Identification and Molecular Characterization of the Homogentisate Pathway Responsible for Pyomelanin Production, the Major Melanin Constituents in Aeromonas media WS

Abstract

The pigmentation of many Aeromonas species has been thought to be due to the production of a L-DOPA (L-3,4-dihydroxyphenylalanine) based melanin. However, in this study we found that although L-DOPA synthesis occurs in the high-melanin-yielding Aeromonas media strain WS, it plays a minor, if any, role in pigmentation. Instead, the pigmentation of A. media strain WS is due to the production of pyomelanin through HGA (homogentisate). Gene products of phhA (encodes phenylalanine hydroxylase), tyrB and aspC (both encode aromatic amino acid aminotransferase), and hppD (encodes 4-hydroxyphenylpyruvate dioxygenase) constitute a linear pathway of converting phenylalanine to HGA and disruption of any one of these genes impairs or blocks pigmentation of A. media strain WS. This HGA biosynthesis pathway is widely distributed in Aeromonas, but HGA is only detectable in the cultures of pigmented Aeromonas species. Heterologous expression of HppD from both pigmented and non-pigmented Aeromonas species in E. coli leads to the production of pyomelanin and thus pigmentation, suggesting that most Aeromonas species have the critical enzymes to produce pyomelanin through HGA. Taken together, we have identified a widely conserved biosynthesis pathway of HGA based pyomelanin in Aeromonas that may be responsible for pigmentation of many Aeromonas species.

Living in an Extremely Polluted Environment: Clues from the Genome of Melanin-Producing Aeromonas salmonicida subsp. pectinolytica 34mel T

“…While the present work was in the process of revision, melanin synthesis in A. media WS was demonstrated to occur through the homogentisate pathway (56), supporting the genetic evidence presented in this study.…”

Identification of a Gene Involved in the Negative Regulation of Pyomelanin Production in Ralstonia solanacearum

“…The culture filtrates of R. solanacearum SL341 grown to stationary phase in liquid culture with tyrosine exhibited eumelanin and pyomelanin accumulation in almost equivalent amounts. Previously, production of two different kinds of melanin has been reported in Aspergillus fumigatus and Aeromonas [37][38][39]. Further study to understand the reason why R. solanacearum produced two different kinds of melanin is necessary.…”

Identification of Homogentisate Dioxygenase as a Target for Vitamin E Biofortification in Oilseeds

“…For example, spectral absorption analysis of alkalinized homogentisate, synthetic pyomelanin, and urine samples of alkaptonuria patients showed a characteristic absorbance peak at 406 nm and 430 nm (Tokuhara et al, 2014;Roberts et al, 2015). Likewise, increased absorbance at 400 to 405 nm due to extracellular pyomelanin production was also reported in microbial HGO mutants (Turick et al, 2008;Schmaler-Ripcke et al, 2009;Wang et al, 2015). Spectrophotometric scan of the brown pigment extracted from MO12 seed coats showed a small peak at 400 to 405 nm and an overall higher absorbance under visible light compared to Williams 82 samples (Supplemental Fig.…”