Several recent studies describe the influence of the gut microbiota on host brain and behavior. However, the mechanisms responsible for microbiota-nervous system interactions are largely unknown. ...Using a combination of genetics, biochemistry, and crystallography, we identify and characterize two phylogenetically distinct enzymes found in the human microbiome that decarboxylate tryptophan to form the β-arylamine neurotransmitter tryptamine. Although this enzymatic activity is exceedingly rare among bacteria more broadly, analysis of the Human Microbiome Project data demonstrate that at least 10% of the human population harbors at least one bacterium encoding a tryptophan decarboxylase in their gut community. Our results uncover a previously unrecognized enzymatic activity that can give rise to host-modulatory compounds and suggests a potential direct mechanism by which gut microbiota can influence host physiology, including behavior.
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•Gut microbiota produce tryptamine via tryptophan (Trp) decarboxylation•Two bacterial Trp decarboxylases from gut Firmicutes were identified and characterized•Structure of one of the tryptophan decarboxylase suggests catalytic mechanism•>10% of healthy humans harbor a Trp decarboxylase in their gut microbiome
Williams et al. describe tryptophan decarboxylases from human microbiota that produce the neurotransmitter tryptamine. Although rare among bacteria more broadly, at least 10% of the human population harbors this activity in their gut community. These results uncover a previously unrecognized enzymatic activity that can give rise to host-modulatory compounds.
Tryptamine, a tryptophan-derived monoamine similar to 5-hydroxytryptamine (5-HT), is produced by gut bacteria and is abundant in human and rodent feces. However, the physiologic effect of tryptamine ...in the gastrointestinal (GI) tract remains unknown. Here, we show that the biological effects of tryptamine are mediated through the 5-HT4 receptor (5-HT4R), a G-protein-coupled receptor (GPCR) uniquely expressed in the colonic epithelium. Tryptamine increases both ionic flux across the colonic epithelium and fluid secretion in colonoids from germ-free (GF) and humanized (ex-GF colonized with human stool) mice, consistent with increased intestinal secretion. The secretory effect of tryptamine is dependent on 5-HT4R activation and is blocked by 5-HT4R antagonist and absent in 5-HT4R−/− mice. GF mice colonized by Bacteroides thetaiotaomicron engineered to produce tryptamine exhibit accelerated GI transit. Our study demonstrates an aspect of host physiology under control of a bacterial metabolite that can be exploited as a therapeutic modality.
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•Tryptamine increases anion and fluid secretion in the proximal colon•Tryptamine-induced effect is mediated by the GPCR serotonin receptor-4 (5-HT4R)•Tryptamine activates epithelial 5-HT4R to increase cAMP level and drive fluid secretion•In vivo tryptamine production by an engineered microbe accelerates whole-gut transit
Bhattarai et al. uncovered the mechanism by which a bacteria-derived small molecule can alter host gastrointestinal function. Tryptamine produced by bacterial decarboxylation of dietary tryptophan accelerates gastrointestinal transit by activating the epithelial G-protein-coupled receptor (GPCR) serotonin receptor-4 (5-HT4R) and increasing anion-dependent fluid secretion in the proximal colon.
While the human gut microbiota are suspected to produce diffusible small molecules that modulate host signaling pathways, few of these molecules have been identified. Species of Bacteroides and their ...relatives, which often comprise >50% of the gut community, are unusual among bacteria in that their membrane is rich in sphingolipids, a class of signaling molecules that play a key role in inducing apoptosis and modulating the host immune response. Although known for more than three decades, the full repertoire of Bacteroides sphingolipids has not been defined. Here, we use a combination of genetics and chemistry to identify the sphingolipids produced by Bacteroides fragilis NCTC 9343. We constructed a deletion mutant of BF2461, a putative serine palmitoyltransferase whose yeast homolog catalyzes the committed step in sphingolipid biosynthesis. We show that the Δ2461 mutant is sphingolipid deficient, enabling us to purify and solve the structures of three alkaline-stable lipids present in the wild-type strain but absent from the mutant. The first compound was the known sphingolipid ceramide phosphorylethanolamine, and the second was its corresponding dihydroceramide base. Unexpectedly, the third compound was the glycosphingolipid α-galactosylceramide (α-GalCer(Bf)), which is structurally related to a sponge-derived sphingolipid (α-GalCer, KRN7000) that is the prototypical agonist of CD1d-restricted natural killer T (iNKT) cells. We demonstrate that α-GalCer(Bf) has similar immunological properties to KRN7000: it binds to CD1d and activates both mouse and human iNKT cells both in vitro and in vivo. Thus, our study reveals BF2461 as the first known member of the Bacteroides sphingolipid pathway, and it indicates that the committed steps of the Bacteroides and eukaryotic sphingolipid pathways are identical. Moreover, our data suggest that some Bacteroides sphingolipids might influence host immune homeostasis.
Recent studies emphasize the role of microbial metabolites in regulating gastrointestinal (GI) physiology through activation of host receptors, highlighting the potential for inter-kingdom signaling ...in treating GI disorders. In this study, we show that tryptamine, a tryptophan-derived bacterial metabolite, stimulates mucus release from goblet cells via activation of G-protein-coupled receptor (GPCR) 5-HT4R. Germ-free mice colonized with engineered Bacteroides thetaiotaomicron optimized to produce tryptamine (Trp D+) exhibit decreased weight loss and increased mucus release following dextran sodium sulfate treatment when compared with mice colonized with control B. thetaiotaomicron (Trp D-). Additional beneficial effects in preventing barrier disruption and lower disease activity index were seen only in female mice, highlighting sex-specific effects of the bacterial metabolite. This study demonstrates potential for the precise modulation of mucus release by microbially produced 5-HT4 GPCR agonist as a therapeutic strategy to treat inflammatory conditions of the GI tract.
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•Tryptamine increases serotonin-receptor4-dependent colonic mucus release•Bacterially derived tryptamine attenuates weight loss in DSS colitis mouse model•Protective effect of tryptamine in DSS colitis is more pronounced in female mice•Tryptamine reduces colitis severity and barrier disruption specifically in female mice
Rodent Gastroenterology; Microbiology
While the human gut microbiota are suspected to produce diffusible small molecules that modulate host signaling pathways, few of these molecules have been identified. Species of Bacteroides and their ...relatives, which often comprise >50% of the gut community, are unusual among bacteria in that their membrane is rich in sphingolipids, a class of signaling molecules that play a key role in inducing apoptosis and modulating the host immune response. Although known for more than three decades, the full repertoire of Bacteroides sphingolipids has not been defined. Here, we use a combination of genetics and chemistry to identify the sphingolipids produced by Bacteroides fragilis NCTC 9343. We constructed a deletion mutant of BF2461, a putative serine palmitoyltransferase whose yeast homolog catalyzes the committed step in sphingolipid biosynthesis. We show that the δ2461 mutant is sphingolipid deficient, enabling us to purify and solve the structures of three alkaline-stable lipids present in the wild-type strain but absent from the mutant. The first compound was the known sphingolipid ceramide phosphorylethanolamine, and the second was its corresponding dihydroceramide base. Unexpectedly, the third compound was the glycosphingolipid α-galactosylceramide (α-GalCerBf), which is structurally related to a sponge-derived sphingolipid (α-GalCer, KRN7000) that is the prototypical agonist of CD1d-restricted natural killer T (iNKT) cells. We demonstrate that α-GalCerBf has similar immunological properties to KRN7000: it binds to CD1d and activates both mouse and human iNKT cells both in vitro and in vivo. Thus, our study reveals BF2461 as the first known member of the Bacteroides sphingolipid pathway, and it indicates that the committed steps of the Bacteroides and eukaryotic sphingolipid pathways are identical. Moreover, our data suggest that some Bacteroides sphingolipids might influence host immune homeostasis.
While the human gut microbiota are suspected to produce diffusible small molecules that modulate host signaling pathways, few of these molecules have been identified. Species of Bacteroides and their ...relatives, which often comprise >50% of the gut community, are unusual among bacteria in that their membrane is rich in sphingolipids, a class of signaling molecules that play a key role in inducing apoptosis and modulating the host immune response. Although known for more than three decades, the full repertoire of Bacteroides sphingolipids has not been defined. Here, we use a combination of genetics and chemistry to identify the sphingolipids produced by Bacteroides fragilis NCTC 9343. We constructed a deletion mutant of BF2461, a putative serine palmitoyltransferase whose yeast homolog catalyzes the committed step in sphingolipid biosynthesis. We show that the Delta 2461 mutant is sphingolipid deficient, enabling us to purify and solve the structures of three alkaline-stable lipids present in the wild-type strain but absent from the mutant. The first compound was the known sphingolipid ceramide phosphorylethanolamine, and the second was its corresponding dihydroceramide base. Unexpectedly, the third compound was the glycosphingolipid alpha -galactosylceramide ( alpha -GalCerBf), which is structurally related to a sponge-derived sphingolipid ( alpha -GalCer, KRN7000) that is the prototypical agonist of CD1d-restricted natural killer T (iNKT) cells. We demonstrate that alpha -GalCerBf has similar immunological properties to KRN7000: it binds to CD1d and activates both mouse and human iNKT cells both in vitro and in vivo. Thus, our study reveals BF2461 as the first known member of the Bacteroides sphingolipid pathway, and it indicates that the committed steps of the Bacteroides and eukaryotic sphingolipid pathways are identical. Moreover, our data suggest that some Bacteroides sphingolipids might influence host immune homeostasis.
Increasing global reliance on stormwater control measures to reduce discharge to surface water, increase groundwater recharge, and minimize contaminant delivery to receiving waterbodies necessitates ...improved understanding of stormwater–contaminant profiles. A multiagency study of organic and inorganic chemicals in urban stormwater from 50 runoff events at 21 sites across the United States demonstrated that stormwater transports substantial mixtures of polycyclic aromatic hydrocarbons, bioactive contaminants (pesticides and pharmaceuticals), and other organic chemicals known or suspected to pose environmental health concern. Numerous organic-chemical detections per site (median number of chemicals detected = 73), individual concentrations exceeding 10 000 ng/L, and cumulative concentrations up to 263 000 ng/L suggested concern for potential environmental effects during runoff events. Organic concentrations, loads, and yields were positively correlated with impervious surfaces and highly developed urban catchments. Episodic storm-event organic concentrations and loads were comparable to and often exceeded those of daily wastewater plant discharges. Inorganic chemical concentrations were generally dilute in concentration and did not exceed chronic aquatic life criteria. Methylmercury was measured in 90% of samples with concentrations that ranged from 0.05 to 1.0 ng/L.
Myxofibrosarcoma (MFS) is a common soft tissue sarcoma of the elderly that typically shows low tumor mutational burden, with mutations in TP53 and in genes associated with cell cycle checkpoints ( ...RB1 , CDKN2A ). Unfortunately, no alterations or markers specific to MFS have been identified and, as a consequence, there are no effective targeted therapies. The receptor tyrosine kinase AXL, which drives cellular proliferation, is targetable by new antibody-based therapeutics. Expression of AXL messenger RNA is elevated in a variety of sarcoma types, with the highest levels reported in MFS, but the pathogenic significance of this finding remains unknown. To assess a role for AXL abnormalities in MFS, we undertook a search for AXL genomic alterations in a comprehensive genomic profiling database of 463,546 unique tumors (including 19,879 sarcomas, of which 315 were MFS) interrogated by targeted next-generation DNA and/or RNA sequencing. Notably, the only genomic alterations recurrent in a specific sarcoma subtype were AXL W451C (n = 8) and AXL W450C (n = 2) mutations. The tumors involved predominantly older adults (age: 44 to 81 median: 72 y) and histologically showed epithelioid and spindle-shaped cells in a variably myxoid stroma, with 6 cases diagnosed as MFS, 3 as undifferentiated pleomorphic sarcoma (UPS), and 1 as low-grade sarcoma. The AXL W451C mutation was not identified in any non-sarcoma malignancy. A review of publicly available data sets revealed a single AXL W451C-mutant case of UPS that clustered with MFS/UPS by methylation profiling. Functional studies revealed a novel activation mechanism: the W451C mutation causes abnormal unregulated dimerization of the AXL receptor tyrosine kinase through disulfide bond formation between pairs of mutant proteins expressing ectopic cysteine residues. This dimerization triggers AXL autophosphorylation and activation of downstream ERK signaling. We further report sarcomas of diverse histologic subtypes with AXL gene amplifications, with the highest frequency of amplification identified in MFS cases without the W451C mutation. In summary, the activating AXL W451C mutation appears highly specific to MFS, with a novel mechanism to drive unregulated signaling. Moreover, AXL gene amplifications and messenger RNA overexpression are far more frequent in MFS than in other sarcoma subtypes. We conclude that these aberrations in AXL are distinct features of MFS and may aid diagnosis, as well as the selection of available targeted therapies.
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•Photocatalyst-enabled selective harmful algal bloom mitigation.•3D printing provides photocatalyst immobilization and accessibility.•Photocatalyst (TiO2) structures are deployable, ...retrievable for in situ treatment.•Printed PLA-TiO2 photocatalytic and pH control to treat toxic microcystin.•Workflow for attainable, sustainable emerging contaminant treatment.
Novel and sustainable solutions are needed for surface water treatment. Photocatalytic TiO2 is studied but is not directly deployable into natural water bodies due to settling and poor recoverability. This research capitalizes on a convergence of the emerging technologies of 3D printing biocompatible polymer (polylactic acid, PLA) composites, nanotechnology, and advanced oxidative processes to immobilize TiO2 into customizable, high surface area, deployable, and retrievable structures with localized kinetic specificity for harmful algal blooms (HAB). PLA-TiO2 composites at varying loadings (3–34 %) were extruded as feedstock for fused filament fabrication (FFF) enabling low cost printing design freedom of photocatalyst structures (disks, lattices). Large surface area, 3D lattices were printed as PLA composites with highly loaded (34 % w/w) TiO2. Prior to HAB cyanotoxin experiments, the photocatalytic performance of the 3D printed PLA-TiO2 lattice composites (t1/2 = 0.8 h) under UV light were confirmed comparable to free TiO2 (t1/2 = 0.9 h). Under environmentally relevant solar simulation, photocatalysis by printed lattices successfully reduced microcystin (MC) cyanotoxin (t1/2 = 3 h) faster than photolysis alone (t1/2 = 36 h). Lattice mediated photocatalysis of MC in presence of cyanobacteria cells (t1/2 = 11 h) was faster than photolysis (t1/2 = 58 h) but slower than water-only treatment due to cell activity and light attenuation. PLA-TiO2 reduces local pH, promoting MC adsorption and degradation. This research is foundational to novel photocatalytic composite optimization for reactive surface area prototyping enabled by 3D printing and scale-up for sustainable water treatment structures, with applicability to traditional and emerging contaminants.
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![Production of [alpha]-Galac...](http://api.summon.serialssolutions.com/2.0.0/image/issn/XR4PS5YY4K/1544-9173/small "Production of [alpha]-Galactosylceramide by a Prominent Member of the Human Gut Microbiota")
