Inhibition of pathogenic Vibrio by the microalgae Isochrysis galbana

Vibrio alginolyticus, Vibrio campbellii, and Vibrio harveyi were inhibited by Isochrysis galbana in batch cultures. I. galbana reduced the V. alginolyticus, V. campbellii, and V. harveyi counts to undetectable levels in 2, 4, and 7 days (< 0.01 Vibrio spp. mL(-1)), respectively, remaining so until the end of the experiment on day 15. Other heterotrophic bacteria reached counts of 10(6) CFU mL(-1) on ZoBell medium at the end of the experiment. Vibrio parahaemolyticus was not inhibited by I. galbana. In all mixed I. galbana and Vibrio spp. cultures, the algal density increased from 3.5 to 4.0 x 10(7) cells mL(-1), higher than that in I. galbana cultures alone, indicating a lack of an inhibitory effect on microalgae in the mixed cultures. The predominant fatty acids (> 82 %) of I. galbana during the stationary growth phase were estearidonic (24.3 %), oleic (15.7 %), myristic (13.8 %), docosahexaenoic (11.0 %), palmitic (10.3 %), and alpha-linolenic (7.2 %) acids. These results demonstrate that I. galbana synthesizes antibacterial fatty acids that inhibit the growth of pathogenic bacteria such as V. alginolyticus, V. campbellii, and V. harveyi.