Diversity and Antimicrobial Activity of Hydrobionts Associated Microorganisms from the Sea of Japan with the Occurrence of Tropodithietic Acid Producing Bacteria

The study was undertaken to survey microorganisms associated with colonial fouling hydrozoans and red alga Polysiphonia sp. collected from the Sea of Japan seashore and to screen them for antimicrobial effects. On the basis of 16S rRNA gene sequences the isolates were assigned to 21 genera of the Alphaproteobacteria, Gammaproteobacteria, Actinobacteria as the dominant followed by Firmicutes, Bacteroidetes and Betaproteobacteria; the most shared 98-99% sequence similarity to recognized species recovered from marine sources. Hydrozoan’s and red alga microbial associations were different in their taxonomic compositions at the generic level. Members of the genera Shewanella, Labrenzia and Streptomyces occured in both specimens. Antimicrobial screening revealed 46 strains capable to inhibit growth of two to seven indicatory cultures. Active hydrozoan’s strains were phylogenetically close to Phaeobacter inhibens. Active isolates from red alga were similar to Pseudovibrio ascidiaceicola, and in addition to Paenibacillus xylanexedens and Bacillus murimartini. Streptomyces strains with antimicrobial activity were found in both specimens. Strains Phaeobacter sp. H8 and Pseudovibrio sp. rh17 were selected to be examined for the production of tropodithietic acid, TDA, which is the known antimicrobial metabolite produced by Phaeobacter and Pseudovibrio bacteria. On the basis of spectral analyses both strains were found to produce TDA, which could be responsible for their antimicrobial activity. Our findings demonstrated that hydrozoans and red alga inhabitating the Peter the Great Bay of the Sea of Japan harbor diverse microbial communities with a high proportion of bacteria capable of antimicrobials production, including TDA-producing strains which are conceivable to be of importance for chemical protection of their host-hydrobionts and bacterial relationships in marine shallow environments.