microcystin

thumb|300px|Lake Erie in October 2011, during an intense cyanobacteria bloom

Microcystins—or cyanoginosins—are a class of cyanotoxins, which are toxins produced by cyanobacteria, sometimes known as blue-green algae. Over 250 different microcystins have been discovered so far, of which microcystin-LR is the most common. Chemically they are cyclic heptapeptides produced through nonribosomal peptide synthases.