Identification and characterization of genes related to the production of organic acids in yeast.

Organic acids contribute to the flavor of many foods and drinks including alcoholic beverages. To study the cellular processes affecting organic acid production, here we screened collections of Saccharomyces cerevisiae deletion mutants and identified 36 yeast mutants forming a yellow halo on YPD plates containing bromocresol purple, indicating that the pH of the medium had been lowered. The disrupted genes encoded TCA cycle enzymes, transcription factors, signal transducers, and ubiquitin-related proteins. Acetate, pyruvate, and succinate are produced by yeast fermentation in rich medium, and their production was affected by mutations of the genes GTR1, GTR2, LIP5, LSM1, PHO85, PLM2, RTG1, RTG2 and UBP3, and also succinate dehydrogenase-related genes including EMI5, SDH1, SDH2, SDH4, TCM62 and YDR379C-A. Among the genes identified, overexpression of only LIP5 affected the production of acetate in S. cerevisiae. However, overexpression of EMI5, LIP5, RTG2 and UBP3 had a significant effect on the production of acetate, citrate, lactate, and succinate in the bottom-fermenting yeast Saccharomyces pastorianus. Furthermore, phenotypic analysis of the S. cerevisiae disruptants involved in organic acid production showed that azaserine, citrate, ethionine, and sulfite are useful compounds by which mutants with altered organic acid production might be selected. Taken together, these results suggest that the regulation of many organic acids might be simultaneously achieved by activation or inactivation of a single gene.