General Cyanobacteria Information
The Toxins of Cyanobacteria-"CYANOTOXINS"
This pond in Beijing has been contaminated
by an overgrowth, or waterbloom, of toxic
cyanobacteria (green scum). These bacteria,
flourishing in the Grandview Garden Park, are
members of the wide-spread genus
Microcystis, many species of which produce
potent liver toxins. The toxins have killed
animals, and the consumption of low doses in
drinking water is suspected of contributing to
a high rate of human liver cancer in certain
parts of China.
The world-wide occurrence of toxic cyanobacteria in fresh, marine and brackish waters creates problems for all life forms. Our laboratory has
assisted in establishing programs to study cyanobacterial-related water
problems in Europe, Asia, Africa, Australia, and North and South America.
Research topics range from the occurrence and distribution of toxic cyanobacteria to studies on toxin regulation.
Most water based poisonings of cyanobacteria occur when heavy surface
growths or scums accumulate near shorelines of lakes, ponds and reservoirs
where animals have easy access to toxic levels of cells. Our lab is also
investigating occurrences of toxic cyanobacteria at levels that can cause
chronic and sub-chronic toxicities, such as tumor promotion.
Close to the shore of Balgavies Loch, near Dundee, Scotland, this photograph of a toxic cyanobacterial waterbloom has the typical appearance of a thick pool of green oil paint. This bloom occurred in 1981 and was found to consist of species in the genus Microcystis.
Scanning Electron Micrographs of Three Common Toxic Cyanobacteria Genera
Cyanobacterial species Microcystis aeruginosa (left micrograph)
and Nodularia spumigena (right micrograph), shown enlarged some
2,500 and 1,250 times, respectively, are among the many forms that synthesize
toxins destructive to liver cells known as hepatocytes. The poisons, including
the two varieties for which chemical structures are shown at the bottom,
are peptides. Those consisting of seven amino acids (distinguished by color)
are called microcystins (because they were first discovered in a strain
of Microcystis); those consisting of five amino acids are called nodularins.
Anabaena flos-aquae (shown here magnified some 2,500 times) is a major producer of neurotoxins,
which are poisons that interfere with the functioning of
the nervous system. The strain shown here was
responsible for the death of hogs in Griggsville, Il.
Toxins studied to date in
our laboratory belong to two groups, which are defined by the symptoms they produce
in animals. Anabaena, Oscillatoria, Lyngbya, and Aphanizomenon produce neurotoxic anatoxins and/or saxitoxins. Anatoxin-a and Anatoxin-a(s) seem unique to cyanobacteria, while saxitoxin also arise in certain marine algae. Anatoxin-a is a potent nicotinic agonist that mimics acetylcholine and is used as a research tool in neurobiology. Anatoxin-a(s) is a structurally new organophosphate that inhibits acetylcholinesterase. Saxitoxin prevents acetylcholine from being released from neurons by blocking the inward flow of sodium ions across the axonal membrane channels, disrupting the communication between neurons and muscle cells.
The preceding photographs may be found in Scientific
American, June 1994, Vol. 270, pp. 78-86 (The Toxins of Cyanobacteria).
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This page was updated on June 12, 2006.
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