Physiological and molecular analysis of the stress response of Saccharomyces cerevisiae imposed by strong inorganic acid with implication to industrial fermentations

Abstract

This work aimed to identify the molecular mechanism that allows yeast cells to survive at low pH environments such as those of bioethanol fermentation. The industrial strain JP1 cells grown at pH 2 was evaluated by microarray analysis showing that most of the genes induced at low pH were part of the general stress response (GSR). Further, an acid-tolerant yeast mutant was isolated by adaptive selection that was prone to grow at low pH in inorganic but weak organic acid. It showed higher viability under acid-temperature synergistic treatment. However, it was deficient in some physiological aspects that are associated with defects in protein kinase A (PKA) pathway. Microarray analysis showed the induction of genes involved in inhibition of RNA and protein synthesis. The results point out that low pH activates GSR, mainly heat shock response, that is important for long-term cell survival and suggest that a fine regulatory PKA-dependent mechanism that might affect cell cycle in order to acquire tolerance to acid environment. These findings might guide the construction of a high-fermentative stress-tolerant industrial yeast strain that can be used in complex industrial fermentation processes.