Updated project metadata. The gut microbiota in our intestinal tract metabolizes non-digestible compounds into essential nutrients and signaling molecules (i.e. short-chain fatty acids), affecting our immune system and the development of various human diseases. Ingested environmental contaminants (xenobiotics) can disrupt the bacterial community and enzymatic activity, ultimately influencing the host. Pervasive xenobiotics include bisphenols and poly- and perfluoroalkyl substances (PFAS). Both classes of chemicals have been reported to affect the immune system and cause adverse effects on human metabolism. Since humans are exposed to a complex mixture of environmental contaminants it is critical to evaluate the effects of xenobiotics in mixtures. In our study, an in vitro bioreactor model system based on the simplified human microbiome model (SIHUMIx) was used to investigate the direct effects of either perfluorooctanoic acid (PFOA), perfluorohexanoic acid (PFHxA) and perfluorobutanoic acid (PFBA) or bisphenol S (BPS) and bisphenol F (BPF) or a combined mixture on the microbiota. We observed an increased production of the short-chain fatty acids (SCFAs) acetate and butyrate following PFAS exposure. A metaproteomics approach revealed changes in molecular pathways in all treatments, including alterations in vitamin and cofactor synthesis and an additional effect on fatty acid synthesis in BPX-treated reactors. This study highlights the need to assess the combined effects of xenobiotics and to better protect public health by considering adverse effects on the microbiome in the risk assessment of environmental chemicals.