Improvement of glycerol production by Candida krusei in batch and continuous cultures using corn steep liquor

No fermentation parameter was affected at phosphate concentration above 0.4 g l^–1 when KH₂PO₄ was used as phosphate source and the glucose consumption rate was difficult to control when corn steep liquor (CSL) was adopted as the phosphate source. However, if CSL was supplemented as a source of growth factors instead of as the phosphate source, not only glucose uptake and glycerol was improved, but also fermentation became easy to control and a steady state of continuous culture was easily obtained.     

Candida krusei in Baker's yeast production

Summary Candida krusei is a harmful contaminant in baker's yeast manufacture, because it grows much faster than Saccharomyces cerevisiae under production conditions. This investigation showed that C. krusei utilizes the ethanol produced by baker's yeast as sole carbon source when molasses is used as a substrate. When the alcohol concentration in the effluent air is used as a parameter for controlling the aeration of the culture, conditions become favourable for the dominance of wild yeast because some of the ethanol produced by the baker's yeast is consumed immediately by C. krusei and aeration is then automatically reduced, leading to increased growth of the wild yeast.     

新一代高产甘油重组菌的构建及其初步发酵

产甘油假丝酵母(Candida glycerinogenes WL2002-5)是一株发酵生产甘油的工业化菌株。为进一步提高其产甘油能力,本研究利用前期研究中成功克隆的产甘油假丝酵母中甘油合成关键酶3-磷酸甘油脱氢酶基因CgGPD1,构建根癌农杆菌双元载体pCAM3300-zeocin-CgGPD1后,电击转化根癌农杆菌LBA4404,通过根癌农杆菌介导法(ATMT)转化产甘油假丝酵母,构建了产甘油假丝酵母重组菌。并从中筛选出一株酶活力和产甘油性能较好的产甘油假丝酵母重组菌株C.g-G8。以葡萄糖为底物摇瓶发酵96h后,重组菌C.g-G8的甘油产量比野生型菌株Candida glycerinogene提高18.06%,平均耗糖速率提高12.97%,平均酶活力提高27.55%。本研究成功利用ATMT法转化产甘油假丝酵母构建新一代高产甘油菌株。     

Optimization of fed-batch fermentation for xylitol production by Candida tropicalis

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     

溶氧对Candida glycerinogenes产甘油发酵过程的影响

研究了溶氧浓度对产甘油假丝酵母分批发酵生产甘油过程的影响。实验结果表明：当溶氧浓度控制在30%时,C. glycerinogenes的甘油产量、得率和产率达到最高,分别为120.7 g/L、0.575 g/g和1.69 g/(L•h),而糖酵解代谢副产物形成最少。当溶氧浓度为10%时,发酵过程呈现出“巴斯德效应”的特征,生成的酵解代谢副产物维持在较高水平。在快速生长阶段,随着溶氧从10%增加到60%,细胞呼吸类型表现为从厌氧呼吸向好氧呼吸转变,酵解代谢副产物依次减少。在生长稳定期,控制的溶氧浓度越高,酵解代谢副产物乙醇、乙酸等的生成减少。分别选用Logistic方程、Luedeking-Piret方程和Luedeking-Piret-like方程,能较好地模拟细胞生长、甘油合成和葡萄糖消耗的动力学过程。     

Application of a two-stage temperature control strategy for enhanced glutathione production in the batch fermentation by Candida utilis

In batch culture for glutathione production with Candida utilis, a higher temperature (30 °C) was required to hasten cell growth while a lower temperature (26 °C) was needed to increase the production of glutathione. A two-stage temperature control strategy was used to enhance both the yield and the productivity of glutathione. As a result, glutathione production was increased by 5% and 23% of that at 26 °C and 30 °C, respectively, and the intracellular glutathione content reached 2.5% (w/w).     

粗壮假丝酵母(Candida valida 20231)产脂肪酶发酵条件的研究

对粗壮假丝酵母(Candida valida 20231)产脂肪酶所需的培养基成分和发酵条件进行了优化。结果表明,粗壮假丝酵母在接种后3 h即进入对数期,18 h后转入稳定期,66 h后进入衰退期;发酵36 h达到最大酶活,至72 h仍然无明显下降趋势。最适合的培养基成分为:4.0%大豆粉,2.0%菜籽油,0.3%葡萄糖,0.3%NH_4NO_3,1.2%K_2HPO_4,0.42%NaH_2PO_4,0.4%MgSO_4·7H_2O。使用优化的培养基,最佳产酶的条件为:装液量80 mL(250 mL摇瓶),初始pH 6,接种量为2.0%,种子菌龄为12 h。在最佳产酶条件下,脂肪酶活力达到32.6 U/mL。     

Modeling of glycerol production by fermentation in different reactor states

A kinetic model of glycerol production by fermentation with the osmophilic yeast Candida krusei was studied firstly by analogies to published works. Considering that the glycerol produced competes with glucose, as a second carbon source for energy maintenance, mathematical models of glucose utilization and glycerol accumulation were modified further. By adjusting only two variable macrokinetic parameters, K_S and β, the model simulations could fit experimental data well when the reactor was changed from Airlift Loop Reactor in different scale or airlift mode to Stirred Vessel. To avoid a significant reduction in glycerol production in the latter fermentation stage, the final condition of the fermentation, determined by the concentration ratio of glycerol to glucose, was also investigated in four different Reactor States. The kinetic models and simulation results can provide certain reference for scale up of glycerol production by fermentation.     

Novel fermentation process strengthening strategy for production of propionic acid and vitamin B12 by Propionibacterium freudenreichii

An efficient fermentation-strengthening approach was developed to improve the anaerobic production of propionic acid and vitamin B12 by co-fermentation with Propionibacterium freudenreichii. Vitamin B12 production from glucose resulted in relatively high productivity (0.35 mg/L h) but a low propionic acid yield (0.55 g/g). By contrast, glycerol gave a high propionic acid yield (0.63 g/g) but low productivity (0.16 g/L h). Co-fermentation of glycerol and glucose with a gradual addition strategy gave high yields (propionic acid: 0.71 g/g; vitamin B12: 0.72 mg/g) and productivities (propionic acid: 0.36 g/L h; vitamin B12: 0.36 mg/L h). Finally, the integrated feedstock and fermentation system strengthening strategy was demonstrated as an efficient method for the economic production of bio-based propionic acid and vitamin B12.     

休哈塔假丝酵母HDYXHT-01利用木糖生产乙醇的发酵工艺优化

采用Plackett-Burman (PB) 方法和中心组合设计 (Ccentral composit design,CCD) 对休哈塔假丝酵母Candida shehataeHDYXHT-01利用木糖发酵生产乙醇的工艺进行优化。PB试验设计与分析结果表明：硫酸铵、磷酸二氢钾、酵母粉和接种量是影响木糖乙醇发酵的4个关键因素,以乙醇产量为响应目标,采用CCD和响应面分析法 (Response surface methodology,RSM),确定了木糖乙醇发酵的最佳工艺为：硫酸铵1.73 g/L、磷酸二氢钾3.56 g/L、酵母粉2.62 g/L和接种量5.66％,其他发酵条件为：木糖80 g/L,MgSO4·7H2O 0.1 g/L,pH 5.0,培养温度30 ℃,装液量100 mL/250 mL,摇床转速140 r/min,发酵时间48 h,在该条件下发酵液中乙醇产量可以达到26.18 g/L,比未优化前提高了1.15倍。     

Glycerol production by Candida krusei employing NaCl as an osmoregulator in batch and continuous fermentations

Addition of 40 g NaCl l^–1 to a chemically defined medium containing 140 g glucose l^–1 in shake-flask culture improved glycerol production by Candida krusei from 16.5 g l^–1 to 47.7 g l^–1. With 40 g NaCl l^–1 at a dilution rate of 0.065 h^–1, glycerol concentration, glycerol yield (based on glucose consumed), and productivity in a four-stage cascade bioreactor were higher by 240%, 27% and 28%, respectively, than in a single-stage continuous culture system.     

纤维素硫酸钠-聚二甲基二烯丙基氯化铵微胶囊固定化Candida krusei产甘油条件优化

研究了利用一种新型的纤维素硫酸钠／聚二甲基二烯丙基氯化铵（Nacs／PDMDAAc）中空微胶囊包埋Can—dida krusei ZJU5205制备甘油的过程。通过摇瓶培养过程中对初始包菌量、胶囊和胶珠、初始甘油浓度、胶囊大小、胶囊体积／发酵液体积等关键固定化参数和培养条件的优化,确立了NaCS／PDMDAAC微胶囊固定化Candida krusei的最佳工艺参数为包菌量为0．6g／L,发酵初加入20g／L甘油,胶囊体积／发酵液体积为0．4。     

A high-throughput screening procedure for enhancing pyruvate production in Candida glabrata by random mutagenesis

Bioprocess and Biosystems Engineering - Candida glabrata is one of the most promising pyruvate producers. A series of experiments was conducted to enhance pyruvate production by C. glabrata via...     

Biohydrogen production by dark fermentation of glycerol using Enterobacter and Citrobacter Sp

Glycerol is an attractive substrate for biohydrogen production because, in theory, it can produce 3 mol of hydrogen per mol of glycerol. Moreover, glycerol is produced in substantial amounts as a byproduct of producing biodiesel, the demand for which has increased in recent years. Therefore, hydrogen production from glycerol was studied by dark fermentation using three strains of bacteria: namely, Enterobacter spH1, Enterobacter spH2, and Citrobacter freundii H3 and a mixture thereof (1:1:1). It was found that, when an initial concentration of 20 g/L of glycerol was used, all three strains and their mixture produced substantial amounts of hydrogen ranging from 2400 to 3500 mL/L, being highest for C. freundii H3 (3547 mL/L) and Enterobacter spH1 (3506 mL/L). The main nongaseous fermentation products were ethanol and acetate, albeit in different ratios. For Enterobacter spH1, Enterobacter spH2, C. freundii H3, and the mixture (1:1:1), the ethanol yields (in mol EtOH/mol glycerol consumed) were 0.96, 0.67, 0.31, and 0.66, respectively. Compared to the individual strains, the mixture (1:1:1) did not show a significantly higher hydrogen level, indicating that there was no synergistic effect. Enterobacter spH1 was selected for further investigation because of its higher yield of hydrogen and ethanol. © 2012 American Institute of Chemical Engineers Biotechnol. Prog., 2013     

Temperature effects on ethanol and isopropanol utilization by Candida krusei

Candida Krusei has a optimum growth temperature of 37°C on SASOL ethanol-isopropanol mixture. The organism was unable to grow on isopropanol, but oxidized it partially to acetone in the presence and absence of ethanol. Growth at 40°C in the alcohol mixture was slightly faster than at 30°C over an ethanol concentration range of 0.43 to 3.6% (v/v), although at both temperatures the growth rate declined continuously with increasing concentration. At an ethanol concentration greater than 3.6% (v/v), the mixture was much more inhibitory to growth at 40 and 30°C. The inhibitory effect was due to the ethanol rather than the isopropanol. Metabolites such as acetate, acetaldehyde, and ethyl acetate accumulated in the medium, but the degree of accumulation depended upon the temperature and alcohol mixture concentration. At 40°C, acetaldehyde and acetate accumulated to a greater extent than 30°C on a 4.0% (v/v) synthetic alcohol mixture and this may also cause the greater inhibition at this temperature. The alcohol mixture is unsuitable for single cell protein (SCP) production in batch culture because of the low cell densities observed at all alcohol concentrations.     

Candida krusei produces ethanol without production of succinic acid; a potential advantage for ethanol recovery by pervaporation membrane separation

The development of fermentative yeasts secreting no organic acids is highly desirable for ethanol production coupled with membrane separation processes, because the acidic byproduct, succinic acid, significantly inhibits the membrane permeation of ethanol. Of the Pichia and Candida yeasts tested, Candida krusei IA-1 showed the highest ethanol productivity [55 g L(-1) day(-1) from 150 g L(-1) (w/v) of glucose], comparable to the strains of Saccharomyces cerevisiae, and produced much less of the acid (0.6 g L(-1) day(-1)) than the Saccharomyces strains (1.5-1.8 g L(-1) day(-1)) under semi-aerobic conditions. Interestingly, under aerobic conditions, strain IA-1 showed no production of the acid. Stain IA-1 exhibited a good assimilation of the acid, while S. cerevisiae NBRC 0216 showed no assimilation. The activity of succinate dehydrogenase (SDH) in strain IA-1 was 37.5 mU mg(-1), and 7.8-fold higher than that in S. cerevisiae strain NBRC 0216. More significantly, SDH1 was abundantly transcribed in strain IA-1, different from that in strain NBRC 0216, regardless of the culture conditions. From these results, C. krusei IA-1 efficiently takes up succinic acid and metabolizes it in the Krebs cycle, producing an extremely low level of byproducts in the culture medium. Therefore, C. krusei is not only a promising alternative to S. cerevisiae but also a suitable model for metabolic engineering of S. cerevisiae.     

Mixed-solid substrate fermentation. A novel process for enhanced lipase production by Candida rugosa

Candida rugosa was cultivated in a mixed-solid substrate containing coconut oil cake (COC) and fine and coarse wheat bran (1:1:1) with an initial water activity (a_w) of 0.92. The substrate was modified by adding a mineral solution (5%), corn steep liquor (6%), maltose (2%), peptone (3%), olive oil (10%), gum arabic (0.4%), different fatty acids (0.3%) and Tweens (0.5%). Fermentation in a column fermenter significantly improved the lipase yield to 118.2 Units per gram of dry fermented substrate [U/gds] at 72 h. This result was obtained 24 hours earlier than in our former studies (87.76 U/gds at 96 h) in COC, and the yield showed a 38% increase. Growth was measured indirectly by determining the glucosamine content in the cell wall of the yeast contained in the fermented matter, after its hydrolysis.     

Formate-removing inoculum dominated by Methanobacterium congolense supports succinate production from crude glycerol fermentation

Journal of Industrial Microbiology & Biotechnology - We developed a formate-removing methanogenic inoculum (FRI) to facilitate succinate production from crude glycerol by Escherichia coli. FRI...     

产朊假丝酵母发酵生产谷胱甘肽的补料研究

为了实现产朊假丝酵母( Candida utilis WSH02-08)的高密度培养和提高谷胱甘肽 ( glutathione, GSH)产量,在分批发酵研究的基础上,考察了指数速率流加和DO-stat反馈流加对产朊假丝酵母合成GSH的影响.结果表明,采用指数速率流加可获得高细胞密度,但不利于GSH的合成,而采用DO-stat反馈流加较适宜细胞积累GSH.因此,提出并运用了指数速率-DO-stat组合流加策略,即采用指数速率流加实现细胞高密度培养,采用DO-stat反馈流加实现GSH的高积累,细胞量、GSH产量和胞内GSH含量分别为82.5 g/L、1120.6 mg/L和1.46%,实现了高细胞密度和高胞内GSH含量的相对统一.