Cyanotoxin occurrence and potentially toxin producing cyanobacteria in freshwaters of Greece: a multi-disciplinary approach.

Cyanobacteria harmful algal blooms (or CyanoHABs) represent one of the most conspicuous waterborne microbial hazards in aquatic environments mostly due to the production of harmful secondary metabolites, known as cyanotoxins. In freshwaters of Greece only the presence of microcystins (MCs) has been reported despite the increasing occurrence of species able to produce other cyanotoxins too. In this paper, we studied the occurrence of potentially toxic cyanobacteria in water samples collected from six lakes and reservoirs in Greece. A multi-technique approach was applied by the use of microscopy, molecular, and immunological methods. Cyanobacteria were found in all the sites ranging from 4.7 × 10³ to 5.3 × 10⁸ individuals L⁻¹, representing >70% of the total phytoplankton abundance. Microcystins (MCs), cylindrospermopsins (CYNs), and saxitoxins (STXs) were detected using ELISA, in concentrations ranging from 3.9 to 108 μg L⁻¹, from 0.3 to 2.8 μg L⁻¹ and from 0.4 to 1.2 μg L⁻¹, respectively. In half of the samples examined more than one cyanotoxins were detected. Our results document the first report on the occurrence of CYN and STX in freshwaters of Greece and show that potential STX producers are Cylindrospermopsis raciborskii and Aphanizomenon flos-aquae. Further studies are needed to assess potential CYN producers. This study provides further data on the distribution and toxicity of C. raciborskii and Aph. flos-aquae and documents a C. raciborskii dominated bloom producing STX in Europe.