Isolation and Characterization of Strain MMB-1 (CECT 4803), a Novel Melanogenic Marine Bacterium

Abstract

A novel marine melanogenic bacterium, strain MMB-1, was isolated from the Mediterranean Sea. The taxonomic characterization of this strain indicated that it belongs to the genus Alteromonas. Under in vivo conditions, L-tyrosine was the specific monophenolic precursor for melanin synthesis. This bacterium contained all types of activities associated with polyphenol oxidases (PPOs), cresolase (EC 1.18.14.1), catecholase (EC 1.10.3.1), and laccase (EC 1.10.3.2). These activities were due to the presence of two different PPOs. The first one showed all the enzymatic activities, but it was not involved in melanogenesis in vivo, since amelanogenic mutant strains obtained by nitrosoguanidine treatment contained levels of this PPO similar to that of the wild-type MMB-1 strain. The second PPO showed cresolase and catecholase activities but no laccase, and it was involved in melanogenesis, since this enzyme was lost in amelanogenic mutant strains. This PPO was strongly activated by sodium dodecyl sulfate below the critical micelle concentration, and it is a tyrosinase-like enzyme showing a lag period in its tyrosine hydroxylase activity that could be avoided by small amounts of L-dopa. This is the first report of a bacterium that contains two PPOs and also the first report of a pluripotent PPO showing all types of oxidase activities. The bacterium and the pluripotent PPO may be useful models for exploring the roles of PPOs in cellular physiology, aside from melanin formation. On the other hand, the high oxidizing capacity of the PPO for a wide range of substrates could make possible its application in phenolic biotransformations, food processing, or the cosmetic industry, where fungal and plant PPOs are being used.

Dimethoxyphenol oxidase activity of different microbial blue multicopper proteins

“…A number of substrates have been used for detecting this activity [2,3,15,21^24], but our data indicate that DMP is the best choice because of the wide capacity of oxidation and the quite high absorption molar coe¤cient and stability of its oxidized dimeric colored form, 3,3P,5,5P-tetramethoxydiphenylquinone. The coe¤cient of this quinone at 468 nm is 14 800 M 31 cm 31 , almost three times higher than the one obtained by oxidation of o-methoxyphenol (guaiacol) to tetraguaiacol (5570 M 31 cm 31 ) [29]. In this work, it has been shown that all the blue multicopper proteins tested have indeed some DMPO activity that can be determined spectrophotometrically at pH 5.…”

Emergence of a laccase-positive variant of Azospirillum lipoferum occurs via a two-step phenotypic switching process

“…Further studies revealed the most unusual polyphenol oxidase activity in this strain: laccase, an enzyme previously found extracellularly in fungi and plants, was shown to be present intracellularly in A. lipoferum 4T [4]. To date, A. lipoferum remains one of the only two bacterial species in which laccase activity has been detected [5]. Laccase activity results in melanin production in A. lipoferum 4T [6], and both the enzyme activity and melani-zation may potentially contribute to scavenging of toxic phenol compounds and oxygen [4,6].…”

Molecular cloning of a copper-dependent laccase from the dye-decolorizing strain Stenotrophomonas maltophilia AAP56

“…Laccase gel staining after polyacrylamide electrophoresis (PAGE) under nondenaturing conditions was performed as previously described (Solano et al 1997). PAGE was run according to the method described by Laemmli (1970) using a separating gel containing 10% acrylamide and 0AE05% SDS in Tris-HCl pH 8AE8.…”