Supplementation with soluble or insoluble rice-bran fibers increases short-chain fatty acid producing bacteria in the gut microbiota in vitro.

Introduction: Studies have shown that a diet high in fiber and prebiotics has a positive impact on human health due largely to the fermentation of these compounds by the gut microbiota. One underutilized source of fiber may be rice bran, a waste product of rice processing that is used most frequently as an additive to livestock feed but may be a good source of fibers and other phenolic compounds as a human diet supplement. Previous studies focused on specific compounds extracted from rice bran showed that soluble fibers extracted from rice bran can improve glucose response and reduce weight gain in mouse models. However, less is known about changes in the human gut microbiota in response to regular rice bran consumption. Methods: In this study, we used a Simulator of the Human Intestinal Microbial Ecology (SHIME®) to cultivate the human gut microbiota of 3 different donors in conditions containing either soluble or insoluble fiber fractions from rice bran. Using 16S rRNA amplicon sequencing and targeted metabolomics via Gas Chromatography-Mass Spectrometry, we explored how gut microbial communities developed provided different supplemental fiber sources. Results: We found that insoluble and soluble fiber fractions increased short-chain fatty acid production, indicating that both fractions were fermented. However, there were differences in response between donors, for example the gut microbiota from donor 1 increased acetic acid production with both fiber types compared with control; whereas for donors 2 and 3, butanoic acid production increased with ISF and SF supplementation. Both soluble and insoluble rice bran fractions increased the abundance of Bifidobacterium and Lachnospiraceae taxa. Discussion: Overall, analysis of the effect of soluble and insoluble rice bran fractions on the human in vitro gut microbiota and the metabolites produced revealed individually variant responses to these prebiotics.

Preservation of conjugated primary bile acids by oxygenation of the small intestinal microbiota in vitro.

Bile acids play a critical role in the emulsification of dietary lipids, a critical step in the primary function of the small intestine, which is the digestion and absorption of food. Primary bile acids delivered into the small intestine are conjugated to enhance functionality, in part, by increasing aqueous solubility and preventing passive diffusion of bile acids out of the gut lumen. Bile acid function can be disrupted by the gut microbiota via the deconjugation of primary bile acids by bile salt hydrolases (BSHs), leading to their conversion into secondary bile acids through the expression of bacterial bile acid-inducible genes, a process often observed in malabsorption due to small intestinal bacterial overgrowth. By modeling the small intestinal microbiota in vitro using human small intestinal ileostomy effluent as the inocula, we show here that the infusion of physiologically relevant levels of oxygen, normally found in the proximal small intestine, reduced deconjugation of primary bile acids, in part, through the expansion of bacterial taxa known to have a low abundance of BSHs. Further recapitulating the small intestinal bile acid composition of the small intestine, limited conversion of primary into secondary bile acids was observed. Remarkably, these effects were preserved among four separate communities, each inoculated with a different small intestinal microbiota, despite a high degree of taxonomic variability under both anoxic and aerobic conditions. In total, these results provide evidence for a previously unrecognized role that the oxygenated environment of the small intestine plays in the maintenance of normal digestive physiology. IMPORTANCE: Conjugated primary bile acids are produced by the liver and exist at high concentrations in the proximal small intestine, where they are critical for proper digestion. Deconjugation of these bile acids with subsequent transformation via dehydroxylation into secondary bile acids is regulated by the colonic gut microbiota and reduces their digestive function. Using an in vitro platform modeling the small intestinal microbiota, we analyzed the ability of this community to transform primary bile acids and studied the effect of physiological levels of oxygen normally found in the proximal small intestine (5%) on this metabolic process. We found that oxygenation of the small intestinal microbiota inhibited the deconjugation of primary bile acids in vitro. These findings suggest that luminal oxygen levels normally found in the small intestine may maintain the optimal role of bile acids in the digestive process by regulating bile acid conversion by the gut microbiota.

A new approach to the treatment of acute infection diseases with antibiotic-pectin formulae.

INTRODUCTION: Intestinal infections are a significant health issue; antibiotics are essential in treating acute intestinal infections. However, evidence in the literature shows that the excessive use of antibiotics has created many threats to human health. This work aimed to study the impact of apple pectin in combination with antibiotics on treating patients with amebiasis and dysentery. METHODOLOGY: Patients suffering from acute intestinal diseases (amebiasis and dysentery) were treated with traditional antibiotic therapy and a new formula containing antibiotics with low and high methoxylated apple pectin in a randomized block design. Four clinical trials were performed at the Infection Disease Hospital from 1998 until 2013. RESULTS: The study demonstrated that the antibiotic-pectin formulae (APF) significantly reduced the severity of acute intestinal infection diseases and allowed patients to recover faster than conventional treatment. APF reduced the patient's stay in the hospital by 3.0 ± 1.0 days. The clinical trial findings demonstrated that applying APF in intestinal infection diseases helped maintain a constant concentration of the antibiotic in the blood and accelerated the clinical recovery of the patients. CONCLUSIONS: It was concluded that using pectin with antibiotics could improve clinical outcomes in patients with acute infectious diseases. Research on elucidating the mechanisms of pectin digestion in the colon, polyphenol content, and its role in dysbiosis recovery, etc., is also considered.

Targeted remodeling of the human gut microbiome using Juemingzi (Senna seed extracts).

The genus Senna contains globally distributed plant species of which the leaves, roots, and seeds have multiple traditional medicinal and nutritional uses. Notable chemical compounds derived from Senna spp. include sennosides and emodin which have been tested for antimicrobial effects in addition to their known laxative functions. However, studies of the effects of the combined chemical components on intact human gut microbiome communities are lacking. This study evaluated the effects of Juemingzi (Senna sp.) extract on the human gut microbiome using SIFR® (Systemic Intestinal Fermentation Research) technology. After a 48-hour human fecal incubation, we measured total bacterial cell density and fermentation products including pH, gas production and concentrations of short chain fatty acids (SCFAs). The initial and post-incubation microbial community structure and functional potential were characterized using shotgun metagenomic sequencing. Juemingzi (Senna seed) extracts displayed strong, taxon-specific anti-microbial effects as indicated by significant reductions in cell density (40%) and intra-sample community diversity. Members of the Bacteroidota were nearly eliminated over the 48-hour incubation. While generally part of a healthy gut microbiome, specific species of Bacteroides can be pathogenic. The active persistence of the members of the Enterobacteriaceae and selected Actinomycetota despite the reduction in overall cell numbers was demonstrated by increased fermentative outputs including high concentrations of gas and acetate with correspondingly reduced pH. These large-scale shifts in microbial community structure indicate the need for further evaluation of dosages and potential administration with prebiotic or synbiotic supplements. Overall, the very specific effects of these extracts may offer the potential for targeted antimicrobial uses or as a tool in the targeted remodeling of the gut microbiome.

Tomato seed extract promotes health of the gut microbiota and demonstrates a potential new way to valorize tomato waste.

The current effort to valorize waste byproducts to increase sustainability and reduce agricultural loss has stimulated interest in potential utilization of waste components as health-promoting supplements. Tomato seeds are often discarded in tomato pomace, a byproduct of tomato processing, yet these seeds are known to contain an array of compounds with biological activity and prebiotic potential. Here, extract from tomato seeds (TSE), acquired from pomace, was evaluated for their ability to effect changes on the gut microbiota using an ex vivo strategy. The results found that TSE significantly increased levels of the beneficial taxa Bifidobacteriaceae in a donor-independent manner, from a range of 18.6-24.0% to 27.0-51.6% relative abundance following treatment, yet the specific strain of Bifidobacteriaceae enhanced was inter-individually variable. These structural changes corresponded with a significant increase in total short-chain fatty acids, specifically acetate and propionate, from an average of 13.3 to 22.8 mmol/L and 4.6 to 7.4 mmol/L, respectively. Together, these results demonstrated that TSE has prebiotic potential by shaping the gut microbiota in a donor-independent manner that may be beneficial to human health. These findings provide a novel application for TSE harvested from tomato pomace and demonstrate the potential to further valorize tomato waste products.

Dietary carbohydrates regulate intestinal colonization and dissemination of Klebsiella pneumoniae.

Bacterial translocation from the gut microbiota is a source of sepsis in susceptible patients. Previous work suggests that overgrowth of gut pathobionts, including Klebsiella pneumoniae, increases the risk of disseminated infection. Our data from a human dietary intervention study found that, in the absence of fiber, K. pneumoniae bloomed during microbiota recovery from antibiotic treatment. We thus hypothesized that dietary nutrients directly support or suppress colonization of this gut pathobiont in the microbiota. Consistent with our study in humans, complex carbohydrates in dietary fiber suppressed the colonization of K. pneumoniae and allowed for recovery of competing commensals in mouse models. In contrast, through ex vivo and in vivo modeling, we identified simple carbohydrates as a limiting resource for K. pneumoniae in the gut. As proof of principle, supplementation with lactulose, a nonabsorbed simple carbohydrate and an FDA-approved therapy, increased colonization of K. pneumoniae. Disruption of the intestinal epithelium led to dissemination of K. pneumoniae into the bloodstream and liver, which was prevented by dietary fiber. Our results show that dietary simple and complex carbohydrates were critical not only in the regulation of pathobiont colonization but also disseminated infection, suggesting that targeted dietary interventions may offer a preventative strategy in high-risk patients.

Metagenomes and metagenome-assembled genomes from ex vivo fecal incubations of six unique donors.

We present a donor-specific collection of 78 metagenomes (13/donor) and 143 metagenome-assembled genomes (MAGs), representing the gut microbiomes of six healthy adult human donors. In addition to adding to the catalog of publicly available human gut MAGs, this resource permits a genome-resolved look into microbial co-occurrence across six individuals.

Enterobacteriaceae Growth Promotion by Intestinal Acylcarnitines, a Biomarker of Dysbiosis in Inflammatory Bowel Disease.

BACKGROUND & AIMS: Altered plasma acylcarnitine levels are well-known biomarkers for a variety of mitochondrial fatty acid oxidation disorders and can be used as an alternative energy source for the intestinal epithelium when short-chain fatty acids are low. These membrane-permeable fatty acid intermediates are excreted into the gut lumen via bile and are increased in the feces of patients with inflammatory bowel disease (IBD). METHODS: Herein, based on studies in human subjects, animal models, and bacterial cultures, we show a strong positive correlation between fecal carnitine and acylcarnitines and the abundance of Enterobacteriaceae in IBD where they can be consumed by bacteria both in vitro and in vivo. RESULTS: Carnitine metabolism promotes the growth of Escherichia coli via anaerobic respiration dependent on the cai operon, and acetylcarnitine dietary supplementation increases fecal carnitine levels with enhanced intestinal colonization of the enteric pathogen Citrobacter rodentium. CONCLUSIONS: In total, these results indicate that the increased luminal concentrations of carnitine and acylcarnitines in patients with IBD may promote the expansion of pathobionts belonging to the Enterobacteriaceae family, thereby contributing to disease pathogenesis.

Impact of Baizhu, Daqingye, and Hehuanhua extracts on the human gut microbiome.

Introduction: In traditional Chinese medicine, the rhizome of Atractylodes macrocephala (Baizhu), the leaves of Isatis indigotica (Daqingye), and the flowers of Albizia julibrissin (Hehuanhua) have been used to treat gastrointestinal illnesses, epidemics, and mental health issues. Modern researchers are now exploring the underlying mechanisms responsible for their efficacy. Previous studies often focused on the impact of purified chemicals or mixed extracts from these plants on cells in tissue culture or in rodent models. Methods: As modulation of the human gut microbiome has been linked to host health status both within the gastrointestinal tract and in distant tissues, the effects of lipid-free ethanol extracts of Baizhu, Daqingye, and Hehuanhua on the human adult gut microbiome were assessed using Systemic Intestinal Fermentation Research (SIFR®) technology (n=6). Results and discussion: Baizhu and Daqingye extracts similarly impacted microbial community structure and function, with the extent of effects being more pronounced for Baizhu. These effects included decreases in the Bacteroidetes phylum and increases in health-related Bifidobacterium spp. and short chain fatty acids which may contribute to Baizhu's efficacy against gastrointestinal ailments. The changes upon Hehuanhua treatment were larger and included increases in multiple bacterial species, including Agathobaculum butyriciproducens, Adlercreutzia equolifaciens, and Gordonibacter pamelaeae, known to produce secondary metabolites beneficial to mental health. In addition, many of the changes induced by Hehuanhua correlated with a rise in Enterobacteriaceae spp., which may make the tested dose of this herb contraindicated for some individuals. Overall, there is some evidence to suggest that the palliative effect of these herbs may be mediated, in part, by their impact on the gut microbiome, but more research is needed to elucidate the exact mechanisms.

Impact of Ivermectin on the Gut Microbial Ecosystem.

Ivermectin is a an anti-helminthic that is critical globally for both human and veterinary care. To the best of our knowledge, information available regarding the influence of ivermectin (IVM) on the gut microbiota has only been collected from diseased donors, who were treated with IVM alone or in combination with other medicines. Results thus obtained were influenced by multiple elements beyond IVM, such as disease, and other medical treatments. The research presented here investigated the impact of IVM on the gut microbial structure established in a Triple-SHIME® (simulator of the human intestinal microbial ecosystem), using fecal material from three healthy adults. The microbial communities were grown using three different culture media: standard SHIME media and SHIME media with either soluble or insoluble fiber added (control, SF, ISF). IVM introduced minor and temporary changes to the gut microbial community in terms of composition and metabolite production, as revealed by 16S rRNA amplicon sequencing analysis, flow cytometry, and GC-MS. Thus, it was concluded that IVM is not expected to induce dysbiosis or yield adverse effects if administered to healthy adults. In addition, the donor's starting community influences the relationship between IVM and the gut microbiome, and the soluble fiber component in feed could protect the gut microbiota from IVM; an increase in short-chain fatty acid production was predicted by PICRUSt2 and detected with IVM treatment.

Lacticaseibacillus rhamnosus Strain GG (LGG) Regulate Gut Microbial Metabolites, an In Vitro Study Using Three Mature Human Gut Microbial Cultures in a Simulator of Human Intestinal Microbial Ecosystem (SHIME).

In the present research, we investigated changes in the gut metabolome that occurred in response to the administration of the Laticaseibacillus rhamnosus strain GG (LGG). The probiotics were added to the ascending colon region of mature microbial communities established in a human intestinal microbial ecosystem simulator. Shotgun metagenomic sequencing and metabolome analysis suggested that the changes in microbial community composition corresponded with changes to metabolic output, and we can infer linkages between some metabolites and microorganisms. The in vitro method permits a spatially-resolved view of metabolic transformations under human physiological conditions. By this method, we found that tryptophan and tyrosine were mainly produced in the ascending colon region, while their derivatives were detected in the transverse and descending regions, revealing sequential amino acid metabolic pathways along with the colonic tract. The addition of LGG appeared to promote the production of indole propionic acid, which is positively associated with human health. Furthermore, the microbial community responsible for the production of indole propionic acid may be broader than is currently known.

Colonization and Dissemination of Klebsiella pneumoniae is Dependent on Dietary Carbohydrates.

Dysbiosis of the gut microbiota is increasingly appreciated as both a consequence and precipitant of human disease. The outgrowth of the bacterial family Enterobacteriaceae is a common feature of dysbiosis, including the human pathogen Klebsiella pneumoniae . Dietary interventions have proven efficacious in the resolution of dysbiosis, though the specific dietary components involved remain poorly defined. Based on a previous human diet study, we hypothesized that dietary nutrients serve as a key resource for the growth of bacteria found in dysbiosis. Through human sample testing, and ex-vivo , and in vivo modeling, we find that nitrogen is not a limiting resource for the growth of Enterobacteriaceae in the gut, contrary to previous studies. Instead, we identify dietary simple carbohydrates as critical in colonization of K. pneumoniae . We additionally find that dietary fiber is necessary for colonization resistance against K. pneumoniae , mediated by recovery of the commensal microbiota, and protecting the host against dissemination from the gut microbiota during colitis. Targeted dietary therapies based on these findings may offer a therapeutic strategy in susceptible patients with dysbiosis.

Modulation of the Gut Microbiota Structure and Function by Two Structurally Different Lemon Pectins.

Pectins are plant polysaccharides consumed as part of a diet containing fruits and vegetables. Inside the gastrointestinal tract, pectin cannot be metabolized by the mammalian cells but is fermented by the gut microbiota in the colon with the subsequent release of end products including short-chain fatty acids (SCFA). The prebiotic effects of pectin have been previously evaluated but reports are inconsistent, most likely due to differences in the pectin chemical structure which can vary by molecular weight (MW) and degree of esterification (DE). Here, the effects of two different MW lemon pectins with varying DEs on the gut microbiota of two donors were evaluated in vitro. The results demonstrated that low MW, high DE lemon pectin (LMW-HDE) altered community structure in a donor-dependent manner, whereas high MW, low DE lemon pectin (HMW-LDE) increased taxa within Lachnospiraceae in both donors. LMW-HDE and HMW-LDE lemon pectins both increased total SCFAs (1.49- and 1.46-fold, respectively) and increased acetic acid by 1.64-fold. Additionally, LMW-HDE lemon pectin led to an average 1.41-fold increase in butanoic acid. Together, these data provide valuable information linking chemical structure of pectin to its effect on the gut microbiota structure and function, which is important to understanding its prebiotic potential.

Persistence of the Probiotic Lacticaseibacillus rhamnosus Strain GG (LGG) in an In Vitro Model of the Gut Microbiome.

The consumption of probiotics is widely encouraged due to reports of their positive effects on human health. In particular, Lacticaseibacillus rhamnosus strain GG (LGG) is an approved probiotic that has been reported to improve health outcomes, especially for gastrointestinal disorders. However, how LGG cooperates with the gut microbiome has not been fully explored. To understand the interaction between LGG and its ability to survive and grow within the gut microbiome, this study introduced LGG into established microbial communities using an in vitro model of the colon. LGG was inoculated into the simulated ascending colon and its persistence in, and transit through the subsequent transverse and descending colon regions was monitored over two weeks. The impact of LGG on the existing bacterial communities was investigated using 16S rRNA sequencing and short-chain fatty acid analysis. LGG was able to engraft and proliferate in the ascending region for at least 10 days but was diminished in the transverse and descending colon regions with little effect on short-chain fatty acid abundance. These data suggest that the health benefits of the probiotic LGG rely on its ability to transiently engraft and modulate the host microbial community.

Resilience of Chemistry: An Introduction to the Agricultural and Food Chemistry Technical Program at the 262nd American Chemical Society National Hybrid Meeting & Exposition, Both Online and in Atlanta, Georgia.

This is the third special issue of the Journal of Agricultural and Food Chemistry (JAFC) based on the Agricultural and Food Chemistry Division (AGFD) technical program, at the 262nd American Chemical Society National Meeting. This was the first national meeting held in a hybrid format, both virtually and in-person in Atlanta, Georgia, U.S.A., on August 22-26, 2021. The AGFD proudly hosted 12 symposia, including three award symposia. There were 34 sessions held in total, with 143 oral presentations and 49 poster presentations. This meeting was highly successful in terms of attendance, and technology issues experienced at the previous virtual meetings were successfully resolved.

The impact of environmental pH on the gut microbiota community structure and short chain fatty acid production.

Environmental pH is a critical parameter for maintenance of the gut microbiota. Here, the impact of pH on the gut microbiota luminal and mucosal community structure and short chain fatty acid (SCFA) production was evaluated in vitro, and data compiled to reveal a donor-independent response to an increase or decrease in environmental pH. The results found that raising environmental pH significantly increased luminal community richness and decreased mucosal community evenness. This corresponded with an increased abundance of Ruminococcaceae Ruminococcus and Erysipelotrichaceae Erysipelatoclostridium, and a decreased abundance of Coriobacteriaceae Collinsella and Enterobacteriaceae Shigella for both the luminal and mucosal communities. Total SCFA levels were significantly higher, primarily due to an increase in acetic and 2-methylbutanoic acids. Lowering pH decreased luminal community evenness and decreased mucosal community evenness and richness. This corresponded with an increased abundance of Lachnospiraceae Enterocloster, Veillonellaceae Megasphaera, Veillonellaceae Sporomusa, Erysipelotrichaceae Eubacterium, and Alcaligenaceae Sutterella, and decreased abundance of Odoribacteraceae Butyricimonas, Fusobacteriaceae Fusobacterium, Veillonellaceae Phascolarctobacterium, and multiple Enterobacteriaceae species for both the luminal and mucosal communities. Total SCFA levels were significantly lower, with an observed drop in acetic and propionic acids, and increased butyric and valeric acids. Taken together, these results indicate that alterations to environmental pH can modulate the gut microbiota community structure and function, and some changes may occur in a donor-independent manner.

Chewing the Fat with Microbes: Lipid Crosstalk in the Gut.

It is becoming increasingly important for any project aimed at understanding the effects of diet on human health, to also consider the combined effect of the trillions of microbes within the gut which modify and are modified by dietary nutrients. A healthy microbiome is diverse and contributes to host health, partly via the production and subsequent host absorption of secondary metabolites. Many of the beneficial bacteria in the gut rely on specific nutrients, such as dietary fiber, to survive and thrive. In the absence of those nutrients, the relative proportion of good commensal bacteria dwindles while communities of opportunistic, and potentially pathogenic, bacteria expand. Therefore, it is unsurprising that both diet and the gut microbiome have been associated with numerous human diseases. Inflammatory bowel diseases and colorectal cancer are associated with the presence of certain pathogenic bacteria and risk increases with consumption of a Western diet, which is typically high in fat, protein, and refined carbohydrates, but low in plant-based fibers. Indeed, despite increased screening and better care, colorectal cancer is still the 2nd leading cause of cancer death in the US and is the 3rd most diagnosed cancer among US men and women. Rates are rising worldwide as diets are becoming more westernized, alongside rising rates of metabolic diseases like obesity and diabetes. Understanding how a modern diet influences the microbiota and how subsequent microbial alterations effect human health will become essential in guiding personalized nutrition and healthcare in the future. Herein, we will summarize some of the latest advances in understanding of the three-way interaction between the human host, the gut microbiome, and the specific class of dietary nutrients, lipids.

Evaluation of Extended-release of Piroxicam-loaded Pectin-zein Hydrogel Microspheres: In vitro, Ex vivo, and In vivo Studies.

OBJECTIVE: This study evaluated drug delivery systems based on Pectin (P) and Zein (Z) hydrogel microspheres. Piroxicam (Px) loaded P/Z hydrogel microspheres (P/Z HM) were developed, and their extended-release pharmacokinetic properties were evaluated. METHODS: Experiments were executed under three different conditions: in vitro, ex vivo, and in vivo. Then, the in vitro-in vivo correlations (IVIVC) and ex vivo-in vivo correlations (EVIVC) were examined. RESULTS: Analysis of drug release mechanisms were evaluated by fitting the in vitro data into the Ritger- Peppas equation, showing the contribution of both polymers' relaxation and drug diffusion from the hydrogel microspheres. The fraction absorbed in vivo was determined by the deconvolution of plasma concentration data using the Loo-Riegelman method. After oral single-dose administration of the two formulations, their basic independent model parameters were calculated. CONCLUSION: P/Z HM had different drug release behaviors in in vitro and in vivo conditions. However, the ex vivo and in vivo characteristics were similar (R² = 0.99). It seemed reasonable to use the ex vivo method to predict the in vivo drug absorption behavior during the polymeric drug delivery system developmental studies. The P/Z HM formulation maintained the drug dose at the colon site for a long duration and could be applied for delivery of active pharmaceutical and food ingredients to the colon site.

Analysis of the Ability of Capsaicin to Modulate the Human Gut Microbiota In Vitro.

Previous studies on capsaicin, the bioactive compound in chili peppers, have shown that it may have a beneficial effect in vivo when part of a regular diet. These positive health benefits, including an anti-inflammatory potential and protective effects against obesity, are often attributed to the gut microbial community response to capsaicin. However, there is no consensus on the mechanism behind the protective effect of capsaicin. In this study, we used an in vitro model of the human gut microbiota to determine how regular consumption of capsaicin impacts the gut microbiota. Using a combination of NextGen sequencing and metabolomics, we found that regular capsaicin treatment changed the structure of the gut microbial community by increasing diversity and certain SCFA abundances, particularly butanoic acid. Through this study, we determined that the addition of capsaicin to the in vitro cultures of the human gut microbiome resulted in increased diversity of the microbial community and an increase in butanoic acid. These changes may be responsible for the health benefits associated with CAP consumption.

Microbial enzymes induce colitis by reactivating triclosan in the mouse gastrointestinal tract.

Emerging research supports that triclosan (TCS), an antimicrobial agent found in thousands of consumer products, exacerbates colitis and colitis-associated colorectal tumorigenesis in animal models. While the intestinal toxicities of TCS require the presence of gut microbiota, the molecular mechanisms involved have not been defined. Here we show that intestinal commensal microbes mediate metabolic activation of TCS in the colon and drive its gut toxicology. Using a range of in vitro, ex vivo, and in vivo approaches, we identify specific microbial ß-glucuronidase (GUS) enzymes involved and pinpoint molecular motifs required to metabolically activate TCS in the gut. Finally, we show that targeted inhibition of bacterial GUS enzymes abolishes the colitis-promoting effects of TCS, supporting an essential role of specific microbial proteins in TCS toxicity. Together, our results define a mechanism by which intestinal microbes contribute to the metabolic activation and gut toxicity of TCS, and highlight the importance of considering the contributions of the gut microbiota in evaluating the toxic potential of environmental chemicals.