Abstract
High- and low-virulence serotypes of the fish pathogen Vibrio anguillarum were challenged with a beneficial bacterium (Sulfitobacter sp. RO3) in the presence of the phytoplankton Nannochloropsis oculata. The inhibitory activity of Sulfitobacter sp. against these V. anguillarum serotypes were observed in (1) phytoplankton culturing control medium (ESM) and (2) NCF, a filtrate prepared from N. oculata cultured in ESM. The presence of Sulfitobacter sp. in ESM significantly reduced the number of viable cells of all V. anguillarum serotypes tested (O2, O3, O4, O9 and O10). In NCF, Sulfitobacter sp. totally eradicated the O2 and O3 serotypes. The viabilities of the low-virulence serotypes O4, O9 and O10 when cultured in NCF in the presence of Sulfitobacter sp. were not significantly different from those cultured in ESM. We conclude, therefore, that phytoplankton cultured in the presence of naturally occurring Sulfitobacter sp. provide an essential tool for inhibiting the growth of the economically significant high-virulence fish pathogen V. anguillarum.
