Isolation,identification, and algicidal activity of marine bacteria against <Emphasis Type="Italic">Cochlodinium polykrikoides</Emphasis>

The aim of this study was to isolate and identify algicidal bacteria against the dinoflagellate Cochlodinium polykrikoides, and to determine the algicidal activity and algicidal range. During the declining period of C. polykrikoides blooms, seven algicidal bacteria were isolated. The algicidal bacteria against C. polykrikoides were enumerated using the most probable number (MPN) method. The number of algicidal bacteria was high (3.7 × 10³ mL⁻¹). Algicidal bacteria were identified on the basis of biochemical and chemotaxonomic characteristics, and analysis of 16S rDNA sequences. Seven algicidal bacteria isolated in this study belonged to the genera Bacillus, Dietzia, Janibacter, and Micrococcus. The most algicidal bacterium, designated Micrococcus luteus SY-13, is assumed to produce secondary metabolites. When 5% culture filtrate of this strain was applied to C. polykrikoides cultures, over 90% of C. polykrikoides cells were destroyed within 6 h. M. luteus SY-13 showed significant algicidal activities against C. polykrikoides and a wide algicidal range against various harmful algal bloom (HAB) species. Taken together, our results suggest that M. luteus SY-13 could be a candidate for controlling HABs.