Abstract
Two bacterial species, a large-celled phototrophic bacterium and Macromonas sp., form steady-state dense populations at an upper boundary of the H2S layer of Lake Kaiike. The two bacterial species are characterized by their intracellular bodies ; the former by numerous sulfur globules and the latter by 2 or 3 large, pearl white, refractile inclusions. The sulfur globules of the large-celled phototrophic bacterium were readily consumed without addition of H2S. The globule-deficient bacterial cells lost the motility, and the bacterium was displaced by fast growing nonmotile unicellular and filamentous algae. Even in the dark the globule-deficient bacterial cells began to deposit the sulfur globules again as soon as H2S was added. The large-celled phototrophic bacterium must depress its photosynthetic activity to maintain the sulfur globules. The bacterial sulfur deposition is considered a cellular device to store environmental H2S.
