Abstract
The identification and study of marine microorganisms with unique physiological traits can be a very powerful tool discovering novel enzymes of possible biotechnological interest. This approach can complement the enormous amount of data concerning gene diversity in marine environments offered by metagenomic analysis, and can help to place the activities associated with those sequences in the context of microbial cellular metabolism and physiology. Accordingly, the detection and isolation of microorganisms that may be a good source of enzymes is of great importance. Marinomonas mediterranea, for example, has proven to be one such useful microorganism. This Gram-negative marine bacterium was first selected because of the unusually high amounts of melanins synthesized in media containing the amino acid l-tyrosine. The study of its molecular biology has allowed the cloning of several genes encoding oxidases of biotechnological interest, particularly in white and red biotechnology. Characterization of the operon encoding the tyrosinase responsible for melanin synthesis revealed that a second gene in that operon encodes a protein, PpoB2, which is involved in copper transfer to tyrosinase. This finding made PpoB2 the first protein in the COG5486 group to which a physiological role has been assigned. Another enzyme of interest described in M. mediterranea is a multicopper oxidase encoding a membrane-associated enzyme that shows oxidative activity on a wide range of substrates typical of both laccases and tyrosinases. Finally, an enzyme very specific for l-lysine, which oxidises this amino acid in epsilon position and that has received a new EC number (1.4.3.20), has also been described for M. mediterranea. Overall, the studies carried out on this bacterium illustrate the power of exploring the physiology of selected microorganisms to discover novel enzymes of biotechnological relevance.
Highlights
It is widely accepted that there is an enormous range of microbial diversity not yet accessed or explored that might serve for possible novel biotechnological applications. This is true in the case of marine environments, as revealed by recent metagenomic analysis showing the enormous range of novel proteins that can be predicted [1]
In addition to the interest in exploiting marine biodiversity using culture-free methods, there is a huge diversity of culturable marine microorganisms belonging to different taxonomic groups that have not been characterized in depth
The activity was reported in the marine bacterium M. mediterranea [8], E. coli [71] and Bacillus subtilis [72], and it is accepted that Multicopper Oxidases (MCOs) are widely distributed in bacteria, where they may be related to different physiological processes such as copper resistance [73]
Summary
It is widely accepted that there is an enormous range of microbial diversity not yet accessed or explored that might serve for possible novel biotechnological applications. In addition to the interest in exploiting marine biodiversity using culture-free methods, there is a huge diversity of culturable marine microorganisms belonging to different taxonomic groups that have not been characterized in depth This is true, for example, in the case of microorganisms living in biofilms on the surface of higher organisms. The possibility of finding novel activities could be increased by the study of selected strains of different taxonomic groups showing unique characteristics. As will be discussed M. mediterranea has proven to be an excellent source of oxidative enzymes, including the tyrosinase responsible for pigmentation, a multicopper oxidase with laccase activity, and a novel lysine oxidase It is the only microorganism described showing such a combination of enzymes of potential biotechnological interest in many different fields in white and red biotechnology. Data from our laboratory suggest that additional oxidative enzymes are synthesized by this strain (Lucas-Elío, P and Sanchez-Amat, A., unpublished results)
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