Abstract
The effects of calcium and EDTA concentration on the growth of cyanobacterium Microcystis aeruginosa were investigated through a series of culture experiments under calcium and/or EDTA limited conditions. The calcium uptake experiment was performed with the calcium and EDTA concentrations of 25 and 13 μmol/l, respectively, to examine the amount of calcium needed by M. aeruginosa. The result showed that the decrease of calcium concentration due to the uptake by M. aeruginosa was hardly observed, although the cell density was reached to 5.0×106 cells/ml. The uptake experiment suggested that M. aeruginosa would require little calcium compared with other nutrients such as nitrogen or phosphorus. The effects of calcium and EDTA on the growth of M. aeruginosa were investigated through the uni-algal culture experiments varying the calcium and EDTA concentrations from 0 to 25 μmol/l and from 0 to 13 μmol/l, respectively. In the medium without the addition of EDTA, the cell density of M. aeruginosa reached to 1.5×107 cells/ml when calcium concentration was higher than 2.5 μmol/l, but the growth was significantly suppressed with the cell density of 9.0×103 cells/ml when calcium concentration was 0 μmol/l. Although the calcium and EDTA concentrations of 2.5 μmol/l and lower than 1.3 μmol/l favored the growth of M. aeruginosa, the growth was significantly restrained when EDTA concentration was raised to 13 μmol/l, implying that the growth of M. aeruginosa would be restrained when the amount of EDTA exceeded that of calcium. The results of the uni-algal culture experiment suggested that the existence of calcium would be essential for the growth of M. aeruginosa, and that the growth was strongly restrained when inorganic calcium did not remain in the medium caused by the formation of complex with EDTA.
