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1.
Physiological responses during growth on xylose and the xylose-degrading pathway of Candida tropicalis and Candida guilliermondii yeasts were investigated. The responses to a linearly decreasing oxygen transfer rate and a simultaneously increasing dilution rate were compared. C. guilliermondii produced acetate but no ethanol, and C. tropicalis ethanol but no acetate under oxygen limitation. Both strains produced glycerol. The D-xylose reductase of C. guilliermondii is exclusively NADPH-dependent. and acetate production regenerated NADPH. The xylose'reductase of C. tropicalis has a dual dependency for both NADH and NADPH. It regenerated NAD by producing ethanol. Both strains regenerated NAD by producing glycerol. The effect of intracellular NADH accumulation to xylose uptake and metabolite production was studied by using formate as a cosubstrate. Formate feeding in C. tropicalis triggered the accumulation of glycerol, ethanol and xylitol. Consequently, the specific xylose consumption increased 28% during formate feeding, from 477 to 609 C-mmol/C-mol cell dry-weight (CDW)/h. In C. guilliermondii cultures. formate feeding resulted only in glycerol accumulation. The specific xylose consumption increased 6%, from 301 to 319 C-mmol/C-mol CDW/h, until glycerol started to accumulate. 相似文献
2.
Summary Production of xylitol by Candida boidinii NRRL Y-17213 occurs under conditions of an oxygen limitation. The extent to which substrate is converted to xylitol and its coproducts (ethanol, other polyols, acetic acid), and the relative flow rates of substrate to energetic and biosynthetic pathways is controlled by the degree of oxygen limitation.With decrease in oxygen concentration in the inlet gas, for a constant dilution rate of 0.05 1/h. the specific oxygen uptake rate decreased from 1.30 to 0.36 mmol/gh Xylitol was not produced at specific oxygen uptake rates above 0.91 mmol/gh. Upon shift to lower oxygen rates, specific xylitol production rate increased more rapidly than specific ethanol production rate:Nomenclature D
dilution rate (1/h)
- DOT
dissolved oxygen tension (%)
- mo2
maintenance coefficient (mmol O2/g cell mass h)
- qo2
specific oxygen uptake rate (mmol O2/g cell mass h)
- qs
specific xylose uptake rate (g xylose/g cell mass h) or (mmol xylose/g cell mass h)
- qx
specific xylitol production rate (g xylitol/ g cell mass h) or (mmol xylitol/ g cell mass h)
- qe
specific ethanol production rate (g ethanol/ g cell mass h) or (mmol ethanol/ g cell mass h)
- qCO2
specific carbon dioxide production rate (mmol CO2/g cell mass h)
- S
xylose concentration (g/1)
- Ycm/s
cell mass yield coefficient, (g cell mass/mmol xylose) or (g cell mass/ g xylose consumed)
- Ycm/O2
cell mass yield coefficient, (g cell mass/mmol O2)
- YX/S
xylitol yield coefficient (g xylitol/g xylose consumed)
- Yx/O2
xylitol yield coefficient (g xylitol/mmol O2)
- Ye/s
ethanol yield coefficient (g ethanol/g xylose consumed)
- OUR
oxygen uptake rate (mmol O2/1h)
-
specific growth rate (1/h) 相似文献
3.
Candida tropicalis, a strain isolated from the sludge of a factory manufacturing xylose, produced a high xylitol concentration of 131 g/l from
150 g/l xylose at 45 h in a flask. Above 150 g/l xylose, however, volumetric xylitol production rates decreased because of
a lag period in cell growth. In fed-batch culture, the volumetric production rate and xylitol yield from xylose varied substantially
with the controlled xylose concentration and were maximum at a controlled xylose concentration of 60 g/l. To increase the
xylitol yield from xylose, feeding experiments using different ratios of xylose and glucose were carried out in a fermentor.
The maximum xylitol yield from 300 g/l xylose was 91% at a glucose/xylose feeding ratio of 15%, while the maximum volumetric
production rate of xylitol was 3.98 g l−1 h−1 at a glucose/xylose feeding ratio of 20%. Xylitol production was found to decrease markedly as its concentration rose above
250 g/l. In order to accumulate xylitol to 250 g/l, 270 g/l xylose was added in total, at a glucose/xylose feeding ratio of
15%. Under these conditions, a final xylitol production of 251 g/l, which corresponded to a yield of 93%, was obtained from
270 g/l xylose in 55 h.
Received: 20 April 1998 / Received revision: 29 May 1998 / Accepted: 19 June 1998 相似文献
4.
Efficient conversion of hexose and pentose (glucose and xylose) by a single strain is a very important factor for the production
of industrially important metabolites using lignocellulose as the substrate. The kinetics of growth and polyol production
by Debaryomyces nepalensis NCYC 3413 was studied under single and mixed substrate conditions. In the presence of glucose, the strain produced ethanol
(35.8 ± 2.3 g/l), glycerol (9.0 ± 0.2 g/l), and arabitol (6.3 ± 0.2 g/l). In the presence of xylose, the strain produced xylitol
(38 ± 1.8 g/l) and glycerol (18 ± 1.0 g/l) as major metabolites. Diauxic growth was observed when the strain was grown with
different combinations of glucose/xylose, and glucose was the preferred substrate. The presence of glucose enhanced the conversion
of xylose to xylitol. By feeding a mixture of glucose at 100 g/l and xylose at 100 g/l, it was found that the strain produced
a maximum of 72 ± 3 g/l of xylitol. A study of important enzymes involved in the synthesis of xylitol (xylose reductase (XR)
and xylitol dehydrogenase (XDH)), glycerol (glycerol-3-phosphate dehydrogenase (G3PDH)) and ethanol (alcohol dehydrogenase
(ADH)) in cells grown in the presence of glucose and xylose revealed high specific activity of G3PDH and ADH in cells grown
in the presence of glucose, whereas high specific activity of XR, XDH, and G3PDH was observed in cells grown in the presence
of xylose. To our knowledge, this is the first study to elaborate the glucose and xylose metabolic pathway in this yeast strain. 相似文献
5.
Summary The ability of C. guilliermondii and C. parapsilosis to ferment xylose to xylitol was evaluated under different oxygen transfer rates in order to enhance the xylitol yield. In C. guilliermondii, a maximal xylitol yield of 0.66 g/g was obtained when oxygen transfer rate was 2.2 mmol/l.h. Optimal conditions to produce xylitol by C. parapsilosis (0.75 g/g) arose from cultures at pH 4.75 with 0.4 mmoles of oxygen/l.h. The response of the yeasts to anaerobic conditions has shown that oxygen was required for xylose metabolism.Nomenclature max
maximum specific growth rate (per hour)
- qSmax
maximum specific rate of xylose consumption (g xylose per g dry biomass per hour)
- qpmax
maximum specific productivity of xylitol (g xylitol per g dry biomass per hour)
- Qp
average volumetric productivity of xylitol (g xylitol per liter per hour)
- YP/S
xylitol yield (g xylitol per g substrate utilized)
- YP'/S
glycerol yield (g glycerol per g substrate utilized)
- YX/S
biomass yield (g dry biomass per g substrate utilized) 相似文献
6.
M. Walfridsson M. Anderlund X. Bao B. Hahn-Hägerdal 《Applied microbiology and biotechnology》1997,48(2):218-224
Saccharomyces cerevisiae was transformed with the Pichia stipitis CBS 6054 XYL1 and XYL2 genes encoding xylose reductase (XR) and xylitol dehydrogenase (XDH) respectively. The XYL1 and XYL2 genes were placed under the control of the alcohol dehydrogenase 1 (ADH1) and phosphoglycerate kinase (PGK1) promoters in the yeast vector YEp24. Different vector constructions were made resulting in different specific activities
of XR and XDH. The XR:XDH ratio (ratio of specific enzyme activities) of the transformed S. cerevisiae strains varied from 17.5 to 0.06. In order to enhance xylose utilisation in the XYL1-, XYL2-containing S. cerevisiae strains, the native genes encoding transketolase and transaldolase were also overexpressed. A strain with an XR:XDH ratio
of 17.5 formed 0.82 g xylitol/g consumed xylose, whereas a strain with an XR:XDH ratio of 5.0 formed 0.58 g xylitol/g xylose.
The strain with an XR:XDH ratio of 0.06, on the other hand, formed no xylitol and less glycerol and acetic acid compared with
strains with the higher XR:XDH ratios. In addition, the strain with an XR:XDH ratio of 0.06 produced more ethanol than the
other strains.
Received: 12 March 1997 / Received revision: 17 April 1997 / Accepted: 27 April 1997 相似文献
7.
The xylose reductase gene (XYL1) was isolated from Pichia stipitis and Candida shehatae, cloned into YEp-based vectors under the control of ADH2 and PGK1 promoter/terminator cassettes and introduced into Saccharomyces cerevisiae Y294 by electroporation. Shake-flask fermentations were carried out with 5% xylose and 1% galactose, glucose or maltose as
co-substrates. Xylose uptake was similar in both the recombinant strains when different co-substrates were used and slowed
once the co-substrate was depleted. The recombinant strains converted xylose to xylitol with yields approaching the theoretical
maxima. Xylitol production was most rapid when the co-substrate was still present. Approximately 50% of the xylose was not
metabolized due to the depletion of the co-substrate.
Received: 23 December 1999 / Received revision: 30 June 2000 / Accepted: 1 July 2000 相似文献
8.
Xylitol and riboflavin accumulation in xylose-grown cultures of Pichia guilliermondii 总被引:1,自引:0,他引:1
Seven strains of Pichia guilliermondii (Candida guilliermondii, asexual state) from diverse isolation sources were examined for the production of xylitol and riboflavin in xylose-grown
cultures. Under the conditions tested, all strains produced xylitol from xylose; conversion efficiencies varied, on a strain-specific
basis, from 7% to 36% of the initial substrate. Four of seven strains metabolized xylitol immediately as xylose levels became
depleted. The remaining three strains metabolized xylitol slowly and incompletely. Surprisingly, utilization of xylitol showed
an apparent relationship with riboflavin production. Strains that readily metabolized xylitol produced at least threefold
greater levels of riboflavin than did strains that used xylitol slowly. Moreover, riboflavin accumulation took place during
xylitol consumption. P. guilliermondii strains that produced the highest levels of riboflavin on xylose produced significantly less riboflavin when grown on glucose
or directly on xylitol.
Received: 24 April 1996 / Received revision: 29 July 1996 / Accepted: 24 August 1996 相似文献
9.
Xylose utilisation by recombinant strains of Saccharomyces cerevisiae on different carbon sources 总被引:1,自引:0,他引:1
van Zyl WH Eliasson A Hobley T Hahn-Hägerdal B 《Applied microbiology and biotechnology》1999,52(6):829-833
Autoselective xylose-utilising strains of Saccharomyces cerevisiae expressing the xylose reductase (XYL1) and xylitol dehydrogenase (XYL2) genes of Pichia stipitis were constructed by replacing the chromosomal FUR1 gene with a disrupted fur1::LEU2 allele. Anaerobic fermentations with 80 g l−1
d-xylose as substrate showed a twofold higher consumption of xylose in complex medium compared to defined medium. The xylose
consumption rate increased a further threefold when 20 g l−1
d-glucose or raffinose was used as co-substrate together with 50 g l−1
d-xylose. Xylose consumption was higher with raffinose as co-substrate than with glucose (85% versus 71%, respectively) after
82 h fermentations. A high initial ethanol concentration and moderate levels of glycerol and acetic acid accompanied glucose
as co-substrate, whereas the ethanol concentration gradually increased with raffinose as co-substrate with no glycerol and
much less acetic acid formation.
Received: 12 March 1999 / Received revision: 31 June 1999 / Accepted: 5 July 1999 相似文献
10.
Xylulose fermentation by mutant and wild-type strains of Zygosaccharomyces and Saccharomyces cerevisiae 总被引:1,自引:0,他引:1
Eliasson A Boles E Johansson B Osterberg M Thevelein JM Spencer-Martins I Juhnke H Hahn-Hägerdal B 《Applied microbiology and biotechnology》2000,53(4):376-382
Anaerobic xylulose fermentation was compared in strains of Zygosaccharomyces and Saccharomyces cerevisiae, mutants and wild-type strains to identify host-strain background and genetic modifications beneficial to xylose fermentation.
Overexpression of the gene (XKS1) for the pentose phosphate pathway (PPP) enzyme xylulokinase (XK) increased the ethanol yield by almost 85% and resulted
in ethanol yields [0.61 C-mmol (C-mmol consumed xylulose)−1] that were close to the theoretical yield [0.67 C-mmol (C-mmol consumed xylulose)−1]. Likewise, deletion of gluconate 6-phosphate dehydrogenase (gnd1Δ) in the PPP and deletion of trehalose 6-phosphate synthase (tps1Δ) together with trehalose 6-phosphate phosphatase (tps2Δ) increased the ethanol yield by 30% and 20%, respectively. Strains deleted in the promoter of the phosphoglucose isomerase
gene (PGI1) – resulting in reduced enzyme activities – increased the ethanol yield by 15%. Deletion of ribulose 5-phosphate (rpe1Δ) in the PPP abolished ethanol formation completely. Among non-transformed and parental strains S. cerevisiae ENY. WA-1A exhibited the highest ethanol yield, 0.47 C-mmol (C-mmol consumed xylulose)−1. Other non-transformed strains produced mainly arabinitol or xylitol from xylulose under anaerobic conditions. Contrary to
previous reports S. cerevisiae T23D and CBS 8066 were not isogenic with respect to pentose metabolism. Whereas, CBS 8066 has been reported to have a high
ethanol yield on xylulose, 0.46 C-mmol (C-mmol consumed xylulose)−1 (Yu et al. 1995), T23D only formed ethanol with a yield of 0.24 C-mmol (C-mmol consumed xylulose)−1. Strains producing arabinitol did not produce xylitol and vice versa. However, overexpression of XKS1 shifted polyol formation from xylitol to arabinitol.
Received: 2 July 1999 / Accepted in revised form: 12 October 1999 相似文献
11.
M G A Felipe M Vitolo I M Mancilha S S Silva 《Journal of industrial microbiology & biotechnology》1997,18(4):251-254
The bioconversion of xylose to xylitol by Candida guilliermondii FTI 20037 cultivated in sugar cane bagasse hemicellulosic hydrolyzate was influenced by cell inoculum level, age of inoculum
and hydrolyzate concentration. The maximum xylitol productivity (0.75 g L−1 h−1) occurred in tests carried out with hydrolyzate containing 54.5 g L−1 of xylose, using 3.0 g L−1 of a 24-h-old inoculum. Xylitol productivity and cell concentration decreased with hydrolyzate containing 74.2 g L−1 of xylose.
Received 02 February 1996/ Accepted in revised form 15 November 1996 相似文献
12.
A physiological and enzymatic study of Debaryomyces hansenii growth on xylose- and oxygen-limited chemostats 总被引:1,自引:0,他引:1
The effect of changing growth rate and oxygen transfer rate (OTR) on Debaryomyces hansenii physiology was studied using xylose-limited and oxygen-limited chemostat cultures, respectively, and complemented with enzymatic
assays. Under xylose-limited chemostat (oxygen-excess), neither ethanol nor xylitol was produced over the entire range of
dilution rate (D). The maximal volumetric biomass productivity was 2.5 g l–1 h–1 at D =0.25 h–1 and cell yield was constant at all values of D. The respiratory rates and xylose consumption rate increased linearly with growth rate but, above 0.17 h–1, oxygen consumption rate had a steeper increase compared to carbon dioxide production rate. Enzymatic analysis of xylose
metabolism suggests that internal fluxes are redirected as a function of growth rate. For values of D up to 0.17 h–1, the xylose reductase (XR) titre is lower than the xylitol dehydrogenase (XDH) titre, whereas above 0.17 h–1 XR activity is about twice that of XDH and the NADPH-producing enzymes sharply increase their titres indicating an internal
metabolic flux shift to meet higher NADPH metabolic requirements. Moreover, the enzymes around the pyruvate node also exhibited
different patterns if D was above or below 0.17 h–1. Under oxygen-limited chemostat (xylose-excess) the metabolism changed drastically and, due to oxidative phosphorylation
limitation, cell yield decreased to 0.16 g g–1 for an OTR of 1.4 mmol l–1 h–1 and xylitol became the major extracellular product along with minor amounts of glycerol. The enzymatic analysis revealed
that isocitrate dehydrogenase is not regulated by oxygen, whereas XR, XDH and the NADPH-producing enzymes changed their levels
according to oxygen availability.
Electronic Publication 相似文献
13.
Hydrogen production with high yield and high evolution rate by self-flocculated cells of Enterobacter aerogenes in a packed-bed reactor 总被引:6,自引:1,他引:5
M. A. Rachman Y. Nakashimada T. Kakizono N. Nishio 《Applied microbiology and biotechnology》1998,49(4):450-454
Continuous hydrogen gas evolution by self-flocculated cells of Enterobacter aerogenes, a natural isolate HU-101 and its mutant AY-2, was performed in a packed-bed reactor under glucose-limiting conditions in
a minimal medium. The flocs that formed during the continuous culture were retained even when the dilution rate was increased
to 0.9 h−1. The H2 production rate increased linearly with increases in the dilution rate up to 0.67 h−1, giving maximum H2 production rates of 31 and 58 mmol l−1 h−1 in HU-101 and AY-2 respectively, at a dilution rate of more than 0.67 h−1. The molar H2 yield from glucose in AY-2 was maintained at about 1.1 at dilution rates between 0.08 h−1 and 0.67 h−1, but it decreased rapidly at dilution rates more than 0.8 h−1.
Received: 27 August 1997 / Received revision: 11 November 1997 / Accepted: 14 December 1997 相似文献
14.
M. A. Alexander V. W. Yang T. W. Jeffries 《Applied microbiology and biotechnology》1988,29(2-3):282-288
Summary
Candida shehatae exhibits different fermentative capacities when grown under different aeration conditions. These studies investigated the titers of xylose reductase, xylitol dehydrogenase, glucose-6-phosphate dehydrogenase and alcohol dehydrogenase in crude extracts ofCandida shehatae grown in continuous culture with various specific aeration rates. Carbon source, aeration rate, dilution rate and temperature were examined as variables. Xylose reductase and xylitol dehydrogenase were induced by xylose and were largely absent in glucose-grown cells. Alcohol dehydrogenae levels were higher in glucose-grown cells than in xylose-grown cells. The levels of this enzyme also correlated with the fermentative character of metabolism, having a low value under fully aerobic conditions, a high value under anaerobic conditions, and intermediate levels under various semi-aerobic conditions. Temperature had no effect on any enzyme level over the range of 20–30°C.Maintained in cooperation with the University of Wisconsin-Madison 相似文献
15.
Efficient fermentation of xylose, which is abundant in hydrolysates of lignocellulosic biomass, is essential for producing
cellulosic biofuels economically. While heterologous expression of xylose isomerase in Saccharomyces cerevisiae has been proposed as a strategy to engineer this yeast for xylose fermentation, only a few xylose isomerase genes from fungi
and bacteria have been functionally expressed in S. cerevisiae. We cloned two bacterial xylose isomerase genes from anaerobic bacteria (Bacteroides stercoris HJ-15 and Bifidobacterium longum MG1) and introduced them into S. cerevisiae. While the transformant with xylA from B. longum could not assimilate xylose, the transformant with xylA from B. stercoris was able to grow on xylose. This result suggests that the xylose isomerase (BsXI) from B. stercoris is functionally expressed in S. cerevisiae. The engineered S. cerevisiae strain with BsXI consumed xylose and produced ethanol with a good yield (0.31 g/g) under anaerobic conditions. Interestingly, significant
amounts of xylitol (0.23 g xylitol/g xylose) were still accumulated during xylose fermentation even though the introduced
BsXI might not cause redox imbalance. We investigated the potential inhibitory effects of the accumulated xylitol on xylose fermentation.
Although xylitol inhibited in vitro BsXI activity significantly (K
I = 5.1 ± 1.15 mM), only small decreases (less than 10%) in xylose consumption and ethanol production rates were observed when
xylitol was added into the fermentation medium. These results suggest that xylitol accumulation does not inhibit xylose fermentation
by engineered S. cerevisiae expressing xylA as severely as it inhibits the xylose isomerase reaction in vitro. 相似文献
16.
The effects of glycerol and the oxygen transfer rate on the xylitol production rate by a xylitol dehydrogenase gene (XYL2)-disrupted mutant of Candida tropicalis were investigated. The mutant produced xylitol near the almost yield of 100% from d-xylose using glycerol as a co-substrate for cell growth and NADPH regeneration: 50 g d-xylose l−1 was completely converted into xylitol when at least 20 g glycerol l−1 was used as a co-substrate. The xylitol production rate increased with the O2 transfer rate until saturation and it was not necessary to control the dissolved O2 tension precisely. Under the optimum conditions, the volumetric productivity and xylitol yield were 3.2 g l−1 h−1 and 97% (w/w), respectively. 相似文献
17.
S. Sánchez V. Bravo E. Castro A. J. Moya F. Camacho 《Applied microbiology and biotechnology》1998,50(5):608-611
We have analysed the influence of the initial pH of the medium and the quantity of aeration provided during the batch fermentation
of solutions of d-xylose by the yeast Hansenula polymorpha (34438 ATCC). The initial pH was altered between 3.5 and 6.5 whilst aeration varied between 0.0 and 0.3 vvm. The temperature
was kept at 30 °C during all the experiments. Hansenula polymorpha is known to produce high quantities of xylitol and low quantities of ethanol. The most favourable conditions for the growth
of xylitol turned out to be: an initial pH of between 4.5 and 5.5 and the aeration provided by the stirring vortex alone.
Thus, at an initial pH of 5.5, the maximum specific production rate (μm) was 0.41 h−1, the overall biomass yield (Y
x/s
G) was 0.12 g g−1, the specific d-xylose-consumption rate (q
s
) was 0.075 g g−1 h−1 (for t = 75 h), the specific xylitol-production rate (q
Xy
) was 0.31 g g−1 h−1 (for t = 30 h) and the overall yields of ethanol (Y
E/s
G) and xylitol (Y
Xy/s
G) were 0.017 and 0.61 g g−1 respectively. Both q
s
and q
Xy
decreased during the course of the experiments once the exponential growth phase had finished.
Received: 26 March 1998 / Received revision: 30 June 1998 / Accepted: 2 July 1998 相似文献
18.
I. Krallish H. Jeppsson A. Rapoport B. Hahn-Hägerdal 《Applied microbiology and biotechnology》1997,47(4):447-451
The effects of dehydration/rehydration on two strains of Saccharomyces cerevisiae: S600, a metabolically engineered xylose-utilising strain, and H158, the non-xylose-utilising host strain; and on the naturally
xylose-utilising yeast Pachysolen tannophilus CBS 4044, were compared after glucose and xylose utilisation respectively. The yeast strains differed in their ability to
excrete and accumulate intracellular xylitol. A high intracellular xylitol content before and after dehydration coincided
with a higher viability after a dehydration/rehydration cycle. The intracellular trehalose content increased during dehydration
in all three yeast strains, but this did not correspond to enhanced cell viability after dehydration/rehydration. The results
are discussed in relation to the ability of xylitol and trehalose to structure water.
Received: 9 July 1996 / Received revision: 29 October 1996 / Accepted: 2 November 1996 相似文献
19.
Kim JH Han KC Koh YH Ryu YW Seo JH 《Journal of industrial microbiology & biotechnology》2002,29(1):16-19
Xylitol, a functional sweetener, was produced from xylose by biological conversion using Candida tropicalis ATCC 13803. Based on a two-substrate fermentation using glucose for cell growth and xylose for xylitol production, fed-batch
fermentations were undertaken to increase the final xylitol concentration. The effects of xylose and xylitol on xylitol production
rate were studied to determine the optimum concentrations for fed-batch fermentation. Xylose concentration in the medium (100
g l−1) and less than 200 g l−1 total xylose plus xylitol concentration were determined as optimum for maximum xylitol production rate and xylitol yield.
Increasing the concentrations of xylose and xylitol decreased the rate and yield of xylitol production and the specific cell
growth rate, probably because of an increase in osmotic stress that would interfere with xylose transport, xylitol flux to
secretion to cell metabolism. The feeding rate of xylose solution during the fed-batch mode of operation was determined by
using the mass balance equations and kinetic parameters involved in the equations in order to increase final xylitol concentration
without affecting xylitol and productivity. The optimized fed-batch fermentation resulted in 187 g l−1 xylitol concentration, 0.75 g xylitol g xylose−1 xylitol yield and 3.9 g xylitol l−1 h−1 volumetric productivity. Journal of Industrial Microbiology & Biotechnology (2002) 29, 16–19 doi:10.1038/sj.jim.7000257
Received 15 October 2001/ Accepted in revised form 30 March 2002 相似文献
20.
Aims: To characterize the kinetics of growth, sugar uptake and xylitol production in batch and fed‐batch cultures for a xylitol assimilation‐deficient strain of Candida tropicalis isolated via chemical mutagenesis. Methods and Results: Chemical mutagenesis using nitrosoguanidine led to the isolation of the xylitol‐assimilation deficient strain C. tropicalis SS2. Shake‐flask fermentations with this mutant showed a sixfold higher xylitol yield than the parent strain in medium containing 25 g l?1 glucose and 25 g l?1 xylose. With 20 g l?1 glycerol, replacing glucose for cell growth, and various concentrations of xylose, the studies indicated that the mutant strain resulted in xylitol yields from xylose close to theoretical. Under fully aerobic conditions, fed‐batch fermentation with repeated addition of glycerol and xylose resulted in 3·3 g l?1 h?1 xylitol volumetric productivity with the final concentration of 220 g l?1 and overall yield of 0·93 g g?1 xylitol. Conclusions: The xylitol assimilation‐deficient mutant isolated in this study showed the potential for high xylitol yield and volumetric productivity under aerobic conditions. In the evaluation of glycerol as an alternative low‐cost nonfermentable carbon source, high biomass and xylitol yields under aerobic conditions were achieved; however, the increase in initial xylose concentrations resulted in a reduction in biomass yield based on glycerol consumption. This may be a consequence of the role of an active transport system in the yeast requiring increasing energy for xylose uptake and possible xylitol secretion, with little or no energy available from xylose metabolism. Significance and Impact of the Study: The study confirms the advantage of using a xylitol assimilation‐deficient yeast under aerobic conditions for xylitol production with glycerol as a primary carbon source. It illustrates the potential of using the xylose stream in a biomass‐based bio‐refinery for the production of xylitol with further cost reductions resulting from using glycerol for yeast growth and energy production. 相似文献