Influence of nutrient availability, initial pH, and species interaction on growth and cyanopeptide production in toxic Microcystis species

Cyanobacterial harmful algal blooms (cyanoHABs) threaten ecosystems and public health through the production of diverse bioactive toxic secondary metabolites, including cyanopeptides. However, environmental factors regulating non-microcystin cyanopeptides remain poorly understood. This study investigates how nutrient availability, initial pH, and species interactions influence the growth and cyanopeptide production in two understudied toxic Microcystis species, M. flos-aquae and M. viridis. Using high-resolution mass spectrometry, we identified 43 cyanopeptides, most of which were non-microcystins, and documented distinct, species-specific profiles. Elevated initial pH showed a trend toward increased M. flos-aquae growth and reduced cyanopeptide production, whereas M. viridis maintained high cyanopeptide levels at intermediate pH. Reduced nitrogen availability increased cyanopeptide quotas in M. flos-aquae despite reduced biomass. Coculture experiments revealed increased cyanopeptide production by M. viridis and the cross-detection of species-specific cyanopeptides, suggesting the transfer of dissolved metabolites between compartments. These results show that cyanopeptide production is a finely tuned, species-specific trait that is shaped by key environmental drivers. Our findings also demonstrate that non-microcystin cyanopeptides represent a substantial and dynamic fraction of the intracellular cyanopeptide pool, responding sensitively to environmental conditions. Effective risk assessment and management frameworks must therefore account for the full spectrum of cyanopeptides and the toxic cyanobacterial species that produce them. © 2026 Elsevier B.V. All rights are reserved, including those for text and data mining, AI training, and similar technologies.