<i>CgMED3</i> Changes Membrane Sterol Composition To Help Candida glabrata Tolerate Low-pH Stress

Abstract

<i>Candida glabrata</i> is a promising microorganism for organic acid production. The present study aimed to investigate the role of <i>C. glabrata</i> Mediator complex subunit 3 (<i>Cg</i>Med3p) in protecting <i>C. glabrata</i> under low-pH conditions. To this end, genes <i>CgMED3A</i> and <i>CgMED3B</i> were deleted, resulting in the double-deletion <i>Cgmed3AB</i>Δ strain. The final biomass and cell viability levels of <i>Cgmed3AB</i>Δ decreased by 64.5% and 35.8%, respectively, compared to the wild-type strain results at pH 2.0. In addition, lack of <i>Cg</i>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 the <i>Cgmed3AB</i>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 <i>Cgmed3AB</i>Δ strain were reduced by 62.7%, 13.0%, and 50.3%, respectively. In contrast, overexpression of <i>CgMED3AB</i> 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 <i>CgMED3AB</i> regulates membrane composition, which in turn enables cells to tolerate low-pH stress. We propose that regulation of <i>Cg</i>Med3ABp may provide a novel strategy for enhancing low-pH tolerance and increasing organic acid production by <i>C. glabrata</i><b>IMPORTANCE</b> The objective of this study was to investigate the role of <i>Candida glabrata</i> Mediator complex subunit 3 (<i>Cg</i>Med3ABp) and its regulation of gene expression at low pH in <i>C. glabrata</i> We found that <i>Cg</i>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 that <i>Cg</i>Med3ABp could play an important role in regulating homeostasis in <i>C. glabrata</i> We propose that controlling membrane lipid composition may enhance the robustness of <i>C. glabrata</i> for the production of organic acids.