Cylindrospermopsin is not degraded by co-occurring natural bacterial communities during a 40-day study

Biodegradation of cylindrospermopsin produced by Aphanizomenon ovalisporum UAM 290 was studied. In the 40-day degradation experiment conducted, bacterial communities from two waterbodies with and without previous exposure to the toxin were used. Further, and in order to study the potential effect of other organic substrates on the degradation of cylindrospermopsin, three different sources of cylindrospermopsin were used: toxic extracts obtained by methanolic extraction and by ultrasonication in water with 5% formic acid and 0.9% NaCl and toxin naturally present in the spent media of an Aphanizomenon ovalisporum culture. Despite active growth of the bacterial population and consumption of DOC in presence of the toxic extracts, no degradation of cylindrospermopsin could be observed during the 40-day period. Considering that cylindrospermopsin is abundant in the extracellular fraction and that photodegradation in the field seems to be limited, a lack of efficient biodegradation as observed in our study could be of greatest importance and further explain the accumulation of this toxin in the dissolved fraction of the waterbodies investigated.