Phylogeography of Cylindrospermopsin and Paralytic Shellfish Toxin-Producing Nostocales Cyanobacteria from Mediterranean Europe (Spain)

PlanktonicNostocales cyanobacteria represent a challenge for microbiological research because of the wide range of cyanotoxins that they synthesize and their invasive behavior, which is presumably enhanced by global warming. To gain insight into the phylogeography of potentially toxicNostocales from Mediterranean Europe, 31 strains ofAnabaena (Anabaena crassa ,A. lemmermannii ,A. mendotae , andA. planctonica ),Aphanizomenon (Aphanizomenon gracile ,A. ovalisporum ), andCylindrospermopsis raciborskii were isolated from 14 freshwater bodies in Spain and polyphasically analyzed for their phylogeography, cyanotoxin production, and the presence of cyanotoxin biosynthesis genes. The potent cytotoxin cylindrospermopsin (CYN) was produced by all 6Aphanizomenon ovalisporum strains at high levels (5.7 to 9.1 μg CYN mg−1 [dry weight]) with low variation between strains (1.5 to 3.9-fold) and a marked extracellular release (19 to 41% dissolved CYN) during exponential growth. Paralytic shellfish poisoning (PSP) neurotoxins (saxitoxin, neosaxitoxin, and decarbamoylsaxitoxin) were detected in 2Aphanizomenon gracile strains, both containing thesxtA gene. This gene was also amplified in non-PSP toxin-producingAphanizomenon gracile andAphanizomenon ovalisporum . Phylogenetic analyses supported the species identification and confirmed the high similarity of SpanishAnabaena andAphanizomenon strains with other European strains. In contrast,Cylindrospermopsis raciborskii from Spain grouped together with American strains and was clearly separate from the rest of the European strains, raising questions about the current assumptions of the phylogeography and spreading routes ofC. raciborskii . The present study confirms that the nostocalean genusAphanizomenon is a major source of CYN and PSP toxins in Europe and demonstrates the presence of thesxtA gene in CYN-producingAphanizomenon ovalisporum .