| Abstrakt: |
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 polymyxatested for fixation of molecular nitrogen, 15 fixed considerable quantities (30 to 150 μg N/ml). Two strains of the closely related B. maceransdid not use N2, but possibly other members of this species may do so. Confirmation of fixation was obtained by showing incorporation of N15into 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. polymyxacontaining an active hydrogenase readily incorporated N15into 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 N2by washed-cell suspensions of B. polymyxa, indicating that high-energy phosphate may be significant for this process. |
