Bacterial composition of the biofilm on valves of Limnoperna fortunei and its role in glyphosate degradation in water

Abstract

Knowledge of the anthropogenic drivers of environmental change is important for understanding ecosystem dynamics. We studied 2 of these factors — an invasive mollusk (golden mussel Limnoperna fortunei) and the herbicide glyphosate — focusing on the effects of the mussel, the herbicide, and their interaction on the abundance and composition of different groups of biofilm bacteria present on the mussel’s valves. We carried out semi-static experiments to assess changes in nutrient and glyphosate concentrations in the presence or absence of the mussel. The catalyzed reporter deposition-fluorescence in situ hybridization technique was used to evaluate changes in biofilm bacteria growing on whole mussels or dissected valves. When the mussel was exposed to glyphosate, there was a significant decrease in the concentration of the herbicide, a significant increase in the concentration of its major metabolite (aminomethylphosphonic acid), and a significant increase in the concentration of nutrients. These results may be explained by the capacity of biofilm bacteria associated with L. fortunei to degrade glyphosate. After exposure to the herbicide, the analysis of 5 groups of Eubacteria (i.e. Alpha-, Beta-, and Gammaproteobacteria, Actinobacteria, and Bacteroidetes) showed a significant increase in the abundance of Gammaproteobacteria, suggesting that they would participate in glyphosate transformation in water. This study represents a starting point for investigating the bacterial component of the biofilm present on the valves of L. fortunei. Moreover, this invasive mussel is a promising tool for glyphosate degradation. However, the liberation of nutrients as a consequence of the degradation of herbicide mediated by the presence of L. fortunei may accelerate eutrophication processes in freshwater ecosystems.