Nitrogen fixation by a facultative bacillus.

A basic problem in biological nitrogen fixation is the distribution of this property among various organisms. Although several decades ago numerous bacteria were reported to fix molecular nitrogen, very few such claims survived because the proof was often based upon an unimpressive increase in visual turbidity or Kjeldahl nitrogen after prolonged culture. The limitation of these methods has been discussed (Wilson, 1952). During his extensive studies on Bacillus asterosporus, now regarded as identical with Bacillus polymyxa, Bredemann (1908) reported nitrogen fixation by some strains. However, owing to uncertainties in the measurement of fixation, not much attention has been paid to this report. For example, this claim is not mentioned in the discussion of Bacillus asterosporus in the 6th edition of Bergey's Manual. Several years ago one of us isolated a spore former from soil in Nagoya, Japan, that rapidly fixed molecular nitrogen anaerobically (Hino, 1955). This bacterium was reported as a strain of Clostridium, as the procedures described by Waksman (1932) for isolation of nitrogen-fixing clostridia were used. Also it formed clostridia and produced acid and gas from carbohydrates. During further studies of nitrogen fixation by this organism, however, properties different from those of the clostridia were observed. Taxonomic investigations were then undertaken and, as will be reported in this paper, the results revealed that the bacterium closely resembles Bacillus polymyxa. Oxygen has a dual effect on the inorganic nitrogen metabolism of this bacteriumspecific inhibition of nitrogen fixation and stimulation of nitrate utilization.