Effect of mercuric ion on the growth, photosynthesis, and nitrogenase activity of Anabaena inaequalis

Anabaena inaequalis was sensitive to mercuric ion (Hg/sup 2 +/) in the ppB (nanogram per milliliter) range. Growth was inhibited significantly at concentrations of metal ion as low as 2 ppB, and 100 ppB was required to inhibit photosynthesis and acetylene reduction. Low levels of Hg/sup 2 +/ stimulated acetylene reduction and photosynthesis. The lysis of vegetative cells was the primary action of mercuric ions, resulting in the inhibition of growth, photosynthesis, and nitrogenase activity. There was a linear relationship between numbers of cells and the amount of Hg/sup 2 +/ required to induce culture lysis. Calculated on the basis of equivalent cell numbers, Hg/sup 2 +/ was toxic to A. inaequalis at 0.006, 0.009, and 0.100 ..mu..g of Hg/sup 2 +/ per 10/sup 5/ cells for photosynthesis, growth, and acetylene reduction, respectively.