Effect of Carbon Source on Production of ␣-
L
-Arabinofuranosidase
by Aureobasidium pullulans
Badal C. Saha, Rodney J. Bothast
Fermentation Biochemistry Research Unit, National Center for Agricultural Utilization Research, Agricultural Research Service,
U.S. Department of Agriculture, Peoria, IL 61604, USA
Received: 16 April 1998 / Accepted: 17 June 1998
Abstract. A color-variant strain of Aureobasidium pullulans (NRRL Y-12974) produced ␣-
L
-
arabinofuranosidase (␣-
L
-AFase) when grown in liquid culture on sugar beet arabinan, wheat arabino-
xylan,
L
-arabinose,
L
-arabitol, xylose, xylitol, oat spelt xylan, corn fiber, or arabinogalactan.
L
-Arabinose
was most effective for production of both whole-broth and extracellular ␣-
L
-AFase activity, followed by
L
-arabitol. Oat spelt xylan, sugar beet arabinan, xylose, xylitol, and wheat arabinoxylan were intermediate
in their ability to support ␣-
L
-AFase production. Lower amounts of enzyme activity were detected in corn
fiber- and arabinogalactan-grown cultures.
Hemicelluloses from agricultural and forestry biomass
represent an important renewablefeedstock for bioconver-
sion into fuels and chemicals and for use in ruminant
diets [10].
L
-Arabinose residues constitute monomeric
and/or oligomeric side chains on the -1,4-linked xylose
or galactose backbones in xylans, arabinoxylans, and
arabinogalactans, and are the cores in arabinans forming
␣-1,5-linkages [20]. These side chains restrict the enzy-
matic hydrolysis of hemicelluloses by xylanases [1, 10].
␣-
L
-Arabinofuranosidases (␣-
L
-arabinofuranoside arabi-
nofuranohydrolase, EC 3.2.1.55, ␣-
L
-AFase) are exo-
type enzymes that hydrolyze terminal nonreducing ␣-
L
-
arabinofuranosyl groups from
L
-arabinose containing
polysaccharides. They are part of the enzyme complex
required for complete breakdown of xylans [1, 8].
Recently, ␣-
L
-AFases have received much attention be-
cause of their practical applications in various agro-
industrial processes such as efficient conversion of hemi-
cellulosic biomass to fuels and chemicals, delignification
of pulp, efficient utilization of plant materials into animal
feed, and hydrolysis of grape monoterpenyl glycosides
during wine fermentation [2, 7, 9]. Microbial ␣-
L
-AFases
have broad range of pH and temperature dependence,
with optimum activity occurring between pH 3.0 and 6.9
and from 40 to 70°C [2, 5, 6]. The ␣-
L
-AFase from
Bacillus stearothermophilus T-6 was most active at 70°C
and pH 5.5–6.0 with a half-life of1hatpH7.0[7]. Our
particular goal is to develop a suitable ␣-
L
-AFase for use
in the conversion of hemicellulose from various agricul-
tural residues to fermentable sugars for the subsequent
production of fuel ethanol and other value-added chemi-
cals. Aureobasidium pullulans, a yeast-like fungus, is
industrially important because of its capability of produc-
ing pullulan (a polysaccharide) [4]. The color variant
strains of Aureobasidium pullulans have been recognized
as excellent producers of amylases, xylanase, and -glu-
cosidase [12, 16, 17]. These color variant strains are
differentiated from typically pigmented (off-white to
black in appearance) strains of A. pullulans by their
brilliant pigments of red, yellow, pink, or purple and low
DNA relatedness [13, 21]. We recently found that a
color-variant strain of A. pullulans produced a highly
thermostable extracellular ␣-
L
-AFase when grown on oat
spelt xylan that had the ability to rapidly hydrolyze both
arabinan and debranchedarabinan, and release
L
-arabinose
from various arabinoxylans [15]. The enzyme purified
from oat spelt xylan-grown culture had a half-life of8hat
75°C and displayed optimal activity at 75°C and pH
4.0–4.5. To our knowledge, this is the first ␣-
L
-AFase
reported to have such a high thermophilicity. We then
Names are necessary to report factually on available data; however, the
USDA neither guarantees nor warrants the standard of the product, and
the use of the name by USDA implies no approval of the product to the
exclusion of others that may also be suitable.
Correspondence to: B.C. Saha
C
URRENT
M
ICROBIOLOGY
Vol. 37 (1998), pp. 337–340
An International Journal
Springer-Verlag New York Inc. 1998