Department of Biochemistry and Technological Chemistry, Instituto de Química de Araraquara, São Paulo State University, UNESP, PO Box 355, Araraquara, São Paulo 14801-970, Brazil.
J Ind Microbiol Biotechnol. 2011 Mar;38(3):405-14. doi: 10.1007/s10295-010-0783-9. Epub 2010 Aug 10.
A fermentation system was continuously fed with sugar-cane syrup and operated with recycling of Saccharomyces cerevisiae cells at temperatures varying from 30 to 47 °C. The aim of the present work was to obtain and study the colonies of isolates showing elongated cells of yeasts which were sporadically observed at the end of this continuous process. Based on a sequence of assays involving methods of classical taxonomy and RAPD-PCR, two groups of isolates showing characteristics of non-Saccharomyces yeasts were identified in the yeast population where S. cerevisiae was the dominant yeast. The largest group of non-Saccharomyces yeasts, resulting from a slow proliferation over the 2 months, reached a final level of 29.6% at the end of the process. RAPD-PCR profiles obtained for the isolates of this dominant non-Saccharomyces yeast indicated that they were isolates of Issatchenkia orientalis. Pichia membranifaciens was the only species of non-Saccharomyces yeast detected together with I. orientalis but at a very low frequency. The optimum temperature for ethanol formation shown by the isolate 195B of I. orientalis was 42 °C. This strain also showed a faster ethanol formation and biomass accumulation than the thermotolerant strain of S. cerevisiae used as the starter of this fermentation process. Some isolates of I. orientalis were also able to grow better at 40 °C than at 30 °C on plates containing glycerol as carbon source. Yeasts able to grow and produce ethanol at high temperatures can extend the fermentation process beyond the temperature limits tolerated by S. cerevisiae.
一个发酵系统持续地以甘蔗糖浆为原料，并在 30 到 47°C 的温度范围内循环使用酿酒酵母细胞。本研究的目的是获得并研究在连续发酵过程结束时偶然观察到酵母细胞变长的分离株的菌落。基于涉及经典分类学方法和 RAPD-PCR 的一系列测定，在以酿酒酵母为主导酵母的酵母种群中，鉴定出了两组具有非酿酒酵母特征的分离株。在这个缓慢增殖的 2 个月过程中，最大的非酿酒酵母群在过程结束时最终达到了 29.6%的水平。对该优势非酿酒酵母分离株的 RAPD-PCR 图谱分析表明，它们是东方伊萨酵母的分离株。膜醭毕赤酵母是与东方伊萨酵母一起检测到的唯一非酿酒酵母，但频率非常低。分离株 195B 的最适乙醇形成温度为 42°C。该菌株比用作发酵过程起始菌株的耐热酿酒酵母的乙醇形成和生物量积累更快。一些东方伊萨酵母的分离株在含有甘油作为碳源的平板上，在 40°C 下比在 30°C 下生长得更好。能够在高温下生长和产生乙醇的酵母可以将发酵过程扩展到酿酒酵母耐受的温度范围之外。
