Physiological ecology of toxic aquatic cyanobacteria

Abstract'Toxicity', a problematic ecophysiological trait of certain cyanobacteria. is largely an anthropomorphic term determined by negative impacts of various secondary metabolites (e.g. alkaloids, peptides. organo-phosphate esters) on mammalian health. Most target organisms are neither natural enemies nor consumers of cyanobacteria. This dichotomy has hindered our understanding of the ecophysiological rationales for toxin production. The physical and chemical factors forcing cyanobacterial bloom initiation and persistence appear to act as controls for metabolite production in a complex and variable manner. Toxin production may simply be a mechanism for shunting excess metabolites during periods of environmental stress and may be metabolically linked to the production of other secondary metabolites, including those causing taste and odour problems. Toxins also may help establish mutually beneficial microbial consortia, by chemotactically attracting and supporting micro-organisms involved in nutrient cycling and production of growth factors. Conversely antagonistic organisms may be repelled by toxins. Evaluations concerning the production of toxins. and the roles these and other secondary metabolites may play, should consider the chemical and biotic interactions cyanobacteria experience during growth and bloom formation.