Figure 4.

Role of RpoS in enhanced acid resistance by rpoS-activating sRNAs. (A) Survival rates of ΔrpoS mutant cells overexpressing DsrA, RprA, and ArcZ, respectively, after exposure to pH 3.0 were determined. As ΔrpoS cells did not survive during acid challenge at pH 2.0, cells were challenged at pH 3.0 instead. Overexpression of sRNAs was induced by 1.0 mmol/L IPTG. (B) Wild-type MG1655 cells overexpressing RpoS were exposed to pH 2.0. Overexpression of RpoS was induced from pBAD-RpoS by 0.002% arabinose in exponentially growing cells. Acid resistance was evaluated by analysis of colony-forming abilities of serial 10-fold dilutions of the cultures. (C) Glutamate dependency of acid resistance. Exponentially growing wild-type MG1655 cells were exposed to pH 2.0, and their colony-forming abilities analyzed by 10-fold serial dilution.