Glyphosate exposure minimally alters the Corbicula fluminea microbiome while associated bacteria exhibit high tolerance and degradation potentia
Glyphosate (GLY), the active ingredient in Roundup, is a broad-spectrum herbicide widely used in commercial agriculture and residential landscaping. Due to its extensive application and high water solubility, GLY is frequently introduced into freshwater ecosystems where it has been shown to negatively impact aquatic life and beneficial microorganisms. The freshwater clam Corbicula fluminea, a nonnative bivalve species widely distributed throughout the United States, is highly tolerant of many environmental stressors and may serve as a reservoir for microbial taxa capable of tolerating or degrading environmental pollutants. As efficient filter-feeders, these clams are continuously exposed to waterborne contaminants, potentially facilitating interactions between pollutants and host-associated microbial communities. In this study, we investigated how glyphosate impacts the structure and diversity of Corbicula fluminea microbiomes and characterized GLY tolerance and degradation potential in individual microbiome members. We found that microbiome taxonomic composition and abundance-based diversity metrics were minimally impacted by glyphosate, while presence/absence-based phylogenetic diversity shifted depending on treatment concentration. Furthermore, high GLY concentrations were linked to reduced Faith''s PD alpha diversity, while other alpha diversity metrics were not impacted. Additionally, we isolated and characterized glyphosate-tolerant bacterial strains from clam tissues and assessed their presence within the microbiome. Several isolates exhibited tolerance to very high GLY levels (up to 1600 mg/L), and several also utilized GLY as a sole phosphorus source and possessed the phnJ gene, suggesting potential degradation capabilities. While isolated bacteria were minority members of the microbiome, more abundant uncultured taxa were phylogenetically related to known glyphosate degraders. Collectively, these findings suggest that freshwater bivalves may harbor diverse microbial taxa capable of tolerating or degrading herbicides, which may contribute to host resilience in contaminated freshwater environments and potentially represent unexplored avenues for bioremediation research.