RESEARCH LETTER
Production of sophorolipid biosurfactants by multiple species ofthe
Starmerella (Candida) bombicola yeast clade
Cletus P. Kurtzman1, Neil P.J. Price2, Karen J. Ray2 & Tsung-Min Kuo2
1
Foodborne Bacterial Pathogens and Mycology Research Unit, National Center for Agricultural Utilization Research, Agricultural Research Service, US
Department of Agriculture, Peoria, IL, USA; and 2Renewable Product Technology Research Unit, National Center for Agricultural Utilization Research,
Agricultural Research Service, US Department of Agriculture, Peoria, IL, USA
Correspondence: Cletus P. Kurtzman,
Foodborne Bacterial Pathogens and Mycology
Research Unit, National Center for
Agricultural Utilization Research, Agricultural
Research Service, US Department of
Agriculture, 1815 N. University St., Peoria, IL
61604, USA. Tel.: 11 309 681 6385; fax: 11
309 681 6672; e-mail:
[email protected]
Received 21 May 2010; revised 19 July 2010;
accepted 21 July 2010.
Final version published online 25 August 2010.
DOI:10.1111/j.1574-6968.2010.02082.x
MICROBIOLOGY LETTERS
Editor: Bernard Prior
Abstract
Sophorolipids are carbohydrate-based, amphiphilic biosurfactants that are of
increasing interest for use in environmentally benign cleaning agents. Sophorolipid production was tested for 26 strains representing 19 species of the Starmerella
yeast clade, including Starmerella bombicola and Candida apicola, which were
previously reported to produce sophorolipids. Five of the 19 species tested showed
significant production of sophorolipids: S. bombicola, C. apicola, Candida
riodocensis, Candida stellata and a new species, Candida sp. NRRL Y-27208. A
high-throughput matrix-assisted laser desorption/ionization-time of flight MS
assay was developed that showed S. bombicola and C. apicola to produce a lactone
form of sophorolipid, whereas C. riodocensis, C. stellata and Candida sp. NRRL
Y-27208 produced predominantly free acid sophorolipids. Phylogenetic analysis of
sequences for the D1/D2 domains of the nuclear large subunit rRNA gene placed
all sophorolipid-producing species in the S. bombicola subclade of the Starmerella
clade.
Keywords
sophorolipids; yeasts; biosurfactant; phylogeny;
MALDI-TOF MS.
Introduction
The annual worldwide production of surfactants has been
reported to be about 10 million tons, with use about equally
divided between household detergents and various industrial applications (Van Bogaert et al., 2007). Currently used
surfactants are often petroleum derived, but production of
these compounds from renewable substrates is now of
considerable interest. Sophorolipids, which consist of the
sugar sophorose linked to a long-chain hydroxy fatty acid,
are among candidate compounds that can be produced from
renewable sources.
Interest in sophorolipids is not limited to production of
surfactants. The unique chemical structure of sophorolipids
can serve as the basis for synthesizing certain hydroxy fatty
acids and other compounds (Van Bogaert et al., 2007).
Perhaps of greater interest are reports that these glycolipids
have antimicrobial activity against certain yeasts (Ito et al.,
1980), plant pathogenic fungi (Yoo et al., 2005) and bacteria
(Mager et al., 1987; Lang et al., 1989). Furthermore, Shah
c 2010 Federation of European Microbiological Societies
Journal compilation Published by Blackwell Publishing Ltd. No claim to original US government works
et al. (2005) showed inhibition of the HIV virus by
sophorolipids, and Chen et al. (2006) provided evidence
that the compounds have anticancer activity.
Sophorolipids are synthesized by a phylogenetically
diverse group of yeasts. The earliest report appears to be
that of Gorin et al. (1961), who demonstrated sophorolipid
biosynthesis by the anamorphic ascomycetous yeast Candida apicola, which was initially identified as Candida magnoliae. Later, Spencer et al. (1970) showed sophorolipid
production by Candida bombicola, and Konoshi et al.
(2008) reported Candida batistae to also form sophorolipids. The preceding three Candida sp. are closely related, but
sophorolipid biosynthesis was also demonstrated for the less
closely related Wickerhamiella domercqiae (Chen et al., 2006)
as well as for the basidiomycetous yeast Rhodotorula bogoriensis (Tulloch et al., 1968).
Phylogenetic analysis of sequences for the D1/D2 domains of the nuclear large subunit (LSU) rRNA gene has
shown that C. apicola and C. bombicola are members of a
clade that is well separated from other ascomycetous yeasts
FEMS Microbiol Lett 311 (2010) 140–146
141
Sophorolipids from yeasts
(Kurtzman & Robnett, 1998). Candida bombicola is the first
member of the clade for which ascospore formation was
discovered and the species was reassigned to the teleomorphic genus Starmerella (Rosa & Lachance, 1998). With
the application of sequence analysis to yeast identification,
the group of yeasts related to Starmerella bombicola, now
termed the Starmerella clade, has increased markedly in the
past decade to over 40 species. Many of these species have
not been described as yet but are presently recognized from
their gene sequences, which have been deposited in GenBank. Candida apicola, C. batistae and S. bombicola are the
only members of the Starmerella clade that have been
reported to produce sophorolipids. In the present work, we
examined additional species of the Starmerella clade for
production of sophorolipids using a matrix-assisted laser
desorption/ionisation-time of flight (MALDI-TOF) MSbased screen similar to that used previously to identify
bacterial biosurfactants, rhamnolipids, surfactins and iturins (Price et al., 2007, 2009; Rooney et al., 2009). From this
analysis, we found three additional sophorolipid-producing
species of the Starmerella clade, one of which is a novel
species, and have determined that two forms of sophorolipids are selectively synthesized by different species within
the clade.
Materials and methods
Yeast cultures
The strains examined in this study were obtained from the
ARS Culture Collection (NRRL), National Center for Agricultural Utilization Research, Peoria, IL, and maintained on
YM agar (3 g L1 yeast extract, 3 g L1 malt extract, 5 g L1
peptone, 10 g L1 glucose and 20 g L1 agar, in distilled
water).
Sophorolipid production medium and
growth conditions
The medium used for production of sophorolipids was
termed SL medium and composed of 100 g L1 glucose,
87.5 g L1 (100 mL L1) oleic acid (Aldrich, technical grade),
1.5 g L1 yeast extract, 4 g L1 NH4Cl, 1 g L1 KH2PO4 H2O,
0.1 g L1 NaCl and 0.5 g L1 MgSO4 7H2O, in distilled
water. The initial pH was adjusted to 4.5 with 6 N KOH.
Unless specified otherwise, cultures were grown at 25 1C in
50-mL Erlenmeyer flasks with 10 mL of SL medium and
shaken at 200 r.p.m. in an Innova 4335 shaker incubator.
Incubation times were either 96 or 168 h and the time is
given with each reported experiment. The pH of the flask
cultures was adjusted to 3.5 twice daily by the addition of
1 N NaOH.
FEMS Microbiol Lett 311 (2010) 140–146
Separation and quantitation of sophorolipids
and oleic acid
The 10 mL of spent SL medium from each shake flask was
acidified with 0.4 mL 6 N HCl and extracted twice with
40 mL of ethyl acetate to remove sophorolipids and unmetabolized oleic acid. The ethyl acetate extract was reduced to
dryness in a rotoevaporator, redissolved in 2 mL chloroform, transferred to a glass vial and reduced to dryness
under a nitrogen gas stream. Oleic acid was separated from
sophorolipids in the mixture by three separate 3 mL hexane
extractions. The hexane was evaporated and the concentration of oleic acid was quantified by weight, which was
confirmed by gas–liquid chromatography (Price et al.,
2009). The residue that remained after hexane extraction
was the sophorolipid fraction and the amount was determined by weight following confirmation of the presence of
sophorolipids by MALDI-TOF MS as described below.
Yields of sophorolipids and consumption of oleic acid are
reported as averages and were determined from duplicate
cultures, which varied no more than 11%.
MALDI-TOF mass spectrometric screen
for sophorolipids
MALDI-TOF MS screening was accomplished using a Bruker
Omniflex instrument in reflectron mode with positive ion
detection. The samples were dissolved in ethyl acetate and the
matrix used was 2,5-dihydroxybenzoic acid. The instrument
conditions were used as described previously (Price et al.,
2009). Determinations were performed in duplicate.
DNA preparation, gene sequencing and
phylogenetic analysis
The methods used for DNA isolation, purification and
sequencing were reported earlier (Kurtzman & Robnett,
1998). DNA characterization was initiated by PCR amplification of the D1/D2 domain of the LSU rRNA gene followed
by sequencing reactions using the ABI Big Dye Terminator
v3.0 Cycle Sequencing Kit. Sequences of both DNA strands
were determined by capillary electrophoresis using an ABI
3130 genetic analyzer (Applied Biosystems, Foster city, CA).
Phylogenetic analysis of the gene sequences was determined
using the maximum parsimony program included in PAUP
4.063a (Swofford, 1998). Sequences were visually aligned for
analysis and Saccharomyces cerevisiae was the designated
outgroup species.
Results and discussion
In the present study, 26 strains representing 19 species of the
Starmerella clade were analyzed for production of sophorolipids. Results are reported in Fig. 1, which gives the yield
for strains of each species, and the phylogenetic placement
c 2010 Federation of European Microbiological Societies
Journal compilation Published by Blackwell Publishing Ltd. No claim to original US government works
142
C.P. Kurtzman et al.
Fig. 1. Phylogenetic tree of the Starmerella clade determined from maximum parsimony analysis of gene sequences for the D1/D2 domains of nuclear
LSU rRNA. Species names are followed by the culture collection strain number and the GenBank accession number for the sequence analyzed. Strains
analyzed in the present study are presented in bold type and the yield of sophorolipids is given in brackets. For sophorolipid production, cultures were
grown in SL medium in a shaker incubator at 25 1C, 200 r.p.m. for 96 h. Strains with Y or YB prefixes designate NRRL numbers. Additional strain
information may be obtained using the GenBank accession numbers. Numbers at tree nodes are bootstrap values based on 1000 replicates. TType strain,
NT
neotype strain. Saccharomyces cerevisiae was designated as outgroup species in the phylogenetic analysis and Candida bombiphila served as an
unrelated reference species for sophorolipid analysis.
c 2010 Federation of European Microbiological Societies
Journal compilation Published by Blackwell Publishing Ltd. No claim to original US government works
FEMS Microbiol Lett 311 (2010) 140–146
143
Sophorolipids from yeasts
of the strains as determined from the analysis of D1/D2 LSU
rRNA gene sequences. Five of the 19 species tested showed
significant production of sophorolipids: C. apicola, S. bombicola, Candida riodocensis, Candida stellata and a new
species of Candida, NRRL Y-27208, which will be described
in a future study. In our earlier work, phylogenetic analysis
detected 12 species in the Starmerella clade (Kurtzman &
Robnett, 1998) and they separated into two subclades, one
represented by C. bombicola and the other by C. magnoliae.
With the widespread application of gene sequence analysis
in yeast taxonomy, 41 separate lineages (species) are
known for the clade and all were included in the phylogenetic analysis shown in Fig. 1 to lend perspective to the
placement of species that were tested for the biosynthesis of
sophorolipids. However, many of the lineages are undescribed species, which are recognized only from their gene
sequences, and cultures are not presently available for
analysis.
Even with the addition of many new lineages to the
Starmerella clade, the two subclades originally recognized
are still evident. Based on the present analysis, sophorolipids
are produced only by members of the S. bombicola subclade.
Although not included in our analysis, C. batistae was
shown by Konoshi et al. (2008) to form sophorolipids, and
this species is a member of the S. bombicola subclade (Fig.
1). As seen from Fig. 1, not all members of the subclade
produce sophorolipids, and of particular interest for C.
apicola, NRRL Y-2481 gave the greatest yield of any strain
tested, whereas NRRL Y-6688, a somewhat divergent strain
of this species, produced essentially no sophorolipids. In
earlier studies of sophorolipid biosynthesis by C. apicola,
Tulloch et al. (1968) reported a yield of 40 g L1 without
optimizing the culture medium, much as we found in our
assays. Our goal in this study was to test previously
unexamined species for sophorolipid production without
optimization. We did, however, examine the effect of
incubation time, shaker speed and glucose concentration
on sophorolipid production by C. bombicola NRRL Y-17069
and Candida sp. NRRL Y-27208, which as described below,
produce sophorolipids with a different molecular structure.
Starmerella bombicola NRRL Y-17069 gave maximum
sophorolipid yield after 144-h incubation, whereas Candida
sp. NRRL Y-27208 produced near-maximum yield after
168 h, the time of the final analysis (Table 1). For both
species, increasing yields of sophorolipids were accompanied by decreasing concentrations of oleic acid, which was
expected because of the incorporation of oleic acid into the
sophorolipid molecule. The requirement for high aeration
in production of sophorolipids was reported earlier (Guilmanov et al., 2002) and again shown in this study for both S.
bombicola NRRL Y-17069 and Candida sp. NRRL Y-27208
(Table 2). The maximum yield of sophorolipids was obtained at a shaker speed of 350 r.p.m.
FEMS Microbiol Lett 311 (2010) 140–146
Table 1. Production of sophorolipids by Starmerella bombicola NRRL Y17069 and Candida sp. NRRL Y-27208 over a period of 168 h
Sophorolipids produced (g L1)/oleic acid consumed
(g L1 residual)
Time (h)
S. bombicola NRRL Y-17069
Candida sp. NRRL Y-27208
24
48
72
96
120
144
168
0.7/83.4
11.8/65.4
54.4/28.7
61.0/33.9
62.6/27.3
64.0/23.5
63.6/16.3
0.6/84.5
3.4/79.2
11.0/64.3
11.4/67.8
30.4/35.9
39.6/14.8
44.5/6.2
Growth was in SL medium, 25 1C, with a shaker speed of 200 r.p.m. The
initial concentration of oleic acid was 87.5 g L1.
Table 2. Effect of glucose concentration and shaker speed on production of sophorolipids by Starmerella bombicola NRRL Y-17069 and
Candida sp. NRRL Y-27208
Sophorolipids produced
(g L1)/oleic acid consumed (g L1 residual)
Growth
conditions
S. bombicola
NRRL Y-17069
Glucose concentration (g L1)
50
48.8/9.7
100
69.9/10.3
150
95.4/10.0
Shaker speed (r.p.m.)w
150
35.6/52.5
200
62.2/34.2
250
62.6/31.1
300
67.9/27.1
350
75.1/19.4
400
76.4/18.3
Candida sp.
NRRL Y-27208
29.0/16.7
38.6/18.3
50.1/8.2
3.5/78.7
19.8/57.8
24.7/50.2
30.9/45.6
27.1/50.3
27.0/51.4
SL medium with glucose concentrations as indicated, shaker speed
200 r.p.m., incubation 168 h, 25 1C.
SL medium with glucose 100 g L1, initial oleic acid concentration
87.5 g L1, incubation 96 h, 25 1C.
w
Glucose concentration noticeably affected sophorolipid
production by both S. bombicola NRRL Y-17069 and Candida sp. NRRL Y-27208 (Table 2). For S. bombicola, 50 g L1
glucose yielded 48.8 g L1 sophorolipid, whereas 150 g L1
glucose yielded 95.4 g L1 sophorolipid. The increased sophorolipid production was not fully reflected in the reduced
concentration of residual oleic acid (Table 2), suggesting
that a portion of the lipid moiety was synthesized by the
yeast. During production of sophorolipids, the pH of the
culture medium declined from 4.5 to as low as 1.8. To
sustain production, the pH was readjusted twice daily to 3.5
with 1 N NaOH. The precipitous decrease in pH during
sophorolipid production and its impact on reducing yield
was reported earlier by Gobbert et al. (1984).
c 2010 Federation of European Microbiological Societies
Journal compilation Published by Blackwell Publishing Ltd. No claim to original US government works
144
C.P. Kurtzman et al.
Fig. 2. Pile-up of MALDI-TOF MS mass spectra of
the sophorolipids from the five major producing
Candida spp. The mass range shown is 620–760
Da. Assignments for the [M1Na]1 molecular
adduct ions shown are listed in Table 3.
The solvent extracts obtained from all 26 strains examined were initially screened for the presence of sophorolipids
by MALDI-TOF MS using techniques developed previously
by Price et al. (2009). The spectra were characterized by
molecular adduct ions for sophorolipids in the mass range
620–720 Da (Fig. 2). Major ions at m/z 711 and m/z 729 are
respectively attributed to the [M1Na]1 molecular adduct
ions for the lactone and free acid forms of the major
diacetylated sophorolipid, 6 0 ,600 -O-diacetyl-b-D-glucopyra
nosyl-21-O-b-D-glucopyranosyl-oxy-octadecenoic acid (Asmer et al., 1988). The observed 18 Da difference between
these two ions corresponds to the mass difference between
the free carboxylic acid form and the ester-linked 4 0 -Olactone (Fig. 2). Less intense ions at m/z 669 and m/z 687
correspond to the monoacetylated forms of the major
sophorolipids, and m/z 627 and m/z 645 correspond to the
non-acetylated forms (Fig. 2). The 18 Da mass difference
between these two sets of ions is again indicative of the free
acid and lactone forms of the minor sophorolipids, and the
42 Da difference between di-, mono- and non-acetylated
species is characteristic of O-linked acetyl groups (Price
et al., 2009). Similar sophorolipid ions were also observed
previously for C. bombicola by fast atom bombardment MS
(Asmer et al., 1988; De Koster et al., 1995).
The five species of the Starmerella clade tested that
showed the most prominent production of sophorolipids:
S. bombicola NRRL Y-17069, C. stellata NRRL Y-1446, the
new species of Candida, NRRL Y-27208, C. riodocensis
NRRL Y-27859 and C. apicola NRRL Y-2481, were further
examined by MALDI-TOF MS. These five strains showed a
clear structural diversity for the sophorolipids produced (Fig. 2).
c 2010 Federation of European Microbiological Societies
Journal compilation Published by Blackwell Publishing Ltd. No claim to original US government works
Starmerella bombicola NRRL Y-17069 produced a major diO-acetylated lactone form of sophorolipid ([M1Na]1, m/z
711), plus a minor component of this as the free acid form
([M1Na]1, m/z 729). This latter ion is complicated by an
adjacent ion at m/z 727 that is assigned as the potassium
adduct ([M1K]1) of the major lactone form. By contrast,
C. stellata, Candida sp. NRRL Y-27208 and C. riodocensis
produced very little of this lactone form (Fig. 2), and the
major ion (m/z 729) for these three species is attributed to a
di-O-acetyl free acid form. These strains also produced free
acid forms of the monoacetylated and non-acetylated sophorolipids characterized by MALDI-TOF MS ions at m/z
687 and m/z 645. Candida riodocensis and Candida sp.
NRRL Y-27208, but not C. stellata, also produced monoacetylated sophorolipid in the lactone form ([M1Na]1, m/z
669). The greatest heterogeneity for sophorolipid production was observed for C. apicola NRRL Y-2481. Similar to S.
bombicola, this strain mainly produced lactone sophorolipids, although with C. apicola, the di-O-acetyl (m/z 711),
mono-O-acetyl (m/z 669) and non-acetyl (m/z 627) forms
were observed. The free acid forms of these three sophorolipids were also observed as minor components from C.
apicola, as characterized by ions 18 Da larger at m/z 729, m/z
687 and m/z 645, respectively (Fig. 2). Interestingly, the free
acid form was the major component of sophorolipids
produced by C. batistae (Konoshi et al., 2008).
Conclusions
This study demonstrated that in addition to S. bombicola, C.
apicola and C. batistae, three other species of the Starmerella
FEMS Microbiol Lett 311 (2010) 140–146
145
Sophorolipids from yeasts
Table 3. Deduced structures of the sophorolipids identified by MALDI-TOF MS
R'O
R'O
O
HO
HO
R''O
O
HO
O
O
O
HO
HO
R''O
O
O
O
O
HO
HO
OH
OH
C
O
HOOC
Sophorolipid lactone form
Sophorolipid - free acid form
[M1Na]1 (m/z)
R 0 /R00
Forms
Formulae
Calc. mass
627.34
645.35
669.36
687.36
711.36
729.37
OH/OH
OH/OH
OH/acetate
OH/acetate
Di-O-acetate
Di-O-acetate
Lactone
Free acid
Lactone
Free acid
Lactone
Free acid
C30H52O12
C30H54O13
C32H54O13
C32H56O14
C34H56O14
C34H58O15
604.35
622.36
646.36
664.37
688.37
706.38
Accurate masses were calculated using ISOPRO 3.0.
clade synthesize significant amounts of sophorolipids, i.e.,
C. riodocensis, C. stellata and Candida sp. NRRL Y-27208.
Based on our phylogenetic analysis, sophorolipids were
produced only by members of the S. bombicola subclade of
the Starmerella clade.
MALDI-TOF MS showed certain of the species to produce sophorolipids predominantly in the lactone form,
whereas the other species predominantly gave the free acid
form. It should be noted that although MALDI-MS is well
suited for the rapid screening and characterization of
sophorolipids with diverse molecular mass, it is unable to
distinguish between positional isomers, such as differences
in the location of acetyl groups, or the fatty acid double
bond or acyl-glycosidic linkage. For this reason, a more
complete structural characterization of the sophorolipids
from Candida sp. NRRL Y-27208 will be published later.
Acknowledgements
We thank Eleanor Basehoar-Powers and Trina Hartman for
technical assistance and Jamie Schroderus for graphics
assistance in preparation of Fig. 1. The mention of firm
names or trade products does not imply that they are
endorsed or recommended by the US Department of Agriculture over other firms or similar products not mentioned.
References
Asmer HJ, Lang S, Wagner F & Wray V (1988) Microbial
production, structural elucidation, and bioconversion of
sophorose lipids. J Am Oil Chem Soc 65: 1460–1466.
FEMS Microbiol Lett 311 (2010) 140–146
Chen J, Song X, Zhang H, Qu YB & Miao JY (2006) Production,
structure elucidation and anticancer properties of
sophorolipid from Wickerhamiella domercqiae. Enzyme Microb
Tech 39: 501–506.
De Koster CG, Heerma W, Pepermans HA, Groenewegen A,
Peters H & Haverkamp J (1995) Tandem mass spectrometry
and nuclear magnetic resonance spectroscopy studies of
Candida bombicola sophorolipids and product formed on
hydrolysis by cutinase. Anal Biochem 230: 135–148.
Gobbert U, Lang S & Wagner F (1984) Sophorose lipid formation
by resting cells of Torulopsis bombicola. Biotechnol Lett 6:
225–230.
Gorin PAJ, Spencer JFT & Tulloch AP (1961) Hydroxy fatty acid
glycosides of sophorose from Torulopsis magnoliae. Can J
Chem 39: 846–855.
Guilmanov V, Ballistreri A, Impallomeni G & Gross RA (2002)
Oxygen transfer rate and sophorose lipid production by
Candida bombicola. Biotechnol Bioeng 77: 489–494.
Ito S, Kinta M & Inoue S (1980) Growth of yeasts on normalalkanes – inhibition by a lactonic sophorolipid produced by
Torulopsis bombicola. Agr Biol Chem 44: 2221–2223.
Konoshi M, Fukuoka T, Morita T, Imura T & Kitamoto D (2008)
Production of new types of sophorolipids by Candida batistae.
J Oleo Sci 57: 359–369.
Kurtzman CP & Robnett CJ (1998) Identification and phylogeny
of ascomycetous yeasts from analysis of nuclear large subunit
(26S) ribosomal DNA partial sequences. Antonie van
Leeuwenhoek 73: 331–371.
Lang S, Katsiwela E & Wagner F (1989) Antimicrobial effects of
biosurfactants. Fat Sci Technol 91: 363–366.
c 2010 Federation of European Microbiological Societies
Journal compilation Published by Blackwell Publishing Ltd. No claim to original US government works
146
Mager H, Röthlisberger R & Wagner F (1987) Use of sophoroselipid lactone for the treatment of dandruffs and body odor.
European Patent 0209783.
Price NPJ, Rooney AP, Swezey JL, Perry E & Cohan FM (2007)
Mass spectrometric analysis of lipopeptides from Bacillus
strains isolated from diverse geographical locations. FEMS
Microbiol Lett 271: 83–89.
Price NPJ, Ray KJ, Vermillion K & Kuo TM (2009) MALDI-TOF
mass spectrometry of naturally occurring mixtures of
monorhamnolipids and dirhamnolipids. Carbohyd Res 344:
204–209.
Rooney AP, Price NPJ, Ray KJ & Kuo T-M (2009) Isolation and
characterization of rhamnolipid-producing bacterial strains
from a biodiesel facility. FEMS Microbiol Lett 295: 82–87.
Rosa C & Lachance MA (1998) The yeast genus Starmerella gen.
nov. and Starmerella bombicola sp. nov., the teleomorph of
Candida bombicola (Spencer, Gorin & Tulloch) Meyer &
Yarrow. Int J Syst Bacteriol 48: 1413–1417.
c 2010 Federation of European Microbiological Societies
Journal compilation Published by Blackwell Publishing Ltd. No claim to original US government works
C.P. Kurtzman et al.
Shah V, Doncel GF, Seyoum T, Eaton KM, Zalenskaya I,
Hagver R, Azim A & Gross R (2005) Sophorolipids, microbial
glycolipids with anti-human immunodeficiency virus and
sperm-immobilizing activities. Antimicrob Agents Ch 49:
4093–4100.
Spencer JFT, Gorin PAJ & Tulloch AP (1970) Torulopsis bombicola
sp. n. Antonie van Leeuwenhoek 36: 129–133.
Swofford DL (1998) PAUP 4.0: Phylogenetic Analysis Using
Parsimony. Sinauer Associates, Sunderland, MA.
Tulloch AP, Spencer JFT & Deinema MH (1968) A new hydroxy
fatty acid sophoroside from Candida bogoriensis. Can J Chem
46: 345–348.
Van Bogaert IN, Saerens K, De Muynck C, Develter D, Soetaert W
& Vandamme EJ (2007) Microbial production and application
of sophorolipids. Appl Microbiol Biot 76: 23–34.
Yoo DS, Lee BS & Kim EK (2005) Characteristics of microbial
biosurfactant as an antifungal agent against plant pathogenic
fungus. J Microbiol Biot 15: 1164–1169.
FEMS Microbiol Lett 311 (2010) 140–146