Elucidation of anti-Vibrio factors associated with green alga Picochlorum sp. strain S1b

The results of our previous study demonstrated that the total Vibrio count in a fish aquarium could be limited to a low level through the introduction of Picochlorum sp. S1b. In subsequent trials, we discovered that Picochlorum sp. S1b demonstrated a strong inhibitory effect on Vibrio only when cultivated in a nonsterile environment. This is a clear indication that the inhibitory effects cannot be attributed to Picochlorum sp. S1b directly, but rather to bacteria associated with it. In the current study, we isolated bacterial strains with a strong inhibitory effect on Vibrio spp. These strains were obtained from nonsterile cultures of Picochlorum sp. S1b. To evaluate the anti-Vibrio activity, we co-cultured these bacterial strains with S1b and later with pathogenic Vibrio harveyi and Vibrio campbellii. Our results indicate that among the 80 strains, only six strains belonging to either the Rhodobacteraceae or Flavobacteriaceae were linked to a significant decrease in total Vibrio count under co-culture conditions. Further study will be required to elucidate the interactions among these six bacterial strains and the Picochlorum sp. S1b with regard to anti-Vibrio activity.