Influence of cultivation parameters on growth and microcystin production of Microcystis aeruginosa (Cyanophyceae) isolated from Lake Chao (China).

Microcystis aeruginosa isolated in 2005 from the shallow eutrophic Lake Chao (Anhui, China) was investigated in terms of growth parameters and microcystin production under varying nutrient concentrations (P, N) and pH values (abiotic factors) as well as under the influence of spent medium of the non-toxic cyanobacterium Synechocystis sp. (biotic factors). Stimulating effects on growth were observed at the alkaline pH value (10.5), whereas toxin production was significantly increased under phosphate-P limitation (0.6 mg L(-1) medium). Within a broad range of nitrate-N concentrations (41.2-247.2 mg L(-1) medium), no significant influence on cell growth and microcystin production was observed; however, N-starvation resulted in a typical decrease of growth and toxicity. In addition, cryopreservation of M. aeruginosa evidenced the decrease of toxin production by time-dependent exposure with the cryoprotectant dimethyl sulfoxide under thawing conditions without affecting the growth of the cyanobacterial cells.