ABSTRACT
Upon infection of host cells, enteropathogenic Escherichia coli (EPEC) delivers a set of effector proteins into the host cell cytoplasm via the type III secretion system (TTSS). The effectors subvert various host cell functions. We found that EPEC interferes with the spreading and ultimately with the attachment of suspended fibroblasts or epithelial cells, and we isolated mini-Tn10kan insertion mutants that failed to similarly affect host cells. In most mutants, the insertion sites were mapped to genes encoding TTSS components, including cesD, escC, escJ, escV, espD, sepL, espB, and escF. Other mutants contained insertions in micC or upstream of bfpP, yehL, or ydeP. The insertion upstream of ydeP was associated with a reduction in TTSS protein production and was studied further. To determine whether the apparent repression was due to constitutive expression of the downstream encoded genes, ydeP and ydeO expression vectors were constructed. Expression of recombinant YdeP, YdeO, or EvgA, a positive regulator of both ydeP and ydeO, repressed TTSS protein production. Our results suggest that upon activation of the EvgAS two-component system, EvgA (the response regulator) activates both ydeP and ydeO expression and that YdeP and YdeO act conjointly, directly or indirectly repressing expression of the TTSS genes.
Subject(s)
Escherichia coli Proteins/metabolism , Escherichia coli/pathogenicity , Fibroblasts/physiology , Gene Expression Regulation, Bacterial , Mutation , Phosphoproteins/metabolism , Transcription Factors/metabolism , Cell Adhesion , Cell Line , Escherichia coli/genetics , Escherichia coli Proteins/genetics , Fibroblasts/microbiology , HeLa Cells , Humans , Phosphoproteins/genetics , Protein Kinases/genetics , Protein Kinases/metabolism , Signal Transduction , Transcription Factors/geneticsABSTRACT
Escherichia coli produces polysaccharide capsules that, based on their mechanisms of synthesis and assembly, have been classified into four groups. The group 4 capsule (G4C) polysaccharide is frequently identical to that of the cognate lipopolysaccharide O side chain and has, therefore, also been termed the O-antigen capsule. The genes involved in the assembly of the group 1, 2, and 3 capsules have been described, but those required for G4C assembly remained obscure. We found that enteropathogenic E. coli (EPEC) produces G4C, and we identified an operon containing seven genes, ymcD, ymcC, ymcB, ymcA, yccZ, etp, and etk, which are required for formation of the capsule. The encoded proteins appear to constitute a polysaccharide secretion system. The G4C operon is absent from the genomes of enteroaggregative E. coli and uropathogenic E. coli. E. coli K-12 contains the G4C operon but does not express it, because of the presence of IS1 at its promoter region. In contrast, EPEC, enterohemorrhagic E. coli, and Shigella species possess an intact G4C operon.