| dc.description.abstract | Microcystis aeruginosa, which is a well known blue-green alga (cyanobacterium), has been extensively studied for its bloom-forming characters and productions of the hepatotoxic microcystins. Microcystins are generally considered remaining within the cells and then releasing are generally considered to be the result of cell is integration due to stress and death. From our studies on the culture of M. aeruginosa clones, we found the toxins were accumulating in the cell-free medium during the log phase of growth in the clones of M.TY-2, M.TN-3 and M.TN-4, while it is absence in the culture of M.TN-2, M.CY-1, M.KS-15 and M.KS-29. Our toxin analysis in the medium showed two groups of clones that release toxin during the log phase or not. In these clones of M. aeruginosa, the sequence of McyH, which is one of microcystin synthetase (mcyA~J), was studied through PCR amplification and transgenic cloning, and then translated into amino acid sequences. Amino acid sequences of these clones were compared with that of previously studied M.TY-1 clone and PCC7806 in Genebank. It was found that the amino acid sequences, especially of McyH in these toxic clones of M. aeruginosa were highly conserved, except at few amino acid sites. From the results, we found that only two amino acid sites, 389th (glutamic acid) and 427th（lysine）amino acid, have mutation among the studied toxic M. aeruginosa clones. However, such mutations could not lead to the toxin releasing difference. By comparison of the amino acid sequence alignment of the entire McyH, the difference of the alignment was found to be no correlation to the toxin releasing ability. | en_US |