Induced Bacteriovory in a Declining Culture of the Mixotrophic DinoflagellateProrocentrum minimum(Pavillard) Schiller

Bacteriovory was reported previously in the dinoflagellate, Prorocentrum minimum, but it was unclear if this is constitutive or induced under certain conditions. We tested the hypothesis that phosphate deficiency, or cessation of autotrophic growth for other reasons, would induce bacteriovory in a culture of P. minimum that is harmful to shellfish. Phosphate-starved cells did not ingest fluorescently labeled bacteria and died. In stationary-phase, full-enrichment cultures, more than half of viable P. minimum cells showed declines in chlorophyll that was coincident with incorporation of fluorescently labeled bacteria. Declining populations of P. minimum increase in toxicity to suspension-feeding shellfish; this suggests a possible association between bacteriovory and toxicity.