Abstract
To cope with environmental stresses, bacteria have evolved various strategies, including the general stress response (GSR). GSR is governed by an alternative transcriptional σ factor named σS (RpoS) that associates with RNA polymerase and controls the expression of numerous genes. Previously, we have reported that posttranslational regulation of σS in the aquatic bacterium Shewanella oneidensis involves the CrsR-CrsA partner-switching regulatory system, but the exact mechanism by which CrsR and CrsA control σS activity is not completely unveiled. Here, using a translational gene fusion, we show that CrsR sequesters and protects σS during the exponential growth phase and thus enables rapid gene activation by σS as soon as the cells enter early stationary phase. We further demonstrate by an in vitro approach that this protection is mediated by the anti-σ domain of CrsR. Structure-based alignments of CsrR orthologs and other anti-σ factors identified a CsrR-specific region characteristic of a new family of anti-σ factors. We found that CrsR is conserved in many aquatic proteobacteria, and most of the time it is associated with CrsA. In conclusion, our results suggest that CsrR-mediated protection of σS during exponential growth enables rapid adaptation of S. oneidensis to changing and stressful growth conditions, and this ability is probably widespread among aquatic proteobacteria.
Highlights
To cope with environmental stresses, bacteria have evolved various strategies, including the general stress response (GSR)
GSR is governed by an alternative transcriptional factor named S (RpoS) that associates with the RNA polymerase and controls the expression of numerous genes; for example, its regulon contains more than 500 genes in Escherichia coli
The question we posed is: what happens to S when S. oneidensis is under favorable conditions? In a previous work, we have clearly identified the protein CrsR as a S anti- factor
Summary
To stresses or signals like, for instance, starvation and pH modifications and to a decrease of this factor under favorable conditions [1, 2]. RsbW is an anti- factor that sequesters B and phosphorylates RsbV when bacteria are under favorable conditions, and RsbV is an anti- factor antagonist that binds RsbW and frees B under stressful conditions [5, 6]. In the latter case, dephosphorylation of RsbV is triggered by specific phosphatases (RsbU and RsbP). CrsR is a three-domain response regulator comprising a receiver domain (D1), a phosphatase domain (D2), and a kinase/anti- factor domain (D3), and CrsA is an anti- factor antagonist. We reveal that CrsRD3 belongs to a new family of anti- factor domains widespread in aquatic proteobacteria
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