Biochemical and molecular characterization of cyanobacterial blooms in Lalla Takerkoust lake-reservoir (Morocco)
Complementary to earlier research carried out since 1994 related to toxic cyanobacteria in different Moroccan lake-reservoirs, this work furnishes new data relating to this research topic. Three major objectives were established: 1) update knowledge concerning the temporal variation of the intracellular contents of cyanotoxines (microcystines, MCs) in cyanobacteria blooms, which frequently occur in the Lalla Takerkoust lake-reservoir; 2) evaluate the MC contamination of raw waters (quantification of extracellular MCs); 3) molecular characterization of cyanobacteria MC producing strains (detection of genes involved in MC synthesis using two methods, multiplex-PCR and RFLP (Restriction fragment length polymorphism)). For bloom samples collected during 2005-2006, the HPLC analysis showed quantitative and qualitative temporal variation in intracellular MCs. Evaluation of the extracellular MC content, determined by ELISA analysis, revealed a maximum concentration of 95.4 μg•L-1 in raw water. This value was measured during December 2005, corresponding to the decline of a Microcystis bloom (cell lysis and MC release into the surrounding water). In general, the dissolved MC concentrations in raw water always remained above the guideline value recommended by the World Health Organization for drinking water (1 μg•L-1). The genetic analysis, based on the detection of the MC synthetase gene ( mcyA gene), confirmed that among the bloom-forming phytoplanktonic fraction, Microcystis aeruginosa is the only MC producing strain. This work thus confirms for the first time in Morocco that during Microcystis blooms, the MC extracellular content greatly exceeds WHO guidelines. It is strongly recommended that the various potential sanitary risks involved in the use of such untreated water (drinking, recreation and irrigation waters) be taken into account. Based on these results, we conclude that the establishment of any successful monitoring programs for cyanobacteria and MC should be based first on biochemical characterization (identification and determination of the amount of produced toxins) and be supplemented by the genetic characterization of the toxin-producing strains.