通信作者: [email protected];cyao@ xmu.edu.cn[中文文摘]从300多种土壤样品中进行筛选,最终得到10株可耐受300 g/L木糖的酵母菌株,且其木糖醇转化率超过64.0%.其中酵母菌株SB18在150 g/L木糖下的木糖醇转化率为68.5%,为相同条件下转化率最大的菌株,并经18SrDNA测序鉴定为热带假丝酵母.酶活测定结果显示SB18木糖还原酶主要依赖辅因子还原型烟酰胺腺嘌呤二核苷酸磷酸(NADPH),其酶活性远大于木糖醇脱氢酶活性.对SB18进行两级法发酵条件研究,确定补充氮源为尿素和酵母提取物,接种量为0.5 g/L,转速转换时间为36 h.在此条件下由250 g/L木糖摇瓶发酵252 h得到207.65 g/L木糖醇,转化率为83.1%,达到理论值的91.8%.本研究表明酵母菌SB18在高浓度木糖醇的工业生产中具有很大的应用潜力.[英文文摘]Xylose-utilizing yeasts isolated from soil samples in Singapore were screened for xylitol production in high xylose concentration.After several round of screening,10 strains were selected for their high tolerance to 300 g/L xylose concentration,which can convert xylose into xylitol with a yield greater than 64.0%.Strain SB18 exhibited the maximal xylitol yield of 68.5% from 150 g/L xylose,and then was identified as Candida tropicalis by 18S rDNA sequencing information.Enzyme assay results indicate that in s...st rain SB18, xylose reductase(XR) is NADPH dependent and its activity is much higher than that of xylitol dehydr ogenase
(XDH) . A two-stage ferment ation process was employed to investigate the cult ivation condition of SB18. The results show that the
best nitro gen so urces ar e yeast extract and urea, innoculum size is 0.5 g/L, initial xylose concentration is 250 g/L, the optimal speed switch time is 36 h with a shaking speed of 250r/ min in the first stage, and a speed o f 100 r/ min afterw ards. Under the optimal cultivation conditions, xylitol final concentration reached 207. 65 g/L after 252 h incubation from 250 g/L, corresponding to a xylitol
yield of 83.1% and 91.8% x ylose- to- x ylitol bio conversio n efficiency. This work demo nstrates that strain C. tropicalis SB18 has great potentials in industrial xylitol bioproduction in high xylose concentration
