Interactions between Lactobacillus kefiranofaciens and Saccharomyces cerevisiae in mixed culture for kefiran production

Since a positive effect on the growth and kefiran production of Lactobacillus kefiranofaciens was observed in a mixed culture with Saccharomyces cerevisiae, the elucidation of the interactions between L. kefiranofaciens and S. cerevisiae may lead to higher productivity. Hence, the microbial interaction of each strain was investigated. Apart from the positive effect of a reduction in the amount of lactic acid by S. cerevisiae, a positive effect of S. cerevisiae on the growth and kefiran production of L. kefiranofaciens in a mixed culture was observed. Various experiments were carried out to study this effect. In this study, the observed increase in capsular kefiran in a mixed culture with inactivated S. cerevisiae correlated well to that in an anaerobic mixed culture. Differences in capsular kefiran production were observed for different initial S. cerevisiae concentrations under anaerobic conditions. From these fermentation results, it was concluded that the physical contact with S. cerevisiae mainly enhanced the capsular kefiran production of L. kefiranofaciens in a mixed culture. Therefore, in an anaerobic mixed culture, this direct contact resulted in higher capsular kefiran production than that in pure culture.     

Enhancement of retinal production by supplementing the surfactant Span 80 using metabolically engineered Escherichia coli

The optimal temperature and pH for retinal production using metabolically engineered Escherichia coli in a 7-l fermentor were found to be 30°C and 7.0, respectively. The agitation speed was a critical factor for retinal production. The optimal agitation speed was 400 rpm (oxygen transfer coefficient, k(L)a, = 92 1/h) in batch culture and 600 rpm (k(L)a=148 1/h) in a fed-batch culture of glycerol. Span 80 was selected as a surfactant for retinal production in metabolically engineered E. coli because Span 80 had proven the most effective for increased retinal production among the tested surfactants. Under the optimal conditions in the fed-batch culture with 5 g/l Span 80, the cell mass and the concentration, content, and productivity of retinal were 24.7 g/l, 600 mg/l, 24.3mg/g-cells, and 18 mg l(-1)h(-1) after 33 h, respectively. They were 1.2-, 2.7-, 2.3-, and 2.7-fold higher than those in the fed-batch culture without Span 80, respectively. The concentration and productivity of retinal in this study were the highest ever reported. The hydrophilic portion of Span 80 (sorbitan) did not affect cell growth and retinal production, but the hydrophobic portion (oleic acid) stimulated cell growth. However, oleic acid plus sorbitan did not stimulate retinal production. Thus, Span 80, as a linked compound of oleic acid and sorbitan produced by esterification, proved to be an effective surfactant for the enhancement of retinal production.     

Lipid production in Porphyridium cruentum grown under different culture conditions

Autotrophic growth of Porphyridium cruentum under 18:12 h and 12:12 h light:dark cycles showed the maximum cell concentration of 2.1 g-dry wt./L, whereas the specific growth rate, 0.042 (1/h), at 18:6 h is faster than that of 12:12 h, 0.031 (1/h), respectively. The highest lipid accumulation level, 19.3 (%, w/w), was achieved at 12:12 h cycle. Under dark cultivation condition with 10 g/L of glucose, the lipid accumulation in the cell was 10.9 (%, w/w), whereas the heterotrophic growth with glycerol as the carbon resource showed low level of cell concentration and lipid production, compared to that of glucose. The glucose was decided to be a suitable carbon resource for the heterotrophic growth of P. cruentum. The lipids from P. cruentum seemed be feasible for biodiesel production, because over 30% of the lipid was C₁₆–C_18:1. The cultivation time and temperature were important factors to increase the maximum cell concentration. Extending the cultivation time helps maintain the maximum cell concentration, and higher lipid accumulation was achieved at 25 °C, compared to 35 °C. The fed-batch cultures showed that, under the light condition, the specific production rate was slightly decreased to 0.4% lipid/g-dry wt./day at the later stage, whereas, under the dark condition, the specific production rate was maintained to be a maximum value of 1.1% lipid/g-dry wt./day, even in the later stage of cultivation. The results indicate that the heterotrophic or 12:12 h cyclic mixotrophic growth of P. cruentum could be used for the production of biodiesel in long-term fed-batch cultivation of P. cruentum.     

Influence of hyaluronidase addition on the production of hyaluronic acid by batch culture of Streptococcus zooepidemicus

Enhancement of hyaluronic acid (HA) production by Streptococcus zooepidemicus through increasing oxygen transfer rate via degradation of HA by hyaluronidase was investigated. Dissolved oxygen (DO) level became a limiting factor for HA production during 8–16 h, and thus hyaluronidase (0.05, 0.10, 0.15, 0.20, 0.25 g/l) was added at 8 h to degrade HA. Oxygen transfer rate coefficient and DO level during 8–16 h increased with increased hyaluronidase concentration. Compared to 5.0 ± 0.1 g/l of the control without hyaluronidase addition, HA production was increased from 5.0 ± 0.1 g/l to 6.0 ± 0.1 g/l when hyaluronidase concentration was 0.15 g/l. Further increase of hyaluronidase concentration had no effect on HA production. The molecular weight of HA decreased with the increased hyaluronidase concentration and decreased to 21 kDa when hyaluronidase concentration was 0.25 g/l from 1300 kDa of the control. The prepared low molecular weight HA (LMW-HA) could function as potential anti-angiogenic substances, antiviral and anti-tumor agents to possibly be used as functional food ingredients.     

Analysis of hemin effect on lactate reduction in Lactococcus lactis

Lactococcus lactis is a facultative anaerobic microorganism that produces lactate as the major product, and acetate and acetoin as by-products; some strains of this species produce an antimicrobial compound, nisin. Lactate has a strong inhibitory effect on L. lactis growth. On the other hand, hemin has a suppressive effect on lactate production during L. lactis growth under aerobic condition. To achieve the optimum effect of hemin on lactate amount reduction in L. lactis ATCC11454, cultures entailing various conditions were performed with and without hemin. In the culture with hemin, L. lactis growth and lactate reduction improved compared with those in the culture without hemin; that is, lactate production was suppressed by 1.8- and 1.3-fold under batch and fed-batch cultures, respectively. In microaerobic fed-batch culture with hemin, lactate production was sufficiently suppressed. This result suggests that microaerobic fed-batch culture could be applied to the maintenance of the low lactate amount. Under this condition, metabolic shift was observed from lactate to acetoin and acetate. However, no increase in nisin production was observed even though lactate production could significantly decrease in L. lactis ATCC11454.     

Increase of xylitol productivity by cell-recycle fermentation of Candida tropicalis using submerged membrane bioreactor

Candida tropicalis, an osmophilic strain isolated from honeycomb, produced xylitol at a maximal volumetric productivity of 3.5 g l(-1) h(-1) from an initial xylose concentration of 200 g l(-1). Even at a very high xylose concentration, e.g., 350 g l(-1), this strain produced xylitol at a moderate rate of 2.07 g l(-1) h(-1). In a fed-batch fermentation of xylose and glucose, 260 g l(-1) xylose was added, and the xylitol production was 234 g l(-1) for 48 h, corresponding to a rate of 4.88 g l(-1) h(-1). To increase xylitol productivity, cells were recycled in a submerged membrane bioreactor with suction pressure and air sparging. For each recycle round in cell-recycle fermentation, the average concentration of xylitol produced, fermentation time, volumetric productivity, and product yield were 180 g l(-1), 19.5 h, 8.5 g l(-1) h(-1), and 85%, respectively. When cell-recycle fermentation was started with the cell mass concentrated twofold after batch fermentation and performed for 10 recycle rounds, we achieved a very high productivity of 12 g l(-1) h(-1). The productivity and total amount of xylitol in cell-recycle fermentation were 3.4- and 11.0-fold higher than those in batch fermentation, respectively.     

Synergistic inhibition effect of 2-phenylethanol and ethanol on bioproduction of natural 2-phenylethanol by Saccharomyces cerevisiae and process enhancement

Natural 2-phenylethanol (PEA) could be produced on a large scale by way of bioconversion with yeast from l-phenylalanine. In this work the synergistic inhibition effect of the target product PEA and the byproduct ethanol on the bioconversion rate by Saccharomyces cerevisiae R-UV3 was systematically studied and a new kinetic model with an item representing the synergistic effect was proposed. Optimization strategies to repress the inhibition effect of PEA and ethanol were carried out in the mode of fed-batch culture with ISPR. The glucose concentration was regulated at the level of 0.2±0.1g/L by controlling a suitable respiratory quotient on line, which could limit the accumulation of the ethanol lower than 10g/L. In the presence of resin FD0816 with a weight of 10% of the medium, PEA was removed from the broth and the overall PEA concentration and the space-time yield reached 13.7g/L and 0.39g L(-1) h(-1) respectively. The semi-continuous process with ISPR was performed, in which the replacement of the resin was operated repeatedly when the aqueous PEA was over 2.7g/L and bioconversion continued until the bioactivity of the yeast cells declined, consequently achieving a final overall PEA concentration of 32.5g/L and a space-time yield of 0.45g L(-1) h(-1).     

Development of a fed-batch culture process for enhanced production of recombinant human antithrombin by Chinese hamster ovary cells

Antithrombin is a serine protease inhibitor that inactivates several coagulation proteases, primarily thrombin and factor Xa. The Chinese hamster ovary (CHO) cell line transfected with a vector expressing recombinant human antithrombin (rAT) and a selectable marker, glutamine synthetase (GS), was cultivated in a 2-l fed-batch culture process using serum-free, glutamine-free medium. To maximize the rAT yield, effects of culture pH, balanced amino acid feeding, and an increased glutamate concentration on cell metabolism and rAT production were investigated. When cells were grown at pH values of 6.6, 6.8, 7.0, and 7.2, the maximum cell density and maximum lactate concentration decreased with decreasing pH. The highest production level of rAT was obtained at culture pH 6.8 due to the extended culture lifetime. Compared to the imbalanced amino acid feeding at culture pH 6.8, the balanced amino acid feeding increased the amount of rAT activity by 30% as a result of an increased viable cell number. A decrease in the specific glucose consumption rate (q(Glc)) with increasing culture time was observed in all the above-mentioned experiments, while the glucose concentration was maintained above 0.7 g l(-1). In addition, a decrease in the specific rAT production rate (q(rAT)) was observed after the depletion of lactate in the late cultivation stage. Taken together, these results suggest that the reduced availability of cellular energy caused by the decrease in q(Glc) and depletion of lactate led to the decrease in q(rAT). This decrease in q(rAT) was partially prevented by increasing the residual glutamate concentration from 1 mM to 7 mM, thus resulting in an additional 30% increase in the amount of rAT activity. The optimized fed-batch culture process yielded 1.0 g l(-1) rAT at 287 h of cultivation.     

High butanol production by Clostridium saccharoperbutylacetonicum N1-4 in fed-batch culture with pH-Stat continuous butyric acid and glucose feeding method

A pH-stat fed-batch culture by feeding butyric acid and glucose has been studied in an acetone-butanol-ethanol (ABE) fermentation using Clostridium saccharoperbutylacetonicum N1-4. The specific butanol production rate increased from 0.10 g-butanol/g-cells/h with no feeding of butyric acid to 0.42 g-butanol/g-cells/h with 5.0 g/l butyric acid. The pH value in broth decreases with butyric acid production during acidogenesis, and then butyric acid reutilization and butanol production result in a pH increase during solventogensis. The pH-stat fed-batch culture was performed to maintain a constant pH and butyric acid concentration in the culture broth, but feeding only butyric acid could not support butyric acid utilization and butanol production. Subsequently, when a mixture of butyric acid and glucose was fed, butyric acid was utilized and butanol was produced. To investigate the effect of the feeding ratio of butyric acid to glucose (B/G ratio), several B/G ratio solutions were fed. The maximum butanol production was 16 g/l and the residual glucose concentration in broth was very low at a B/G ratio of 1.4. Moreover, yields of butanol in relation to cell mass and glucose utilization were 54% and 72% higher in pH-stat fed-batch culture with butyric acid than that of conventional batch culture, respectively.     

Development of a fed-batch cultivation strategy for the enhanced production and secretion of cutinase by a recombinant Saccharomyces cerevisiae SU50 strain

Saccharomyces cerevisiae SU50 strain was cultivated with different concentrations of glucose and galactose with the aim of increasing cutinase activity, cutinase yield on the carbon source, and bioreactor productivity. Cultivations in shake flasks with galactose as the sole carbon source, with sugar concentrations between 10 and 40 g/l, exhibited growth-associated cutinase production and a constant specificity of cutinase secretion. Furthermore, as the galactose concentration increased to values higher than 15 g/l, a progressively higher maximum specific galactose consumption rate and a consequent higher alcoholic fermentation occurred, resulting in progressively lower biomass yields on the carbon source and cutinase yields on biomass. Using high glucose and galactose concentrations in a well-aerated bioreactor resulted in a high biomass productivity (0.5 g dcw/l/h), a high cutinase yield on biomass (21.5 U/mg dew), a final high cutinase secretion efficiency (97%), and plasmid stability (99%). Based on these studies, a two phase fed-batch cultivation strategy was developed. A batch phase with high glucose and galactose concentrations, followed by a fed-batch with a constant feed rate with galactose as the sole carbon source in order to minimize the repression of the GAL 7 promoter, were established. The feed rate was estimated to maintain a pre-determined concentration of galactose (20 g/l) on the culture medium in order to maximize the efficiency of cutinase secretion and minimize the galactose alcoholic fermentation. By this cultivation strategy, enhancements of 3.6-fold in cutinase activity, 1.2-fold in cutinase yield on the carbon source, and 8.7-fold culture productivity were obtained in relation to a batch cultivation performed in shake flasks with 20 g/l of galactose.     

Production of extracellular bifidogenic growth stimulator (BGS) from Propionibacterium shermanii using a bioreactor system with a microfiltration module and an on-line controller for lactic acid concentration

Production of a bifidogenic growth stimulator (BGS) by Propionibacterium freudenreichii subsp. shermanii (Propionibacterium shermanii) using lactic acid as a carbon source was investigated using different cultivation methods. When a continuous bioreactor system with a filtration device was used at a dilution rate of 0.075 h(-1), the average BGS concentration was 2.4 mg/l, which corresponds to a BGS productivity per cultivation time of 1.8 x 10(-1) mg x l(-1) x h(-1). The BGS productivity per cultivation time in continuous cultivation with filtration was 1.9-fold that (9.4 x 10(-2) mg x l(-1).h(-1)) in a conventional batch cultivation. In fed-batch cultivation with feed-back control using an on-line lactic acid controller with a lactic acid biosensor, it was possible to prevent substrate inhibition by maintaining the lactic acid concentration in culture broth low at 3.3 g/l, and an enhanced BGS production (31 mg/l) was successfully attained. The BGS productivity per cultivation time (2.1x10(-1) mg x l(-1) x h(-1)) in the fed-batch cultivation with feed-back control was 2.2-fold that in the conventional batch cultivation. A new bioreactor system was developed by coupling a continuous bioreactor system with a filtration device to an on-line lactic acid controller. Using the new bioreactor system, we produced BGS continuously at a high level of 47 mg/l. The BGS productivities per cultivation time (3.5 mg.l(-1) x h(-1)) and the total volume of medium used (1.7 x 10(-1) mg x l(-1) x h(-1)) obtained in the new bioreactor system were 37-fold and 2.1-fold those in the conventional batch cultivation, respectively. These results described above clearly demonstrate the positive effects of both the continuous filtration for removal of metabolites (propionic and acetic acids) inhibitory to cell growth and feed-back control of lactic acid concentration in the culture broth on BGS production by P. shermanii. This paper is the first report on BGS production by the propionic acid bacterium using lactic acid as a carbon source.     

Maximizing yellow pigment production in fed-batch culture of Monascus sp

Yellow pigment production in exponential fed-batch cultivation of Monascus sp. was studied. Due to the difficulty of measuring the optical density for accurate determination of the cell concentration, a capacitance probe was employed on-line. The feed rate needed to keep the specific growth rate, mu, constant in fed-batch culture was determined on the basis of the cell concentration measured by the capacitance probe. Control of mu was improved by using updated information on the cell concentration compared with the simple feed-forward determination method using the initial cell concentration only. The highest specific pigment production rate was achieved with a mu of 0.02 h(-1) in the feeding phase. However, among several fermentation examined, the largest pigment production in the final step was obtained at a mu of 0.01 h(-1); in each case the same amount of substrates was used. An investigation of the optimal initial glucose concentration revealed that pigment production was maximum when the initial glucose concentration in the batch mode was 10 g/l and mu was 0.01 h(-1) in the fed-batch mode. It was also found that the pellet weight in the fermentation could be accurately estimated by image analysis. The ratio of the mycelium weight to the total cell weight estimated from information on the total cell weight and the estimated pellet weight was found to be more than 80%. However, no clear quantitative relationship could be discerned between the specific pigment production rate, rho, and the ratio of mycelium in the cell population.     

Enhanced 2,3-butanediol production by addition of acetic acid in Paenibacillus polymyxa

By the addition of 150 mM acetate into a batch culture at an initial pH of 6.8, the production of 2,3-butanediol (BDL) by Paenibacillus polymyxa reached 248 mM, yielding 0.87 mol.mol(-1) glucose, where the ratio of acetate consumed to glucose consumed (A/C ratio) was calculated as 0.35 mol acetate mol(-1) glucose. Therefore, a fed-batch culture was carried out by feeding glucose and acetate at a ratio of 0.35 mol acetate mol(-1) glucose. In the fed-batch culture performed at pH 6.8, BDL production reached 637 mM, yielding 0.81 mol.mol(-1) glucose, although the A/C ratio was only 0.18 mol acetate mol(-1) glucose. By decreasing pH to 6.3 in the fed-batch culture, BDL production reached 566 mM, yielding 0.88 mol.mol(-1) glucose and the A/C ratio was 0.32 mol acetate mol(-1) glucose. The optical purity of BDL, which was expressed as enantiomeric excess, was retained at more than 98% of the (R, R)-stereoisomer at the end of culture, which was comparable to that without acetate addition.     

Ethanol yield and volatile compound content in fermentation of agave must by Kluyveromyces marxianus UMPe-1 comparing with Saccharomyces cerevisiae baker's yeast used in tequila production

In tequila production, fermentation is an important step. Fermentation determines the ethanol productivity and organoleptic properties of the beverage. In this study, a yeast isolated from native residual agave must was identified as Kluyveromyces marxianus UMPe-1 by 26S rRNA sequencing. This yeast was compared with the baker's yeast Saccharomyces cerevisiae Pan1. Our findings demonstrate that the UMPe-1 yeast was able to support the sugar content of agave must and glucose up to 22% (w/v) and tolerated 10% (v/v) ethanol concentration in the medium with 50% cells survival. Pilot and industrial fermentation of agave must tests showed that the K. marxianus UMPe-1 yeast produced ethanol with yields of 94% and 96% with respect to fermentable sugar content (glucose and fructose, constituting 98%). The S. cerevisiae Pan1 baker's yeast, however, which is commonly used in some tequila factories, showed 76% and 70% yield. At the industrial level, UMPe-1 yeast shows a maximum velocity of fermentable sugar consumption of 2.27g·L(-1)·h(-1) and ethanol production of 1.38g·L(-1)·h(-1), providing 58.78g ethanol·L(-1) at 72h fermentation, which corresponds to 96% yield. In addition, the major and minor volatile compounds in the tequila beverage obtained from UMPe-1 yeast were increased. Importantly, 29 volatile compounds were identified, while the beverage obtained from Pan1-yeast contained fewer compounds and in lower concentrations. The results suggest that the K. marxianus UMPe-1 is a suitable yeast for agave must fermentation, showing high ethanol productivity and increased volatile compound content comparing with a S. cerevisiae baker's yeast used in tequila production.     

Production of single-chain variable fragment antibody (scFv) in fed-batch and continuous culture of Pichia pastoris by two different methanol feeding methods

This study examined the effects of two methods of methanol feeding, DO-stat and methanol concentration control, in fed-batch and continuous cultures of Pichia pastoris on cell growth and single-chain variable fragment antibody (scFv) expression. By maintaining the methanol concentration at 3.9 g l(-1) in fed-batch culture, a scFv concentration of 198 mg l(-1) was obtained. In continuous culture using both methanol feeding methods, the scFv concentration in the fermentation broth increased with a decreasing dilution rate. A maximum scFv concentration of 810 mg l(-1) at a dilution rate of 0.0094 h(-1) was obtained by maintaining the methanol concentration at 3.9 g l(-1). Although the specific methanol consumption rate was the same for both methods, the specific productivity of scFv was higher in methanol concentration control from 0.0094 to 0.049 h(-1) than it was in DO-stat control. Therefore, continuous culture with methanol feeding by the concentration control method shows promise for the industrial scale production of recombinant proteins by Pichia pastoris.     

Regulation of lactate production in Streptococcus bovis: A spiraling effect that contributes to rumen acidosis

When Streptococcus bovis was grown in batch culture with 6 g/L glucose at pH 6.7, maximum specific growth rate was 1.47 h(-1), and lactate was the primary fermentation product. In continuous culture at pH 6.7 and growth rate equal to .10 h(-1), little lactate was formed, and formate, acetate, and ethanol accounted for most of the product. When extra-cellular pH decreased to 4.7, intra-cellular pH declined to 5.4, and organisms switched back to lactate production. Intracellular concentration of fructose 1,6-diphosphate of batch culture cells was greater than 12 mM, a concentration that allowed maximal lactate dehydrogenase activity. When Streptococcus bovis was grown in continuous culture at pH 6.7, intracellular fructose-l,6-diphosphate declined to .4 mM, a concentration which gave little lactate dehydrogenase activity at pH 6.5 or greater. Decreasing pH of continuous culture to 4.7 increased intracellular fructose-1,6-diphosphate concentration to .8 mM. This concentration was still limiting if lactate dehydrogenase was assayed at pH 6.5, but nearly maximal activity was obtained when enzyme was assayed at pH 5.5. The small increase in fructose-l,6-diphosphate and decreased requirement of lactate dehydrogenase for fructose-l,6-diphosphate under acidic assay conditions, accounted for increased lactate production during low pH (4.7) continuous culture. These and other aspects of lactate regulation by Streptococcus bovis are discussed as factors leading to rumen acidosis. This pattern of regulation also helps to explain why rumen acidosis is difficult to reverse.     

Development of a novel method for feeding a mixture of -lactic acid and acetic acid in fed-batch culture of Ralstonia eutropha for poly- -3-hydroxybutyrate production

Fermentative production of poly- -3-hydroxybutyrate [P(3HB)] from a mixture of -lactic acid and acetic acid by Ralstonia eutropha was investigated. For fed-batch culture with cell density, it is necessary to control the concentration of these organic acids in the culture medium below the inhibitory level for cell growth. Therefore, a novel feeding method, termed the computer-controlled pH-stat substrate feeding method, was developed using the rate of increase of the pH (pH-increasing rate) of the culture medium as an indicator for feed control. The pH-increasing rate, which was calculated every minute by a pH meter-linked computer, represented secondary information regarding substrate consumption by cells. When the pH-increasing rate decreased to 5% of the maximum increasing rate, acidic substrate solution was fed into the fermentor until the pH was reduced to 7.00. Using this feeding strategy, the cell concentration and PHA content obtained in 42 h were 75.0 g/l and 73.1% (w/w), respectively, resulting in a high P(3HB) productivity of 1.30 g/l·h.     

Effects of pH and dissolved oxygen on cellulose production by Acetobacter xylinum BRC5 in agitated culture

Acetobacter xylinum BRC5 was cultivated in a jar fermentor using glucose as the sole carbon source. Strain BRC5 oxidized almost all of the glucose to gluconic acid; thereafter, it biosynthesized cellulose by utilizing gluconic acid accumulated in the broth. The optimal pH for metabolizing glucose to gluconic acid was 4.0, while a pH of 5.5 was preferred for cell growth and cellulose production from the accumulated gluconic acid in the medium. Shifting the pH from 4.0 to 5.5 during the cellulose production phase in batch cultures improved cellulose production and reduced the total fermentation time, compared to batch cultures at constant pH. In constant fed-batch culture, 10 g/l of cellulose was obtained from 40 g/l of glucose, a yield which was approximately 2-fold higher than in batch culture with the same initial glucose concentration, even without control of the level of dissolved oxygen. The highest cellulose yield was obtained in fed-batch cultures in which the dissolved oxygen concentration was controlled at 10% saturation. Control of pH and dissolved oxygen to optimal levels was effective for improving the production rate and yield of cellulose, to achieve a high cellulose productivity of 0.3 g cellulose/l x h. Approximately 15 g/l of cellulose was considered to be the highest yield obtainable using conventional fermentors because the culture broth then became too viscous to allow satisfactory aeration.     

木糖浓度及补料发酵对树干毕赤酵母乙醇发酵的影响

探究不同浓度木糖及补料对树干毕赤酵母（Pichia stipitis）菌株1K-9发酵木糖产乙醇的影响,提高木糖产乙醇的发酵水平,为扩大规模发酵木糖产乙醇打下基础。结果表明,菌株1K-9先采用10%木糖进行乙醇发酵,36 h补加与10%木糖培养基等体积的20%木糖培养基继续发酵,发酵至108 h时菌数也达到了（12.16±0.07）×108个/mL,较未补料发酵时有所提高;发酵108 h时醪液中残留的木糖含量为（1.03±0.02）g/L,较未补料发酵时有所降低;乙醇含量达到了6.56%vol,较未补料时提高了1.85%vol。因此补料发酵是有效的。     

Novel high butanol production from lactic acid and pentose by Clostridium saccharoperbutylacetonicum

We previously reported a butanol production process with pH-stat continuous feeding of dl-lactic acid and glucose as the co-substrate (Oshiro et al., Appl. Microbiol. Biotechnol., 87, 1177-1185, 2010). To accomplish butanol production from completely inedible substrates, in this study, we investigated acetone-butanol-ethanol (ABE) fermentation of Clostridium saccharoperbutylacetonicum N1-4 with lactic acid by using pentose as the co-substrate. Examination for optimum co-substrate indicated that arabinose was superior to glucose and xylose for ABE fermentation. Actually batch culture with lactic acid and arabinose without pH control exhibited higher butanol production (7.11?g/l) and lactic acid consumption (2.02?g) than those (6.62?g/l and 1.45?g, respectively) with glucose. Fed-batch culture without pH control increased these values to 12.08?g/l and 15.60?g/l butanol production, and to 3.83?g and 5.91?g lactic acid consumption by feeding the substrate once and twice, respectively. Finally, the result of gas chromatography-mass spectroscopy analysis using [1,2,3-(13)C(3)]-lactic acid indicated that lactic acid was converted to butanol with the efficiency of 51.9%. Thus, we established a novel high butanol production from lactic acid using arabinose as the co-substrate in simple fed-batch culture.