Isolation of an algicidal marine bacterium with activity against the harmful dinoflagellate Heterocapsa circularisquama (Dinophyceae)

Red tides of a harmful dinoflagellate, Heterocapsa circularisquama, have ca used mass mortality of bivalves such as oysters in western Japan since 1988 . For the purpose of microbial control of the occurrence of these red tides , H. circularisquama-killing bacteria were screened. Although the frequency of H. circularisquama-killing microorganisms was low during the sampling p eriod, a marine bacterium strain EHK-1, which had a strong algicidal activi ty against H. circularisquama, was isolated from the seawater of Etajima Ba y, in the Seto Inland Sea of Japan. Strain EHK-1 killed H. circularisquama within 24 hours when the H. circularisquama culture in exponential phase wa s inoculated with this bacterium at a density of 1 x 10(5) cells ml(-1). St rain EHK-1 lysed both the vegetative cells and temporary cysts of H. circul arisquama. Strain EHK-1 is a novel algicidal bacterium according to 16S rRN A-based phylogenetic analysis.