Mutual interplay between ArcA and σ^E orchestrates envelope stress response in Shewanella oneidensis

Abstract

Summary To survive and thrive in harsh and ever‐changing environments, intricate mechanisms have evolved for bacterial cells to monitor perturbations impacting the integrity of their envelope and to mount an appropriate response to contain or repair the damage. In this study, we report in Shewanella oneidensis a previously undescribed mechanism for the envelope defect resulting from the loss of Arc, a two‐component transcriptional regulatory system crucial for respiration. We uncovered σE, a master regulator establishing and maintaining the integrity of the cell envelope in γ‐proteobacteria, as the determining factor for the cell envelope defect of the arcA mutant. When ArcA is depleted, σE activity is compromised by enhanced production of anti‐σE protein RseA. Surprisingly, S. oneidensis σE is not essential for viability, but becomes so in the absence of ArcA. Furthermore, we demonstrated that there is an interplay between these two regulators as arcA expression is affected by availability of σE. Overall, our results underscore functional interplay of regulatory systems for envelope stress response: although each of the systems may respond to perturbation of particular components of the envelope, they are functionally intertwined, working together to form an interconnected safety net.

Shewanella oneidensis arcA Mutation Impairs Aerobic Growth Mainly by Compromising Translation

“…Despite the difference in SDS susceptibility between these two strains, the manipulated production of RpsA by up to 1 mM showed no significant impacts on their resistance to SDS, suggesting that the cell envelope defect is not associated with ribosome quantity. Therefore, the reduced ribosome abundance is not accountable for the cell envelope defect of the arcA mutant, further supporting the notion that two major defects caused by the ArcA loss are independent of each other [ 28 ].…”

“…In S. oneidensis, another major phenotype resulting from the ArcA loss is the severe defect in the cell envelope integrity [27][28][29]. The Arc system of E. coli was initially recognized to confer resistance to dyes such as toluidine blue O and methylene blue, implying that the ArcA loss compromises the outer membrane, but the underlying mechanism still remains largely elusive [57].…”

“…In addition to the slow aerobic growth, the S. oneidensis ∆arcA strain also carries a severe defect in the cell envelope integrity [27][28][29]. Both phenotypes are attributed to the ArcBA-mediated signal transduction and regulation because the manipulated production of ArcA but not ArcA D54N (a mutant which could not be phosphorylated) corrects the two defects [24,27,28].…”

“…In addition to the slow aerobic growth, the S. oneidensis ∆arcA strain also carries a severe defect in the cell envelope integrity [27][28][29]. Both phenotypes are attributed to the ArcBA-mediated signal transduction and regulation because the manipulated production of ArcA but not ArcA D54N (a mutant which could not be phosphorylated) corrects the two defects [24,27,28]. We have recently demonstrated that the cell envelope defect of the ArcA mutant is linked to activity of σ E (RpoE), an alternative sigma factor which plays a primary role in mediating envelope biogenesis and envelope stress response [30], and appears independent of the aerobic growth defect [28,29].…”

“…Both phenotypes are attributed to the ArcBA-mediated signal transduction and regulation because the manipulated production of ArcA but not ArcA D54N (a mutant which could not be phosphorylated) corrects the two defects [ 24 , 27 , 28 ]. We have recently demonstrated that the cell envelope defect of the ArcA mutant is linked to activity of σ E (RpoE), an alternative sigma factor which plays a primary role in mediating envelope biogenesis and envelope stress response [ 30 ], and appears independent of the aerobic growth defect [ 28 , 29 ]. The goal of this study was to unravel the mechanisms for the growth defect of the S. oneidensis ArcA mutant.…”