Pyrosequencing reveals specific associations of bacterial clades Roseobacter and Flavobacterium with the harmful dinoflagellate Cochlodinium polykrikoides growing in culture

Harmful algal blooms of the dinoflagellate Cochlodinium polykrikoides are of worldwide environmental concern. Previous field studies have demonstrated the association of such algal blooms with free-living bacteria (FLB) and particle-associated bacteria (PAB). In the present study, we report evidence for bacterial association with C.polykrikoides in laboratory culture. Sampling was performed at different growth stages (lag, exponential and stationary) and pyrosequencing was used to identify taxa. As a result, the community structures of FLB and PAB were elucidated and significant differences between FLB and PAB were identified by hierarchical cluster analysis and the similarity profiles test (p=.05). The relative abundances of bacterial operational taxonomic units distinctly changed in response to the different phases of C.polykrikoides growth. The Roseobacter genus Marivita and the Flavobacterium genus Winogradskyella were dominant in the FLB and PAB associated with C.polykrikoides, respectively. The Roseobacter clade, which has also exhibited associations with C.polykrikoides blooms in field samples, may influence host cell growth through the provision of vitamins.