Effects of Harmful Dinoflagellate Heterocapsa circularisquama Cells on the Growth of Intracellular Bacteria

Abstract

The red tide dinoflagellate Heterocapsa circularisquama Horiguchi has intracellular bacteria. The isolation and cultivation of these bacteria were attempted for three-clonal strains of H. circularisquama (HY9423, HA92-1, and HU9433) using various culture media containing cell components of the host alga prepared by homogenization and heat killing, in addition to different organic materials (peptone and extracts). Only one intracellular bacterium of the bacterial population UBb in H. circularisquama strain HU9433 was successfully cultivated on many kinds of culture media. The intracellular bacterial populations of Yb and Ab in the algal clones HY9423 and HA92-1, respectively, could not grow in the culture media used. The presence of live algal cells is thought to be essential for the growth and survival of the bacterial populations Yb and Ab. These results indicate that the degree of dependence of the intracellular bacteria on the host algal cells differs greatly among the algae-bacteria sets of strains.