Researchers Identify Mutations in Saccharomyces cerevisiae Genes that Conferred Acetic Acid Tolerance

Acetic acid, released during hydrolysis of lignocellulosic feedstocks during bioethanol production, inhibits yeast growth and alcoholic fermentation. Yeast should therefore express a high and constitutive level of acetic acid tolerance. However, strategies for increasing acetic acid tolerance of Saccharomyces cerevisiae, based on prolonged cultivation in acetic acid, selected inducible rather than constitutive tolerance.

Serial microaerobic batch cultivation, with alternating transfers to fresh medium with and without acetic acid, generated S. cerevisiae cultures with constitutive acetic acid tolerance. Five single-cell lines from evolution experiments and a constitutively acetic acid tolerant mutant generated from UV-mutagenesis were selected for further studies.

The mutants showed an increased fraction of growing cells upon a transfer to a medium with acetic acid. From the mutants, researchers identified genes with distinct mutations. Further analysis revealed that mutations in the ASG1, ADH3, SKS1 and GIS4 genes conferred acetic acid tolerance. Effects of the mutations in ASG1, ADH3 and SKS1 on acetic acid tolerance were also found to be additive.