Euglena sanguinea Ehrenberg is the only known species of euglenids which forms toxic blooms causing tangible losses to fish farms. Euglena sanguinea produces euglenophycin, a toxin similar in structure to solenopsin, an alkaloid found in fire ant venom. It was proved that euglenophycin exhibits not only ichthyotoxic but also herbicidal and anticancer activity. Recently, a specific mass spectrometric method of identification and quantitation of euglenophycin was developed to facilitate monitoring of that toxin in freshwater ponds. Despite the recent taxonomic verifications, proper identification of E. sanguinea is still difficult, especially for less experienced researchers. Herein, we describe a simple method based on nested PCR amplification of the nSSU rDNA fragments to identify a single E. sanguinea cell and its detection in a sample of water. The method will further facilitate monitoring of water reservoirs, especially estimating the risk of toxic blooms. . . . . Keywords Euglena sanguinea Euglenophycin Toxic blooms DNA barcoding Molecular identification Introduction herbicidal and anticancer activity (Zimba et al. 2010, 2016). Recently, a specific mass spectrometric method of identifica- At the beginning of the twenty-first century, the occurrence of tion and quantitation of euglenophycin was developed to facil- toxic algae blooms in freshwater aquaculture ponds was report- itate monitoring of that toxin in freshwater ponds (Gutierrez ed 13 times in the USA (North and South Carolina, Texas, et al. 2013). The latest laboratory experiments revealed that Arkansas, and Mississippi). Lost revenue from these events euglenophycin is produced not only by E. sanguinea but also exceeded US$1.1 million (Zimba et al. 2004, 2010). The dom- by seven other euglenid species: Euglena sociabilis P. A. inant algae species was a euglenid (Excavata, Euglenozoa, Dangeard, Euglena stellata Mainx, Euglenaria clavata Euglenida), which was isolated, cultured, and recognized as (Skuja) Karnkowska-Ishikawa & E.W. Linton, Euglenaria the fish mortality-inducing factor. The euglenid species present anabaena (Mainx) Karnkowska-Ishikawa & E.W. Linton, in toxic blooms was identified as Euglena sanguinea. The Strombomonas borystehnienis (Y. V. Roll) T. G. Popova, toxicity was observed both for isolates taken from the infested Trachelomonas ellipsoidalis K. P. Singh, and Lepocinclis acus ponds as well as for the clonal strain from the culture collec- (O. F. Müll.) B. Marin & Melkonian (Zimba et al. 2017). tion. The toxin produced by E. sanguinea, called However, E. sanguinea remains the only known species of euglenophycin, was identified and described. It is an alkaloid euglenids to form toxic blooms. similar in structure to fire ant venom, solenopsin. It was proved Euglena sanguinea is a cosmopolitan species which can be that euglenophycin exhibits not only ichthyotoxic but also found in shallow, calm, and eutrophic freshwater systems. It was one of the first green euglenid species described in the literature (Ehrenberg 1831). However, its correct identifica- Electronic supplementary material The online version of this article (https://doi.org/10.1007/s10811-017-1376-z) contains supplementary tion was problematic due to complicated chloroplast morphol- material, which is available to authorized users. ogy—the original diagnostic feature (Pringsheim 1956). In effect, during over 200 years of studying euglenids, 12 new * Rafał Milanowski taxa resembling E. sanguinea were named, although their cor- email@example.com rect identification based on morphology alone was practically impossible. Recently, a review of the description of E. Department of Molecular Phylogenetics and Evolution, Institute of sanguinea and species similar to it was conducted by verify- Botany, Faculty of Biology, Biological and Chemical Research Center, University of Warsaw, ul. Żwirki i Wigury 101, ing morphological and molecular data. The result of the anal- 02-089 Warsaw, Poland ysis was a reduction of the number of species from 12 to four 1760 J Appl Phycol (2018) 30:1759–1763 (E. sanguinea, E. sociabilis, Euglena splendens P. A. of Coimbra, Portugal). In the control group experiments, Dangeard, and Euglena laciniata E. G. Pringsheim). DNA samples from nine Euglena species were used: E. Furthermore, new epitypes and updated diagnostic descrip- rubra A. D. Hardy (MI 103), E. splendens (MI 47), E. tristella tions were also established for them (Karnkowska-Ishikawa S. P. Chu (NJ, New Jersey isolate Triemer Lab, Department of et al. 2013). Finally, the most significant diagnostic features Plant Biology Michigan State University), E. sociabilis were recognized: the presence of fusiform mucocysts, the (ACOI 920), E. deses Ehrenberg (ASW08075, now available number of chloroplasts, the size of the double-sheathed pyre- from CCAC, Culture Collection of Algae, University of noids, and the presence of the large paramylon grain in the Cologne, Germany as E. intermedia Matvienko CCAC 2443 vicinity of the stigma. However, despite taxonomic verifica- B), E. clara Skuja (SAG 25.98), E. gracilis G. A. Klebs (SAG tions, proper identification of this species is still challenging, 1224-5/25), E. laciniata (SAG 1224-31), and E. viridis particularly for less experienced researchers. The method Ehrenberg (SAG 1224-17d). All strains were cultivated in a allowing unambiguous recognition of E. sanguinea is based liquid soil–water medium enriched with a small piece of gar- on the use of its nSSU rDNA as a molecular barcode. den pea (medium 3c, Schlösser 1994) and kept in a growth DNA barcoding is a powerful method for species-level chamber maintained at 17 °C and a 16:8-h light/dark cycle, ca. −2 −1 identification (Hajibabaei et al. 2007), particularly for inexpe- 27 μmol photons m s provided by cool white fluorescent rienced researchers. It is fast, accurate, and does not require tubes. Additionally, three environmental fresh water samples morphological analyses (Blaxter 2004). There is no universal from Poland containing E. sanguinea cells were used. barcode—several markers, such as COI, ITS, nSSU rDNA, Environmental sample 1 was collected from a small pond in matK,and rbcL, are used for different eukaryotic organisms. Rudawka village (53° 51′ 56.5″ N, 23° 30′ 52.6″ E) in For phototrophic euglenids, the variable regions V2–V3 and July 2015; the other two samples were collected from field V4 of nSSU rDNA seem to be the best barcodes (Łukomska- ponds near Urwitałt village: sample 2 (53° 49′ 09.5″ N, 21° Kowalczyk et al. 2016). Unfortunately, E. sanguinea is the 39′ 21.8″ E) in June 2011 and sample 3 (53° 50′ 43.1″ N, 21° sole species of the group for which the use of standard 36′ 42.3″ E) in June 2012. From each pond, a 10-L sample methods of nSSU rDNA amplification has proved unsatisfac- was collected, and plankton nets with a mesh size of 10, 50, tory. The reason is the unusual structure of this sequence, and 100 μm were used to increase density (up to 1 L) and which is much longer than in any other species. The length exclude bigger plankton organisms and other macroscopic of the sequence from the strain SAG 1224-30 is over 6000 bp objects. Samples were transported to the laboratory and were and seems to be the longest known SSU rDNA sequence centrifuged (100 mL of each sample); the sediment was (Karnkowska-Ishikawa et al. 2013). The amplification of very suspended in 10 mL of water and split into separate long variable regions V2–V3 and V4 is far from efficient and Eppendorf tubes (1 mL) and stored at − 20 °C until needed molecular identification of E. sanguinea using standard for DNA isolation. The presence of E. sanguinea cells in methods is problematic. Therefore, we decided to refine the samples was confirmed with a NIKON Eclipse E-600 micro- species-specific PCR test, which enables recognition of E. scope with a differential interference contrast, equipped with sanguinea through the peculiarity of its nSSU rDNA. This the NIS-Elements Br 3.1 software (Nikon). Also, the popula- method can further facilitate monitoring of freshwater ponds tion density of each species was estimated as follows: (o) cells and estimating the risk of toxic blooms formed by E. very occasionally observed in one drop (50 μL of the 10-mL sanguinea. sample after centrifugation), (+) 5–10 cells, (++) 11–20 cells, (+++) 21–30 cells, and (++++) over 30 cells. Materials and methods Primer designing Strains, culture conditions, and environmental Based on the alignment of all available euglenid nSSU rDNA samples sequences, the regions for primer design were chosen accord- ing to the following principles: (i) regions conserved for E. Five strains of Euglena sanguinea from algae collections were sanguinea (GenBank numbers: strain Argentina JQ281804, used in the study: SAG 1224-30 (SAG, Sammlung von Henderson JQ281805, and SAG 1224-30 JQ281806), but dis- Algenkulturen, Pflanzenphysiologisches Institut der similar to any other species of euglenids, were chosen; (ii) Universität Göttingen, Germany, as Euglena magnifica intraspecific variations within the region were flanked by the E.G.Pringsheim), Henderson (the strain isolated from toxic primers; and (iii) the length of the PCR product had to be bloom from a pond in Texas), MI-20 and MI-51 (MI, appropriate for efficient amplification. Two sets of species- Michigan isolate Triemer Lab, Department of Plant Biology, specific primers were designed manually—the external Michigan State University), and ACOI 1267 (ACOI, Culture primers sangF0/R0 (encompassing the region between helix Collection of Algae at the Department of Botany, University 29 and 45 in the secondary structure of nSSU rDNA; sangF0: J Appl Phycol (2018) 30:1759–1763 1761 CTGYGGGCGCCACGCCCCCTTG, s angR0: 60 °C, and 20 s at 72 °C. The final extension step was per- ACGGACTTGCRGGGTTTCCCAGC) and the internal formed for 5 min at 72 °C. The control PCR reactions were primers sangF1/R1 (between helix 30 and 45; sangF1: also performed with DNA stemming from various Euglena CGCCCCCTTGACCGAGAAATCCG, sangR1: species. All PCR reactions were carried out in the presence GCCRGGGCCCRCAGAARACGAGG). of positive (DNA from E. sanguinea) and negative (water or buffer) controls. Chosen PCR products were sized on agarose PCR templates gels, purified and sequenced directly from both strands using the BigDye Terminator Cycle Sequencing Ready Reaction Kit Three types of templates were used: (i) DNA isolated from 3.1 (Applied Biosystems). cultures, (ii) DNA from lysis of a single cell/a defined number of cells, and (iii) DNA isolated from environmental samples (fresh water reservoirs). Total genomic DNA from cell cul- Results tures and environmental samples had been purified with DNeasy Tissue Kit (Qiagen) in accordance with the animal Designed primer pairs amplified efficiently and specifically tissues protocol. Single cell lysis was performed according to thefragmentofnSSUrDNAfrom E. sanguinea strains (length the Lax and Simpson (2013) procedure, slightly modified. of PCR products with sangF0/R0: SAG 1224-30—921 bp, Single cells were isolated with a micropipette using a micro- Henderson, MI-20 and ACOI 1267—743 bp; sangF1/R1: manipulator (MM-89, Narishiege) installed on a Nikon Ni-U SAG 1224-30—878 bp, Henderson, MI-20 and ACOI microscope and collected in 0.2-mL PCR tubes. Probes with 1267—700 bp, MI-51—717 bp, GenBank no. KY928280) 1, 5, 30, and 100 cells of E. sanguinea were prepared. Liquid in a wide range of annealing temperatures (54–64 °C for traces were removed by centrifuging in a Speed Vac concen- sangF0/R0 and 50–66 °C for sangF1/R1). The optimal tem- trator, followed by the addition of 5 μLof the Phusion GC perature for the pair of external primers sangF0/R0 was 62 °C. PCR buffer (no additional buffer was used in the subsequent For internal primers sangF1/R1, the optimal temperature was PCR reaction). The cells were lysed using five freeze/thaw 60 °C. The obtained sequences of PCR products were identi- cycles (liquid nitrogen/heating block 95 °C) and used directly cal for the strains Henderson, MI-20, and ACOI 1267. in PCR. Therefore, they were considered as genetically indistinguish- able and the latter two strains were not included in subsequent PCR amplification and sequencing analyses. The test for a minimal amount of template in PCR reactions revealed that 1 pg of DNA is enough for effi- The annealing temperature for the two sets of primers was cient amplification in the case of the three examined strains of optimized independently in a gradient PCR reaction (50– E. sanguinea. The reaction proved to be the most sensitive for 72 °C). The final conditions were as follows: a 25-μLreaction strain SAG 1224-30—even the amount of 0.01 pg of DNA mixture contained 0.5 U Phusion High-Fidelity DNA resulted in PCR products of good quality (Fig. 1a). The spec- Polymerase (Thermo Scientific), 0.2 mM dNTPs, 1.5 mM ificity of primers used in reactions was also tested. Single PCR MgCl , 5 pmol of each primer, reaction buffer GC (Thermo reactions with primers sangF0/R0 and sangF1/R1, as well as Scientific), and Q-solution (Qiagen). The PCR protocol nested amplification, gave negative results for nine Euglena consisted of 2 min at 98 °C, followed by nine initial cycles species, including E. rubra, E. splendens, E. laciniata,and E. comprising the following steps: 30 s at 98 °C, 30 s at 62 sociabilis, the species most closely related to E. sanguinea.In (sangF0/R0) or 60 °C (sangF1/R1), and 20 s at 72 °C, then turn, nested PCR tests enabled efficient amplification of the by 39 cycles comprising steps of 15 s at 98 °C, 15 s at 62 or selected nSSU rDNA region even from single cells of E. 60 °C, and 20 s at 72 °C. The final extension step was per- sanguinea. This test gave positive results for 1–30 cells lysed formed for 5 min at 72 °C. As a template, 10–50 ng of DNA by the freeze/thaw method. However, using cell numbers great- was used in standard PCR reaction, but low concentrations of er than 30 led to a decrease in efficiency, most likely due to the DNA were also tested in the range 1–0.001 pg. Nested PCR higher concentration of PCR inhibitors in unpurified samples. was used in order to make the reaction more sensitive and The nested PCR test was also used successfully for detection of specific (sangF0/R0 primers in the first round, sangF1/R1 in E. sanguinea in three environmental probes (Fig. 1b), where its the second round), particularly for amplification of DNA de- presence along with other species of euglenids (representing rived from single/defined number of cells. The conditions genera Discoplastis, Euglena, Euglenaria, Euglenaformis, were as described above. In the second round as a template, Lepocinclis, Monomorphina, Phacus, Strombomonas,and 1 μL of the mixture from the first round was used. The PCR Trachelomonas) had been confirmed earlier by microscopic protocol for the first round was as described above (annealing analysis (supplementary tables S1–3, supplementary material 62 °C); the second round consisted of the initial step 2 min at online). In the first environmental probe (sample 1), besides 98 °C, followed by 39 cycles comprising 15 s at 98 °C, 15 s at E. sanguinea, E. splendens was equally abundant; both species 1762 J Appl Phycol (2018) 30:1759–1763 Fig. 1 a Agarose gel electrophoresis of PCR products from a dilution DNA ladder; (c) negative control. b Agarose gel electrophoresis of series of template DNA from three strains of E. sanguinea (A, D) PCR products for DNA isolated form environmental fresh water samples Henderson, (B, E) SAG 1224-30, and (C, F) MI-51; (A–C) amplified with confirmed presence of E. sanguinea cells; (s1) sample; (s2) sample with the sangF0/sangR0 primer pair; (D–F) amplified with the sangF1/ 2; (s3) sample 3; (m) GeneRuler 100 bp Plus DNA lader; (c) negative sangR1 primer pair; lanes (1–4) PCR products from 1, 0.1, 0.01, and control 0.001 pg of template DNA, respectively; (m) GeneRuler 100 bp Plus are closely related and morphologically very similar niches. This, however, is of little importance to the economy. (supplementary table S1, supplementary material online). In The situation differs in the case of E. sanguinea, as its dense sample 2, no euglenids closely related or morphologically sim- blooms constitute a real threat to aquaculture, and thus to ilar to E. sanguinea were present (supplementary table S2, human population. supplementary material online). In sample 3, E. sanguinea As mentioned in BIntroduction,^ using classic microscopic and E. splendens coexisted together, but this time the E. methods for identification of E. sanguinea is challenging, splendens population was significantly larger (supplementary even for experts from the field (Karnkowska-Ishikawa et al. table S3, supplementary material online). Sequencing of PCR 2013). Therefore, the ability to identify the species based on products confirmed genetic similarity of E. sanguinea in envi- molecular data seems to be very useful. The effectiveness of ronmental samples to the strain Henderson. such identification has been demonstrated both in laboratory tests with breeding strains and environmental samples. It has been shown that a very small amount of DNA template gives Discussion positive result even in one-rounded PCR reaction. The test enabled also efficient amplification of target region in the Euglenids have been researched for almost 200 years now. strain of E. sanguinea (MI-51) which nSSU rDNA sequence During that time, more than 3000 species have been described was not previously published and was not used in primer (3200 validly published names listed in Algaebase: http:// designing. It leads to a conclusion that developed test would www.algaebase.org) and intensive research regarding the work properly also for other E. sanguinea strains which are biochemistry, molecular biology, and phylogeny of currently unknown. Moreover, the nucleotide sequence of ob- euglenids has been carried out (Zakryś et al. 2017). For this tained PCR products brings additional information, allowing reason, it is surprising that the toxicity of E. sanguinea,which for assignment of examined sample to previously described can cause measurable damage to the economy, has been strain or its qualification as the new one. On the other hand, no severely overlooked. Furthermore, recent studies have products were observed in PCR reactions for the closest rela- shown that euglenid species other than E. sanguinea tives of E. sanguinea, which proves specificity of the test. The produce euglenophycin (E. stellata, E. sociabilis, Eu. analysis of environmental samples, in which E. sanguinea anabaena, Eu. clavata, L. acus, T. ellipsoidalis, S. was present at various densities and accompanied by many borystehnienis; Zimba et al. 2017). The analysis included 33 closer or further related eugenid taxa (supplementary tables species and seven different isolates of E. sanguinea. S1–3, supplementary material online), gave similar results as Interestingly, it was revealed that the species capable of pro- for breeding strains. Particular attention should be paid to ducing toxins are not closely related but occur in different sample 3 in which the presence of E. sanguinea was detected branches of the phylogenetic tree. On this basis, it can be despite a very low abundance. Such result suggests that de- expected that many other species of euglenids that were not veloped method may be a very useful tool for monitoring included in the analysis can also produce and accumulate water reservoirs in terms of the presence of E. sanguinea cells. euglenophycin. The toxicity of some euglenids certainly plays At present, PCR-based methods are commonly used to an important role in their functioning in specific ecological detect and identify a variety of organisms, including toxic J Appl Phycol (2018) 30:1759–1763 1763 Galluzzi L, Magnani M, Saunders N, Harms C, Bruce IJ (2007) Current algae (Galluzzi et al. 2007). The test presented herein also molecular techniques for the detection of microbial pathogens. Sci utilizes this methodology and allows for analysis of E. Prog 90:29–50 sanguinea at various levels: (1) the detection of E. sanguinea Gutierrez DB, Rafalski A, Beauchesne K, Moeller PD, Triemer RE, in a sample of water taken from the environment, (2) identifi- Zimba PV (2013) Quantitative mass spectrometric analysis and post-extraction stability assessment of the euglenoid toxin cation of individual cells, and (3) sequences of obtained PCR euglenophycin. Toxins 5:1587–1596 products can be used as barcodes allowing for estimation of Hajibabaei M, Singer GA, Hebert PD, Hickey DA (2007) DNA intraspecific genetic variation and comparison of particular barcoding: how it complements taxonomy, molecular phylogenetics isolates to examined strains, including those of confirmed tox- and population genetics. Trends Genet 23:167–172 icity. This assay, together with a specific mass spectrometric Karnkowska-Ishikawa A, Milanowski R, Triemer RE, Zakryś B(2013)A redescription of morphologically similar species from the genus method of identification and quantitation of euglenophycin Euglena: E. laciniata, E. sanguinea, E. sociabilis,and E. splendens. (Gutierrez et al. 2013), will further facilitate monitoring of JPhycol 49:616–626 water reservoirs, particularly estimation of the risk of E. Lax G, Simpson AG (2013) Combining molecular data with classical sanguinea toxic blooms. morphology for uncultured phagotrophic euglenids (Excavata): a single-cell approach. J Eukaryot Microbiol 60:615–625 Acknowledgments We thank Prof. Richard Triemer, MI, USA, for pro- Łukomska-Kowalczyk M, Karnkowska A, Krupska M, Milanowski R, viding euglenid strains. Zakryś B (2016) DNA barcoding in autotrophic euglenids: evalua- tion of COI and 18S rDNA. J Phycol 52:951–960 Funding information This work was supported by grant OPUS 2016/23/ Pringsheim EG (1956) Contributions towards a monograph of the genus B/NZ8/00919 from the National Science Centre, Poland. Euglena. Nova Acta Leopoldina 18:1–168 Schlösser UG (1994) SAG-Sammlung von Algenkulturen at University Open Access This article is distributed under the terms of the Creative of Göttingen. Catalogue of Strains 1994. Bot Acta 107:111–186 Commons Attribution 4.0 International License (http:// Zakryś B, Milanowski R, Karnkowska A (2017) Evolutionary origin of creativecommons.org/licenses/by/4.0/), which permits unrestricted use, Euglena. In: Schwartzbach S, Shigeoka S (eds) Euglena:biochem- distribution, and reproduction in any medium, provided you give istry, cell and molecular biology. Springer, Berlin, pp 3–17 appropriate credit to the original author(s) and the source, provide a link Zimba PV, Rowan M, Triemer RE (2004) Identification of euglenoid to the Creative Commons license, and indicate if changes were made. algae that produce ichthyotoxin(s). J Fish Dis 27:115–117 Zimba PV, Moeller PD, Beauchesne K, Lane HE, Triemer RE (2010) Identification of euglenophycin-a toxin found in certain euglenoids. Toxicon 55:100–104 References Zimba PV, Ordner P, Gutierrez DB (2016) Selective toxicity and angio- genic inhibition by euglenophycin: a role in cancer therapy? J Blaxter ML (2004) The promise of a DNA taxonomy. Philos Trans R Soc Cancer Biol Treat 3:008 B 359:669–679 Zimba PV, Huang IS, Gutierrez D, Shin W, Bennett MS, Triemer RE Ehrenberg CG (1831) Über die Entwickelung und Lebensdauer der (2017) Euglenophycin is produced in at least six species of eugle- Infusionsthiere; nebst ferneren Beiträgen zu einer Vergleichung ihrer noid algae and six of seven strains of Euglena sanguinea.Harmful organischen Systeme. Abhandlungen der Königlichen Akademie Algae 63:79–84 der Wissenschaften Berlin. 1831:1–154; Tafeln I–IV
Journal of Applied Phycology – Springer Journals
Published: Jan 9, 2018
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