Abstract
N2 fixation rate of a large Phototrophic bacterium, which prevails at the bacterial plate of Lake Kaiike (Kamikoshiki Island), and has been isolated using the medium of PFENNIG (1965), was measured by the C2H2 reduction method. The N2 fixation rate was closely associated with the bacterial growth and required light and H2S. In situ measurement revealed a very low N2 fixation rate at the bacterial plate on 22 May 1986. But when the bacterial plate sample was exposed at a high light intensity, and particularly when it was supplied with H2S at the same light intensity, it showed a significantly elevated rate of N2 fixation. At the bacterial plate the bacterium was suggested to grow at an extremely low rate due to limitation by both factors.
