Diversity and dynamics of bioactive metabolites in cyanobacteria of southern perialpine lakes

Cyanobacteria proliferation in natural and artificial water bodies represents a sanitary threat since these organisms have the capability of producing potent toxins (e.g. microcystins, nodularins, anatoxins, and cylindrospermopsins). Cyanobacteria have indeed an impressive chemical machinery that leads to the production of hundreds of secondary metabolites, many of which are bioactive. The nature and quantity of these metabolites vary from species to species, and even in the same species the production of these compounds is not constant. The metabolic profiling can therefore provide valuable informations on the ecology of cyanobacteria at different levels (species, population). We have conducted a metabolic profiling of the most important cyanobacteria species in southern perialpine lakes, namely Aphanizomenon flos-aquae, Dolichospermum lemmermannii, Microcystis aeruginosa, Planktothrix rubescens, and Tychonema bourrellyi. LC-MS/MS analyses were conducted on natural sample as well as on cultured strains. We conducted targeted analysis aimed at identifying the most common toxins (microcystins, nodularins, anatoxins, cylindrospermopsins, paralytic shellfish poisons). We also conducted untargeted analysis aimed at identifying as many secondary metabolites as possible. Targeted analysis showed that M. aeruginosa and P. rubescens produced toxic peptides (microcystins), T. bourrellyi produced toxic alkaloids (anatoxin-a and possibly some paralytic shellfish toxins), Aph. flos-aquae and D. lemmermannii did not produce any of the analyzed toxins. Untargeted analysis confirmed the ability of M. aeruginosa and P. rubescens in producing a large number of peptidic metabolites, mainly belonging to three categories: microcystins, aeruginosins and anabaenopeptins. The remaining species showed a lower propency in producing peptides, being their metabolism apparently more oriented toward the production of alkaloids.