Ecology of a Large-Celled Phototrophic Bacterium Densely Populating the Upper Boundary of H₂S Water of Lake Kaiike

Abstract

Two species of bacteria, a Macromonas-like bacterium and a large-celled phototrophic one, probably a new species of Chromatiaceae family, are densely populating the upper boundary of H₂S water of Lake Kaiike forming a purplish red colored bacterial plate. The large phototrophic bacterium grows slowly even under an optimal condition; the maximum growth rate is 1.0·day^-1, and its in situ growth rate is suggested to be lower than thus estimated due to a limitation by light and H₂S. Comparison of the light-limited growth between the large phototrophic bacterium and Chromatium buderi DSM 176 shows that the bacterium could maintain the dense population by keeping its physiological activity to a minimum level.