title: Role of melanin pigment in expression of Vibrio cholerae virulence factors.
abstract: We identified the mutated gene locus in a pigment-overproducing Vibrio cholerae mutant of strain A1552. The deduced gene product is suggested to be an oxidoreductase based on partial homology to putative homogentisate 1,2-dioxygenase in Pseudomonas aeruginosa and Mesorhizobium loti, and we propose that the gene VC1345 in the V. cholerae genome be denoted hmgA in accordance with the nomenclature for other species. The hmgA::mini-Tn5 mutant showed a nonpigmented phenotype after complementation with a plasmid clone carrying the WT hmgA(+) locus. Microarray transcription analysis revealed that expression of hmgA and the neighboring genes encoding a postulated two-component sensor system was growth phase dependent. Results from quantitative reverse transcription-PCR analysis showed that hmgA operon expression was reduced in the rpoS mutant, but pigment production by the WT V. cholerae or the hmgA mutant was not detectably influenced by the stationary-phase regulator RpoS. The pigmented mutant showed increased UV resistance in comparison with the WT strain. Interestingly, the pigment-producing mutant expressed more toxin-coregulated pilus and cholera toxin than WT V. cholerae. Moreover, the hmgA mutant showed a fivefold increase in the ability to colonize the intestines of infant mice. A possible mechanism by which pigment production might cause induction of the ToxR regulon due to generation of hydrogen peroxide was supported by results from tests showing that externally supplied H(2)O(2) led to higher TcpA levels. Taken together, our findings suggest that melanin pigment formation may play a role in V. cholerae virulence factor expression.
authors.affiliation: Department of Molecular Biology, Umeå University, Umeå, Sweden.
authors.forename: Soni Priya
authors.initials: SP
authors.lastname: Valeru
authors.forename: Pramod Kumar
authors.initials: PK
authors.lastname: Rompikuntal
authors.forename: Takahiko
authors.initials: T
authors.lastname: Ishikawa
authors.forename: Karolis
authors.initials: K
authors.lastname: Vaitkevicius
authors.forename: Asa
authors.initials: A
authors.lastname: Sjöling
authors.forename: Nadia
authors.initials: N
authors.lastname: Dolganov
authors.forename: Jun
authors.initials: J
authors.lastname: Zhu
authors.forename: Gary
authors.initials: G
authors.lastname: Schoolnik
authors.forename: Sun Nyunt
authors.initials: SN
authors.lastname: Wai
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics; D015153:Blotting, Western; D004251:DNA Transposable Elements; D015964:Gene Expression Regulation, Bacterial / Q000235:genetics*; D005798:Genes, Bacterial / Q000235:genetics*; D008543:Melanins / Q000235:genetics / Q000378:metabolism*; D009154:Mutation; D020411:Oligonucleotide Array Sequence Analysis; D010088:Oxidoreductases / Q000235:genetics*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012808:Sigma Factor / Q000235:genetics; D014734:Vibrio cholerae / Q000235:genetics* / Q000472:pathogenicity; D037521:Virulence Factors / Q000235:genetics*
chemical_list: D001426:Bacterial Proteins; D004251:DNA Transposable Elements; D008543:Melanins; D012808:Sigma Factor; D037521:Virulence Factors; C069567:sigma factor KatF protein, Bacteria; D010088:Oxidoreductases