Regulation of type 1 fimbriae synthesis and biofilm formation by the transcriptional regulator LrhA of Escherichia coli

Abstract

Type 1 fimbriae of Escherichia coli facilitate attachment to the host mucosa and promote biofilm formation on abiotic surfaces. The transcriptional regulator LrhA, which is known as a repressor of flagellar, motility and chemotaxis genes, regulates biofilm formation and expression of type 1 fimbriae. Whole-genome expression profiling revealed that inactivation of lrhA results in an increased expression of structural components of type 1 fimbriae. In vitro, LrhA bound to the promoter regions of the two fim recombinases (FimB and FimE) that catalyse the inversion of the fimA promoter, and to the invertible element itself. Translational lacZ fusions with these genes and quantification of fimE transcript levels by real-time PCR showed that LrhA influences type 1 fimbrial phase variation, primarily via activation of FimE, which is required for the ON-to-OFF transition of the fim switch. Enhanced type 1 fimbrial expression as a result of lrhA disruption was confirmed by mannose-sensitive agglutination of yeast cells. Biofilm formation was stimulated by lrhA inactivation and completely suppressed upon LrhA overproduction. The effects of LrhA on biofilm formation were exerted via the changed levels of surface molecules, most probably both flagella and type 1 fimbriae. Together, the data show a role for LrhA as a repressor of type 1 fimbrial expression, and thus as a regulator of the initial stages of biofilm development and, presumably, bacterial adherence to epithelial host cells also.

Regulation of Aerobic and Anaerobicd-Malate Metabolism ofEscherichia coliby the LysR-Type Regulator DmlR (YeaT)

“…Gene fusions of dmlA and dmlR with lacZ were constructed essentially as described previously using the reporter gene fusion plasmids pJL28 and pJL30 (3,52). To obtain the dmlA-lacZ and dmlR-lacZ fusions in a plasmid, the promoter regions of the dmlA and dmlR genes were amplified with primers yeaU_eco20 (5Ј-CGC GCA GAG AAT TCG GTA AT-3Ј) and yeaU_sal20 (5Ј-CCG ATT CCT GAA TGT CGA CT-3Ј) and primers yeaU_EcoRI_for (5Ј CTT CTT TGC GAA TTC CGT CTC C) and yeaT_HindIII_rev (5Ј GCG CAA AGC TTT CAG CAG C), respectively, from genomic DNA of E. coli LJ1.…”

Xenorhabdus nematophila lrhAIs Necessary for Motility, Lipase Activity, Toxin Expression, and Virulence inManduca sextaInsects

“…In the insect pathogen Photorhabdus temperata, the hexA mutant is attenuated in virulence for Galleria mellonella insects, and HexA represses extracellular enzymes and bioluminescence but has no effect on motility (40). Escherichia coli LrhA represses the transcription of genes involved in motility, chemotaxis, and the formation of type I fimbriae (involved in adherence to host cells) and is necessary for biofilm formation (5,45). Furthermore, E. coli LrhA has been shown to bind directly to the promoter of flhDC (45).…”

“…Here, we identify the lysR homolog A (lrhA) gene necessary for this activity. LrhA homologs are LysR-type transcriptional regulators involved in the expression of virulence factors in several gram-negative bacterial pathogens (5,26,31,40,45,55). For example, in the plant pathogen Pectobacterium carotovorum (formerly Erwinia carotovora subsp.…”

LrhA RegulatesrpoSTranslation in Response to the Rcs Phosphorelay System inEscherichia coli

“…One example is the transcription factor LrhA, which represses expression of several other global regulators, including the stationary-phase sigma factor RpoS and the master regulator of flagellar biosynthesis FlhDC (10,18). It also influences biofilm development and adherence by repressing type 1 fimbrial expression (1,18). Motility has been shown to be a key aspect of bacterial virulence in plants, and homologs of LrhA, such as HexA in Erwinia carotovora and PecT in Erwinia chrysanthemi, have been shown to play critical roles in the pathogenic response (4,5,12,25).…”