Abstract:[Background] The acid tolerance of industrial strains is a significant challenge in the fermentation process. The bacterium Serratia marcescens is part of the Enterobacteriaceae family of eubacteria. It can produce 2,3-butanediol, acetoin, prodigiosin and other high value-added products. However, the molecular mechanism behind S. marcescens acid resistance is not properly understood. [Objective] By mining of the transcriptional regulator XrpA and studying its functions, the molecular mechanism of acid tolerance of S. marcescens was preliminarily investigated, and a new direction was provided for improving the acid-resistant ability of industrial strains. [Methods] A Tn5G transposon insertion mutant library was constructed by transposon insertion mutation of S. marcescens, and an acid-sensitive mutant strain was screened from the library for sequencing identification. Then, the transcription level of key genes related to acid tolerance and the changes of cell membrane permeability, cell membrane integrity and H+-ATPase activity in the mutant strain were detected. Finally, the mechanism of XrpA regulating the acid tolerance of the S. marcescens was studied by analyzing the experimental data. [Results] we screened for novel regulators that respond to acidic conditions and found mutations in a gene encoding for the HTH_XRE super-family regulatory protein member, here named xrpA. We showed that the xrpA disruption conferred pleiotropic phenotype changes, including highly decreased biomass, H+-ATPase activity, and deficiency of cell membrane permeability and integrity, compared with those of the parent (JNB5-1) strain at low pH. [Conclusion] These data revealed that the molecular mechanism by which xrpA affects acid resistance of S. marcescens is through positive regulation of cell membrane permeability, integrity, and H+-ATPase activity to maintain intracellular homeostasis at low pH. Meanwhile, these results indicated that XrpA regulates tolerance to low pH by transcriptional regulation of acid stress response genes to maintain cell membrane function in S. marcescens.
