Les cyanobactéries et leurs toxines

One of the consequences of environmental and human perturbations on aquatic ecosystems is the increase of blooms of photosynthetic microorganisms (in freshwater and marine ecosystems), which extent and frequency are currently increasing. Among these microorganisms, cyanobacterial blooms strongly affect the aquatic ecosystems functioning by the biomass they produce and through the possible production of toxins. Cyanobacteria are microorganisms that belong to the kingdom of bacteria. They have a wide variety of shapes and sizes, grouped into three main types : i) unicellular ii) colonial and iii) filamentous multicellular. Cyanobacteria produce a large variety of molecules and metabolites including toxins. They are grouped into three main families according to their toxic effects : hepatotoxins, neurotoxins and dermatotoxins. Hepatotoxins are most frequently encountered in the environment, but the number of species producing neurotoxins is in constant increase. Various mechanisms are involved in toxin production by cyanobacteria. They involve, among others, the change in biomass of cyanobacteria, the genetic diversity of populations or species, the diversity of variants of toxins and the physiological state of cells. The interdependence of these mechanisms and the environmental factors controlling them are complex. Thus, levels of toxicity observed in situ are highly variable making it difficult to manage the risk posed by the toxic potential and toxicity of cyanobacteria. In order to better manage the risks associated with cyanobacteria and cyanotoxins in the context of human population's exposition (e.g. bathing, sealing, fishing, drinking water…), management measures are proposed to combine the best uses and risks of freshwater water ecosystems.