Tracking Extensive\nPortfolio of Cyanotoxins in Five-Year\nLake Survey and Identifying Indicator Metabolites of Cyanobacterial\nTaxa

Cyanobacterial blooms require monitoring, as they pose\na threat\nto ecosystems and human health, especially by the release of toxins.\nAlong with widely reported microcystins, cyanobacteria coproduce other\nbioactive metabolites; however, information about their dynamics in\nsurface waters is sparse. We investigated dynamics across full bloom\nsuccessions throughout a five-year lake monitoring campaign (Greifensee,\nSwitzerland) spanning 150 sampling dates. We conducted extensive suspect\nscreening of cyanobacterial metabolites using the database CyanoMetDB.\nAcross all 850 samples, 35 metabolites regularly co-occurred. Microcystins\nwere present in 70% of samples, with [d-Asp<sup>3</sup>,(<i>E</i>)-Dhb<sup>7</sup>]MC-RR reaching concentrations of 70 ng/L.\nAnabaenopeptins, meanwhile, were detected in 95% of all samples with\nconcentrations of Oscillamide Y up to 100-fold higher than microcystins.\nBased on LC-MS response and frequency, we identified indicator metabolites\nexclusively produced by one of three cyanobacteria isolated from the\nlake, these being [d-Asp<sup>3</sup>,(<i>E</i>)-Dhb<sup>7</sup>]MC-RR from <i>Planktothrix</i> sp. G2020, Microginin\n761B from <i>Microcystis</i> sp. G2011, and Ferintoic acid\nB from <i>Microcystis</i> sp. G2020. These indicators showed\ndistinct temporal trends and peaking seasons that reflect the variance\nin either the abundance of the producing cyanobacteria or their toxin\nproduction dynamics. Our approach demonstrates that selecting high\nLC-MS response and frequent and species-specific indicator metabolites\ncan be advantageous for cyanobacterial monitoring.