Extreme Low Cytosolic pH Is a Signal for Cell Survival in Acid Stressed Yeast.

Rodrigo Mendonça Lucena,Marcos Antonio De Morais,Stanley Brul,Laura Dolz-Edo,Gertien Smits

doi:10.3390/genes11060656

Rodrigo Mendonça Lucena, Marcos Antonio De Morais + Show 3 more

Open Access

https://doi.org/10.3390/genes11060656

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Journal: Genes	Publication Date: Jun 16, 2020
Citations: 17	License type: CC BY 4.0

Affiliation: Universidade Federal de Pernambuco, University of Amsterdam

Abstract

Yeast biomass is recycled in the process of bioethanol production using treatment with dilute sulphuric acid to control the bacterial population. This treatment can lead to loss of cell viability, with consequences on the fermentation yield. Thus, the aim of this study was to define the functional cellular responses to inorganic acid stress. Saccharomyces cerevisiae strains with mutation in several signalling pathways, as well as cells expressing pH-sensitive GFP derivative ratiometric pHluorin, were tested for cell survival and cytosolic pH (pHc) variation during exposure to low external pH (pHex). Mutants in calcium signalling and proton extrusion were transiently sensitive to low pHex, while the CWI slt2Δ mutant lost viability. Rescue of this mutant was observed when cells were exposed to extreme low pHex or glucose starvation and was dependent on the induced reduction of pHc. Therefore, a lowered pHc leads to a complete growth arrest, which protects the cells from lethal stress and keeps cells alive. Cytosolic pH is thus a signal that directs the growth stress-tolerance trade-off in yeast. A regulatory model was proposed to explain this mechanism, indicating the impairment of glucan synthesis as the primary cause of low pHex sensitivity.

Highlights

Yeast growing cells can face extracellular pH changes when they naturally acidify the environment because of the action of metabolism, or during human usage in biotechnological processes.Human-made acidic environments occur, for instance, in the process of bioethanol production in which yeast biomass is recycled using sulphuric acid to control the bacterial population [1,2], by addition of weak organic acids (WOAs) to prevent food contaminations [3], or even for probiotic yeast which has to pass through the acidic gastrointestinal tract [4]
While survival at low pHex requires proper cell wall maintenance or repair, a reduction of pHc leading to reduced growth can compensate for the lack of this cell wall integrity (CWI) mediated process
We previously reported the importance of the protein kinase C (PKC) and Ca2+ signalling pathways in inorganic acid tolerance in rich (YPD) media [25]

Summary

Introduction

Yeast growing cells can face extracellular pH (pHex ) changes when they naturally acidify the environment because of the action of metabolism, or during human usage in biotechnological processes.Human-made acidic environments occur, for instance, in the process of bioethanol production in which yeast biomass is recycled using sulphuric acid to control the bacterial population [1,2], by addition of weak organic acids (WOAs) to prevent food contaminations [3], or even for probiotic yeast which has to pass through the acidic gastrointestinal tract [4]. Yeast growing cells can face extracellular pH (pHex ) changes when they naturally acidify the environment because of the action of metabolism, or during human usage in biotechnological processes. The nature of the plasma membrane architecture makes it almost impermeable to protons, which keeps cytosolic pH (pHc ) highly regulated. The proton gradient over the plasma membrane provides the energy for the import of many nutrients, including amino acids, phosphate, several (non-preferred) sugars and other carbon sources [7]. Uptake of these nutrients, through proton symport, results in the influx of protons. The cells counteract this acidification through the activation of the plasma membrane H+ -ATPase pump

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