Cyanobacterial blooms from several British freshwaters have been toxic by mouse bioassay each year since annual sampling began in 1981. Toxic blooms of Microcystis aeruginosa, Anabaena spp., Gloeotrichia echinulata, Oscillatoria spp., and Aphanizomenon flos‐aquae occur, with peptide toxin‐producing Microcystis and Anabaena being most often encountered. We are developing a range of detection and quantification methods for cyanobacterial peptide and alkaloid toxins to supplement the standard mouse bioassay. Both types of toxins can be readily assayed by high performance liquid chromatography, and we have developed facile high performance thin layer chromatographic procedures for their detection from natural blooms and laboratory cultures. We have also produced polyclonal and monoclonal antibodies for the assay of Microcystis toxins by enzyme‐linked immunosorbent assay and have developed in vitro fibroblast cytotoxicity assays for the toxins of Microcystis and other cyanobacteria.

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Correlations were sought between toxicity and the presence of plasmids in toxic and non‐toxic strains of Microcystis aeruginosa. Plasmids were present in toxic and non‐toxic cultures. Cultivation of the toxic Microcystis PCC7820 in the presence of novobiocin did not influence toxicity, although extrachromosomal DNA was no longer detected after novobiocin treatment. The data indicate that it is unlikely that plasmids are involved in the toxicity of Microcystis PCC7820.