CYANOBACTERIAL TOXINS: THEIR ACTIONS AND MULTIPLE FATES IN MICROBES, ANIMALS AND PLANTS

Abstract

Codd, J. A.University of Dundee, UKUnderstanding of the significance of cyanobacterial toxins in natural and anthropogenic environments and of the possible roles of these compounds in the life of the producer‐cells is currently advancing. This is partly because of increasing knowledge of the occurrence, molecular structure and toxicity (largely in animal vertebrate systems) of the toxins. However, as more investigations are performed on the effects and fates of cyanobacterial toxins in aquatic, terrestrial and aerial laboratory and environmental systems, so our understanding of their significance and multiple fates is increasing. Cyanobacterial poisoning in animal vertebrates is relatively well recognised. This is due to improved case descriptions and methods for the extraction of the toxins, including microcystins, nodularins, saxitoxins, anatoxins and cylindrosperm‐ opsins, from exposure sources and exposed material (fish, birds and mammals, including humans). However, there are now wider indications of the significance of cyanobacterial toxins to microbes, lower animals, the early developmental stages of vertebrates and in plants. Examples of outcomes of exposure to cyanobacterial toxins, at environmentally relevant concentrations, are presented, including: adverse effects on the avoidance, respiration and growth of protozoa (Paramecium, Tetrahymena); stress and developmental aberrations in fish and amphibian eggs, embryos and juveniles; uptake of microcystins by rooted and non‐rooted aquatic plants (Ceratophyllum, Phragmites) and terrestrial plants (Phaseolus, Zea, Sinapis), and inhibitory effects on plant photosynthesis. In addition to causing a wide range of adverse effects, cyanobacterial toxins can undergo various fates including biodegradation in aquatic bacteria, and enzymic detoxication. Individual cyanobacterial toxins may have multiple roles in terms of the producer‐cells. Whether their primary functions are due to their toxicity is unclear. To some eyes, the molecules include metal chelators and cell signalling messengers and, for microcystins, there is evidence for both of these possibilities.