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The intestinal bacterial community is now recognized as an important factor for health and implicated in numerous states of disease. Despite the fairly extensive regulatory demands for risk assessment of pesticides in relation to human exposure, there is currently very little knowledge related to potential effects on the gut microbiota. It has however recently been speculated that glyphosate based herbicides may affect the gut microbiota of humans and animal husbandry due to inhibition of the Shikimate pathway in bacteria causing loss of aromatic amino acid synthesis and thus growth inhibition. In this study Sprague Dawley rats were exposed to glyphosate at 5x and 50x the acceptable daily intake (ADI) for humans. Profiling of the bacterial community and aromatic amino acids and their downstream metabolites was performed on intestinal samples obtained after two weeks of oral dossing. The results suggest that glyphosate had very limited effects on bacterial community composition even at the highest exposure concentration. Also relatively high concentrations of aromatic amino acids were measured in the intestine of the animals. The data show that glyphosate inhibits bacterial growth in minimal medium but this inhibitory effect is relieved in the presence of aromatic amino acids in the growth medium. Results from the animal trial therefor suggest that sufficient levels of aromatic amino acids are present in the rat intestine to alleviate the need for bacterial synthesis and thus prevent an antimicrobial effect of glyphosate in vivo.PrefaceThis report is written as an extended summary of the scientific work conducted during the PestiGut project “Tarmmikrobiota som følsom indikator for biologisk relevante restkoncentrationer af kemiske pesticider i fødevarer eksemplificeret ved glyphosat (Roundup®)”. The report includes an introduction to the area, overview of methods, main results and conclusions. For a more detailed presentation of the work please refer to the accompanying scientific manuscript entitled: “Glyphosate has limited short-term effects on commensal bacterial community composition in the gut environment due to sufficient aromatic amino acid levels” 1.