Chemical profiling of the bioactive metabolites produced by invasive cyanobacteria in perialpine lakes

Cyanobacteria are known to produce toxic metabolites, such as microcystins, nodularins, anatoxins, and saxitoxins. Cyanobacteria proliferation represents, therefore, a serious risk in natural and artificial water bodies. Besides the ones mentioned above, cyanobacteria produce many other bioactive compounds, which are less investigated but are equally important because they can be also toxic. The full determination of the chemical profile can be therefore very useful for a correct determination of the toxic potential inside a cyanobacteria population. Moreover, the chemical profile can have very important applications from an ecological point of view, since secondary metabolites play an important role in determining the cyanobacteria success over other organisms. The chemical profile (and consequently the toxic potential) is specific for any single species, and, within one species, can be subject to changes in response to environmental (biotic and abiotic) factors. We have started a detailed investigation aimed at defining the chemical profiling inside the cyanobacteria populations typical of the perialpine lakes. These lakes are experiencing the colonization of new algal species (i.e. Dolichospermum lemmermannii and Tychonema bourrellyi) and therefore we focused our attention on these species. We used LC-MS techniques for the determination of a wide panel of secondary metabolites classified in two major classes: i) alkaloids (anatoxins, cylindrospermopsins, saxitoxins) and ii) peptides (microcystins, nodularins, anabaenopeptins, aeruginosins, micropeptins, microviridins). We analyzed cultures of selected species as well as field samples. Analysis carried out on cultures allowed to identify molecules produced in lower concentrations. We found considerable differences among species in terms of nature and amount of secondary metabolites. For example, T. bourrellyi resulted to produce two neurotoxic alkaloids (anatoxin-a and homoanatoxin-a), while D. lemmermannii and Planktothrix rubescens did not; P. rubescens, instead, resulted to produce five different epatotoxic peptides (microcystins). A number of peptides in the mass range between 400 and 1100 dalton were also identified. The investigation allowed us to determine that the investigated cyanobacteria produce and release in the water many different compounds belonging to different chemical classes (anatoxins, microcystins, cyanopeptolins, aeruginosins, anabaenopeptins) and that each species has a specific chemical finger print.