[Effect of nitrogen and phosphorous on the production of microcystin under laboratory conditions]

To explore the effect of phosphorus, nitrogen on the production of microcystin under specific laboratory condition.

The microcystis were ampliatively cultured for three times in N and P free culture. Then the microcysitis were inoculated in the culture at the concentrations of 0, 0.5, 1.0, 5.0 and 10.0 mg/L P for 20 days. The microcystis were inoculated in the BG-11 cultures at the concentrations of 0.05 mg/L and 5.0 mg/L P, NaNO3 were added in the culture according to the mol ratios of N/P were 5:1, 10:1, 20:1, 50:1, 100:1 and were cultured for 20 days. The changes of the count of the microcystis were observed. The microcystis cell were breaked at the 8th, 12th, 16th and 20th days after the beginning of culturing, the the microcystin were extracted and detected by HPLC.

When the concentrations of phosphorus were lower than 5.0 mg/L, The productions of microcystin increased with the phosphorus concentrations. But when the concentrations of phosphorus were 10.0 mg/L, the productions of microcystin significantly decreased. In the culture at the concentrations of 0.05 mg/L P, the microcystin concentration per cell (MCYST fg/cell) and the microcystin concentrations per milliliter (MCYST microg/ml culture) presented the greatest value when the N/P ratio was 50:1. But, In the culture at the concentrations of 5.0 mg/L P, the microcystin concentrations per cell (MCYST fg/cell) and the microcystin concentrations per milliliter (MCYST microg/ml culture) presented the greatest value when the N/P ratio was 20:1.

P concentrations significantly incluence the production of microcystin. The P concentrations in water should be controlled through different way to control the production of microcystins.