Characterization of the Melanogenic System in Vibrio cholerae, ATCC 14035

Abstract

The nature of the pigment formed by Vibrio cholerae and the characterization of its biosynthetic pathway is shown. This microorganism is able to synthesize melanin-like pigment when cultured in the presence of L-tyrosine. Other phenolic chemicals related to L-tyrosine do not lead to pigment production. The microorganism has no tyrosine hydroxylase activity, and the levels of dopa oxidase activity are very low, making the existence of a tyrosinase very unlikely. However, Vibrio cholerae contained transaminases that transforms L-tyrosine into p-hydroxyphenylpyruvate. Moreover, Vibrio cholerae is able to go further in the catabolic pathway, releasing a great amount of homogentisic acid. This acid can spontaneously be oxidized to its p-quinone form, which subsequently polymerizes leading to pigment formation. It is concluded that the pigment formed by Vibrio cholerae is not synthesized by the Raper-Mason pathway, but by a L-tyrosine catabolism pathway leading to homogentisic acid. Some simple properties of that melanin are compared to model eu- and pheomelanin, but no clear distinction could be stated, indicating the similarity between all these pigments.

VanT, a Homologue of Vibrio harveyi LuxR, Regulates Serine, Metalloprotease, Pigment, and Biofilm Production in Vibrio anguillarum

“…Figure 4A shows a spectrophotometric profile of colored supernatant from the wild-type and the vanT mutant strains containing pDM5-S13 at various times during growth. The V. anguillarum strains were grown in the presence or absence of L-tyrosine, which has been shown to enhance pigment production in V. cholerae (55). As shown in Fig.…”

“…The homogentistate pathway for the production of melaninlike pigments has been shown for several bacteria (16,41,55), and homogentistate is the primary precursor of melanin-like pigments for marine bacteria, including V. cholerae, Shewanella colwelliana, and a Hyphomonas strain (28). The V. anguillarum HPPD enzyme was shown to be highly homologous to that of V. cholerae (VC1344) (26) and S. colwelliana (23).…”

Melanins: Skin Pigments and Much More—Types, Structural Models, Biological Functions, and Formation Routes

“…More recently, this type of melanin has also been characterized in Burkholderia cenocepacia, a gram-negative opportunistic pathogen that can survive within phagocytic cells, and the synthesis of this melanin is a defense mechanism against the host cell [149], similarly to some pathogenic fungus, such as Aspergillus fumigates [124]. Moreover, pyomelanin from HGA has some relevance since the situation is comparable to the human alkaptonuria [147,148], a rare disease due to mutations in the homogentisate dioxygenase human gene. This inactive enzyme leads to deposits of pyomelanin in the cartilage.…”

“…As stated above, this type of melanin is also formed in some fungi. Shewanella colweliana [145] and Vibrio cholerae [146][147][148] synthesize pyomelanin in response to specific physiological conditions that are stressful to the bacteria. Under those conditions, there is accumulation of homogentisic acid because of the low activity of homogentisate dioxygenase.…”

Inactivation of the hmgA gene of Pseudomonas aeruginosa leads to pyomelanin hyperproduction, stress resistance and increased persistence in chronic lung infection

“…Vibrio cholerae melanin-producing mutants have been shown to be more virulent than the non-melanogenic isogenic strain (Ivins & Holmes, 1980, 1981Ruzafa et al, 1995), and the production of a melanin-like pigment may protect Burkholderia cepacia from host free-radicals, and thus may be considered a virulence factor (Zughaier et al, 1999). …”