CgMED3 Changes Membrane Sterol Composition To Help Candida glabrata Tolerate Low-pH Stress

Candida glabrata is a promising microorganism for organic acid production. The present study aimed to investigate the role ofC. glabrata Mediator complex subunit 3 (Cg Med3p) in protectingC. glabrata under low-pH conditions. To this end, genesCgMED3A andCgMED3B were deleted, resulting in the double-deletionCgmed3AB Δ strain. The final biomass and cell viability levels ofCgmed3AB Δ decreased by 64.5% and 35.8%, respectively, compared to the wild-type strain results at pH 2.0. In addition, lack ofCg Med3ABp 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 theCgmed3AB 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 theCgmed3AB Δ strain were reduced by 62.7%, 13.0%, and 50.3%, respectively. In contrast, overexpression ofCgMED3AB 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 thatCgMED3AB regulates membrane composition, which in turn enables cells to tolerate low-pH stress. We propose that regulation ofCg Med3ABp may provide a novel strategy for enhancing low-pH tolerance and increasing organic acid production byC. glabrata .IMPORTANCE The objective of this study was to investigate the role ofCandida glabrata Mediator complex subunit 3 (Cg Med3ABp) and its regulation of gene expression at low pH inC. glabrata . We found thatCg Med3ABp 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 thatCg Med3ABp could play an important role in regulating homeostasis inC. glabrata . We propose that controlling membrane lipid composition may enhance the robustness ofC. glabrata for the production of organic acids.