Identification of the gene for the monomeric alkaline phosphatase of Vibrio cholerae serogroup O1 strain

Alkaline phosphatase (APase) of Vibrio cholerae is the first monomeric alkaline phosphatase reported [Roy, N.K., Ghosh, R.K., Das, J., 1982a. Monomeric alkaline phosphatase of V. cholerae. J. Bacteriol. 150, 1033-1039.]. The gene (phoAVC) encoding this enzyme is not identified in the published genome sequence of the V. cholerae serogroup O1 El Tor strain N16961 [Heidelberg et al., 2000, DNA sequence of both the chromosome of cholera pathogen V. cholerae. Nature 406, 477-484.]. However two genes (phoBVC and phoRVC) regulating the synthesis of alkaline phosphatase in this organism, equivalent to phoB and phoR of Escherichia coli, are located in tandem on chromosome I of V. cholerae. We have identified the phoAVC gene on the N16961 genome sequence by amino acid sequence analysis of the purified alkaline phosphatase of V. cholerae classical strain 569B followed by BLAST search. The gene was found to be located on the hypothetical protein locus VCA0033 of chromosome II. The identity of the gene was confirmed by expressing the cloned VCA0033 locus in phoA mutant E. coli E15 and JC9223 cells and isolating V. cholerae monomeric alkaline phosphatase. Insertional inactivation of the gene also resulted in complete loss of the phenotype. Unlike in E. coli where phoB, phoR and phoA are closely linked, phoAVC is not linked to phoBVC and phoRVC.