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

Abstract

Red tides of a harmful dinoflagellate, Heterocapsa circularisquama, have caused 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 period, a marine bacterium strain EHK-I, which had a strong algicidal activity against H. circularisquama, was isolated from the seawater of Etajima Bay, in the Seto Inland Sea of Japan. Strain EHK-1 killed H. circularisquama within 24 hours when the H. circularisquama culture in exponential phase was inoculated with this bacterium at a density of 1 × 105 cells ml−1. Strain EHK-1 lysed both the vegetative cells and temporary cysts of H. circularisquama. Strain EHK-1 is a novel algicidal bacterium according to 16S rRNA-based phylogenetic analysis.