Glyphosate & the Gut Microbiome

What is this study?

This study describes the effects of glyphosate and a Roundup formulation (MON 52276, representing the EU market) on the gut microbiome and serum metabolome in Sprague-Dawley rats using shotgun metagenomics and metabolomics. It was conducted by an international team based in London, France, Italy, and the Netherlands, led by the group of Dr Michael Antoniou at King's College London.

The study is published in Environmental Health Perspectives (EHP) — ranked 1st among Toxicology journals that publish original research according to Clarivate Journal Impact Factor.

Why did we do this study?

Our gut is home to trillions of bacteria critical to good health. Because glyphosate can kill bacteria in a petri dish, theories that it acts as an antibiotic in the human gut have gained prominence. Whether and how glyphosate affects the gut microbiome was still an open question — this study was designed to answer it with high-resolution methods.

What is shotgun metagenomics?

Shotgun metagenomics entails studying genetic material sampled from environmental sources. In this study, that meant the contents of the large intestine from glyphosate-treated rats. We sequenced ~20 million DNA sequences per sample — approximately 5 billion letters of DNA code — covering every gene from every microorganism in the rat gut.

A key challenge was separating rat DNA and food DNA from microbial DNA. The microbial sequences were used to identify and quantify the different species composing the gut microbiome.

What is metabolomics?

Metabolomics is the study of small molecules called metabolites — products of chemical reactions in living organisms. We measured ~700 small molecules in both gut contents and blood, giving us a comprehensive picture of how microbiome changes translate to systemic effects.

Did glyphosate act as an antibiotic?

The short answer is no. For glyphosate to act as an antibiotic it must cause a significant shortage of aromatic amino acids in bacteria by inhibiting the shikimate pathway. We confirmed that glyphosate does inhibit the shikimate pathway in the rat gut microbiome. However, bacteria do not need this pathway to get aromatic amino acids — like us, they obtain them from food.

Instead, glyphosate's phosphorus atom likely served as an energy source for some bacteria, causing compositional shifts without the antibiotic effect.

Did glyphosate's impact in the gut stay in the gut?

Shikimate pathway-derived metabolites were mostly unchanged in blood. However, other chemicals were disrupted, indicating glyphosate caused oxidative stress. This effect was even more pronounced with Roundup Bioflow (MON 52276, the representative EU glyphosate herbicide).

Oxidative stress is produced when free radicals overwhelm the body's defences. It is not yet fully clear whether the changes caused by glyphosate in the gut are pathological, but this study establishes important biomarkers for future investigation. To be continued!