Recent Advances of Toxic Cyanobacteria Researches

Toxic blooms of cyanobacteria occur in eutrophicated lakes, pond and river over the world. Cyanobacteria have produced acute toxins such as hepatotoxic peptides, microcystins and nodularins, and neurotoxic alkaloids, anatoxin-a, anatoxin-a(s) and saxitoxins. Microcystis, Oscillatoria, Anabaena, Aphanizomenon and Nodularia produce these toxins and have been responsible for the death of wild and domestic animals drinking water contaminated with blooms. A new hepatotoxin, cylindrospermopsin was also isolated from Cylindrospermopsis and Umezakia. The principal species under investigation is Microcystis aeruginosa, which has been frequently cited in animal poisoning incidents and produces strongly hepatotoxic cyclic heptapeptides named microcystins. Very recently, a toxic accident of 50 person's death occurred in Brazil in 1996 due to microcystin in the water for hemodialysis. The toxins consist of seven amino acids and approximately 60 components have been isolated so far. The toxins also inhibit protein phosphatases 1 and 2A in a manner similar to okadaic acid and have a tumor-promoting activity on the rat liver. Now microcystins are threatening human health and life, and many problems associated with microcystins remains to be solved. Since the total structures of microcystins were determined in 1984 by Botes group, many results obtained from various fields have been extensively accumulated. They are mainly classified into the following categories : 1) ecological aspects including taxonomy and toxic waterbloom formation, 2) production, occurrence and fate of microcystins, 3) chemistry and detection, 4) toxicology and health effects, 5) regulation of toxic cyanobacteria and 6) water treatment for removal of microcystins. Thie review overviews mainly the recent advance of microcystin researches in addition to the Caruaru incident.