Identification of multiple σ54-dependent transcriptional activators in Vibrio cholerae

In the pathogenic bacterium Vibrio cholerae, the alternate sigma factor sigma(54) is required for expression of multiple sets of genes, including an unidentified gene(s) necessary for enhanced colonization within the host. To identify sigma(54)-dependent transcriptional activators involved in colonization, PCR was performed with V. cholerae chromosomal DNA and degenerate primers, revealing sis novel and distinct coding sequences with homology to sigma(54)-dependent activators. One sequence had high homology to the luxO gene of V. harveyi, which in that organism is involved in quorum sensing. Phenotypes of V. cholerae strains containing mutations in each of the sis putative sigma(54)-dependent activator genes identified one as a probable ntrC homologue. None of the mutant strains exhibited a defect in the ability to colonize infant mice, suggesting the presence of additional sigma(54)-dependent activators not identified by this technique.