Copper‐iron interactions in the N2‐fixing cyanobacteriumNostoc muscorum

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Abstract
The N2‐fixing cyanobacterium Nostoc muscorum was found to be sensitive to CuSO4 and CuCl2. Copper salt at lower concentrations interfered with the nitrogenase activity and growth of the organism in minimal (nitrogen‐free) medium, but its inhibitory effects were reversed on exogenous Fe supplementation in the form of FeSO4 or FeCl3. The effects of Cu may be due to Cu‐induced Fe‐deficiency in N. muscorum resulting from the inactivation of the Fe‐Mo co‐factor responsible for cyanobacterial N2 fixation and growth. Higher concentrations of Cu have been found toxic and lytic to the organism, thus leaving no scope of protection by exogenous Fe. Copper had no pronounced effect on heterocyst‐forming capacity or on NH+ 4‐ assimilation in the cyanobacterium. This experiment has strongly suggested the Cu‐Fe antagonism in Nostoc muscorum.