title: Broad-host-range vectors for delivery of TnphoA: use in genetic analysis of secreted virulence determinants of Vibrio cholerae.
abstract: Gene fusions between the cholera toxin structural genes and phoA, which encodes bacterial alkaline phosphatase, were identified after TnphoA mutagenesis of the cloned genes in Escherichia coli and were then mobilized into Vibrio cholerae. The activities of the hybrid proteins were detectable in V. cholerae and suggested that, like cholera toxin, they were secreted beyond the cytoplasm. To extend the utility of TnphoA to identify additional genetic export signals in V. cholerae and other gram-negative bacteria, TnphoA delivery vectors utilizing broad-host-range plasmids were developed. By using V. cholerae as a model system, insertion mutants carrying active phoA gene fusions were identified as colonies expressing alkaline phosphatase, which appeared blue on agar containing the indicator 5-bromo-4-chloro-3-indolyl phosphate. Since alkaline phosphatase is active only upon export from the cytoplasm, PhoA+ colonies resulting from the mutagenesis procedure were enriched for insertions in genes that encode secreted proteins. Insertion mutations were identified in the gene encoding a major outer membrane protein, OmpV, and in tcpA, which encodes a pilus (fimbrial) subunit. Mutant strains harboring chromosomal insertions isolated in this manner can be used to assess the role of the corresponding inactivated gene products on survival of V. cholerae in vivo. The expression of the hybrid proteins as determined by measuring alkaline phosphatase activity also allowed the convenient study of virulence gene expression.
authors.affiliation: Harvard Medical School, Department of Microbiology and Molecular Genetics, Boston, Massachusetts 02115.
authors.forename: R K
authors.initials: RK
authors.lastname: Taylor
authors.forename: C
authors.initials: C
authors.lastname: Manoil
authors.forename: J J
authors.initials: JJ
authors.lastname: Mekalanos
mesh_terms: D000469:Alkaline Phosphatase / Q000235:genetics; D000595:Amino Acid Sequence; D001425:Bacterial Outer Membrane Proteins / Q000235:genetics; D001483:Base Sequence; D002772:Cholera Toxin / Q000235:genetics; D004251:DNA Transposable Elements; D004269:DNA, Bacterial / Q000235:genetics; D036781:Fimbriae Proteins; D005798:Genes, Bacterial; D005822:Genetic Vectors; D008969:Molecular Sequence Data; D011993:Recombinant Fusion Proteins / Q000235:genetics; D014734:Vibrio cholerae / Q000235:genetics* / Q000472:pathogenicity
chemical_list: D001425:Bacterial Outer Membrane Proteins; D004251:DNA Transposable Elements; D004269:DNA, Bacterial; D011993:Recombinant Fusion Proteins; D036781:Fimbriae Proteins; D002772:Cholera Toxin; D000469:Alkaline Phosphatase