The Fate of Microcystins in the Environment and Challenges for Monitoring

Abstract

Microcystins are secondary metabolites produced by cyanobacteria that act as hepatotoxins in higher organisms. These toxins can be altered through abiotic processes, such as photodegradation and adsorption, as well as through biological processes via metabolism and bacterial degradation. Some species of bacteria can degrade microcystins, and many other organisms metabolize microcystins into a series of conjugated products. There are toxicokinetic models used to examine microcystin uptake and elimination, which can be difficult to compare due to differences in compartmentalization and speciation. Metabolites of microcystins are formed as a detoxification mechanism, and little is known about how quickly these metabolites are formed. In summary, microcystins can undergo abiotic and biotic processes that alter the toxicity and structure of the microcystin molecule. The environmental impact and toxicity of these alterations and the metabolism of microcystins remains uncertain, making it difficult to establish guidelines for human health. Here, we present the current state of knowledge regarding the alterations microcystins can undergo in the environment.

Microcystin-Bound Protein Patterns in Different Cultures of Microcystis aeruginosa and Field Samples

“…Miles et al [38] pointed out that the environmental and toxicological consequences of the reversibility in aquatic organisms need further investigation. A similar view was also presented by Schmidt et al [44] who proposed that more studies on this reversible conjugation are essential for complete understanding of the toxicity, transport and transformation of MC in living cells. With respect to reversibility as well as the high amount and the exposure of protein-bound MC, we suggest that the fraction of protein-bound MC should not be ignored and should be taken into account for risk assessment of MC.…”

Transfer of microcystin from freshwater lakes to Puget Sound, WA and toxin accumulation in marine mussels (Mytilus trossulus)

“…This can lead to variability in toxin concentration in individuals of the same species harvested from the same environment (Schmidt et al, 2013). In addition, conspecific variability of MCs in mussels makes it difficult to determine if any individual organism exposed to MC is actually contaminated with the toxin (Schmidt et al, 2014). In our study, for example, on dates mussels tested positive for MC, not all samples (n¼1-4 out of 5) showed MC presence.…”

Contribution of the A. baumannii A1S_0114 Gene to the Interaction with Eukaryotic Cells and Virulence

“…Glutathione conjugation most commonly occurs via a nucleophilic attack by the glutathione cysteinyl thiol on an electrophilic carbon such as a lactone or epoxide (Wang and Ballatori, 1998). The γ-glutamyl residue can then be cleaved by a γ-glutamyl transpeptidase localized outside the plasma membrane, leaving the conjugated Cys-Gly, as occurs in the case of the glutathione-modified microcystin (Schmidt et al, 2014), a cyanobacteria toxin and intra- and extra-cellular signaling molecule (Makower et al, 2015). …”