Identification of YfiH and the Catalase CatA As Polyphenol Oxidases of Aeromonas media and CatA as a Regulator of Pigmentation by Its Peroxyl Radical Scavenging Capacity

Abstract

Pyomelanin is the major constituent of pigment in melanogenic Aeromonas strains of bacteria. However, eumelanin, synthesized from tyrosine via L-DOPA and polyphenol oxidases (PPOs), may also be present in this genus since L-DOPA is frequently detected in culture fluids of several species. To address this question, we used a deletion mutant of Aeromonas media strain WS, in which pyomelanin synthesis is completely blocked under normal culture conditions. When tyrosine was supplied to the medium, we observed residual melanin accumulation, which we interpret as evidence for existence of the DOPA-melanin pathway. We traced enzymatic activity in this bacterium using native-polyacrylamide gel electrophoresis. Two PPOs: YfiH, a laccase-like protein, and CatA, a catalase, were identified. However, neither protein was critical for the residual pigmentation in pyomelanin-deficient mutant. We speculate that eumelanin synthesis may require other unknown enzymes. Deletion of yfiH did not affect pigmentation in A. media strain WS, while deletion of the CatA-encoding gene katE resulted in a reduction of melanin accumulation, but it started 9 h earlier than in the wild-type. Since catalases regulate reactive oxygen species levels during melanogenesis, we speculated that CatA affects pigmentation through its peroxyl radical scavenging capacity. Consistent with this, expression of the catalases Hpi or Hpii from Escherichia coli in the katE deletion strain of A. media strain WS restored pigmentation to the wild-type level. Hpi and Hpii also exhibited PPO activity, suggesting that catalase may represent a new class of PPOs.

Metagenomics analysis of the polymeric and monomeric phenolic dynamic changes related to the indigenous bacteria of black tea spontaneous fermentation

“…Several dominant genera were predicted to possess yfiH functional genes, including Methylobacterium, Sphingomonas and Aureimonas . According to Chai et al., the yfiH gene, through its laccase-like protein, was identified in melanogenic Aeromonas strains of bacteria, and CatA possesses PPO activity [89] . The substrate specificity of laccase is relatively broader.…”

Solubilized melanin suppresses macrophage function

“…One type of pigment component is pyomelanin . Pyomelanin is a water‐soluble polymer in which HA is synthesized by the catalysis of homogentisic acid 1,2‐dioxygenase . Pyomelanin acts defensively against antibacterial drugs and oxidative stress in P. aeruginosa .…”

“…produce pigment components. One type of pigment component is pyomelanin . Pyomelanin is a water‐soluble polymer in which HA is synthesized by the catalysis of homogentisic acid 1,2‐dioxygenase .…”

“…In recent years, genetic studies have demonstrated the pathogenicity of pigments in various microorganisms . For example, pyomelanin, a soluble pigment component produced by Pseudomonas aeruginosa and Aeromonas spp., is involved in the defensive mechanism against antibiotics and oxidative stress . Melanin‐producing strains of Cryptococcus can suppress the host immune response and inflammatory response , and can result in fatal infections in the central nervous system with damage to the brain.…”