Glyphosate exposure minimally alters the Corbicula fluminea microbiome while associated bacteria exhibit high tolerance and degradation potentia

Glyphosate, the active ingredient in Roundup, is a widely-used, broad-spectrum herbicide known for its high water solubility. This chemical is frequently released into freshwater ecosystems due to its extensive use in agriculture and landscaping, often leading to negative impacts on aquatic life and beneficial microorganisms. The freshwater clam Corbicula fluminea, a nonnative bivalve species present in many U.S. regions, demonstrates remarkable tolerance to various environmental stressors, making it a potential reservoir for microbial species that can tolerate or degrade environmental pollutants.

As filter-feeders, these clams are in constant contact with waterborne contaminants, which could facilitate interactions between pollutants and their resident microbial communities. This study aimed to assess the effects of glyphosate on the structure and diversity of Corbicula fluminea microbiomes, as well as the tolerance and degradation potential of individual microbiome members.

The researchers discovered that while the taxonomic composition and abundance-based diversity metrics of the microbiomes were barely affected by glyphosate, presence/absence-based phylogenetic diversity varied depending on the concentration of the chemical.

High glyphosate concentrations were associated with reduced Faith's PD alpha diversity, while other alpha diversity metrics remained unaffected. The researchers isolated and characterized glyphosate-tolerant bacterial strains from the clam tissues and examined their presence within the microbiome. Some of these isolated bacteria displayed tolerance to extremely high glyphosate levels (up to 1600 mg/L), and several also utilized glyphosate as their sole phosphorus source and possessed the phnJ gene, indicating potential degradation capabilities.

Although these isolated bacteria were minor members of the microbiome, related uncultured taxa were found to be phylogenetically associated with known glyphosate degraders. Overall, these findings suggest that freshwater bivalves may harbor a diverse array of microbial taxa capable of tolerating or degrading herbicides. This capacity could contribute to host resilience in polluted freshwater environments and may represent novel opportunities for bioremediation research.