The σ^E stress response is required for stress‐induced mutation and amplification in Escherichia coli

Abstract

Pathways of mutagenesis are induced in microbes under adverse conditions controlled by stress responses. Control of mutagenesis by stress responses may accelerate evolution specifically when cells are maladapted to their environments, i.e. are stressed. Stress-induced mutagenesis in the Escherichia coli Lac assay occurs either by ‘point’ mutation or gene amplification. Point mutagenesis is associated with DNA double-strand-break (DSB) repair and requires DinB error-prone DNA polymerase and the SOS DNA-damage- and RpoS general-stress responses. We report that the RpoE envelope-protein-stress response is also required. In a screen for mutagenesis-defective mutants, we isolated a transposon insertion in the rpoE P2 promoter. The insertion prevents rpoE induction during stress, but leaves constitutive expression intact, and allows cell viability. rpoE insertion and suppressed null mutants display reduced point mutagenesis and maintenance of amplified DNA. Furthermore, σE acts independently of stress responses previously implicated: SOS/DinB and RpoS, and of σ32, which was postulated to affect mutagenesis. I-SceI-induced DSBs alleviated much of the rpoE phenotype, implying that σE promoted DSB formation. Thus, a third stress response and stress input regulate DSB-repair-associated stress-induced mutagenesis. This provides the first report of mutagenesis promoted by σE, and implies that extracytoplasmic stressors may affect genome integrity and, potentially, the ability to evolve.

Impact of a stress-inducible switch to mutagenic repair of DNA breaks on mutation in Escherichia coli

“…These processes promote base-substitutions (56,58), frame-shift mutations (40), amplification (40), mobileintron movement (57), and transposon excision (49,57). These examples illustrate the apparently multiple evolutions of mechanisms that couple genomic instability pathways with stress responses and stress.…”

“…Bacillus subtilis (55), the stringent (56, 57) cAMP (49,58) responses to starvation, and RpoE membrane-protein stress response (40) in E. coli. These processes promote base-substitutions (56,58), frame-shift mutations (40), amplification (40), mobileintron movement (57), and transposon excision (49,57).…”

Stress-induced mutagenesis and complex adaptation

“…These responses can be activated due to deteriorating environmental conditions (see §3e) or due to mutations that impair important cell functions, thereby reducing fitness and inducing a stress response. For example, a frameshift mutation in the lac gene causes cells to starve on lactose, thus inducing mutagenesis via a stress response [17,53]. The main analysis assumes that SIM induces mutagenesis in individuals less fit than the wild-type; that is, the mutation rate U of individuals with fitness v is…”

Roles of Nucleoid-Associated Proteins in Stress-Induced Mutagenic Break Repair in Starving Escherichia coli

“…Five-milliliter cultures of SMR4562 (Rec + ), isogenic NAP deletion mutants, and an isogenic DrecA control strain were grown in triplicate to saturation at 37°in LBH medium, as indicated by Gibson et al (2010). Dilutions of each culture were plated on LBH medium to determine viable cell titers.…”