The asexual facultative aerobic haploid yeast Candida glabrata is widely used in the industrial production of various organic acids. To elucidate the physiological function of the C. glabrata transcription factor Crz1p (CgCrz1p) and its role in tolerance to acid stress, we deleted or overexpressed the corresponding gene, CgCRZ1. Deletion of CgCRZ1 resulted in a 60% decrease in the dry weight of cells (DCW) and a 50% drop in cell viability compared with those of the wild type at pH 2.0. Expression of lipid metabolism-associated genes was also significantly downregulated. Consequently, the proportion of C 18:1 fatty acids, the ratio of unsaturated to saturated fatty acids, and the ergosterol content decreased by 30%, 46%, and 30%, respectively. Additionally, membrane integrity, fluidity, and H ؉ -ATPase activity were reduced by 45%, 9%, and 50%, respectively. In contrast, overexpression of CgCrz1p increased C 18:1 and ergosterol contents by 16% and 40%, respectively. Overexpression also enhanced membrane integrity, fluidity, and H ؉ -ATPase activity by 31%, 6%, and 20%, respectively. Moreover, in the absence of pH buffering, the DCW and pyruvate titers increased by 48% and 60%, respectively, compared to that of the wild type. Together, these results suggest that CgCrz1p regulates tolerance to acidic conditions by altering membrane lipid composition in C. glabrata. IMPORTANCEThis study provides insight into the metabolism of Candida glabrata under acidic conditions, such as those encountered during the industrial production of organic acids. We found that overexpression of the transcription factor CgCrz1p improved viability, biomass, and pyruvate yields at a low pH. Analysis of plasma membrane lipid composition indicated that CgCrz1p might play an important role in its integrity and fluidity and that it enhanced the pumping of protons in acidic environments. We propose that altering the structure of the cell membrane may provide a successful strategy for increasing C. glabrata productivity at a low pH.T he asexual facultative aerobic haploid yeast Candida glabrata is the only microorganism used for the industrial production of pyruvic (1), fumaric (2), malic (3), and ␣-ketoglutaric (4) acids. However, the accumulation of extracellular acid causes a significant reduction in the pH of the fermentation broth, thereby inhibiting cell growth and decreasing the synthesis of the target compound (5). To maintain the culture medium at a suitable pH, alkaline reagents, such as NaOH, Na 2 CO 3 , and CaCO 3 , are added, although this can result in increased osmotic stress (6). Improving the tolerance of C. glabrata to low-pH conditions should boost the economic efficiency of organic acid production. Various approaches have been attempted in this sense, including the addition of exogenous auxiliary energy substrates (7), chemical mutagenesis of microorganisms (8), rational genetic engineering (9), and adaptive evolution (10). Such approaches have achieved improvements in the titer and yield of some target organic acids ...

is a promising microorganism for organic acid production. The present study aimed to investigate the role of Mediator complex subunit 3 (Med3p) in protecting under low-pH conditions. To this end, genes and were deleted, resulting in the double-deletionΔ strain. The final biomass and cell viability levels of Δ decreased by 64.5% and 35.8%, respectively, compared to the wild-type strain results at pH 2.0. In addition, lack ofMed3ABp resulted in selective repression of a subset of genes in the lipid biosynthesis and metabolism pathways. Furthermore, C18:1, lanosterol, zymosterol, fecosterol, and ergosterol were 13.2%, 80.4%, 40.4%, 78.1%, and 70.4% less abundant, respectively, in the Δ strain. In contrast, the concentration of squalene increased by about 44.6-fold. As a result, membrane integrity, rigidity, and H-ATPase activity in the Δ strain were reduced by 62.7%, 13.0%, and 50.3%, respectively. In contrast, overexpression of increased the levels of C18:0, C18:1, and ergosterol by 113.2%, 5.9%, and 26.4%, respectively. Moreover, compared to the wild-type results, dry cell weight and pyruvate production increased, irrespective of pH buffering. These results suggest that regulates membrane composition, which in turn enables cells to tolerate low-pH stress. We propose that regulation ofMed3ABp may provide a novel strategy for enhancing low-pH tolerance and increasing organic acid production by The objective of this study was to investigate the role of Mediator complex subunit 3 (Med3ABp) and its regulation of gene expression at low pH in We found thatMed3ABp was critical for cellular survival and pyruvate production during low-pH stress. Measures of the levels of plasma membrane fatty acids and sterol composition indicated that Med3ABp could play an important role in regulating homeostasis in We propose that controlling membrane lipid composition may enhance the robustness of for the production of organic acids.