A Greek Raphidiopsis raciborskii strain and Microcystins: A toxic relationship

The cyanobacterium Raphidiopsis raciborskii is extensively studied for its toxicity and invasive behavior, which is presumably enhanced by global warming. The widening of its geographic distribution and the isolation of strains showing high optimum growth temperature underline its ecological heterogeneity, suggesting the existence of different ecotypes. In this study, we investigate the ecotoxicology of Raphidiopsis raciborskii TAU-MAC 1414 strain, isolated from Lake Karla, Greece. The effect of different growth conditions (temperature, light intensity, phosphorus concentration, co-culture with toxic and non-toxic Microcystis spp. extracts) on microcystin production by R. raciborskii was examined. MC-LR and MC-HilR were detected with LC-MS/MS, mainly during the cultivation of R. raciborskii with toxic or non-toxic Microcystis spp. strains’ extracts. Further, the subcellular phytotoxic effects of R. raciborskii on Oryza sativa (rice) are discussed. Our research demonstrated unambiguously for the first time that R. raciborskii is able to produce microcystins under certain conditions, shedding new light in the ecotoxicology of the species, whereas the triggering of microcystin production remains to be further investigated.