Abstract
Growth responses of fresh water cyanobacteria cultures of Microcystis and Oscillatoria to various organic compounds were studied. L-Lysine was shown to be a potent inhibitor of the growth of five species of Microcystis, i.e., M.ichthyoblabe TAC 110, M. aeruginosa TAC 192, M. novacekii TAC 65, M, viridis TAC 64 and M, wesenbergii TAC 52. L-Lysine inhibited specifically the growth of Microcystis cyanobacteria at low concentrations of 0.5 to 1 mg per liter added to the culture medium, while three amino acid could not block the growth of three species of Oscillatoria i.e., O. tennis 1001, O. limnetica NIES 36, and O. animalis NIES 206 even at a concentration of 50 mg per liter. L-Histidine as well as L-lysine also inhibited preferentially the growth of Microcystis cultures except for M, viridis TAC 64 though the inhibition by L-histidine was weaker than that by L-lysine. The growth inhibition was provoked when the amino acids were added at the beginning of growth period, while either L-lysine or L-histidine failed to block the growth when added during the logarithmic phase. In the mixed culture of M. novacekii TAC 65 with O. limnetica NIES 36, L-lysine or L-histidine added singly to the mixed culture inhibited preferentially the growth of M. novacekii TAC 65. The significance of the specific growth inhibition by L-lysine and L-histidine for Microcystis cyanobacteria was discussed from an ecological standpoint of the algal succession in Lake Kasumigaura.
