Effects of humic and fulvic acids on the growth of Microcystis aeruginosa

The effects of chelate substances on the growth of Microcystis aeruginosa K-5 in Lake Kasumigaura water were investigated. A chelate compound, EDTA (Ethylenediaminetetraacetic acid disodium salt) and natural chelate substances, such as humic and fulvic adds isolated from Lake Kasumigaura sediment, stimulated the growth of the K-5 strain. We investigated the mechanism of this stimulation by chelate compounds. The toxicity of heavy metals such as copper, nickel, and zinc, and the alleviation of heavy metal toxicity by chelate compounds were determined. The 50% growth inhibition (EC50) values of copper and zinc for the K-5 strain were 8.4 and 11.4 mu g l(-1), respectively, close to levels measured in Lake Kasumigaura. Humic and fulvic adds mitigated copper and zinc toxicity. Humic and fulvic adds may significantly affect the occurrence of water blooms of Microcystis in Lake Kasumigaura.