In fuel ethanol production, recycling of yeast biomass includes treatment of cells with diluted sulphuric acid in order to control bacterial population. However, this strategy might lead to a loss of cell viability, with potential negative consequences to the fermentation yield. In a recent paper we showed that the proteins Slt2 and Hog1 are essential for yeast tolerance to sulphuric acid. As a complement of the aforementioned work, we used DNA microarray technology to search for differentially expressed genes in hog1Δ and slt2Δ deletion mutants after treatment with sulphuric acid. Our results show how Slt2p and Hog1p could coordinate the interplay among protein kinase A (PKA), protein kinase C and high-osmolarity glycerol pathways. Moreover, the SSK22 and KDX1 genes may be part of this network, although their proteins were shown to be non-essential for cell growth/survival at low pH. These proteins might work by enhancing the signal which downregulates the PKA pathway leading to cell cycle arrest, in order to regenerate the integrity of yeast cell wall and cell homeostasis under acid shock.

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