ABSTRACT
In order to get data about toxic cyanobacteria and their potential sanitary risk in 12 waterbodies situated in the north of Tunisia, some taxonomic, ecological and toxicological studies were undertaken since 2001. This paper provides the first screening of the potential toxic species of cyanobacteria as well as their geographical distribution. The microscopic examination of the phytoplankton samples show 42 species of cyanobacteria; 9 are frequently quoted by the literature as being potentially toxic. Among the inventoried cyanobacteria genera there are Pseudanabaena, Planktothrix Phormidium, Lyngbya, Microcystis, Oscillatoria constitutes the most widespread one. The content of total microcystin [MCYST] was determined by protein phosphatase inhibition assays [PP2A]. The total microcystin, detected in dissolved and paniculate fractions in all the examined samples is generally low and varies between 2 and 7455 ng/l microcystin-LR equivalent per liter. The highest MCYST concentration is observed in autumn and generally in paniculate MCYST concentrations