| Research Abstract |
In the embayments of central and western Japan, the harmful dinoflagellate Heterocapsa circularisquama has caused large scale red tides, which brought on mass mortalities to both natural and cultured bivalves. The alga has bacteria inside the cells and occasionally in their food vacuoles. It is suspected that these bacteria give some effects on the algal ecophysiology. The mutual relationships were investigated between the groth of H. circularisquama and intracellular bacteria with laboratory culture experiments. The five algal strains (Y, UA, UB, A, and I) were isolated from different locations of western Japan. Each strain culture was established with elaborate micro-pipette washings, nevertheless, each culture strain contains intracellular and extracellular bacterial populations, designated as Yb, Uab, Ubb, Ab, Ib, respectively. The extracellular bacteria were presumably released from the algal cells. The total number of bacterial cells in the each algal culture increased during the algal exponential growth phase. According to the final cell yields, the five bacterial populations are divided into three groups, Yb and Uab, Ab and Ib, and Ubb group, respectively. The bacterial growth depended on live algal cells. Growth experiments were carried out on the five H. circularisquama strains with bacteria and a bacteria-free strain, established from the dtrain UB, under the conditions of five different light intensities and in five different strengths of medium. There appeared to be no significant advantages for the growth and survival of the algal strains with intracellular bactera, as compared with the bacteria-free strain. Intracellular bacteria, however, might contribute to H. circularisquama populations in some aspects such as life cycle and toxin production.
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