Role of Cobalt in Nitrogen Fixation by Azotobacter chroococcum

Abstract

COBALT is known to accelerate nitrogen fixation by the blue-green algae, and the lowest cobalt requirement of Nostoc muscorum was observed to be 0.05 p.p.m.¹. Its influence on Azotobacter does not seem to have been examined critically. The experiment recorded here was therefore planned to examine the effect of cobalt at different concentrations varying from 0.02 to 5.0 p.p.m. on nitrogen fixation by Azotobacter chroococcum in Jensen's medium². The results obtained were compared with those observed with molybdenum, which was already known to be essential for Azotobacter. The basal medium was tested for cobalt and molybdenum by ‘Nitroso-R-salt’ method³ and Aspergillus niger method respectively. While cobalt could not be detected in the medium, molybdenum of the order of 0.00028 p.p.m. was found to be present. The cobalt salt CoCl₂·6H₂O used was also tested for molybdenum by the same method as mentioned here, and it contained 0.0001 p.p.m. of molybdenum at 0.1 p.p.m. concentration of cobalt, at which nitrogen fixation was found to be enhanced.