Metabolic profiles of cyanobacteria isolated from Italian perialpine lakes

A comparative profiling of the secondary metabolism of cyanobacteria isolated from Italian perialpine lakes has been attempted. Cultures of Aphanizomenon flos-aquae, Dolichospermum lemmermannii, Microcystis aeruginosa, Planktothrix rubescens, and Tychonema bourrellyi were obtained from lakes Garda, Idro, and Caldonazzo. LC-MS/MS analysis were used for characterizing the strains’ extracts. A target analyis aimed at assessing the the toxic profile (microcystins, nodularins, anatoxins, cylindrospermopsins, PSP) was performed; it revealed the production of toxic peptides (microcystins) in M. aeruginosa and P. rubescens, of toxic alkaloids (anatoxin-a and possibly some paralytic shellfish toxins) in T. Bourrellyi, and finally no production of toxins in Aph. flos-aquae and D. Lemmermannii. An untargeted analysis aimed at comparing the capability of the cyanobacterial species to produce peptidic metabolites, allowed the detection of over 300 different peptides, in a mass range between 400 and 2000 Da. The majority of compounds with masses between 500 and 1200 Da (corresponding to many non-ribosomal peptides) was produced by the two species M. aeruginosa and P. rubescens, which show a much higher capability of producing these compounds compared to the others. Microcystins, aeruginosins and anabaenopeptins were the most represented classes of compounds.