On the Purple Sulfur Bacterium, Chromatium sp., Densely Populating the Mid-Depth of Lake Kaiike, Kamikoshiki Island, Kagoshima Prefecture

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The growth of Chromatium sp. in Lake Kaiike, a small coastal lake on the Kamikoshiki Island, was considered from the viewpoint of growth responses of Chromatium sp. in culture to different gradients of environmental factors such as temperature, light, pH and H2S. In July, 1978, Chromatium sp. densely populated the upper part of the H2S layer and the density and assimilation rate of the bacterium attained to 2×106 cells/ml and 700 mg C m-3 day-1, respectively. Incident light and H2S concentration at the habitat, being less than 1% of that just beneath the surface and less than 3 mg S/l, lay within the ranges where the growth of laboratory-cultured Chromatium sp. increased in proportion to their quantities. But the fact that the habitat of Chromatium sp. is confined to a depth below the algal compensation depth indicates that light condition does not exert such a pronounced effect on the in situ growth of Chromatium sp. On the contrary, the supply of H2S to the habitat supposedly would have an important effect on the growth of this bacterium.