Laboratory evolution yields novel lactate transporters and aneuploidy

Laboratory evolution is a powerful approach in applied and fundamental yeast research, but complete elucidation of the molecular basis of evolved phenotypes remains a challenge. In this study, DNA microarray-based transcriptome analysis and whole-genome resequencing were used to investigate evolution of novel lactate transporters in Saccharomyces cerevisiae that can replace Jen1p, the only documented S. cerevisiae lactate transporter. To this end, a jen1Δ mutant was evolved for growth on lactate in serial batch cultures. Single-nucleotide changes were found in the acetate transporter gene ADY2, which were confirmed to mutate ADY2 into an efficient lactate transporter. Due to the strong selective advantage of having more copies of this novel lactate transporter, its gene became triplicated by formation of a novel isochromome III, carrying two additional ADY2 copies.