Repression of bacterial motility by a novel fimbrial gene product

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Abstract
Proteus mirabilis is a common uropathogen in patients with long‐term catheterization or with structural or functional abnormalities in the urinary tract. The mannose‐resistant, Proteus‐like (MR/P) fimbriae and flagellum are among virulence factors of P.mirabilis that contribute to its colonization in a murine model of ascending urinary tract infection. mrpJ, the last of nine genes of the mrp operon, encodes a 107 amino acid protein that contains a putative helix–turn–helix domain. Using transcriptional lacZ fusions integrated into the chromosome and mutagenesis studies, we demonstrate that MrpJ represses transcription of the flagellar regulon and thus reduces flagella synthesis when MR/P fimbriae are produced. The repression of flagella synthesis by MrpJ is confirmed by electron microscopy. However, a gel mobility shift assay indicates that MrpJ does not bind directly to the regulatory region of the flhDC operon. The isogenic mrpJ null mutant of wild‐type P.mirabilis strain HI4320 is attenuated in the murine model. Our data also indicate that PapX encoded by a pap (pyelonephritis‐ associated pilus) operon of uropathogenic Escherichia coli is a functional homolog of MrpJ.