Genome changes associated with a Zymomonas mobilis sodium acetate-tolerant mutant (AcR)

We report the genome changes associated with a Zymomonas mobilis sodium acetate-tolerant mutant (AcR). We used comparative genomics, transcriptomics, and genetics to show nhaA over-expression conferred sodium acetate (NaAc) tolerance in Z. mobilis. We observed a synergistic effect for sodium and acetate ions that enhanced toxicity against the wild-type strain (ZM4), which was not observed for similar concentrations of potassium and ammonium acetate under controlled laboratory conditions. We extended our studies and demonstrated that Saccharomyces cerevisiae sodium-proton antiporter genes contribute to NaAc tolerance for this important ethanologen. The application of classical and systems biology tools is a paradigm for industrial strain improvement and combines benefits of few a priori assumptions with detailed, rapid, mechanistic studies. Finally, our studies reinforce the idea that one obtains what one selects for in mutant screens and that a genetic system is important for industrial strain development. ZM4_ACr_NaCl_NaAc_study. Whole-genome expression profiles of exponential and stationary phase cells were analyzed for the wild-type Zymomonas mobilis ZM4 and the acetate-tolerant mutant AcR under 12g/L sodium acetate and same molar concentration of sodium chloride (8.55g/L) control conditions.