The first scientific report of the potent toxicity of cyanobacterial blooms was made in Nature by George Francis in 1878. The author reported that stock deaths had occurred as a result of drinking from a bloom infested lake in Australia. The organism resposible for this bloom was later described as Nodularia spumigena and the toxin has since been isolated and characterised (Rinehart et al., 1988*) as "Nodularin."
The structure of nodularin is related to the potent cyclic heptapeptide hepatotoxins, the microcystins, but differs in that nodularin is composed of only five amino acids in the peptide ring. Not only are the stucture of these two cyanobacterial toxins similar, but they both show the same hepatotoxic effect through the potent inhibition of protein phosphatases and similar IC50 and LD50 values.
*Rinehart, K. L., K. Harada, M. Namikoshi, C. Chen, and C. A. Harvis. 1988. Nodularin, microcystin and the configuration of Adda. J. Am. Chem. Soc. 110(25):8557-8558.