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

Anabaena inaequalis was sensitive to mercuric ion (Hg2+) 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 Hg2+ 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 Hg2+ required to induce culture lysis. Calculated on the basis of equivalent cell numbers, Hg2+ was toxic to A. inaequalis at 0.006, 0.009, and 0.100 micrograms of Hg2+ per 10(5) cells for photosynthesis, growth, and acetylene reduction, respectively.