Biology subjects

Fischbach, M. A.

Publications and source records attributed to Fischbach, M. A..

At least 19 recordsLinked to original sources

bioRxiv2026

Enzymatic attachment of antigens to probe immune modulation by skin commensals

The skin colonist Staphylococcus epidermidis induces potent T and B cell responses, which can be redirected against antigens of interest by genetic engineering. However, since many taxa in the microbiome are genetically intractable, the utility of this method is limited. Here, we use recombinant sortase to conjugate antigens to the surface of a wide range of Gram-positive bacterial species, and we show that this non-genetic method can be used to generate protective immunity in vivo.

immunology↗

bioRxiv2026

Coevolutionary mining of prokaryotic non-coding elements with a genome language model

Microbial genomes encode compact molecular machines and diverse non-coding RNAs (ncRNAs) essential to gene regulation, pathogenesis, and many foundational biotechnologies. However, annotation remains largely protein-centric and homology-driven. Here, we introduce Minerva, a framework for coevolutionary mining that uses genome language models to predict local interactions directly from sequence as two-dimensional maps. Introducing two complementary techniques, categorical Jacobian fingerprinting and interaction heads, we demonstrate fast, accurate, alignment-free prediction of ncRNA base-pairing, monomeric protein contacts, and repetitive sequence motifs. Applied to 150 bacterial genomes, Minerva recovers known systems and predicts that 84.3% of predicted intergenic base-pairing falls outside of known annotations. In Pseudomonas, we find that the widespread TwoAYGGAY ncRNA family carries large secondary-structure extensions and is often flanked by short upstream repetitive motifs and larger downstream genomic repeats. Interpreting the coevolution maps, we find that Minerva emergently detects open-reading-frame (ORF) signatures at the DNA level despite never being trained to do so. In prophages within these genomes, we discover that Unknown Group 27 (UG27) reverse transcriptase systems encode arrays of structurally conserved yet sequence-diverse ncRNAs that template complementary DNA (cDNA) hairpin products. Together, these results establish coevolutionary mining as a scalable route to genome annotation and biological discovery across the rapidly expanding microbial universe.

bioinformatics↗

bioRxiv2026

Microbiota- and diet-specific T cells become Tregs by default

CD4+ T cells recognize antigens from microbiota, diet, and pathogens via T cell receptors (TCRs) and orchestrate immunity by differentiating into tolerogenic regulatory (Treg) or pro-inflammatory effector (Teff) lineages (e.g. TH1 or TH17) (1). Dysregulation of these responses underlies numerous gastrointestinal inflammatory and infectious diseases (2-6). The prevailing paradigm suggests that individual microbes and dietary antigens drive distinct cell fates (e.g., segmented filamentous bacteria [SFB] induce TH17 cells (7) whereas Helicobacter hepaticus (8) and diet (9) induce Tregs). However, the generality of this model is uncertain: several key organisms are atypical, and foundational studies often omitted a complex microbiome or a diverse polyclonal TCR repertoire. Here we develop a high-throughput pipeline to screen hundreds of TCRs from mice colonized from birth with a 116-strain human microbiota (hCom2v), demonstrating that TCRs recognizing microbiota or dietary antigens are overwhelmingly enriched in the induced Treg (iTreg) lineage. Endogenous CD4+ T cells specific for these antigens adopt a uniform iTreg phenotype in vivo, both in hCom2v-colonized and conventional mice. This baseline tolerance is robust to acute inflammation but breaks down following a 'two-hit' combination of inflammation and genetic susceptibility, allowing Teff to emerge against otherwise Treg-restricted antigens. These data support a revised paradigm in which antigen-specific Treg induction is the default response to foreign antigens in the healthy gut, and effector responses are an exception reflecting a perceived threat. Reframing gastrointestinal immunity as a tolerance-first system provides a framework for understanding inflammatory disease pathogenesis and suggests that therapeutic strategies should aim to restore a Treg-predominant baseline.

immunology↗

bioRxiv2026

Microbial mechanistic requirements for eliciting a topical and intranasal immune response

The skin colonist Staphylococcus epidermidis elicits a potent antibody response that can be redirected against an antigen of interest, but this process relies on genetic engineering.1 Here, by adapting bioorthogonal chemistry methods to conjugate antigens to the cell surface, we make the process of generating a commensal vaccine rapid and efficient. A wide variety of bacteria displaying tetanus toxin fragment C (TTFC) elicit an antibody response when applied to mice topically, indicating that the inductive process is not limited to colonists. Colonization occurs at two different sites, the skin and nostril; by colonizing each with S. epidermidis-TTFC, we show that skin colonization yields a moderate IgG response, while nostril colonization elicits a highly potent systemic IgG response and an exuberant IgA response in the nostrils, lungs, and intestine. Two lines of evidence are consistent with the nasal-associated lymphoid tissue (NALT) as the inductive site for nostril colonization: imaging suggesting robust bacterial translocation, and the induction of commensal-specific B cells following colonization. On the skin, TTFC must be conjugated to live S. epidermidis to elicit an antibody response; in the nostrils, live S. epidermidis-TTFC and S. epidermidis mixed with TTFC are equally potent. Commensal vaccination yields a robust response in pet shop mice, and chemical conjugation facilitates antibody responses to a broad array of antigens, including a whole viral capsid and a rotavirus immunogen. Collectively, these findings provide compelling evidence of a translational path for commensal vaccines.

microbiology↗

bioRxiv2026

Ecology and engineering to modify the bile acid output of a defined microbial community

The bile acid pool, which is synthesized collaboratively by the host and its microbiome, impacts metabolism, immunity, and disease risk. Targeted microbiome interventions could in principle reshape the bile acid pool for therapeutic benefit, but practical strategies remain elusive. In the course of screening a complex defined community for metabolic phenotypes by dropping out individual strains, we observed that several of the single-strain dropout communities had markedly increased deoxycholic and lithocholic acid levels and a larger bile acid pool. In each of these communities, a second strain--Lactobacillus plantarum--had bloomed. The bile salt hydrolase activity of L. plantarum was necessary and sufficient to expand the size of the bile acid pool. An engineered community in which the bsh gene is overexpressed in multiple Lactobacillus strains confers on mice increased levels of secondary bile acid levels and a larger pool size. By overexpressing a different pair of bile acid metabolic genes in multiple strains of Lactobacillus--7- and 7{beta}-hydroxysteroid dehydrogenase--we changed the composition of the bile acid pool, enlarging it and redirecting it toward ursodeoxycholic acid. Together, these results demonstrate that fine details of the microbiomes strain composition can have a substantial effect on bile acid metabolism, and that rational manipulation of the microbiome can alter the size and composition of the bile acid pool.

microbiology↗

bioRxiv2026

A single-strain dropout screen reveals mechanistic links between microbial ecology and metabolism

The complexity of the gut microbiome has made it challenging to define the role of individual species in community-level function. Here, we constructed 56 single-strain dropout variants of a defined 118-member community and used each one to colonize a group of germ-free mice. In many cases, removing a single strain triggered a large reordering of a small group of species, which in turn altered the communitys metabolic output. En bloc removal of the eight-strain acetogen compartment markedly reduced acetate production and caused intestinal H2 accumulation and bloating; a specific subset of four acetogens was sufficient to relieve bloating and restore acetate production. Together, these data show that small disturbances in community composition can trigger a confined ecological reorganization with a large chemical phenotype, and they reveal novel strategies for engineering communities with altered metabolic output.

microbiology↗

bioRxiv2025

Gut microbe-derived short-chain fatty acids regulate joint inflammation and activation of infiltrating and resident myeloid cells after alphavirus infection

Although oral antibiotics can predispose to joint inflammation, this phenomenon remains poorly understood. Here, we leverage mouse models of alphavirus-induced arthritis to investigate the roles of gut commensals, metabolites, and host immune mechanisms in promoting musculoskeletal inflammation. Mice treated with a short course of oral antibiotics exhibited worsened arthritis after chikungunya (CHIKV) or Mayaro virus infections. This phenotype was associated with loss of short chain fatty acids (SCFA), greater intestinal permeability, and activation of gut-associated immune cells, and required TLR4 signaling, MyD88 expression, monocytes, antigen-specific and bystander CD4+ T cells, and pro-inflammatory cytokines. Administration of exogenous SCFA or colonization of mice with bacterial species that generate SCFA mitigated CHIKV-induced joint inflammation. Single-cell RNA sequencing revealed that gut-derived SCFA ameliorate the inflammatory phenotype of synovial CD4+ T cells, infiltrating monocytes, and resident osteoclast-like cells. Thus, antibiotic-triggered gut dysbiosis exacerbates alphavirus arthritis by shaping the inflammatory profile of both infiltrating and resident immune cells in joint tissues.

immunology↗

bioRxiv2025

Gut microbial composition modulates food-specific CD4+ T cells in food allergy

The growing food allergy epidemic is thought to be related to changing environmental factors, particularly changes in the gut microbiome. While prior work has demonstrated that food allergy can be modulated by gut microbes, little is known about how food allergen-specific CD4+ T cells are affected by gut microbial composition. Here, we report that food allergy severity differs between mice obtained from two different specific pathogen-free mouse vendors (Jackson Labs [Jax] and Taconic Biosciences [Tac]). Mice from Tac develop diarrhea and anaphylaxis after fewer allergen exposures than mice from Jax. Using food allergen peptide:MHCII tetramers, we also find that Tac mice have fewer allergen-specific regulatory T cells in the small intestine compared to mice from Jax. In addition, Tac mice have a greater abundance of small intestinal mucosal mast cells and increased intestinal permeability. The increased food allergy severity phenotype is transferable via co-housing, which corresponds to a shift in Jax microbial communities towards those found in Tac mice. Our findings demonstrate for the first time that food allergen-specific Treg cells can be modulated by gut microbial community composition, which in turn is correlated to food allergy severity.

immunology↗

bioRxiv2025

Systematic identification and characterization of regulators of aryl hydrocarbon receptor signaling

The human aryl hydrocarbon receptor (AHR) integrates chemical signals derived from the environment, gut microbes, and endogenous sources to regulate processes ranging from intestinal barrier integrity to xenobiotic detoxification. Despite strong evidence that dysregulation of AHR signaling is a causal factor in metabolic and autoimmune disorders, we currently lack a comprehensive understanding of the factors that regulate AHR activity in human cells. Here, we use genome-scale CRISPR screening to systematically identify regulators of AHR signaling in hepatocytes. The resulting datasets recapitulate the core AHR signaling pathway and identify a large network of regulators. Many of these factors have roles beyond AHR signaling, reflecting that AHR signaling is deeply integrated into human cell biology. We further dissect this network to reveal novel modes of regulation of AHR expression, protein levels, and signaling. For example, we find that the E3 ubiquitin ligase UBR5 sustains AHR signaling by counteracting degradation of ligand-bound AHR. Finally, we identify components of the AHR regulatory network that are specific to cell types and ligands as potential nodes to manipulate AHR signaling in a targeted manner for therapeutic benefit. Overall, our results define the regulatory network that underpins AHR activation, with implications for our understanding of host-microbe interactions and integrative chemosensation and the etiology of metabolic and inflammatory disorders.

genomics↗

bioRxiv2024

A PTER-dependent pathway of taurine metabolism linked to energy balance

Taurine is a conditionally essential micronutrient and one of the most abundant amino acids in humans1-3. In endogenous taurine metabolism, dedicated enzymes are involved in biosynthesis of taurine from cysteine as well as the downstream derivatization of taurine into secondary taurine metabolites4,5. One such taurine metabolite is N-acetyltaurine6. Levels of N-acetyltaurine are dynamically regulated by diverse physiologic perturbations that alter taurine and/or acetate flux, including endurance exercise7, nutritional taurine supplementation8, and alcohol consumption6,9. While taurine N-acetyltransferase activity has been previously detected in mammalian cells6,7, the molecular identity of this enzyme, and the physiologic relevance of N-acetyltaurine, have remained unknown. Here we show that the orphan body mass index-associated enzyme PTER (phosphotriesterase-related)10 is the principal mammalian taurine N-acetyltransferase/hydrolase. In vitro, recombinant PTER catalyzes bidirectional taurine N-acetylation with free acetate as well as the reverse N-acetyltaurine hydrolysis reaction. Genetic ablation of PTER in mice results in complete loss of tissue taurine N-acetyltransferase/hydrolysis activities and systemic elevation of N-acetyltaurine levels. Upon stimuli that increase taurine levels, PTER-KO mice exhibit lower body weight, reduced adiposity, and improved glucose homeostasis. These phenotypes are recapitulated by administration of N-acetyltaurine to wild-type mice. Lastly, the anorexigenic and anti-obesity effects of N-acetyltaurine require functional GFRAL receptors. Together, these data uncover enzymatic control of a previously enigmatic pathway of secondary taurine metabolism linked to energy balance.

biochemistry↗

bioRxiv2024

Gut microbiota gate host exposure to metabolites from dietary Solanums

Dietary plants are molecularly rich but the fates of these compounds post-ingestion and their implications for human health are largely unknown. Here, we systematically characterized the major chemical contributions of widely consumed Solanum species (nightshades) to the human metabolome. Using untargeted metabolomics, we found that a series of steroidal alkaloids resulting from glycoalkaloids tomatine, solanine, and chaconine are dominant diet-derived compounds in systemic circulation following ingestion of tomato and potato. By comparing serum and tissue metabolomes of colonized and microbiome-depleted mice, we determined that the gut microbiota modifies these compounds extensively, altering their absorption and gating host exposure. By screening the metabolic products in human urine and stool samples, we established that steroidal glycoalkaloid metabolism varies inter-individually in a population. Furthermore, using a collection of representative human commensal type strains, we found that a limited set of strains is responsible for steroidal glycoalkaloid metabolism, with the chemical output of a community determined by its strain-level composition. These findings enabled the rational design of complex synthetic microbial communities that controlled host exposure to steroidal alkaloid metabolites in vivo. Importantly, microbial metabolism of Solanum metabolites alters their acetylcholinesterase inhibition in vitro and gut motility in vivo. Our study provides insights into the molecular mechanisms of a diet-microbiome interactions and the effects of dietary metabolites on host physiology.

microbiology↗

bioRxiv2024

Discovery and engineering of the antibody response against a prominent skin commensal

The ubiquitous skin colonist Staphylococcus epidermidis elicits a CD8+ T cell response pre-emptively, in the absence of an infection1. However, the scope and purpose of this anti-commensal immune program are not well defined, limiting our ability to harness it therapeutically. Here, we show that this colonist also induces a potent, durable, and specific antibody response that is conserved in humans and non-human primates. A series of S. epidermidis cell-wall mutants revealed that the cell surface protein Aap is a predominant target. By colonizing mice with a strain of S. epidermidis in which the parallel {beta}-helix domain of Aap is replaced by tetanus toxin fragment C, we elicit a potent neutralizing antibody response that protects mice against a lethal challenge. A similar strain of S. epidermidis expressing an Aap-SpyCatcher chimera can be conjugated with recombinant immunogens; the resulting labeled commensal elicits high titers of antibody under conditions of physiologic colonization, including a robust IgA response in the nasal mucosa. Thus, immunity to a common skin colonist involves a coordinated T and B cell response, the latter of which can be redirected against pathogens as a novel form of topical vaccination.

microbiology↗

bioRxiv2023

Identification of human skin microbiome odorants that manipulate mosquito landing behavior - towards engineering a repellent skin flora

The resident human skin microbiome is responsible for the production of most of the human scents that are attractive to mosquitoes. Hence, engineering the human skin microbiome to synthesize less of mosquito attractants or produce repellents could potentially reduce bites and prevent the transmission of deadly mosquito-borne pathogens. In order to further characterize the human skin volatilome, we quantified the major volatiles of 39 strains of skin commensals (Staphylococci and Corynebacterium). Importantly, to validate the behavioral activity of these volatiles, we first assessed landing behavior triggered by human skin bacteria volatiles. We demonstrated that this behavioral step is gated by the presence of carbon dioxide and L-(+)-lactic acid, similar to the combinatorial coding triggering short range attraction. Repellency behavior to selected skin volatiles and the geraniol terpene was tested in the presence of carbon dioxide and L-(+)-lactic acid. In a 2-choice landing behavior context, the skin volatiles 2- and 3-methyl butyric acids reduced mosquito landing by 62.0-81.6% and 87.1-99.6%, respectively. Similarly, geraniol was capable of reducing mosquito landing behavior by 74.9%. We also tested the potential repellency effects of geraniol on mosquitoes at short-range using a 4-port olfactometer. In these assays, geraniol reduced mosquito attraction (69-78%) to a mixture of key human kairomones carbon dioxide, L-(+)-lactic acid, and ammonia. These findings demonstrate that carbon dioxide and L-(+)-lactic acid changes the valence of other skin volatiles towards mosquito landing behavior. Moreover, this study offers candidate odorants to be targeted in a novel strategy to reduce attractants or produce repellents by the human skin microbiota that may curtail mosquito bites, and subsequent mosquito-borne disease.

zoology↗

bioRxiv2022

Strain dropouts reveal interactions that govern the metabolic output of the gut microbiome

The gut microbiome is complex, raising questions about the role of individual strains in the community. Here, we address this question by focusing on a functional unit within the community, the metabolic niche that controls bile acid 7-dehydroxylation. By constructing variants of a complex defined community in which we drop out strains that occupy this niche, we explore how interactions within and between niches shape community-level metabolism. Omitting both members of the niche, Clostridium scindens (Cs) and Clostridium hylemonae (Ch), eliminates secondary bile acid production and reshapes the community in a highly specific manner: eight strains go up or down in relative abundance by >100-fold, while the remaining strains are largely unaffected. In single-strain dropout communities (i.e., a strain swap within the niche), Cs and Ch reach the same relative abundance and dehydroxylate bile acids to a similar extent. However, the effect on strains in other niches differs markedly: Clostridium sporogenes increases >1000-fold in the {Delta}Cs but not {Delta}Ch dropout, reshaping the pool of microbiome-derived phenylalanine metabolites. Thus, strains that are functionally redundant within a niche can have widely varying impacts outside the niche, and a strain swap can ripple through the community in an unpredictable manner, resulting in a large impact on an unrelated community-level phenotype. Mice colonized by the {Delta}Cs{Delta}Ch community show decreased liver steatosis relative to those colonized by the {Delta}Ch community, demonstrating that a single strain from the microbiome can have a substantive impact on host physiology. Our work opens the door to the mechanistic studies of the role of an individual strain on community ecology and host physiology.

microbiology↗

bioRxiv2022

Mapping the T cell repertoire to a complex gut bacterial community

Certain bacterial strains from the microbiome induce a potent, antigen-specific T cell response1-5. However, the specificity of microbiome-induced T cells has not been explored at the strain level across the gut community. Here, we colonize germ-free mice with a complex defined community (97 or 112 bacterial strains) and profile T cell responses to each strain individually. Unexpectedly, the pattern of T cell responses suggests that many T cells in the gut repertoire recognize multiple bacterial strains from the community. We constructed T cell hybridomas from 92 T cell receptor (TCR) clonotypes; by screening every strain in the community against each hybridoma, we find that nearly all of the bacteria-specific TCRs exhibit a one-to-many TCR-to-strain relationship, including 13 abundant TCR clonotypes that are polyspecific for 18 Firmicutes in the community. By screening three pooled bacterial genomic libraries against 13 pooled hybridomas, we discover that they share a single target: a conserved substrate-binding protein (SBP) from an ABC transport system. Treg and Th17 cells specific for an epitope from this protein are abundant in community-colonized and specific-pathogen-free mice. Our work reveals that T cell recognition of Firmicutes is focused on a widely conserved cell-surface antigen, opening the door to new therapeutic strategies in which colonist-specific immune responses are rationally altered or redirected.

immunology↗

bioRxiv2021

Impact of a 7-day homogeneous diet on interpersonal variation in human gut microbiomes and metabolomes

Metabolism of dietary compounds by the gut microbiota generates a vast array of microbiome-dependent metabolites (MDMs), which are highly variable between individuals. The uremic MDMs (uMDMs) phenylacetylglutamine (PAG), p-cresol sulfate (PCS) and indoxyl sulfate (IS) accumulate during renal failure and are associated with poor outcomes. Targeted dietary interventions may reduce toxic MDMs generation; however, it is unclear if interindividual differences in diet or gut microbiome dominantly contribute to MDM variance. Here we use a 7-day homogeneous average American diet to standardize dietary precursor availability in 21 healthy individuals. Notably, the coefficient of variation in three uMDMs of interest, PAG, PCS, and IS (primary outcome), did not significantly decrease. The majority of circulating MDMs maintained variation despite identical diets. These results highlight the highly personalized profile of MDMs and limited contribution of short-term dietary heterogeneity, suggesting that dietary modification may need to be paired with microbial therapies to control MDM profiles.

microbiology↗

bioRxiv2021

Systematic dissection of a complex gut bacterial community

Efforts to model the gut microbiome have yielded important insights into the mechanisms of interspecies interactions, the impact of priority effects on ecosystem dynamics, and the role of diet and nutrient availability in determining community composition. However, the model communities studied to date have been defined or complex but not both, limiting their utility. Here, we construct a defined community of 104 bacterial strains composed of the most common taxa from the human gut microbiota. By propagating this community in growth media missing one amino acid at a time, we show that branched-chain amino acids have an outsize impact on community structure and identify a pathway in Clostridium sporogenes for generating ATP from arginine. We constructed and propagated the complete set of single-strain dropout communities, revealing a sparse network of strain-strain interactions including a novel interaction between C. sporogenes and Lactococcus lactis driven by metabolism. This work forms a foundation for studying strain-strain and strain-nutrient interactions in highly complex defined communities, and it provides a starting point for interrogating the rules of synthetic ecology at the 100+ strain scale.

microbiology↗

bioRxiv2021

In vivo augmentation of a complex gut bacterial community

Efforts to model the human gut microbiome in mice have led to important insights into the mechanisms of host-microbe interactions. However, the model communities studied to date have been defined or complex but not both, limiting their utility. In accompanying work, we constructed a complex synthetic community (104 strains, hCom1) containing the most common taxa in the human gut microbiome. Here, we used an iterative experimental process to improve hCom1 by filling open metabolic and/or anatomical niches. When we colonized germ-free mice with hCom1 and then challenged it with a human fecal sample, the consortium exhibited surprising stability; 89% of the cells and 58% of the taxa derive from the original community, and the pre- and post-challenge communities share a similar overall structure. We used these data to construct a second version of the community, adding 22 strains that engrafted following fecal challenge and omitting 7 that dropped out (119 strains, hCom2). In gnotobiotic mice, hCom2 exhibited increased stability to fecal challenge and robust colonization resistance against pathogenic Escherichia coli. Mice colonized by hCom2 versus human feces are similar in terms of microbiota-derived metabolites, immune cell profile, and bacterial density in the gut, suggesting that this consortium is a prototype of a model system for the human gut microbiome.

microbiology↗