Cyanobacteria of the genus Microcystis have been found to liberate large amounts of β-cyclo- citral. While all seven strains of Microcystis studied possessed this property, it has not been found in any other cyanobacterial species. This chemical characteristic of the genus Microcystis enables the unequivocal systematic arrangement of controversial species. Another chemical property allows two chemotypes to be distinguished within the genus Microcystis: one exhibits an intensive release of

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... pylmethyl disulfide, diisopropyl disulfide and diisopropyl trisulfide, substances which have not been previously found in any microorganism. The second chemotype excretes dimethyl disulfide and in some cases also dimethyl trisulfide and dimethyl tetrasulfide. Species producing isopropyl sulfides emanate an intensive sulphurous malodour.