Phylogenetic identification of epibiotic bacteria possessing antimicrobial activities isolated from red algal species of Japan

We investigated the diversity of epibiotic bacteria possessing antimicrobial activity isolated from nine species of red algae, and identified their phylogenetic position. For the isolation of epibiotic bacteria, nine species of red algae, Pachymeniopsis lauceolata, Plocamium telfairiae, Gelidium amansii, Chondrus oncellatus, Grateloupia filicina, Ceramium kondoi, Lomentaria catenata, Schizymenia dubyi and Porphyra yezoensis, were collected from the intertidal zone of Awaji Island, Japan. In total 92 bacteria were collected from the above red algal species. Primary screening results using disc diffusion assay revealed that 33% of bacteria possess antibacterial activity. Ten bacteria that showed high antibacterial activity were further studied for their ability to inhibit a set of fouling bacteria, some luminescent Vibrio and Photobacterium species and a panel of pathogenic bacteria. In general, the inhibitory activities were high against fouling and luminescent bacteria, while low against various pathogenic bacteria tested. These results suggest that some epibiotic bacteria have adapted to defend their position in their surface environment through the production of antibacterial metabolites giving defense against a broad spectrum of bacterial competitors. The phylogenetic analysis using 16 S rRNA sequences identified 7 of the 10 strains as belonging to the genus Bacillus, and other strains each 1 belonging to genus Microbacterium, Psychrobacter, and Vibrio species.