Coordinate gene regulation by fimbriae-induced signal transduction

Fimbriae are thread-like polymers displayed in large amounts on the bacterial 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 whether fimbriae expression can affect expression of other genes. Analysis of gene expression in two E.coli strains, differing in the fim locus, indicated the flu gene to be affected. The flu gene encodes the antigen 43 (Ag43) surface protein, specifically involved in bacterial aggregation, and microcolony and biofilm formation. Ag43 production is repressed by the global regulator OxyR, which monitors the cell's thiol-disulfide status. Only the thiol form of OxyR represses Ag43 production. We demonstrate that production of several different disulfide-containing fimbriae results in the abolition of Ag43 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 expression of other disease- and colonization-related genes.