title: Characterization of mutations in the PAS domain of the EvgS sensor kinase selected by laboratory evolution for acid resistance in Escherichia coli.
abstract: Laboratory-based evolution and whole-genome sequencing can link genotype and phenotype. We used evolution of acid resistance in exponential phase Escherichia coli to study resistance to a lethal stress. Iterative selection at pH 2.5 generated five populations that were resistant to low pH in early exponential phase. Genome sequencing revealed multiple mutations, but the only gene mutated in all strains was evgS, part of a two-component system that has already been implicated in acid resistance. All these mutations were in the cytoplasmic PAS domain of EvgS, and were shown to be solely responsible for the resistant phenotype, causing strong upregulation at neutral pH of genes normally induced by low pH. Resistance to pH 2.5 in these strains did not require the transporter GadC, or the sigma factor RpoS. We found that EvgS-dependent constitutive acid resistance to pH 2.5 was retained in the absence of the regulators GadE or YdeO, but was lost if the oxidoreductase YdeP was also absent. A deletion in the periplasmic domain of EvgS abolished the response to low pH, but not the activity of the constitutive mutants. On the basis of these results we propose a model for how EvgS may become activated by low pH.
authors.affiliation: Institute of Microbiology and Infection, School of Biosciences, University of Birmingham, Birmingham, B15 2TT, UK; Drug Delivery, Disposition & Dynamics, Monash Institute of Pharmaceutical Sciences, 381 Royal Parade, Parkville, 3062, Vic., Australia.
authors.forename: Matthew D
authors.initials: MD
authors.lastname: Johnson
authors.forename: James
authors.initials: J
authors.lastname: Bell
authors.forename: Kim
authors.initials: K
authors.lastname: Clarke
authors.forename: Rachel
authors.initials: R
authors.lastname: Chandler
authors.forename: Prachi
authors.initials: P
authors.lastname: Pathak
authors.forename: Yandong
authors.initials: Y
authors.lastname: Xia
authors.forename: Robert L
authors.initials: RL
authors.lastname: Marshall
authors.forename: George M
authors.initials: GM
authors.lastname: Weinstock
authors.forename: Nicholas J
authors.initials: NJ
authors.lastname: Loman
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Winn
authors.forename: Peter A
authors.initials: PA
authors.lastname: Lund
mesh_terms: D000143:Acids / Q000378:metabolism*; D000595:Amino Acid Sequence; D004926:Escherichia coli / Q000737:chemistry / Q000201:enzymology* / Q000235:genetics / Q000378:metabolism; D029968:Escherichia coli Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D019143:Evolution, Molecular; D006863:Hydrogen-Ion Concentration; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009154:Mutation; D011494:Protein Kinases / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D017434:Protein Structure, Tertiary
chemical_list: D000143:Acids; D029968:Escherichia coli Proteins; C465223:EvgS protein, E coli; D011494:Protein Kinases