Diversity and antagonistic activity of sea ice bacteria isolated from the sea of Japan.

The aim of the study was to survey cultivable heterotrophic bacteria from sea ice samples collected from Peter the Great Bay of the Sea of Japan, and to test the isolates for antagonistic activity. A total of 195 strains were isolated and investigated by a phenotypic approach. The 16S rRNA gene sequence analysis of thirty eight strains revealed primarily representatives of the class Gammaproteobacteria, phylum Bacteroidetes, and phylum Actinobacteria. Members of the class Alphaproteobacteria were a minor component. Most strains shared 98-99% sequence similarity to recognized species, including those recovered previously from Antarctic or Arctic sea ice or polar environments, Shewanella frigidimarina, Psychrobacter urativorans, Psychrobacter glacincola, Psychrobacter fozii, Pseudomonas veronii, or Pseudomonas proteolytica. At least seven bacterial groups may represent novel species within known genera. Five isolates have been previously described as the novel species Marinomonas primoryensis and Psychrobacter maritimus. Antagonistic activity assays revealed a number of strains-antagonists of the Pseudomonas fluorescens group, Bacillus and Nocardioides displaying remarkable antifungal and antibacterial activities. For the first time our findings show that sea ice offshore in the Sea of Japan represents an untapped source of bacterial biodiversity and microorganisms capable of antibacterial and antifungal metabolite production.