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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 dia toms, 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 cul ture, all of the host cells were killed by the 4 strains of algicidal bacteria within 7 days. All of the 4 bac terial strains could proliferate in filter-sterilized seawater, indicating their ubiquitous 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.

A bacterium 5N-3 possessing a remarkable inhibitory effect on the growth of Gymnodinium nagasakiense was isolated from Uranouchi Inlet, Kochi. This bacterium was tentatively identified as Flavobacterium sp. The growth inhibiting effect of 5N-3 on G. nagasakiense was drastic in particular when the alga was in the logarithmic growth phase, and cell density decreased to less than 1% of the initial concentration within 4 days after inoculating 5N-3, indicating that the effect was algicidal.The effect was obtained when the density of the bacterium was more than 106 cells/ml. However, they grew very rapidly up to 108 cells/ml by using extracellular released organic carbon from various phytoplankton species. On the other hand, the algicidal effect of 5N-3 was only observed on G. nagasakiense but not on Chattonella antiqua, Heterosigma akashiwo, or Skeletonema costatum.These results indicate that the effect of 5N-3 was G. nagasakiense-specific and suggest that it grows to a level of cell density effective in inhibiting the alga in the field by using naturally occurring organic carbon from phytoplankton.

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SUMMARY: An analytical procedure using a new high performance liquid chromatography (HPLC) for the sensitive measurement of thiosulfate (S2O32−) in natural water was examined. Using a Shodex Asahipak NH2P‐50 (4E) column and the HPLC system, thiosulfate was identified clearly by UV absorption at 215 nm with 100 mM Na2HPO4 (pH 8.5) as a solvent. Thiosulfate could be quantified in less than 20 min with a detection limit of about 10 pmol which corresponds to an injection of 20 μL from a standard with a concentration of 0.5 μM. Starting at the lowest detectable concentration, the calibration curve for thiosulfate was linear over a concentration range of four orders of magnitude. Thiosulfate analysis was not affected by the saline concentration of samples at up to 1 M NaCl. This procedure was applied to water samples of a meromictic lake, Lake Suigetsu, Fukui, Japan. Thiosulfate was found in lake water sampled below the chemocline at a concentration of less than 1–60 μM but not in the oxic surface water.