Seminars

Industrial Saccharomyces cerevisiae strains are subjected to various stressful conditions during fuel ethanol production, such as the toxic level of ethanol and inhibitors from cellulosic hydrolysates, high temperature and so on. Improvement of stress tolerance of yeast strains benefits economic production of fuel ethanol as well as other biofuels products. In this talk, effect of cell flocculation and zinc addition on yeast stress tolerance will be discussed, and recent progress on functional gene analysis related to yeast stress tolerance in our group will be introduced. In our previous studies, improved stress tolerance of S. cerevisiae flocculating strain SPSC01 was observed comparing with its mutant with the disruption of FLO1, the gene encoding the flocculin. On the other hand, protective effect of zinc against ethanol toxicity was also revealed in SPSC01. Improvement of ethanol tolerance and thermal tolerance was observed by zinc supplementation during continuous high concentration ethanol fermentation, and the ethanol production of the self-flocculating yeast SPSC01 was greatly increased by suitable concentration of zinc. Transcriptome analysis was performed and compared between SPSC01 and its FLO1 disruptant, as well as SPSC01 with various zinc addition in presence of acetic acid, one of the major inhibitor for cellulosic ethanol production. Analysis of the transcriptome data identified previously unknown targets for metabolic engineering of acetic acid tolerance in industrial yeast, and the mutants also showed improved tolerance to high temperature, oxidative stress as well as toxic level of ethanol. These results demonstrated that stress tolerance of S. cerevisiae is regulated by zinc status through various molecular events including transcription factors, metabolic enzymes as well as previously unknown genes involved in stress tolerance. 

References:

1. Zhao XQ, Bai FW. Zinc and yeast stress tolerance: Micronutrient plays a big role, Journal of Biotechnology, 2012, 158: 176-183.

2. Xue C, Zhao XQ, Bai FW. Effect of the size of yeast flocs and zinc supplementation on continuous ethanol fermentation performance and metabolic flux distribution under very high gravity conditions. Biotechnology and Bioengineering 2010, 105: 935-944.