Isolation, characterization and implications of the bacterial communities associated with established cultures of Chattonella marina(Raphidophyceae) and Skeletonema costatum(Bacillariophyceae)

Cultivable bacteria coexisting in the cultures of two microalgal species, Chattonella marina(Raphidophyceae)and Skeletonema costatum(diatom, Bacillariophyceae), which have been maintained in the laboratory for several years, were examined in this study. Forty-eight and thirty-four cultivable bacterial strains were isolated from different growth stages of C. marina and S. costatum cultures, respectively. A total of twelve unique bacterial phylotypes were isolated. These bacterial phylotypes belonged to Alphaproteobacteria, Gammaproteobacteria,Bacteroidetes, and Actinobacteria. Alphaproteobacteria predominated in phycospheres of both microalgae, and Rhodobacteraceae was the most common family. Bacterial phylotypes were more diversified in cultures of S.costatum than in those of C. marina. Bacterial concentrations increased remarkably after the late stationary phase of C. marina, which might account for the decline in algal cells. One phylotype of S. costatum-associated bacteria had inhibitory effects on Chaetoceros curvisetus(Bacillariophyceae). However, most bacterial phylotypes from cultures of C. marina showed significant inhibition of the growth of C. curvisetus. The results suggested that bacteria associated with C. marina might have some ecological roles in its competition with diatoms.