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The article presents a study on the role of Rcs phosphorelay in controlling the levels of sigma factor σS in Escherichia coli biofilm formation. The Rcs phosphorelay was studied and used a screen to look for suppresor mutants which helped restore biofilm formation in the mutant background of rcsC. It concludes that the maintenance of appropriate levels of σS during biofilm formation in E. coli involves the Rcs phosphorelay.

The article shows that the genes yjbE, yjbF, yjbG and yjbH are transcribed as a single operon and it is confirmed that the expression of this operon is controlled by the Rcs phosphorelay. The RcsCDB phosphorelay was originally identified as the main regulator of colanic acid biosynthesis in Escherichia coli K-12. The article provides evidence that the overexpression of yjbEFGH affects colony morphology.

The Rcs phosphorelay is composed of RcsC, RcsD and the response regulator RcsB, and this signalling pathway has been implicated in virulence and biofilm formation in many enteric bacteria. It was previously shown that a mutation in rcsC resulted in defective biofilm formation in Escherichia coli [Ferrières, L. & Clarke, D. J. (2003) Mol Microbiol 50, 1665-1682]. To identify the molecular mechanisms underlying the observed biofilm defect we carried out a screen looking for suppressor mutants that restored biofilm formation in the rcsC mutant background. One of the mutants was identified to be in rprA, a gene encoding a small RNA molecule that is involved in the post-transcriptional control of the alternative sigma factor, sigma(S). The expression of rprA is regulated by the Rcs phosphorelay, and there are elevated sigma(S) levels present in the rcsC mutant due to the overexpression of rprA in this background. Using different approaches, we have established that the increase in sigma(S) levels is responsible for the biofilm defect. Therefore, the Rcs phosphorelay is involved in maintaining appropriate levels of sigma(S) during biofilm formation in E. coli.