TOXIC POTENTIAL OF ANABAENOPSIS ELENKINII (CYANOBACTERIA) ISOLATED FROM A BLOOM IN LAKE VAYA (BULGARIA)

Abstract

Cyanobacteria are ancient photosynthetic organisms that under certain conditions (high temperature, eutrophication) can grow rapidly and form "cyanobacterial blooms". Very often, these blooms are accompanied by production of cyanotoxins, which in most cases are dangerous to the other organisms. Knowing the producers of cyanotoxins is of utmost importance, especially today when climate change has been shown to increase the frequency of toxic cyanobacterial blooms worldwide. The aim of the present study was to characterize the toxic potential of the cyanobacterium Anabaenopsis elenkinii V.V.Miller 1923 isolated from Lake Vaia during a cyanobacterial bloom. The isolated strain (Anabaenopsis elenkinii) was identified based on a morphological analysis using light microscopy, and its taxonomic affiliation and phylogenetic position were confirmed by applying the Maximum Likelihood (ML) method for phylogenetic analysis based on the 16S rDNA sequence. The production of cyanotoxins was analyzed by applying immunological methods (ELISA) for detection of microcystins, cylindrospermopsin and saxitoxins. The toxic potential of Anabaenopsis elenkinii was evaluated in vitro by methyl-thiazole-tetrazolium (MTT) cytotoxicity and superoxide dismutase (SOD) activity assays using HT-29 cells. Our analyzes indicated that Anabaenopsis elenkinii produces microcystins (0.42 ng/mL), cylindrospermopsin (0.10 ng/mL) and saxithixins (0.05 ng/mL). The MTT cytotoxicity assay showed that the medium, in which the cyanobacterial strain was grown, significantly reduced the viability of HT-29 cells and this effect was dose- and time-dependent. In addition, 50% inhibition of the SOD activity was also observed. This is the first report of Anabaenopsis elenkinii as a producer of cyanotoxins. Our results provide valuable information about the toxin-producing cyanobacteria. They demonstrate the potential danger of "cyanobacterial blooms" where Anabaenopsis elenkinii is a dominant species.