Physiology of nitrogen fixation by Bacillus polymyxa.

Grau, F. H. (University of Wisconsin, Madison) and P. W. Wilson. Physiology of nitrogen fixation by Bacillus polymyxa. J. Bacteriol. 83:490-496. 1962.-Of 17 strains of Bacillus polymyxa tested for fixation of molecular nitrogen, 15 fixed considerable quantities (30 to 150 mug N/ml). Two strains of the closely related B. macerans did not use N(2), but possibly other members of this species may do so. Confirmation of fixation was obtained by showing incorporation of N(15) into cell material. Both iron and molybdenum are specifically required for fixation; without the addition of these metals to the nitrogen-free medium, the growth rate and the total nitrogen fixed were reduced about 30 to 50%. No requirement for added molybdenum could be shown when ammonia was the nitrogen source, and the absence of iron caused only a slight decrease in growth. Washed-cell suspensions of B. polymyxa containing an active hydrogenase readily incorporated N(15) into cell materials when provided with mannitol, glucose, or pyruvate but not when formate was the substrate. Hydrogen is a specific inhibitor of fixation, reducing both the rate and final amount of nitrogen fixed; it did not reduce growth on ammonia. Fixation was strictly anaerobic, 1% oxygen in the gas phase being sufficient to stop fixation. Arsenate is a powerful inhibitor of fixation of N(2) by washed-cell suspensions of B. polymyxa, indicating that high-energy phosphate may be significant for this process.