Transport of acetate in mutants of Saccharomyces cerevisiae defective in monocarboxylate permeases

The strain Saccharomyces cerevisiae W303-1a, able to grow in a medium containing acetic acid as the sole carbon and energy source, was subjected to mutagenesis in order to obtain mutants deficient in monocarboxylate permeases. Two mutant clones exhibiting growth in ethanol, but unable to grow in a medium with acetic acid as the sole carbon and energy source, were isolated (mutants Ace12 and Ace8). In both mutants, the activity for the acetate carrier was strongly affected. The mutant Ace8 revealed not to be affected in the transport of lactate, while the mutant Ace12 did not display activity for that carrier. These results reinforced those previously found in the strain IGC 4072, where two distinct transport systems for monocarboxylates have been described, depending on the growth carbon source. It is tempting to postulate that the Ace8 mutant seems to be affected in the gene coding for an acetate permease. In contrast, the absence of activity for both monocarboxylate permeases in mutant Ace12 could be attributed to a mutation in a gene coding for a regulatory protein not detected before.