Influence of trace metals on growth and toxin production of Microcystis aeruginosa.

The growth and toxicity of various Microcystis aeruginosa strains were tested. Six of 14 strains were lethal to mice, five of which produced microcystin. Of these, M. aeruginosa PCC 7806 produced the most toxin per biomass and was thus used to examine the influence of various trace metals on exponential growth rate and production of microcystin. Zinc was shown to be required for optimal growth as well as toxin production. Al, Cd, Cr, Cu, Mn, Ni, and Sn did not significantly affect toxin yield at non-toxic concentrations of the metals. In contrast, iron had a pronounced effect on growth rate and toxin yield. In the absence and at low concentrations of Fe (< or = 2.5 microM), the cells grew much more slowly, but produced 20-40% more toxin. This is in agreement with the hypothesis that production of microcystins may be a response to specific environmental stress conditions.