We discuss freshwater algae briefly on our website under the menu “About Algae”. Here though, we will look at freshwater algal toxins specifically in a little more detail.
It is the cyanobacteria that are responsible for the production of algal toxins in freshwaters. Hence these toxins are typically referred to as cyanotoxins.
Cyanotoxins are produced by cyanobacteria as secondary metabolites. Unlike primary metabolites which are biological compounds that serve an intrinsic function for an organism (i.e. being directly involved in normal growth, development, and reproduction), secondary metabolites do not serve an intrinsic function for a given organism. Secondary metabolites are not necessary for survival, but they often play an important role in protection against herbivory, competition and other interspecies interactions.
There are greater than 2,500 described species of cyanobacteria and, of these, around 50 have been shown to cause toxic effects in vertebrates. Many of these 50 toxigenic species are ubiquitous and capable of forming blooms.
Some of the cyanotoxins produced by cyanobacteria are amoung the most powerful natural toxins known, some of which can cause rapid death by respiratory failure.
Cyanotoxins are typically grouped according to their biological effects into hepatotoxins, neurotoxins, cytotoxins, dermatotoxins and irritant toxins. The chemical structure of these cyanotoxins falls into three broad groups: cyclic peptides, alkaloids and lipopolysaccharides (endotoxins). The main cyanotoxins are Microcystins, Nodularins, Anatoxins (Anatoxin-a, Anatoxin-a(S)), Cylindrospermopsins, Lyngbyatoxin-a, Saxitoxin, Lipopolysaccharides, Aplysiatoxins and BMAA (beta-Methylamino-L-alanine).
These toxins will be discussed in upcoming blog posts.