Overexpression of vacuolar H+‐ATPase‐related genes in bottom‐fermenting yeast enhances ethanol tolerance and fermentation rates during high‐gravity fermentation

Vacuolar H+-ATPase (V-ATPase) is thought to play a role in stress tolerance. In this study it was found that bottom-fermenting yeast strains, in which the V-ATPase-related genes DBF2, VMA41/CYS4/NHS5 and RAV2 were overexpressed, exhibited stronger ethanol tolerance than the parent strain and showed increased fermentation rates in a high-sugar medium simulating high-gravity fermentation. Among the strains examined, the DBF2-overexpressing bottom-fermenting yeast strain exhibited the highest ethanol tolerance and fermentation rate in YPM20 medium. Using this strain, high-gravity fermentation was performed by adding sugar to the wort, which led to increased fermentation rates and yeast viability compared with the parent strain. These findings indicate that V-ATPase is a stress target in high-gravity fermentation and suggests that enhancing the V-ATPase activity increases the ethanol tolerance of bottom-fermenting yeast, thereby improving the fermentation rate and cell viability under high-gravity conditions. Copyright © 2012 The Institute of Brewing & Distilling