| Summary: | The marine environment is a rich source of antimicrobial compounds with promising pharmaceutical and biotechnological applications. The <i>Pseudoalteromonas</i> genus harbors one of the highest proportions of bacterial species producing antimicrobial molecules. For decades, the presence of proteins with L-amino acid oxidase (LAAO) and antimicrobial activity in <i>Pseudoalteromonas luteoviolacea</i> has been known. Here, we present for the first time the identification, cloning, characterization and phylogenetic analysis of Pl-LAAO, the enzyme responsible for both LAAO and antimicrobial activity in <i>P. luteoviolacea</i> strain CPMOR-2. Pl-LAAO is a flavoprotein of a broad substrate range, in which the hydrogen peroxide generated in the LAAO reaction is responsible for the antimicrobial activity. So far, no protein with a sequence similarity to Pl-LAAO has been cloned or characterized, with this being the first report on a flavin adenine dinucleotide (FAD)-containing LAAO with antimicrobial activity from a marine microorganism. Our results revealed that 20.4% of the sequenced <i>Pseudoalteromonas</i> strains (specifically, 66.6% of <i>P. luteoviolacea</i> strains) contain <i>Pl-laao</i> similar genes, which constitutes a well-defined phylogenetic group. In summary, this work provides insights into the biological significance of antimicrobial LAAOs in the <i>Pseudoalteromonas</i> genus and shows an effective approach for the detection of novel LAAOs, whose study may be useful for biotechnological applications.
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