Figure 5. ROS induce transcription of sRNAs that upregulate σ^S general stress response.

(A) sRNAs DsrA and ArcZ and the Hfq RNA chaperone are required for cipro-induction of σ^S protein. Stationary phase (24h) with MAC cipro. RssB facilitates degradation of σ^S protein. The increase of σ^S levels in ΔrssB cells without cipro, but not with, implies reduced σ^S degradation when cipro-induced ROS upregulate σ^S. Means ± SEM, 3 experiments. *Different from WT with cipro (top half) or WT without cipro (bottom half), p<0.01, one-way ANOVA with Tukey’s post- hoc test.

(B) DsrA, ArcZ, and Hfq allow cipro induction of σ^S activity, stationary-phase (24h). Representative flow cytometry histograms show loss of σ^S-high cells in dsrA, arcZ and hfq null mutants. Means ± SEM, 3 experiments. *p<0.01, one-way ANOVA with Tukey’s post-hoc test; n.s. not significant.

(C) DsrA and ArcZ required for cipro-induced mutagenesis and act in the same pathway. Means ± range, ≥2 experiments. *p<0.01, one-way ANOVA with Tukey’s post-hoc test.

(D) Artificial upregulation of σ^S substitutes for Hfq in mutagenesis indicating that Hfq promotes mutagenesis by σ^S upregulation. Means ± 95% CIs, ≥3 experiments. *p<0.01, one-way ANOVA with Tukey’s post-hoc test.

(E) Cipro-induced ROS induce the dsrA and arcZ promoters. β-galactosidase activity, P_dsrAlacZ and P_arcZlacZ reporters in log (16h) and stationary phase (24h), ± ROS reducers TU, BP, or edaravone. Means ± range, 2 experiments. *p<0.01, one-way ANOVA with Tukey’s post-hoc test.

(F) Summary: Cipro-induced ROS in subpopulation cells induce transcription of DsrA and ArcZ sRNAs which, with the Hfq RNA chaperone, upregulate σ^S in the ROS-high cells (Figure 4).

See also Figures S2, S5, and Tables S1 and S2.