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

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. Overall design: 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.

本研究报道了与运动发酵单胞菌（Zymomonas mobilis）乙酸钠耐受突变株（AcR）相关的基因组变化。本研究采用比较基因组学、转录组学及遗传学手段，证实nhaA基因过表达可赋予运动发酵单胞菌乙酸钠（NaAc）耐受能力。
我们观察到，钠离子与乙酸根离子存在协同毒性效应，可增强对野生型菌株ZM4的毒害作用；而在可控实验室条件下，等摩尔浓度的乙酸钾与乙酸铵并未呈现类似协同效应。
本研究进一步拓展验证，证实酿酒酵母（Saccharomyces cerevisiae）钠氢反向转运蛋白基因可提升这一重要工业产乙醇微生物的乙酸钠耐受能力。
经典生物学与系统生物学工具的联合应用为工业菌株改良提供了可行范式，其优势在于无需过多先验假设，同时可开展细致、快速的机制研究。
最后，本研究进一步佐证了两项核心观点：在突变筛选中可获得定向筛选的目标性状，且遗传操作系统对工业菌株开发至关重要。
整体实验设计：ZM4_ACr_NaCl_NaAc_study。对野生型运动发酵单胞菌ZM4及乙酸钠耐受突变株AcR，在12g/L乙酸钠及等摩尔浓度氯化钠（8.55g/L）对照条件下，分别分析其指数生长期与稳定期细胞的全基因组表达谱。