Isolation and characterisation of a Vibrio cholerae ompR homologue

Vibrio cholerae is the pathogenic agent of the diarrhoeal disease cholera and the major determinant of the disease is the elaboration by the bacteria of the potent enterotoxin cholera toxin (CT). In order to successfully colonise a host V. cholerae must co-ordinately regulate the expression of genes necessary for survival and virulence. ToxR regulates the expression of 17 virulence genes including CT in response to environmental signals like temperature, pH and osmolarity. The change in environment from the external to the human host activates ToxR and the expression of virulence genes under its control. Although this regulon is well characterised it is possible that other regulators are involved.;Two-component regulators are a family of proteins that have been isolated from different bacteria which control gene expression in response to environmental signals. The proteins in the family share a high degree of similarity which was exploited in the design of degenerate primers that were used successfully to amplify four response regulator gene fragments from the V. cholerae chromosome.;The complete sequence of one of the response regulator fragments has been cloned and shares 80% identity to ompR from E. coli. The sequence of a sensor gene 40% similar to envZ from E. coli has been identified downstream of the V. cholerae gene indicating that the two genes may form part of a two-component regulatory system. The two genes complement E. coli ompR and envZ mutants by altering the expression of E. coli porins indicating that they share functional similarity. Preliminary studies in V. cholerae however, show that the genes do not control porin expression under the conditions analysed. Mutation of the V. cholerae ompR/ envZ homologues will show what proteins are regulated by this system in response to varying environmental signals and whether they play any role in virulence.