Algicidal activity of a killer bacterium against the harmful red tide dinoflagellate Heterocapsa circularisquama isolated from Ago Bay, Japan

Abstract

Algicidal activity of a bacterium strain Cytophaga sp. AA8-2 against the harmful red tide causing alga Heterocapsa circularisquama was investigated. Physiological conditions of host cells, incubation temperature and existence of ambient organic substrates or co-existing bacteria affected the lethal effect of Cytophaga sp. AA8-2. Bacterial lysis of H. circularisquama was caused more rapidly at higher incubation temperature (20-30°C). Growth of 6 among 7 H. circularisquama strains tested was inhibited by Cytophaga sp. AA8-2, the levels of which were varied. A part of H. circularisquama cells in a culture formed temporary cysts to survive the bacterial attack. The envelope of the temporary cyst of H. circularisquama was composed of a markedly thicker layered structure (209±72 nm) than that of the vegetative cell (40±15 nm).