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.

A Putative ABC Transporter, HatABCDE, Is among Molecular Determinants of Pyomelanin Production inPseudomonas aeruginosa

“…In addition to the mutation in hmgA already described to occur in several bacterial species (8,49,63), we identified 26 candidate genes. Statistically, genome coverage in our library was unsaturated (ϳ90%), yet we hit each gene in the homogentisate pathway and some genes multiple times.…”

“…Proposed roles for pyomelanin include the enhancement of bacterial surface attachment (20), extracellular electron transfer (61), iron reduction/acquisition (8), induction of virulence factor expression (63), heavy metal binding (21), and protection from environmental stress (11,28,32,44,53,65). A protective role has also been proposed to occur in P. aeruginosa PA14, where pyomelanin was shown to contribute to the persistence of an overproducing strain in a chronic CF infection model in mice (49).…”

Pathoadaptive Conditional Regulation of the Type VI Secretion System in Vibrio cholerae O1 Strains

“…RNA extraction and quantitative reverse transcription (qRT)-PCR were performed as described previously (53). Three independent samples were tested in triplicate.…”

Disorders of Pigmentation of the Skin - Hypotheses Underlying Interventions by Multiple Systems of Medicine:Is there a Role for Integrated Medicine?

“…Whereas millions of years earlier primitive organisms found uses for melanin unrelated to sunlight such as the role of tyrosinase in the production of dopamine, acting to safeguard contact between unicellular organisms, many millions of years earlier 8 . There has also been the recent observation of the presence of melanin as a virulence factor in Vibrio cholera 9 . Melanocyte manufactures melanin and transfers it to keratinocyte, and in hyperproliferative states in which the keratinocyte is exfoliated taking melanin with it.…”