MIrA, a novel regulator of curli (AgF) and extracellular matrix synthesis by Escherichia coli and Salmonella enterica serovar typhimurium

Production of curli (AgF) adhesins by Escherichia coli and Salmonella enterica serovar Typhimurium (S. typhimurium) is associated with extracellular matrix production and is optimal at low temperature during stationary phase. Curli and extracellular matrix synthesis involves a complex regulatory network that is dependent on the CsgD (AgfD) regulator. We have identified a novel regulator, termed mIrA, that is required for curli production and extracellular matrix formation. Two cosmids from a genomic library of avian pathogenic E. coli _χ7122 conferred mannose-resistant haemagglutination (HA) and curli production to E. coli HB101, which is unable to produce curli owing to a defective regulatory pathway. The rpoS gene, encoding a known positive regulator of curli synthesis, and the E. coli open reading frame (ORF) of unknown function, yehV, identified on each of these cosmids, respectively, conferred curli production and HA to E. coli HB101. We have designated yehV as the mIrA gene for MerR-like regulator A because its product shares similarities with regulatory proteins of the MerR family. HA and curli production by strain _χ7122 were abolished by disruption of rpoS, mIrA or csgA, the curli subunit gene. Both csgD and csgBA transcription, required for expression of curli, were inactive in an mIrA mutant grown under conditions that promote curli production. An mIrA homologue was identified in S. typhimurium. Analysis of mIrA-lac operon fusions demonstrated that mIrA was positively regulated by rpoS. mIrA mutants of wild-type S. typhimurium SL1344 or SR-11 no longer produced curli or rugose colony morphology, and exhibited enhanced aggregation and extracellular matrix formation when complemented with the mIrA gene from either S. typhimurium or E. coli present on a low-copy-number plasmid. However, inactivation of mIrA did not affect curli production and aggregative morphology in an upregulated curli producing S. typhimurium derivative containing a temperature-and RpoS-independent agfD promoter region. These results indicate that MIrA is a newly defined transcriptional regulator of csgD/agfD that acts as a positive regulator of RpoS-dependent curli and extracellular matrix production by E. coli and S. typhimurium.