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.

Phylogenetic analysis of intracellular bacteria of a harmful marine microalga, Heterocapsa circularisquama (Dinophyceae)

“…Most intracellular bacteria need living alga for their growth and survival, except the intracellular bacteria of H. circularisquama strain HU9433 (Maki & Imai 2001b). Only bac-F of strain HU9433 is culturable on the medium for heterotrophic bacteria, but those of strains HA92-1 and HI9428 are not (data not shown).…”

“…Accordingly, H. circularisquama would spontaneously maintain 2 specific bacteria, by supporting their growth and survival (Maki & Imai 2001b). It is suggested that the relationship between H. circularisquama and 2 ribotypes of bacteria is considerably close and should be termed as endosymbiosis.…”

“…This implies the possibility that the intracellular BLPs are endosymbionts of H. circularisquama. Although there may be a special relationship between the intracellular bacteria and H. circularisquama, and the bacteria influence algal metabolism and reproduction, unfortunately it is not feasible to cultivate and identify the intracellular bacteria through conventional cultivation methods (Maki & Imai 2001b).Recently, microbial species compositions in a variety of natural samples have been analyzed through 16S ribosomal RNA gene (16S rDNA) sequence analyses without cultivation (Amann et al 1995). The cultureindependent analyses with molecular biological techniques have suggested that some novel bacteria, which have yet to be cultivated, exist in the ocean (Giovannoni et al 1990, Fuhrman et al 1993, hot springs (Ward et al 1990), freshwater lakes (Shin et al 1997), soil (Torsvik et al 1990), and various other environments.…”