Toxicity of the cells of a newly established axenic Microcystis aeruginosa K-139 strain to mice was studied. LD50 of the cells harvested in the mid-log phase was 7.3mg/kg. The organs of acute dead mice were examined histopathologically.The blood congestion and necrosis of the parenchymal cells around the central veins in the liver were observed, but other organs seemed to be normal. The liver damage was confirmed by the tests of glutamic oxaloacetic transaminase (GOT) and glutamic pyruvic transaminase (GPT) activities in the sera of the mice after the injection with the K-139 cells. Furthermore, the K-139 cells were capable of inducing interleukin 1 (IL-1) production by peritoneal macrophages in vitro.Cyanobacteria (blue-green algae) belonging to the genus Microcystis were mostly responsible for the development of massive surface blooms in eutrophic waters (4, 6). Water pollution by Microcystis and other cyanobacteria is becoming a serious problem in many countries, including Japan. Natural cases of poisoning of large domestic animals by the blue-green alga Microcystis aeruginosa are not uncommon (3,4,6). Some strains and blooms of Microcystis were reported to contain toxins (1,3,4,(6)(7)(8)13). The toxins produced by M. aeruginosa are a related family of cyclic heptapeptides with molecular weights ranging from 909 to 1,044 (2). These toxins had cytotoxic properties which caused extensive hemorrhage in the liver (5,8,13). Lake Kasumigaura in Ibaraki prefecture has such blooms especially in summer, and M. aeruginosa is the most dominant alga in this lake. In a previous paper (12), we demonstrated that there were toxic and non-toxic algal blooms consisting of Microcystis grown in Lake Kasumigaura, and the mice that had received nontoxic Microcystis showed delayed-type hypersensitivity after the injection of specific antigen. Since Microcystis organisms form mucilaginous colonies and some bacteria are usually tightly associated with the colonies, isolation of axenic strains from the colonies is very difficult. However, we have succeeded in isolating them by developing a solid media suitable for the growth of Microcystis species (manuscript in preparation). In the present study, we deal with the toxicity of a newly established 787
Microcystis strains (2 toxic and 18 nontoxic to mice) were isolated from toxic waterblooms that had been collected from Lake Kasumigaura, Ibaraki Prefecture, Japan, in August 1985. Thirteen of the strains (2 toxic and 11 nontoxic) were Microcystis aeruginosa, 2 (nontoxic) were Microcystis wesenbergii, and the other 5 were difficult to identify. Six (1 toxic and 4 nontoxic M. aeruginosa and 1 M. wesenbergit) of these 20 strains were established as axenic cultures. A toxic and axenic strain of M. aeruginosa, K-139, was used to study the relationship between growth conditions and toxicity. Cells in early-to-mid-log phase showed the highest toxicity (50% lethal dose, 7.5 mg of cells per kg of mouse), and maximum toxicity was not affected by growth temperatures between 22 and 30°C. Purification and characterization of the toxins from K-139 cells were also conducted, and at least two toxins were detected. One of the toxins (molecular mass, 980 daltons) has not been reported previously. The main target of the toxin in mice was the liver. Marked congestion and necrosis in the parenchymal cells around the central veins of the liver were observed microscopically in specimens that had been prepared from the mice with acute toxicity after injection with the toxin.
Prefecture, Japan, were hepatotoxic. The 50% lethal doses (LD50s) of the blooms to mice ranged from 76 to 556 mg/kg of body weight. Sixty-eight Microcystis cell clones (67 Microcystis aeruginosa and 1 M. viridis) were isolated from the blooms. Twenty-three strains (including the M. viridis strain) were toxic. However, the ratio of toxic to nontoxic strains among the blooms varied (6 to 86%). Microcystins were examined in six toxic strains. Five toxic strains produced microcystin-RR,-YR, and-LR, with RR being the dominant toxin in these strains. Another strain produced 7-desmethylmicrocystin-LR and an unknown microcystin. This strain showed the highest toxicity. Establishment of axenic strains from the Microcystis cells exhibiting extracellularly
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