Ecological and molecular investigations of cyanotoxin production

Cyanobacteria, broadly classified as oxygenic phototrophs containing chlorophyll- a and accessory pigments, are among the oldest life forms on earth. They may be unicellular, colonial or filamentous, with cell sizes varying from less than 2 μm to 40 μm in diameter. They may live as symbionts with plants and fungi, in the benthos or in the water column. Cyanobacteria have a cosmopolitan distribution and are common in all kinds of habitats, including Antarctic lakes, thermal springs, arid deserts and tropical acidic soils. Most commonly they are known for their existence as planktonic members of the water column in marine and freshwater environments. Cyanobacteria have special adaptations such as; nitrogen fixation, ability to regulate buoyancy, light harvesting pigments, and differentiated cell types for reproduction or resting, allowing them an advantage over many competitors. Anthropogenic factors such as increased nutrient loading in freshwater and coastal environments, have lead to the occurrence of cyanobacterial blooms world wide. While blooms are unpleasant both visually and due to released odour and taste factors, certain metabolites produced by some cyanobacterial species pose a more serious problem [1]. Due to their adverse effects on higher organisms, these compounds have been labelled as ‘toxins’ and from here on are referred to as such. The chemical structures of many cyanotoxins and their adverse effect on animals have been elucidated and recently reviewed [2]. However, the actual physiological function and ecological regulation of cyanobacterial toxins remain largely a mystery. Studies on regulation and function of cyanotoxins are interrelated and have focused on their effect on the local ecosystem, as well as the effect of environmental parameters on toxin production. Hypotheses regarding the ecophysiology of the cyanotoxins, stemming from such studies, are discussed in this review. With advances in molecular biology, it has more recently been possible …