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1.
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
2.
J R Kastner W J Jones R S Roberts 《Journal of industrial microbiology & biotechnology》1999,22(2):65-70
Candida shehatae cells pre-grown on D-xylose simultaneously consumed mixtures of D-xylose and D-glucose, under both non-growing (anoxic) and actively growing conditions (aerobic), to produce ethanol. The rate of D-glucose consumption was independent of the D-xylose concentration for cells induced on D-xylose. However, the D-xylose consumption rate was approximately three times lower than the D-glucose consumption rate at a 50% D-glucose: 50% D-xylose mixture. Repression was not observed (substrate utilization rates were approximately equal) when the percentage of
D-glucose and D-xylose was changed to 22% and 78%, respectively. In fermentations with actively growing cells (50% glucose and D-xylose), ethanol yields from D-xylose increased, the % D-xylose utilized increased, and the xylitol yield was significantly reduced in the presence of D-glucose, compared to anoxic fermentations (YETOH,xylose = 0.2–0.40 g g−1, 75–100%, and Yxylitol = 0–0.2 g g−1 compared to YETOH,xylose = 0.15 g g−1, 56%, Yxylitol = 0.51 g g−1, respectively). To increase ethanol levels and reduce process time, fed-batch fermentations were performed in a single stage
reactor employing two phases: (1) rapid aerobic growth on D-xylose (μ = 0.32 h−1) to high cell densities; (2) D-glucose addition and anaerobic conditions to produce ethanol (YETOH,xylose = 0.23 g g−1). The process generated high cell densities, 2 × 109 cells ml−1, and produced 45–50 g L−1 ethanol within 50 h from a mixture of D-glucose and D-xylose (compared to 30 g L−1 in 80 h in the best batch process). The two-phase process minimized loss of cell viability, increased D-xylose utilization, reduced process time, and increased final ethanol levels compared to the batch process.
Received 23 February 1998/ Accepted in revised form 15 July 1998 相似文献
3.
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
4.
Candida shehatae cells, cultivated on d-glucose and d-xylose, were subjected to a shift from fully aerobic to anaerobic fermentative conditions. After anaerobic conditions were
imposed, growth was limited to approximately one doubling or less as C. shehatae rapidly entered a stationary phase of growth. Following the shift to anoxia, cell viability rapidly declined and the total
cell volume declined in the d-xylose fermentations. Moreover, the cell volume distribution shifted to smaller volumes. Cell viability, measured by plate
counts, declined nine times faster for d-xylose fermentations than for d-glucose fermentations. Anaerobic growth did not occur on either d-glucose or d-xylose. Selected vitamins and amino acids did not stimulate anaerobic growth in C. shehatae, but did enhance anaerobic growth on d-glucose in S. cerevisiae. The decline in cell viability and lack of anaerobic growth by C. shehatae were attributed to oxygen deficiency and not to ethanol inhibition. The results shed light on why C. shehatae anaerobic fermentations are not currently practical and suggest that research directed towards a biochemical understanding
of why C. shehatae can not grow anaerobically will yield significant improvements in ethanol fermentations from d-xylose.
Received 26 October 1998 / Received revision: 26 January 1999 / Accepted: 12 February 1999 相似文献
5.
Yeasts that ferment both hexose and pentose are important for cost-effective ethanol production. We found that the soil yeast
strain NY7122 isolated from a blueberry field in Tsukuba (East Japan) could ferment both hexose and pentose (d-xylose and l-arabinose). NY7122 was closely related to Candida subhashii on the basis of the results of molecular identification using the sequence in the D1/D2 domains of 26S rDNA and 5.8S-internal
transcribed spacer region. NY7122 produced at least 7.40 and 3.86 g l−1 ethanol from 20 g l−1
d-xylose and l-arabinose within 24 h. NY7122 could produce ethanol from pentose and hexose sugars at 37°C. The highest ethanol productivity
of NY7122 was achieved under a low pH condition (pH 3.5). Fermentation of mixed sugars (50 g l−1 glucose, 20 g l−1
d-xylose, and 10 g l−1
l-arabinose) resulted in a maximum ethanol concentration of 27.3 g l−1 for the NY7122 strain versus 25.1 g l−1 for Scheffersomyces stipitis. This is the first study to report that Candida sp. NY7122 from a soil environment could produce ethanol from both d-xylose and l-arabinose. 相似文献
6.
Corynebacterium glutamicum R was metabolically engineered to broaden its sugar utilization range to d-xylose and d-cellobiose contained in lignocellulose hydrolysates. The resultant recombinants expressed Escherichia coli xylA and xylB genes, encoding d-xylose isomerase and xylulokinase, respectively, for d-xylose utilization and expressed C. glutamicum R bglF
317A
and bglA genes, encoding phosphoenolpyruvate:carbohydrate phosphotransferase system (PTS) β-glucoside-specific enzyme IIBCA component
and phospho-β-glucosidase, respectively, for d-cellobiose utilization. The genes were fused to the non-essential genomic regions distributed around the C. glutamicum R chromosome and were under the control of their respective constitutive promoter trc and tac that permitted their expression even in the presence of d-glucose. The enzyme activities of resulting recombinants increased with the increase in the number of respective integrated
genes. Maximal sugar utilization was realized with strain X5C1 harboring five xylA–xylB clusters and one bglF
317A
–bglA cluster. In both d-cellobiose and d-xylose utilization, the sugar consumption rates by genomic DNA-integrated strain were faster than those by plasmid-bearing
strain, respectively. In mineral medium containing 40 g l−1
d-glucose, 20 g l−1
d-xylose, and 10 g l−1
d-cellobiose, strain X5C1 simultaneously and completely consumed these sugars within 12 h and produced predominantly lactic
and succinic acids under growth-arrested conditions. 相似文献
7.
Simultaneous bioconversion of glucose and xylose to ethanol by Saccharomyces cerevisiae in the presence of xylose isomerase 总被引:3,自引:0,他引:3
Simultaneous isomerisation and fermentation (SIF) of xylose and simultaneous isomerisation and cofermentation (SICF) of a
glucose/xylose mixture was carried out by Saccharomyces cerevisiae in the presence of xylose isomerase. The SIF of 50 g l−1 xylose gave an ethanol concentration and metabolic yield of 7.5 g l−1 and 0.36 g (g xylose consumed)−1. These parameters improved to 13.4 g l−1 and 0.40 respectively, when borate was added to the medium. The SICF of a mixture of 50 g l−1 glucose and 50 g l−1 xylose gave an ethanol concentration and metabolic yield of 29.8 g l−1 and 0.42 respectively, in the presence of borate. Temperature modulation from 30 °C to 35 °C during fermentation further
enhanced the above parameters to 39 g l−1 and 0.45 respectively. The approach was extended to the bioconversion of sugars present in a real lignocellulose hydrolysate
(peanut-shell hydrolysate) to ethanol, with a fairly good yield.
Received: 14 May 1999 / Received revision: 27 September 1999 / Accepted: 2 October 1999 相似文献
8.
Miho Sasaki Toru Jojima Hideo Kawaguchi Masayuki Inui Hideaki Yukawa 《Applied microbiology and biotechnology》2009,85(1):105-115
Corynebacterium glutamicum strains CRA1 and CRX2 are able to grow on l-arabinose and d-xylose, respectively, as sole carbon sources. Nevertheless, they exhibit the major shortcoming that their sugar consumption
appreciably declines at lower concentrations of these substrates. To address this, the C. glutamicum ATCC31831 l-arabinose transporter gene, araE, was independently integrated into both strains. Unlike its parental strain, resultant CRA1-araE was able to aerobically
grow at low (3.6 g·l−1) l-arabinose concentrations. Interestingly, strain CRX2-araE grew 2.9-fold faster than parental CRX2 at low (3.6 g·l−1) d-xylose concentrations. The corresponding substrate consumption rates of CRA1-araE and CRX2-araE under oxygen-deprived conditions
were 2.8- and 2.7-fold, respectively, higher than those of their respective parental strains. Moreover, CRA1-araE and CRX2-araE
utilized their respective substrates simultaneously with d-glucose under both aerobic and oxygen-deprived conditions. Based on these observations, a platform strain, ACX-araE, for
C. glutamicum-based mixed sugar utilization was designed. It harbored araBAD for l-arabinose metabolism, xylAB for d-xylose metabolism, d-cellobiose permease-encoding bglF
317A
, β-glucosidase-encoding bglA and araE in its chromosomal DNA. In mineral medium containing a sugar mixture of d-glucose, d-xylose, l-arabinose, and d-cellobiose under oxygen-deprived conditions, strain ACX-araE simultaneously and completely consumed all sugars. 相似文献
9.
Lactic acid production from xylose by the fungus Rhizopus oryzae 总被引:1,自引:1,他引:0
Lignocellulosic biomass is considered nowadays to be an economically attractive carbohydrate feedstock for large-scale fermentation of bulk chemicals such as lactic acid. The filamentous fungus Rhizopus oryzae is able to grow in mineral medium with glucose as sole carbon source and to produce optically pure l(+)-lactic acid. Less is known about the conversion by R. oryzae of pentose sugars such as xylose, which is abundantly present in lignocellulosic hydrolysates. This paper describes the conversion of xylose in synthetic media into lactic acid by ten R. oryzae strains resulting in yields between 0.41 and 0.71 g g−1. By-products were fungal biomass, xylitol, glycerol, ethanol and carbon dioxide. The growth of R. oryzae CBS 112.07 in media with initial xylose concentrations above 40 g l−1 showed inhibition of substrate consumption and lactic acid production rates. In case of mixed substrates, diauxic growth was observed where consumption of glucose and xylose occurred subsequently. Sugar consumption rate and lactic acid production rate were significantly higher during glucose consumption phase compared to xylose consumption phase. Available xylose (10.3 g l−1) and glucose (19.2 g l−1) present in a mild-temperature alkaline treated wheat straw hydrolysate was converted subsequently by R. oryzae with rates of 2.2 g glucose l−1 h−1 and 0.5 g xylose l−1 h−1. This resulted mainly into the product lactic acid (6.8 g l−1) and ethanol (5.7 g l−1). 相似文献
10.
Fábio Coelho Sampaio Janaína Teles de Faria Jane Sélia R. Coimbra Flávia M. Lopes Passos Attilio Converti Luis Antônio Minin 《Bioprocess and biosystems engineering》2009,32(6):747-754
To develop a new enzymatic xylose-to-xylitol conversion, deeper knowledge on the regulation of xylose reductase (XR) is needed.
To this purpose, a new strain of Debaryomyces hansenii (UFV-170), which proved a promising xylitol producer, was cultivated in semi-synthetic media containing different carbon
sources, specifically three aldo-hexoses (d-glucose, d-galactose and d-mannose), a keto-hexose (d-fructose), a keto-pentose (d-xylose), three aldo-pentoses (d-arabinose, l-arabinose and d-ribose), three disaccharides (maltose, lactose and sucrose) and a pentitol (xylitol). The best substrate was lactose on which
cell concentration reached about 20 g l−1 dry weight (DW), while the highest specific growth rates (0.58–0.61 h−1) were detected on lactose, d-mannose, d-glucose and d-galactose. The highest specific activity of XR (0.24 U mg−1) was obtained in raw extracts of cells grown on d-xylose and harvested in the stationary growth phase. When grown on cotton husk hemicellulose hydrolyzates, cells exhibited
XR activities five to seven times higher than on semi-synthetic media. 相似文献
11.
Inhibition of Clostridium butyricum by 1,3-propanediol and diols during glycerol fermentation 总被引:3,自引:0,他引:3
1,3-Propanediol inhibition during glycerol fermentation to 1,3-propanediol by Clostridium butyricum CNCM 1211 has been studied. The initial concentration of the 1,3-propanediol affected the growth of the bacterium more than
the glycerol fermentation. μ
max was inversely proportional to the initial concentration of 1,3-propanediol (0–65 g l−1). For glycerol at 20 g l−1, the growth and fermentation were completely stopped at an initial 1,3-propanediol concentration of 65 g l−1. However, for an initial 1,3-propanediol concentration of 50 g l−1 and glycerol at 70 g l−1, the final concentration (initial and produced) of 1,3-propanediol reached 83.7 g l−1(1.1 M), with complete consumption of the glycerol. Therefore, during the fermentation, the strain tolerated a 1,3-propanediol
concentration higher than the initial inhibitory concentration (65 g l−1). The addition of 1,2-propanediol or 2,3-butanediol (50 g l−1) in the presence of glycerol (50–100 g l−1), showed that 2-diols reduced the μ
max in a similar way to 1,3-propanediol. The measurement of the osmotic pressure of glycerol solutions, diols and diol/glycerol
mixtures did not indicate any differences between these compounds. The hypothesis of diol inhibition was discussed. Taking
into account the strain tolerance of highly concentrated 1,3-propanediol during fermentation, the fermentation processes for
optimising production were considered.
Received: 15 November 1999 / Revision received: 1 February 2000 / Accepted: 4 February 2000 相似文献
12.
A comparative study was carried out in anaerobic batch cultures on 20 g/l of either glycerol or glucose using two propionibacteria
strains, Propionibacterium acidipropionici and Propionibacterium freudenreichii ssp. shermanii. In all cases, fermentation end-products were the same and consisted of propionic acid as the major product, acetic acid
as the main by-product and two minor metabolites, n-propanol and succinic acid. Evidence was provided that greater production of propionic acid by propionibacteria was obtained
with glycerol as carbon and energy sources. P. acidipropionici showed higher efficiency in glycerol conversion to propionic acid with a faster substrate consumption (0.64 g l−1 h−1) and a higher propionic acid production (0.42 g l−1 h−1 and 0.79 mol/mol). The almost exclusive production of propionic acid from glycerol by this bacterium suggested an homopropionic
tendency of this fermentation. Acetic acid final concentration was two times lower on glycerol (2 g/l) than on glucose (4 g/l)
for both micro-organisms. P. freudenreichii ssp. shermanii exhibited a glycerol fermentation pattern typical of non-associated glycerol-consumption-product formation. This could indicate
a particular metabolism for P. freudenreichii ssp. shermanii oriented towards the production of other specific components. These results tend to show that glycerol could be an excellent
alternative to conventional carbon sources such as carbohydrates for propionic acid production.
Received: 21 May 1999 / Accepted: 1 November 1999 相似文献
13.
J R Kastner W J Jones R S Roberts 《Journal of industrial microbiology & biotechnology》1998,20(6):339-343
The kinetics of biomass formation, D-xylose utilization, and mixed substrate utilization were determined in a chemostat using the yeast Candida shehatae. The maximum growth rate of C. shehatae grown aerobically on D-xylose was 0.42 h−1 and the Monod constant, K
s, was 0.06 g L−1. The biomass yield, Y
{X/S}, ranged from 0.40 to 0.50 g g−1 over a dilution rate range of 0.2–0.3 h−1, when C. shehatae was grown on pure D-xylose. Mixtures of D-xylose and glucose (∼1 : 1) were simultaneously utilized over a dilution rate from 0.15 to 0.35 h−1 at pH 3.5 and 4.5, but pH 3.5 reduced μmax and reduced the dilution rate range over which D-xylose was utilized in the presence of glucose. At pH 4.5, μmax was not reduced with the mixed sugar feed and the overall or lumped K
s value was not significantly increased (0.058 g L−1
vs 0.06 g L−1), when compared to a pure D-xylose feed. Kinetic data indicate that C. shehatae is an excellent candidate for chemostat production of value added products from renewable carbon sources, since simultaneous
mixed substrate utilization was observed over a wide range of growth rates on a 1 : 1 mixture of glucose and D-xylose.
Received 21 August 1997/ Accepted in revised form 28 May 1998 相似文献
14.
S. S. Sudge K. B. Bastawde D. V. Gokhale U. R. Kalkote T. Ravindranathan 《Applied microbiology and biotechnology》1998,49(5):594-599
About 1000 bacterial colonies isolated from sea water were screened for their ability to convert dl-5-phenylhydantoin to d(−)N-carbamoylphenylglycine as a criterion for the determination of hydantoinase activity. The strain M-1, out of 11 hydantoinase-producing
strains, exhibited the maximum ability to convert dl-5-phenylhydantoin to d(−)N-carbamoylphenylglycine. The strain M-1 appeared to be a halophilic Pseudomonas sp. according to morphological and physiological characteristics. Optimization of the growth parameters revealed that nutrient
broth with 2% NaCl was the preferred medium for both biomass and enzyme production. d-Hydantoinase of strain M-1 was not found to be inducible by the addition of uracil, dihydrouracil, β-alanine etc. The optimum
temperature for enzyme production was about 25 °C and the organism showed a broad pH optimum (pH 6.5–9.0) for both biomass
and hydantoinase production. The organism seems to have a strict requirement of NaCl for both growth and enzyme production.
The optimum pH and temperature of enzyme activity were 9–9.5 and 30 °C respectively. The biotransformation under the alkaline
conditions allowed the conversion of 80 g l−1
dl-5-phenylhydantoin to 82 g l−1
d(−)N-carbamoylphenylglycine within 24 h with a molar yield of 93%.
Received: 15 September 1997 / Received revision: 5 January 1998 / Accepted: 6 January 1998 相似文献
15.
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
16.
Takashi Nemoto Taisuke Watanabe Yutaka Mizogami Jun-ichi Maruyama Katsuhiko Kitamoto 《Applied microbiology and biotechnology》2009,82(6):1105-1114
The recombinant Pichia pastoris harboring an improved methionine adenosyltransferase (MAT) shuffled gene was employed to biosynthesize S-adenosyl-l-methionine (SAM). Two l-methionine (l-Met) addition strategies were used to supply the precursor: the batch addition strategy (l-Met was added separately at three time points) and the continuous feeding strategies (l-Met was fed continuously at the rate of 0.1, 0.2, and 0.5 g l−1 h−1, respectively). SAM accumulation, l-Met conversion rate, and SAM productivity with the continuous feeding strategies were all improved over the batch addition
strategy, which reached 8.46 ± 0.31 g l−1, 41.7 ± 1.4%, and 0.18 ± 0.01 g l−1 h−1 with the best continuous feeding strategy (0.2 g l−1 h−1), respectively. The bottleneck for SAM production with the low l-Met feeding rate (0.1 g L−1 h−1) was the insufficient l-Met supply. The analysis of the key enzyme activities indicated that the tricarboxylic acid cycle and glycolytic pathway
were reduced with the increasing l-Met feeding rate, which decreased the adenosine triphosphate (ATP) synthesis. The MAT activity also decreased as the l-Met feeding rate rose. The reduced ATP synthesis and MAT activity were probably the reason for the low SAM accumulation when
the l-Met feeding rate reached 0.5 g l−1 h−1. 相似文献
17.
J. M. Obón J. R. Maiquez M. Cánovas H.-P. Kleber J. L. Iborra 《Applied microbiology and biotechnology》1999,51(6):760-764
The use of a biological procedure for l-carnitine production as an alternative to chemical methods must be accompanied by an efficient and highly productive reaction
system. Continuous l-carnitine production from crotonobetaine was studied in a cell-recycle reactor with Escherichia coli O44 K74 as biocatalyst. This bioreactor, running under the optimum medium composition (25 mM fumarate, 5 g/l peptone), was
able to reach a high cell density (26 g dry weight/l) and therefore to obtain high productivity values (6.2 g l-carnitine l−1 h−1). This process showed its feasibility for industrial l-carnitine production. In addition, resting cells maintained in continuous operation, with crotonobetaine as the only medium
component, kept their biocatalytic capacity for 4 days, but the biotransformation capacity decreased progressively when this
particular method of cultivation was used.
Received: 10 December 1998 / Received revision: 19 February 1999 / Accepted: 20 February 1999 相似文献
18.
J. Q. Liu M. Odani T. Dairi N. Itoh S. Shimizu H. Yamada 《Applied microbiology and biotechnology》1999,51(5):586-591
A new enzymatic resolution process was established for the production of l-threo-3-[4-(methylthio)phenylserine] (MTPS), an intermediate for synthesis of antibiotics, florfenicol and thiamphenicol, using
the recombinant low-specificity d-threonine aldolase from Arthrobacter sp. DK-38. Chemically synthesized dl-threo-MTPS was efficiently resolved with either the purified enzyme or the intact recombinant Escherichiacoli cells overproducing the enzyme. Under the optimized experimental conditions, 100 mM (22.8 g l−1) l-threo-MTPS was obtained from 200 mM (45.5 g l−1) dl-threo-MTPS, with a molar yield of 50% and a 99.6% enantiomeric excess.
Received: 2 September 1998 / Received revision: 27 October 1998 / Accepted: 29 November 1998 相似文献
19.
Methee Khamduang Kanoktip Packdibamrung Jarun Chutmanop Yusuf Chisti Penjit Srinophakun 《Journal of industrial microbiology & biotechnology》2009,36(10):1267-1274
The production of l-phenylalanine is conventionally carried out by fermentations that use glucose or sucrose as the carbon source. This work
reports on the use of glycerol as an inexpensive and abundant sole carbon source for producing l-phenylalanine using the genetically modified bacterium Escherichia coli BL21(DE3). Fermentations were carried out at 37°C, pH 7.4, using a defined medium in a stirred tank bioreactor at various
intensities of impeller agitation speeds (300–500 rpm corresponding to 0.97–1.62 m s−1 impeller tip speed) and aeration rates (2–8 L min−1, or 1–4 vvm). This highly aerobic fermentation required a good supply of oxygen, but intense agitation (impeller tip speed
~1.62 m s−1) reduced the biomass and l-phenylalanine productivity, possibly because of shear sensitivity of the recombinant bacterium. Production of l-phenylalanine was apparently strongly associated with growth. Under the best operating conditions (1.30 m s−1 impeller tip speed, 4 vvm aeration rate), the yield of l-phenylalanine on glycerol was 0.58 g g−1, or more than twice the best yield attainable on sucrose (0.25 g g−1). In the best case, the peak concentration of l-phenylalanine was 5.6 g L−1, or comparable to values attained in batch fermentations that use glucose or sucrose. The use of glycerol for the commercial
production of l-phenylalanine with E. coli BL21(DE3) has the potential to substantially reduce the cost of production compared to sucrose- and glucose-based fermentations. 相似文献
20.
Summary Cells ofCandida shehatae repressed by growth in glucose- or D-xylose-medium produced a facilitated diffusion system that transported glucose (K
s±2 mM,V
max±2.3 mmoles g−1 h−1),d-xylose (K
s±125 mM,V
max±22.5 mmoles g−1 h−1) and D-mannose, but neither D-galactose norl-arabinose.
Cells derepressed by starvation formed several sugar-proton symports. One proton symport accumulated 3-0-methylglucose about
400-fold and transported glucose (K
s±0.12 mM,V
max ± 3.2 mmoles g−1 h−1) andd-mannose, a second proton symport transportedd-xylose (K
s± 1.0 mM,V
max 1.4 mmoles g−1 h−1) andd-galactose, whilel-arabinose apparently used a third proton symport. The stoicheiometry was one proton for each molecule of glucose or D-xylose
transported. Substrates of one sugar proton symport inhibited non-competitively the transport of substrates of the other symports.
Starvation, while inducing the sugar-proton symports, silenced the facilitated diffusion system with respect to glucose transport
but not with respect to the transport of D-xylose, facilitated diffusion functioning simultaneously with thed-xylose-proton symport. 相似文献