Abstract

Studies were carried out to establish the feasibility of incorporating bacteria with the ability to produce inhibitory substances (BPI) into axenic cultures of Isochrysis galbana with the object of using this microalga as a vector for transmitting BPI into cultures of larval bivalves as antagonists of pathogenic bacteria in these cultures. As a first step, the ability of seven strains of BPI to grow in extracellular products of I. galbana was evaluated, with positive results with four of these (334, C33, 11 and 77). Subsequently, the effect of the addition of these strains on the growth of I. galbana was evaluated. Comparison of growth rates of I. galbana with and without the addition of BPI showed no significant differences (P>0.05). A stable and persistent inhibitory capacity of strain C33 on the pathogen Vibrio anguillarum was also observed. Finally, studies were made on the ingestion of BPI by larvae of Argopecten purpuratus (Lamarck 1819). Results demonstrated a significant ingestion of strain 11 (P > 0.05), when it was inoculated directly into the water, and bacterium C33, when delivered in conjunction with the microalga. Upon evaluating incorporation and maintenance of BPI strains 11 and C33 after 5 days of larval culture, we observed the major presence of strain C33 (3 x 102 cfu/larva) compared with strain 11 (90 cfu/larva). The results obtained suggested that it was feasible to use microalgal cultures as vectors for the introduction of bacterial antagonists to bacterial pathogens in molluscan larval culture.