The effect of glyphosate on bacteria and archaea community composition in freshwater biofilms

Abstract

Glyphosate-based herbicides are some of the most widely used herbicides in the world today, however, there is still much to learn about how glyphosate affects non-target ecosystems. Specifically, freshwater aquatic biofilms are often exposed to glyphosate-based herbicides through anthropogenic activities. This study aims to understand the effects of glyphosate on bacteria and archaea components of freshwater biofilms through a simulated agricultural pulse-dose exposure of 0.5 mg glyphosate a.e./L biweekly over 21 days. Biofilms were cultured in situ from a variety of wetlands in Rondeau Bay, Ontario and were transported to lab microcosms for the exposure experiment. We found that glyphosate exposure did not have a significant effect on the richness or Shannon-Weiner diversity of bacteria or archaea within biofilm communities. These communities did significantly change over time due to glyphosate exposure, but the exposure did not drive the microbial communities toward greater homogeneity or heterogeneity in composition. We also found evidence that amplicon sequence variants that were indicative of glyphosate-exposed communities may be resistant to glyphosate through class II EPSPS enzymes and some may be able to use glyphosate as a phosphorus source through C-P lyase. This suggests that biofilm communities are structurally resilient to pulsed exposures of glyphosate over chronic exposure durations at realistic environmental exposure levels. Additionally, some bacteria or archaea may be useful indicators of episodic glyphosate contamination in wetland ecosystems. Given their complexity, ubiquity, and functional importance in shallow waters, biofilm ecology is a growing field of study.