Unveiling the reason why freshwater heterothophic bacteria are no affected by microcystins: antioxidant system vs. degradation

Microcystins are the class of hepatotoxins most commonly produced by cyanobacteria. These are found in aquatic ecosystems where they coexist with other microorganisms such as Aeromonas hydrophila and Flavobacterium sp. There are already a fair amount of studies on the effect of microcystins in eukaryotic organisms, but there are only a few studies about the effects of these toxins in microorganisms. The scarce existing studies show that microcystins can cause a decrease of the microbial growth, even though not being fully inhibited by it [1]. In this study the aim is to determine the reason why aquatic heterobacteria are not very affected by the presence of microcystins in their growth medium. Therefore, the activity of some enzymes of the antioxidant system was evaluated and the presence of genes responsible for microcystin degradation (mlrA-D) was assessed in isolates recovered from freshwaters where microcystins are commonly found. These results were compared with the pre-existing bases on the literature to evaluate the relevance of the presence or absence of the genes responsible for microcystin degradation with the natural resistance found in heterobacteria from aquatic environments. Moreover, the activity of the enzymes from the antioxidant system also was accounted to explain this behavior.