From Gut to Brain: Glyphosate and Triclosan Impair Microbiome Composition, Neuroactive Metabolites, and Cognitive and Ecological Fitness in Daphnia magna

Gut microbiome dysbiosis is a major off-target effect of many pharmaceuticals, personal care products (PPCP), and plant protection products (PPP). This study aims to characterize these effects for two compounds, glyphosate (a PPP) and triclosan (a PPCP), in Daphnia magna juveniles and to trace the downstream consequences for gut- and brain-associated metabolite levels, reproductive performance, and behavior. Both compounds altered levels of neurotransmitters and related metabolites in both head and gut at the ppb–ppt dose range, promoting anxiogenic behavior and inhibiting reproductive traits in a concentration-related manner. These effects occurred concomitantly with alterations in the gut microbiome, analyzed by 16S rDNA sequencing. Correlation analyses between the observed metabolic, reproductive, and behavioral effects and the changes in the metabolic pathway prediction for the treated gut microbiomes revealed an enrichment in pathways related to the biosynthesis of vitamins, of essential fatty acids, and production of short chain fatty acids, which are known to affect systemic serotonin levels. The results suggest a direct link between gut microbiome dysbiosis and cognitive and reproduction effects in D. magna, with implications for the environmental and human health hazard assessment of these and other substances with broad antimicrobial spectra.