Abstract
Candida glabrata is an important microorganism used in commercial fermentation to produce pyruvate, but very little is known about its mechanisms for surviving acid stress in culture. In this study, it was shown that transcription factors Asg1p and Hal9p play essential roles in C. glabrata in the tolerance of acid stress, as the deletion of CgASG1 or CgHAL9 resulted in the inability to survive in an acidic environment. Cgasg1Δ and Cghal9Δ mutant strains are unable to maintain pH homeostasis, as evidenced by a decrease in intracellular pH and an increase in reactive oxygen species production, which results in metabolic disorders. The results showed that intracellular acidification was partly due to the diminished activity of the plasma membrane proton pump, CgPma1p. In addition, transcriptome sequencing revealed that Cgasg1Δ and Cghal9Δ mutant strains displayed a variety of changes in gene expression under acidic conditions, including genes in the MAPK signaling pathway, plasma membrane, or cell wall organization, trehalose accumulation, and the RIM101 signaling pathway. Lastly, quantitative reverse-transcribed PCR and cellular localization showed that CgAsg1p and CgHal9p played independent roles in response to acid stress.
Highlights
Candida glabrata, a kind of haploid, asexual, ascomycetous yeast, is a major industrial microorganism that is used to produce organic acids, such as fumaric acid (Chen et al, 2015), malic acid (Chen et al, 2013), and α-ketoglutaric acid (Huang et al, 2006; Liang et al, 2008)
Previous studies revealed that the transcription factors Msn2p and Msn4p are essential for resistance to various stresses in C. glabrata (Roetzer et al, 2008)
This study focused on the functional identity of the novel roles played by CgAsg1p and CgHal9p in regulating pH homeostasis under acidic conditions
Summary
A kind of haploid, asexual, ascomycetous yeast, is a major industrial microorganism that is used to produce organic acids, such as fumaric acid (Chen et al, 2015), malic acid (Chen et al, 2013), and α-ketoglutaric acid (Huang et al, 2006; Liang et al, 2008). The pH of C. glabrata cultures gradually decreases due to acid accumulation. The traditional method of solving this problem is to maintain the ambient pH by adding alkaline materials, such as NaOH, CaCO3, and Na2CO3, to the culture broth. This does not solve the problem fundamentally. Compared with Saccharomyces cerevisiae, the mechanism of tolerance to acid stress has not been investigated extensively in C. glabrata. Proteomic analysis of the pH response revealed that C. glabrata perceives low pH as less stressful than high pH (Schmidt et al, 2008). Studies on GPI-linked aspartyl proteases showed that CgYps is required to survive in low external pH environments by regulating the activity
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