Low ergosterol content in yeast adh1 mutant enhances chitin maldistribution and sensitivity to paraquat-induced oxidative stress

Alcohol dehydrogenases catalyse the reversible oxidation of alcohols to aldehydes or ketones, with concomitant reduction of NAD(+) or NADP(+). Adh1p is responsible for the reduction of acetaldehyde to ethanol, while Adh2p catalyses the reverse reaction, the oxidation of ethanol to acetaldehyde. Lack of Adh1p shifts the cellular redox balance towards excess NADH/NADPH and acetaldehyde, while absence of Adh2p does the opposite. Yeast mutant adh1 Delta had a slow growth rate, whereas adh2 Delta grew like the isogenic wild-type (WT) during prediauxic shift fermentative metabolism. After 48 h WT and mutants reached the same number of viable cells. When exponentially growing (LOG) cells were exposed to calcofluor white, only mutant adh1 Delta displayed an irregular deposition of chitin. Quantitative analyses of both LOG and stationary-phase cells showed that adh1 Delta mutant contained significantly less ergosterol than cells of WT and adh2 Delta mutant, whereas the erg3 Delta mutant contained extremely low ergosterol pools. Both adh1 Delta and adh2 Delta mutants showed higher-than-WT resistance to heat shock and to H2O2 but had WT resistance when exposed to ultraviolet (UV) light and the DNA cross-linking agent diepoxyoctane, indicating normal DNA repair capacity. Mutant adh1 Delta was specifically sensitive to acetaldehyde and to membrane peroxidizing paraquat. Our results link the pleiotropic phenotype of adh1 Delta mutants to low pools of ergosterol and to reductive stress, and introduce the two new phenotypes, resistance to heat shock and to H2O2, for the adh2 Delta mutant, most probably related to increased ROS production in mitochondria, which leads to the induction of oxidative stress protection. Copyright (C) 2011 John Wiley & Sons, Ltd.