Cyanopeptide Co-Production Dynamics beyond Mirocystins and Effects of Growth Stages and Nutrient Availability

Intensified cyanobacterial bloom events are of increasing global concern because of adverse effects associated with the release of bioactive compounds, including toxic cyanopeptides. Cyanobacteria can produce a variety of cyanopeptides, yet our knowledge about their abundance and co-production remains limited. We applied a suspect-screening approach, including 700 structurally known cyanopeptides, and identified 11 cyanopeptides in Microcystis aeruginosa and 17 in Dolichospermum flos-aquae. Total cyanopeptide concentrations ranged from high nmol to μmol g_dry^-1 with slightly higher cell quotas in the mid-exponential growth phase. Relative cyanopeptide profiles were unchanged throughout the growth cycle. We demonstrate that quantification based on microcystin-LR equivalents can introduce an error of up to 6-fold and recommend a class-equivalent approach instead. In M. aeruginosa, rarely studied cyclamides dominated (>80%) over cyanopeptolins and microcystins. While all nutrient reductions caused less growth, only lowering phosphorous and micronutrients reduced cyanopeptide production by M. aeruginosa. Similar trends were observed for D. flos-aquae and only lowering nitrogen decreased cyanopeptide production while the relative abundance of individual cyanopeptides remained stable. The synchronized production of other cyanopeptides along with microcystins emphasizes the need to make them available as reference standards to encourage more studies on their occurrence in blooms, persistence, and potential toxicity.