Biodegradation of microcystin-LR by indigenous mixed bacterial populations

Microcystin-LR is a potent mammalian toxin which is known to have been responsible for the deaths of domesticated animals, and consequently there is concern as to its environmental fate. In laboratory experiments conducted using low levels (10 μg l−1) of microcystin-LR in reservoir water, primary biodegradation of the toxin was shown to occur in less than 1 week. An experiment designed to ascertain the degree of mineralisation of microcystin-LR, using natural microbial populations under aerobic conditions, showed that the peptide ring appears to be fairly resistant to biodegradation, as the degree of mineralisation was not high. However, as the toxicity of microcystin-LR is critically dependent on the orientation of the peptide ring with respect to the “Adda” (the β-amino acid which is unique to the blue-green algal toxins) side-chain, and it appears that this side chain is affected during biodegradation, it seems likely that a reduction in toxicity occurs.