Monday, August 11, 2008
P2

Elevation of intracellular zinc level improved ethanol tolerance of self-flocculating yeast in continous ethanol fermentation

Xinqing Zhao, Chuang Xue, Xumeng Ge, Wenjie Yuan, and Fengwu Bai. Department of Bioscience and Bioengineering, Dalian University of Technology, No2 Linggong Road, Dalian, China

Zinc sulfate was supplemented at the concentrations of 0.01, 0.05 and 0.1g l–1, respectively in the culture media of self-flocculating yeast during continuous ethanol fermentation. The intracellular accumulation of zinc was elevated to about 6-fold similarly in different zinc addition levels comparing with the control level. The adsorption of zinc was quantified by measuring the zinc concentration in the outflow, and very different ratios of intracellular zinc content and zinc concentration in the culture broth were revealed in different zinc addition cultures. Ethanol tolerance as well as thermal tolerance was greatly improved in all zinc-supplemented cultures, which correlated well with the increased ergosterol and trehalose contents in the yeast flocs. Enhanced ethanol production was also observed in all zinc-supplemented cultures, and the most significant effect on ethanol production (8.4% higher than control) was observed when 0.05 g l–1 zinc sulfate was presented. Glycerol production was decreased by zinc supplementation; with the lowest level about 58% of control when 0.05g l–1 zinc was fed. These studies suggest that the elevated intracellular zinc level resulted from exogenous zinc addition led to a reprogramming of cellular metabolic network, which resulted in enhanced ethanol tolerance and ethanol production.

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