Effects of exogenous amino acids on the growth and microcystins production of Microcystis aeruginosa

The effects of four amino acids (glutamic acid, phenylalanine, leucine, and arginine) and two inorganic nitrogen (nitrate and ammonium) on regulating the growth and microcystins (MCs) production of Microcystis aeruginosa were studied in batch culture. Algal cell density, the concentrations of five variants of MCs (MC-LR, RR, YR, LW, LF) and free amino acid were determined. Results indicated that the growth of M. aeruginosa enhanced with increasing of N concentrations, but decreased obviously in high concentration (8 mg-N/L) of ammonium, phenylalanine and leucine compared with other nitrogen source. Leucine, phenylalanine and glutamic acid can increase the quota of free amino acids in cells, and promote the synthesis of MCs with the corresponding amino acid in the variant’s structures, respectively. The total concentrations and quotas of MCs cultured in glutamic acid and arginine was similar to that in inorganic nitrogen medium, but lower than that cultured in phenylalanine and leucine. Among the four amino acids, the glutamic acid medium has the highest extracellular MCs levels. In conclusion, exogenous amino acids had different effects on synthesis of free amino acids and MCs in cells, resulting in different MCs productions and variants.