X.M. Ge

Impact of zinc supplementation on the improvement of ethanol tolerance and yield of self-flocculating yeast in continuous ethanol fermentation

The effects of zinc supplementation were investigated in the continuous ethanol fermentation using self-flocculating yeast. Zinc sulfate was added at the concentrations of 0.01, 0.05 and 0.1 g l(-1), respectively. Reduced average floc sizes were observed in all the zinc-supplemented cultures. Both the ethanol tolerance and thermal tolerance were significantly improved by zinc supplements, which correlated well with the increased ergosterol and trehalose contents in the yeast flocs. The highest ethanol concentration by 0.05 g l(-1) zinc sulfate supplementation attained 114.5 g l(-1), in contrast to 104.1 g l(-1) in the control culture. Glycerol production was decreased by zinc supplementations, with the lowest level 3.21 g l(-1), about 58% of the control. Zinc content in yeast cells was about 1.4 microMol g(-1) dry cell weight, about sixfold higher than that of control in all the zinc-supplemented cultures, and close correlation of zinc content in yeast cells with the cell viability against ethanol and heat shock treatment was observed. These studies suggest that exogenous zinc addition led to a reprogramming of cellular metabolic network, resulting in enhanced ethanol tolerance and ethanol production.

Ethanol fermentation with Kluyveromyces marxianus from Jerusalem artichoke grown in salina and irrigated with a mixture of seawater and freshwater

Aims:  To study fuel ethanol fermentation with Kluyveromyces marxianus ATCC8554 from Jerusalem artichoke (Helianthus tuberosus) grown in salina and irrigated with a mixture of seawater and freshwater.

Metabolic flux and cell cycle analysis indicating new mechanism underlying process oscillation in continuous ethanol fermentation with Saccharomyces cerevisiae under VHG conditions

Process oscillation characterized by long oscillation period and large oscillation amplitude was observed in continuous ethanol fermentation with Saccharomyces cerevisiae under very high gravity conditions. Metabolic flux analysis was applied to the fermentation system, and the results indicated that carbon flux distributions at the metabolic notes oscillated, correspondingly, and the root reason for the process oscillation was the intracellular metabolism of yeast cells. Cell cycle analysis with the flow cytometry showed that no cell-cycle-dependent synchronization of the daughter and mother cells occurred within the duration of the oscillation, and thus different mechanism existed compared with the oscillation observed in the continuous culture of Saccharomyces cerevisiae and triggered by the synchronization of the daughter and mother cells under specific conditions. Furthermore, the overall metabolic activity of the yeast cells was examined, which was found not exactly out of phase but lag behind ethanol concentration that accumulated within the fermentation system and its inhibition on the yeast cells as well, which supported the mechanistic speculation for the process oscillation: the lag response of yeast cells to ethanol inhibition.