Algicidal Marine Bacteria Isolated from Northern Hiroshima Bay, Japan

抄録

Marine bacteria that kill the noxious red tide flagellate Chattonella antiqua (Raphidophyceae) were screened and isolated from northern Hiroshima Bay, the Seto Inland Sea, Japan in 1991. Four strains (S, K, D, R) of Alteromonas spp. were selected and examined on characteristics of algicidal activities. Strains S and R showed wide algicidal range killing all cells of the 3 raphidophycean flagellates, 2 diatoms, and one dinoflagellate examined, in co-culture. Algicidal activities of the strains K and D depend on prey phytoplahkton species. Bacterial culture filtrate experiment shows that the bacterial strains K and D give lethal effects on C. antiqua by means of extracellular products, and the strains S and R not by such substances but by predation. If one or two bacterial cells were inoculated into C. antiqua culture, all of the host cells were killed by the 4 strains of algicidal bacteria within 7 days. All of the 4 bacterial strains could proliferate in filter-sterilized seawater, indicating theirubiquitous existence in the coastal sea. We suggest that the algicidal activity by bacteria may be a significant factor influencing the population dynamics of phytoplankton, and potentially might account for rapid termination of red tides in the coastal sea.