Characterization and diversity of microcystins in natural blooms and strains of the genera Microcystis and Planktothrix from German freshwaters

Fifteen microcystins (MC) were isolated from field samples dominated by Microcystis spp., Planktothrix agardhii or Planktothrix rubescens using reversed phase high-performance liquid chromatography (HPLC). Characterization of microcystins was performed with amino acid analysis followed by fast atom bombardment mass spectrometry (FABMS), and/or matrix assisted laser desorption ionization mass spectrometry (MALDI-TOF MS). In blooms of Microcystis spp. major microcystins were usually MC-RR, MC-YR and MC-LR, while in one strain [D-Asp³] MC-LR and [D-Asp³] MC-RR were also quantitatively abundant. The main microcystins found in field samples of Planktothrix agardhii were [D-Asp³] MC-RR followed by [D-Asp³] MC-LR and a [D-Asp³] variant of MC-HtyR. Planktothrix agardhii strain HUB 076 produced [D-Asp³] MC-RR as a single component. In all Planktothrix rubescens populations [D-Asp³, Dhb⁷] MC-RR was the most abundant microcystin. Furthermore we found that microcystin composition in field populations of single species scarcely changed over time as long as dominance of this species persisted.