Effect of nickel and silver ions on survival, growth, carbon fixation and nitrogenase activity in Nostoc muscorum: Regulation of toxicity by EDTA and calcium.

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Abstract
The effects of different concentrations of nickel (2.1, 4.2, 5.04 .mu.M) and silver (0.013, 0.026, 0.052 .mu.M) on survival, growth, carbon fixation and acetylene reduction of Nostoc muscorum has been studied. All concentrations of the heavy metals except 2.1 .mu.M Ni were inhibitory. At 2.1 .mu.M nickel chloride stimulated carbon fixation and nitrogenase activity. Silver seems to be much more toxic than nickel because concentrations as low as 0.026 .mu.M silver chloride inhibited approximately 90% of the carbon fixation. EDTA protected carbon fixation and calcium ameliorated the nitrogenase activity in the test alga. However, none of these ameliorative agents were so effective against silver toxicity. This study suggests that (i) calcium plays an important role in nitrogen fixation, (ii) like hydrogen production and uptake hydrogenase, nickel seems to have some role in regulating nitrogenase activity, and (iii) carbon fixation is a more sensitive parameter than growth and nitrogenase in evaluating metal toxicity.
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