Production of a bisdemethylated microcystin variant by Planktothrix rubescens.

Reservoir samples from a bloom of Planktothrix rubescens were analyzed by ELISA and LC-MS/MS. The comparison of the results of both methods points to the presence of a microcystin variant not yet available as analytical standard and therefore, not detectable by LC-MS/MS analysis. It is proposed that the unknown cyanotoxin variant is a bisdemethylated microcystin variant, presumably [Asp3,Dha7]-microcystin-RR. [Asp3,Dha7]-MC-RR has not been described for a bloom of P. rubescens before.