 804 10.1126/science.1139612 Google Scholar Crossref Search ADS PubMed WorldCat 162. Suihko ML , Stackebrandt E Identification of aerobic mesophilic Bacilli isolated from board and paper products containing recycled fibres J Appl Microbiol 2003 94 25 34 10.1046/j.1365-2672.2003.01803.x Google Scholar Crossref Search ADS PubMed WorldCat 163. Sung S, Raskin L, Duangmanee T, Padmasiri S, Simmons JJ (2002) Hydrogen production by anaerobic microbial communities exposed to repeated heat treatments. In: Proceedings of the 2002 U.S. DOE hydrogen program review NREL/CP-610–32405 164. Suntornsuk W , Suntornsuk L Feather degradation by Bacillus sp. FK46 in submerged cultivation Bioresour Technol 2003 86 239 243 10.1016/S0960-8524(02)00177-3 Google Scholar Crossref Search ADS PubMed WorldCat 165. Taguchi F , Mizukami N, Hasegawa K, Saito-Taki T Microbial conversion of arabinose and xylose to hydrogen by a newly isolated Clostridium sp. no. 2 Can J Microbiol 1994 40 228 233 10.1139/m94-037 Google Scholar Crossref Search ADS WorldCat 166. Taguchi F , Mizukami N, Saito-Taki T, Hasegawa K Hydrogen production from continuous fermentation of xylose during growth of Clostridium sp. strain no.2 Can J Microbiol 1995 41 536 540 10.1139/m95-071 Google Scholar Crossref Search ADS WorldCat 167. Tanisho S , Ishiwata Y Continuous hydrogen production by molasses by the bacterium Enterobacter aerogenes Int J Hydrogen Energy 1994 19 807 812 10.1016/0360-3199(94)90197-X Google Scholar Crossref Search ADS WorldCat 168. Thangaraj A , Kulandaivelu G Biological hydrogen photoproduction using dairy and sugarcane waste waters Bioresour Technol 1994 48 9 12 10.1016/0960-8524(94)90127-9 Google Scholar Crossref Search ADS WorldCat 169. Thauer RK , Jungermann K, Decker K Energy conservation in chemotrophic anaerobic bacteria Bacteriol Rev 1977 41 100 180 413997 Google Scholar Crossref Search ADS PubMed WorldCat 170. Tibelius KH , Knowles R Effect of hydrogen and oxygen on uptake-hydrogenase activity in nitrogen-fixing ammonium-grown Azospirillum brasilense Can J Microbiol 1983 29 1119 1125 10.1139/m83-172 Google Scholar Crossref Search ADS WorldCat 171. Tortoriello V , DeLancey GB Optimal biocatalyst loading in a fixed bed J Ind Microbiol Biotechnol 2007 34 475 481 10.1007/s10295-007-0217-5 Google Scholar Crossref Search ADS PubMed WorldCat 172. Troshina O , Serebryakova L, Sheremetieva M, Lindblad P Production of H2 by the unicellular cyanobacterium Gloeocapsa alpicola CALU 743 during fermentation Int J Hydrogen Energy 2002 27 1283 1289 10.1016/S0360-3199(02)00103-9 Google Scholar Crossref Search ADS WorldCat 173. Turner JA Sustainable hydrogen production Science 2004 305 972 974 10.1126/science.1103197 Google Scholar Crossref Search ADS PubMed WorldCat 174. Ueno Y , Kawai T, Sato S, Otsuka S, Morimoto M Biological production of hydrogen from cellulose by mixed anaerobic microflora J Ferment Bioeng 1995 79 395 397 10.1016/0922-338X(95)94005-C Google Scholar Crossref Search ADS WorldCat 175. Ueno Y , Otsuka S, Morimoto M Hydrogen production from industrial wastewater by anaerobic microflora in chemostat culture J Ferment Bioeng 1996 82 194 197 10.1016/0922-338X(96)85050-1 Google Scholar Crossref Search ADS WorldCat 176. Ueno Y , Haruta S, Ishii M, Igarashi Y Characterization of a microorganism isolated from the effluent of hydrogen fermentation by microflora J Biosci Bioeng 2001 92 397 400 10.1016/S1389-1723(01)80247-4 Google Scholar Crossref Search ADS PubMed WorldCat 177. Valdez-Vazquez I , Sparling R, Risbey D, Rinderknecht-Seijas N, Poggi-Varaldo HM Hydrogen generation via anaerobic fermentation of paper mill wastes Bioresour Technol 2005 96 1907 1913 10.1016/j.biortech.2005.01.036 Google Scholar Crossref Search ADS PubMed WorldCat 178. Van Ginkel SW , Sung S, Lay JJ Biohydrogen production as a function of pH and substrate concentration Environ Sci Technol 2001 35 4726 4730 10.1021/es001979r Google Scholar Crossref Search ADS PubMed WorldCat 179. Van Niel EWJ , Budde MAW, de Haas GG, van der Wal FJ, Claassen PAM, Stams AJM Distinctive properties of high hydrogen producing extreme thermophiles, Caldicellulosiruptor saccharolyticus and Thermotoga elfii Int J Hydrogen Energy 2002 27 1391 1398 10.1016/S0360-3199(02)00115-5 Google Scholar Crossref Search ADS WorldCat 180. VenkataMohan S, Babu VL, Sarma PN (2007) Effect of various pretreatment methods on anaerobic mixed microflora to enhance biohydrogen production utilizing dairy wastewater as substrate. Bioresour Technol. doi:10.1016/j.biortech.2006/.12.004 181. Veziroglu TN , Barbir F Hydrogen: the wonder fuel Int J Hydrogen Energy 1992 17 391 404 10.1016/0360-3199(92)90183-W Google Scholar Crossref Search ADS WorldCat 182. Veziroglu TN Twenty years of hydrogen movement 1974–1994 Int J Hydrogen Energy 1995 20 1 7 10.1016/0360-3199(94)00099-L Google Scholar Crossref Search ADS WorldCat 183. Vincenzini M , Marchini A, Ena A, De Philippis R H2 and poly-β-hydroxybutyrate, two alternative chemicals from purple non-sulfur bacteria Biotechnol Lett 1997 19 759 762 10.1023/A:1018336209252 Google Scholar Crossref Search ADS WorldCat 184. Walter J , Mangold M, Tannock GW Construction, analysis, and β-glucanasae cscreening of a bacterial artifical chromosome library from the large bowel microbiota of mice Appl Environ Microbiol 2005 71 2347 2354 1087578 10.1128/AEM.71.5.2347-2354.2005 Google Scholar Crossref Search ADS PubMed WorldCat 185. Wani A , Surakasi VP, Siddharth J, Raghavan RG, Patole MS, Ranade D, Shouche YS Molecular analyses of microbial diversity associated with the Lonar soda lake in India: an impact crater in a basalt area Res Microbiol 2006 157 928 937 10.1016/j.resmic.2006.08.005 Google Scholar Crossref Search ADS PubMed WorldCat 186. Wawrzkiewicz K , Wolski T, Lobarzewski J Screening of keratinolytic activity of dermatophytes in vitro Mycophtholodgia 1991 114 1 8 10.1007/BF00436684 Google Scholar Crossref Search ADS WorldCat 187. Weaver P , Lien S, Seibert M Photobiological production of hydrogen Solar Energy 1980 24 3 10.1016/0038-092X(80)90018-3 Google Scholar Crossref Search ADS WorldCat 188. Wolin MJ The rumen fermentation: a model for microbial. interactions in anaerobic ecosystems Adv Microb Ecol 1979 3 49 77 10.1007/978-1-4615-8279-3_2 Google Scholar Crossref Search ADS WorldCat 189. Wu SY , Lin CN, Lee KS, Chang JS, Kin PJ Microbial hydrogen production with immobilized sewage sludge Biotechnol Prog 2002 18 921 926 10.1021/bp0200548 Google Scholar Crossref Search ADS PubMed WorldCat 190. Wu SY , Lin CN, Chang JS, Chang JS Biohydrogen production with anaerobic sludge immobilized by ethylene-vinyl acetate copolymer Int J Hydrogen Energy 2005 30 1375 1381 10.1016/j.ijhydene.2004.09.011 Google Scholar Crossref Search ADS WorldCat 191. Wunschiers R , Lindblad P Hydrogen in education—a biological approach Int J Hydrogen Energy 2002 27 1131 1140 10.1016/S0360-3199(02)00098-8 Google Scholar Crossref Search ADS WorldCat 192. Yeonghee A , Eun-Jung P, You-Kwan O, Sunghoon P, Gordion W, Weightman AJ Biofilm microbial community of a thermophilic trickling biofilter used for continuous biohydrogen production FEMS Microbiol Lett 2005 249 31 38 10.1016/j.femsle.2005.05.050 Google Scholar Crossref Search ADS PubMed WorldCat 193. Yigit DO , Gunduz U, Turker L, Yucel M, Eroglu I Identification of by-products in hydrogen producing bacteria; Rhodobacter sphaeroides O.U. 001 grown in the wastewater of a sugar refinery J Biotechnol 1999 70 125 131 10.1016/S0168-1656(99)00066-8 Google Scholar Crossref Search ADS WorldCat 194. Yilmaz M , Soran H, Beyatli Y Determination of poly-β-hydroxybutyrate (PHB) production by some Bacillus spp World J Microbiol Biotechnol 2005 21 565 566 10.1007/s11274-004-3274-1 Google Scholar Crossref Search ADS WorldCat 195. Yokoi H , Maeda Y, Hirose J, Hayashi S, Takasaki Y H2 production by immobilized cells of Clostridium butyricum on porous glass beads Bioresour Technol 1997 11 431 433 Google Scholar OpenURL Placeholder Text WorldCat 196. Yokoi H , Mori S, Hirose J, Hayashi S, Takasaki Y H2 production from starch by mixed culture of Clostridium butyricum and Rhodobacter sp M-19 Biotechnol Lett 1998 20 895 899 10.1023/A:1005327912678 Google Scholar Crossref Search ADS WorldCat 197. Yokoi H , Tokushige T, Hirose J, Hayashi S, Takasaki Y H2 production from starch by mixed culture of Clostridium buytricum and Enterobacter aerogenes Biotechnol Lett 1998 20 143 147 10.1023/A:1005372323248 Google Scholar Crossref Search ADS WorldCat 198. Yokoi H , Saitsu AS, Uchida H, Hirose J, Hayashi S, Takasaki Y Microbial hydrogen production from sweet potato starch residue J Biosci Bioeng 2001 91 58 63 10.1016/S1389-1723(01)80112-2 Google Scholar Crossref Search ADS PubMed WorldCat 199. Yokoi H , Maki R, Hirose J, Hayashi S Microbial production of hydrogen from starch manufacturing wastes Biomass Bioenergy 2002 22 89 395 10.1016/S0961-9534(02)00014-4 Google Scholar Crossref Search ADS WorldCat 200. Yokoyama H , Waki M, Moriya N, Yasuda T, Tanaka Y, Haga K Effect of fermentation temperature on hydrogen production from cow waste slurry by using anaerobic microflora within the slurry Appl Microbiol Biotechnol 2007 74 474 483 10.1007/s00253-006-0647-4 Google Scholar Crossref Search ADS PubMed WorldCat 201. Yokoyama H , Waki M, Ogino A, Ohmori H, Tanaka Y Hydrogen fermentation properties of undiluted cow dung J Biosci Bioeng 2007 104 82 85 10.1263/jbb.104.82 Google Scholar Crossref Search ADS PubMed WorldCat 202. Yu Z , Mohn WW Bioaugmentation with the resin acid-degrading bacterium Zoogloea resiniphila DhA-35 to counteract pH stress in an aerated lagoon treating pulp and paper mill effluent Water Res 2002 36 2793 2801 10.1016/S0043-1354(01)00496-1 Google Scholar Crossref Search ADS PubMed WorldCat 203. Zajic JE , Margaritis A, Brosseau JD Microbial hydrogen production from replenishable resources Int J Hydrogen Energy 1979 4 385 402 10.1016/0360-3199(79)90101-0 Google Scholar Crossref Search ADS WorldCat 204. Zeikus JG The biology of methanogenic bacteria Bacteriol Rev 1977 41 514 541 414011 Google Scholar Crossref Search ADS PubMed WorldCat 205. Zeikus JG Chemical and fuel production by anaerobic bacteria Annu Rev Microbiol 1980 34 423 464 10.1146/annurev.mi.34.100180.002231 Google Scholar Crossref Search ADS PubMed WorldCat 206. Zhang T , Liu H, Fang HHP Biohydrogen production from starch in wastewater under thermophilic condition J Environ Manage 2003 69 149 156 10.1016/S0301-4797(03)00141-5 Google Scholar Crossref Search ADS PubMed WorldCat 207. Zhu H , Suzuki T, Tsygankov AA, Asada Y, Miyake J Hydrogen production from tofu wastewater by Rhodobacter sphaeroides immobilized in agar gels Int J Hydrogen Energy 1999 24 305 310 10.1016/S0360-3199(98)00081-0 Google Scholar Crossref Search ADS WorldCat 208. Zinder SH Brock TD Thermophilic waste treatment systems Thermophiles: general, molecular and applied biology 1986 New York Wiley-Interscience 257 Google Scholar Google Preview OpenURL Placeholder Text WorldCat COPAC 209. Zurrer H , Bachofen R Aspects of growth and H2 production of the photosynthetic bacterium Rhodospirillum rubrum Biomass 1982 2 165 174 10.1016/0144-4565(82)90027-0 Google Scholar Crossref Search ADS WorldCat 210. http://nai.arc.nasa.gov/news_stories/news_detail.cfm?article=deepbugs.cfm 211. http://rdp.cme.msu.edu 212. http://www.genome.ad.jp/ 213. http://www.ncbi.nlm.nih.gov/ 214. http://www.eere.energy.gov/hydrogenandfuelcells/pdfs/fermentation_wkshp.pdf 215. http://www.thilo-ruehle.de/Biblio/Biblio.htm © Society for Industrial Microbiology 2008 This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/open_access/funder_policies/chorus/standard_publication_model) © Society for Industrial Microbiology 2008
TI - Microbial diversity and genomics in aid of bioenergy
JF - Journal of Industrial Microbiology and Biotechnology
DO - 10.1007/s10295-007-0300-y
DA - 2008-05-01
UR - https://www.deepdyve.com/lp/oxford-university-press/microbial-diversity-and-genomics-in-aid-of-bioenergy-XVItsroZ2N
SP - 403
EP - 419
VL - 35
IS - 5
DP - DeepDyve
ER -