Coordinate gene regulation by fimbriae-induced signal transduction

Fimbriae are thread-like polymers displayed in large amounts on the bacteri al surface and used by many pathogens to attach to receptors on host tissue surfaces. Fimbriae contain disulfide bridges, contrary to many Escherichia coli surface proteins produced in bulk amounts. Here we investigate whethe r fimbriae expression can affect expression of other genes, Analysis of gen e expression in two E.coli strains, differing in the fim locus, indicated t he flu gene to be affected. The flu gene encodes the antigen 43 (Ag43) surf ace protein, specifically involved in bacterial aggregation, and microcolon y and biofilm formation. Ag43 production is repressed by the global regulat or OxyR, which monitors the cell's thiol-disulfide status. Only the thiol f orm of OxyR represses Ag43 production, We demonstrate that production of se veral different disulfide-containing fimbriae results in the abolition of A g43 production. No effect was observed in an oxyR mutant. We conclude that fimbriae expression per se constitutes a signal transduction mechanism that affects a number of unrelated genes via the thiol-disulfide status of OxyR . Thus, phase variation in fimbrial expression is coordinated with the expr ession of other disease- and colonization-related genes.