A dietary commensal microbe enhances antitumor immunity by activating tumor macrophages to sequester iron.

Innate immune cells generate a multifaceted antitumor immune response, including the conservation of essential nutrients such as iron. These cells can be modulated by commensal bacteria; however, identifying and understanding how this occurs is a challenge. Here we show that the food commensal Lactiplantibacillus plantarum IMB19 augments antitumor immunity in syngeneic and xenograft mouse tumor models. Its capsular heteropolysaccharide is the major effector molecule, functioning as a ligand for TLR2. In a two-pronged manner, it skews tumor-associated macrophages to a classically active phenotype, leading to generation of a sustained CD8+ T cell response, and triggers macrophage 'nutritional immunity' to deploy the high-affinity iron transporter lipocalin-2 for capturing and sequestering iron in the tumor microenvironment. This process induces a cycle of tumor cell death, epitope expansion and subsequent tumor clearance. Together these data indicate that food commensals might be identified and developed into 'oncobiotics' for a multi-layered approach to cancer therapy.

Microbially Produced Imidazole Propionate Impairs Insulin Signaling through mTORC1.

Interactions between the gut microbiota, diet, and the host potentially contribute to the development of metabolic diseases. Here, we identify imidazole propionate as a microbially produced histidine-derived metabolite that is present at higher concentrations in subjects with versus without type 2 diabetes. We show that imidazole propionate is produced from histidine in a gut simulator at higher concentrations when using fecal microbiota from subjects with versus without type 2 diabetes and that it impairs glucose tolerance when administered to mice. We further show that imidazole propionate impairs insulin signaling at the level of insulin receptor substrate through the activation of p38γ MAPK, which promotes p62 phosphorylation and, subsequently, activation of mechanistic target of rapamycin complex 1 (mTORC1). We also demonstrate increased activation of p62 and mTORC1 in liver from subjects with type 2 diabetes. Our findings indicate that the microbial metabolite imidazole propionate may contribute to the pathogenesis of type 2 diabetes.

Exopolysaccharide is detrimental for the symbiotic performance of Sinorhizobium fredii HH103 mutants with a truncated lipopolysaccharide core.

The nitrogen-fixing rhizobia-legume symbiosis relies on a complex interchange of molecular signals between the two partners during the whole interaction. On the bacterial side, different surface polysaccharides, such as lipopolysaccharide (LPS) and exopolysaccharide (EPS), might play important roles for the success of the interaction. In a previous work we studied two Sinorhizobium fredii HH103 mutants affected in the rkpK and lpsL genes, which are responsible for the production of glucuronic acid and galacturonic acid, respectively. Both mutants produced an altered LPS, and the rkpK mutant, in addition, lacked EPS. These mutants were differently affected in symbiosis with Glycine max and Vigna unguiculata, with the lpsL mutant showing a stronger impairment than the rkpK mutant. In the present work we have further investigated the LPS structure and the symbiotic abilities of the HH103 lpsL and rkpK mutants. We demonstrate that both strains produce the same LPS, with a truncated core oligosaccharide devoid of uronic acids. We show that the symbiotic performance of the lpsL mutant with Macroptilium atropurpureum and Glycyrrhiza uralensis is worse than that of the rkpK mutant. Introduction of an exoA mutation (which avoids EPS production) in HH103 lpsL improved its symbiotic performance with G. max, M. atropurpureum, and G. uralensis to the level exhibited by HH103 rkpK, suggesting that the presence of EPS might hide the truncated LPS produced by the former mutant.

Gut Microbiota Alterations and Circulating Imidazole Propionate Levels Are Associated With Obstructive Coronary Artery Disease in People With HIV.

BACKGROUND: The impact of gut microbiota and its metabolites on coronary artery disease (CAD) in people with human immunodeficiency virus (PWH) is unknown. Emerging evidence suggests that imidazole propionate (ImP), a microbial metabolite, is linked with cardiometabolic diseases. METHODS: Fecal samples from participants of the Copenhagen Comorbidity in HIV infection (COCOMO) study were processed for 16S rRNA sequencing and ImP measured with liquid chromatography-tandem mass spectrometry. CAD severity was investigated by coronary computed tomography-angiography, and participants grouped according to obstructive CAD (n = 60), nonobstructive CAD (n = 80), or no CAD (n = 114). RESULTS: Participants with obstructive CAD had a gut microbiota with lower diversity and distinct compositional shift, with increased abundance of Rumiococcus gnavus and Veillonella, known producers of ImP. ImP plasma levels were associated with this dysbiosis, and significantly elevated in participants with obstructive CAD. However, gut dysbiosis but not plasma ImP was independently associated with obstructive CAD after adjustment for traditional and HIV-related risk factors (adjusted odds ratio, 2.7; 95% confidence interval, 1.1-7.2; P = .048). CONCLUSIONS: PWH with obstructive CAD displays a distinct gut microbiota profile and increased circulating ImP plasma levels. Future studies should determine whether gut dysbiosis and related metabolites such as ImP are predictive of incident cardiovascular events.

Increasing outer membrane complexity: the case of the lipopolysaccharide lipid A from marine Cellulophaga pacifica.

Gram-negative bacteria living in marine waters have evolved peculiar adaptation strategies to deal with the numerous stress conditions that characterize aquatic environments. Among the multiple mechanisms for efficient adaptation, these bacteria typically exhibit chemical modifications in the structure of the lipopolysaccharide (LPS), which is a fundamental component of their outer membrane. In particular, the glycolipid anchor to the membrane of marine bacteria LPSs, i.e. the lipid A, frequently shows unusual chemical structures, which are reflected in equally singular immunological properties with potential applications as immune adjuvants or anti-sepsis drugs. In this work, we determined the chemical structure of the lipid A from Cellulophaga pacifica KMM 3664T isolated from the Sea of Japan. This bacterium showed to produce a heterogeneous mixture of lipid A molecules that mainly display five acyl chains and carry a single phosphate and a D-mannose disaccharide on the glucosamine backbone. Furthermore, we proved that C. pacifica KMM 3664T LPS acts as a weaker activator of Toll-like receptor 4 (TLR4) compared to the prototypical enterobacterial Salmonella typhimurium LPS. Our results are relevant to the future development of novel vaccine adjuvants and immunomodulators inspired by marine LPS chemistry.

The additional value of the combined use of EUS and ERCP for the evaluation of unclear biliary strictures.

OBJECTIVE: Assessing unclear biliary strictures is challenging. We analyzed the diagnostic performance of radiology, EUS, and ERCP. METHODS: All patients referred for EUS and ERCP to assess an unclear biliary stricture were prospectively included. The data from radiology, EUS, ERCP, and tissue sampling were recorded. The diagnostic modalities were analyzed separately and in combination, with a focus on PSC. RESULTS: Between 2013 and 2020, 78 patients were included; 31% had PSC. A cholangioscopy was not performed in this study. The final diagnosis indicated that the biliary stricture was benign in 62% of the patients and malignant in 38%. The differences among the modalities were numerical, not significant. The modalities showed an accuracy between 78 and 83% in all the patients and between 75 and 83% in the patients with PSC. The combination of radiology and EUS showed the highest sensitivity of 94% in all the patients and a sensitivity of 100% in PSC. Tissue sampling showed the highest specificity of 93% in all patients and 89% in PSC. In 22 cases with combined EUS, ERCP, and tissue sampling, the accuracy, sensitivity, and specificity were 82%, 70%, and 92%, respectively. Minor differences were observed between the intention-to-diagnose analysis and the per-protocol analysis. Adverse events were recorded in 4% of cases. CONCLUSION: The combination of EUS and ERCP with tissue sampling seems to be useful and safe for excluding malignancy in unclear biliary strictures. In cases with a reduced suspicion of malignancy, radiology with an EUS may be sufficient.

A Journey from Structure to Function of Bacterial Lipopolysaccharides.

Lipopolysaccharide (LPS) is a crucial constituent of the outer membrane of most Gram-negative bacteria, playing a fundamental role in the protection of bacteria from environmental stress factors, in drug resistance, in pathogenesis, and in symbiosis. During the last decades, LPS has been thoroughly dissected, and massive information on this fascinating biomolecule is now available. In this Review, we will give the reader a third millennium update of the current knowledge of LPS with key information on the inherent peculiar carbohydrate chemistry due to often puzzling sugar residues that are uniquely found on it. Then, we will drive the reader through the complex and multifarious immunological outcomes that any given LPS can raise, which is strictly dependent on its chemical structure. Further, we will argue about issues that still remain unresolved and that would represent the immediate future of LPS research. It is critical to address these points to complete our notions on LPS chemistry, functions, and roles, in turn leading to innovative ways to manipulate the processes involving such a still controversial and intriguing biomolecule.

The Astounding World of Glycans from Giant Viruses.

Viruses are a heterogeneous ensemble of entities, all sharing the need for a suitable host to replicate. They are extremely diverse, varying in morphology, size, nature, and complexity of their genomic content. Typically, viruses use host-encoded glycosyltransferases and glycosidases to add and remove sugar residues from their glycoproteins. Thus, the structure of the glycans on the viral proteins have, to date, typically been considered to mimick those of the host. However, the more recently discovered large and giant viruses differ from this paradigm. At least some of these viruses code for an (almost) autonomous glycosylation pathway. These viral genes include those that encode the production of activated sugars, glycosyltransferases, and other enzymes able to manipulate sugars at various levels. This review focuses on large and giant viruses that produce carbohydrate-processing enzymes. A brief description of those harboring these features at the genomic level will be discussed, followed by the achievements reached with regard to the elucidation of the glycan structures, the activity of the proteins able to manipulate sugars, and the organic synthesis of some of these virus-encoded glycans. During this progression, we will also comment on many of the challenging questions on this subject that remain to be addressed.

Serum bile acid measurements in women of European and South Asian ethnicity with or without gestational diabetes mellitus: A cohort study.

OBJECTIVE: Investigation of serum bile acid profiles in pregnancies complicated by gestational diabetes mellitus (GDM) in a multi-ethnic cohort of women who are lean or obese. DESIGN: Prospective cohort study. SETTING: UK multicentre study. POPULATION: Fasting serum from participants of European or South Asian self-reported ethnicity from the PRiDE study, between 23 and 31 weeks of gestation. METHODS: Bile acids were measured using ultra-performance liquid chromatography-tandem mass spectrometry. Log-transformed data were analysed using linear regression in STATA/IC 15.0. MAIN OUTCOME MEASURES: Total bile acids (TBAs), C4, fasting glucose and insulin. RESULTS: The TBAs were 1.327-fold (1.105-1.594) increased with GDM in European women (P = 0.003). Women with GDM had 1.162-fold (1.002-1.347) increased levels of the BA synthesis marker C4 (P = 0.047). In South Asian women, obesity (but not GDM) increased TBAs 1.522-fold (1.193-1.942, P = 0.001). Obesity was associated with 1.420-fold (1.185-1.702) increased primary/secondary BA ratio (P < 0.001) related to 1.355-fold (1.140-1.611) increased primary BA concentrations (P = 0.001). TBAs were positively correlated with fasting glucose (P = 0.039) in all women, and with insulin (P = 0.001) and the Homeostatic Model Assessment for Insulin Resistance (HOMA-IR) (P = 0.001) in women with GDM. CONCLUSIONS: Serum BA homeostasis in late gestation depends on body mass index and GDM in ethnicity-specific ways. This suggests ethnicity-specific aetiologies may contribute to metabolic risk in European and South Asian women, with the relationship between BAs and insulin resistance of greater importance in European women. Further studies into ethnicity-specific precision medicine for GDM are required.

Methicillin-resistant Staphylococcus aureus alters cell wall glycosylation to evade immunity.

Methicillin-resistant Staphylococcus aureus (MRSA) is a frequent cause of difficult-to-treat, often fatal infections in humans1,2. Most humans have antibodies against S. aureus, but these are highly variable and often not protective in immunocompromised patients3. Previous vaccine development programs have not been successful4. A large percentage of human antibodies against S. aureus target wall teichoic acid (WTA), a ribitol-phosphate (RboP) surface polymer modified with N-acetylglucosamine (GlcNAc)5,6. It is currently unknown whether the immune evasion capacities of MRSA are due to variation of dominant surface epitopes such as those associated with WTA. Here we show that a considerable proportion of the prominent healthcare-associated and livestock-associated MRSA clones CC5 and CC398, respectively, contain prophages that encode an alternative WTA glycosyltransferase. This enzyme, TarP, transfers GlcNAc to a different hydroxyl group of the WTA RboP than the standard enzyme TarS7, with important consequences for immune recognition. TarP-glycosylated WTA elicits 7.5-40-fold lower levels of immunoglobulin G in mice than TarS-modified WTA. Consistent with this, human sera contained only low levels of antibodies against TarP-modified WTA. Notably, mice immunized with TarS-modified WTA were not protected against infection with tarP-expressing MRSA, indicating that TarP is crucial for the capacity of S. aureus to evade host defences. High-resolution structural analyses of TarP bound to WTA components and uridine diphosphate GlcNAc (UDP-GlcNAc) explain the mechanism of altered RboP glycosylation and form a template for targeted inhibition of TarP. Our study reveals an immune evasion strategy of S. aureus based on averting the immunogenicity of its dominant glycoantigen WTA. These results will help with the identification of invariant S. aureus vaccine antigens and may enable the development of TarP inhibitors as a new strategy for rendering MRSA susceptible to human host defences.

Deciphering the Chemical Language of the Immunomodulatory Properties of Veillonella parvula Lipopolysaccharide.

Veillonella parvula, prototypical member of the oral and gut microbiota, is at times commensal yet also potentially pathogenic. The definition of the molecular basis tailoring this contrasting behavior is key for broadening our understanding of the microbiota-driven pathogenic and/or tolerogenic mechanisms that take place within our body. In this study, we focused on the chemistry of the main constituent of the outer membrane of V. parvula, the lipopolysaccharide (LPS). LPS molecules indeed elicit pro-inflammatory and immunomodulatory responses depending on their chemical structures. Herein we report the structural elucidation of the LPS from two strains of V. parvula and show important and unprecedented differences in both the lipid and carbohydrate moieties, including the identification of a novel galactofuranose and mannitol-containing O-antigen repeating unit for one of the two strains. Furthermore, by harnessing computational studies, in vitro human cell models, as well as lectin binding solid-phase assays, we discovered that the two chemically diverse LPS immunologically behave differently and have attempted to identify the molecular determinant(s) governing this phenomenon. Whereas pro-inflammatory potential has been evidenced for the lipid A moiety, by contrast a plausible "immune modulating" action has been proposed for the peculiar O-antigen portion.

Computational toolbox for the analysis of protein-glycan interactions.

Protein-glycan interactions play pivotal roles in numerous biological processes, ranging from cellular recognition to immune response modulation. Understanding the intricate details of these interactions is crucial for deciphering the molecular mechanisms underlying various physiological and pathological conditions. Computational techniques have emerged as powerful tools that can help in drawing, building and visualising complex biomolecules and provide insights into their dynamic behaviour at atomic and molecular levels. This review provides an overview of the main computational tools useful for studying biomolecular systems, particularly glycans, both in free state and in complex with proteins, also with reference to the principles, methodologies, and applications of all-atom molecular dynamics simulations. Herein, we focused on the programs that are generally employed for preparing protein and glycan input files to execute molecular dynamics simulations and analyse the corresponding results. The presented computational toolbox represents a valuable resource for researchers studying protein-glycan interactions and incorporates advanced computational methods for building, visualising and predicting protein/glycan structures, modelling protein-ligand complexes, and analyse MD outcomes. Moreover, selected case studies have been reported to highlight the importance of computational tools in studying protein-glycan systems, revealing the capability of these tools to provide valuable insights into the binding kinetics, energetics, and structural determinants that govern specific molecular interactions.

Pushing the Boundaries of Structural Heterogeneity with the Lipid A of Marine Bacteria Cellulophaga.

Marine bacteria, which are often described as chemical gold, are considered an exceptional source of new therapeutics. Considerable research interest has been given to lipopolysaccharides (LPSs), the main components of the Gram-negative outer membrane. LPS and its lipid A portion from marine bacteria are known to exhibit a tricky chemistry that has been often associated with intriguing properties such as behaving as immune adjuvants or anti-sepsis molecules. In this scenario, we report the structural determination of the lipid A from three marine bacteria within the Cellulophaga genus, which showed to produce an extremely heterogenous blend of tetra- to hexa-acylated lipid A species, mostly carrying one phosphate and one D-mannose on the glucosamine disaccharide backbone. The ability of the three LPSs in activating TLR4 signaling revealed a weaker immunopotential by C. baltica NNO 15840T and C. tyrosinoxydans EM41T , while C. algicola ACAM 630T behaved as a more potent TLR4 activator.

Synthesis of Unprecedented α/ß-Alternate (1→4)-Glucans via Stereoselective Iterative Glycosylation.

Glucans are major biomaterials on the earth, with α-(1→4)-glucans (i. e., amylose) and ß-(1→4)-glucans (i. e., cellulose) being the most abundant ones, which are relevant to energy storage and structural function, respectively. Interestingly, (1→4)-glucans with alternate α/ß-linkages, namely herewith amycellulose, have never been disclosed in nature. Here we report a robust glycosylation protocol for the stereoselective construction of the 1,2-cis-α- and 1,2-trans-ß-glucosidic linkages, which employs an optimal combination of glycosyl N-phenyltrifluoroacetimidates as donors, TMSNTf2 as promoter, CH2 Cl2 /nitrile or CH2 Cl2 /THF as solvents. A broad substrate scope has been demonstrated by coupling five imidate donors with eight glycosyl acceptors, in which most of the glycosylations lead to high yield and exclusively 1,2-cis-α- or 1,2-trans-ß-selectivity. Applying this glycosylation protocol and with an iterative manner, the unprecedented α/ß-alternate (1→4)-glucans up to a 16-mer have been synthesized. Differently from amylose, that adopts a compact helicoidal arrangement, the synthetic amycellulose features an extended ribbon-like conformation, comparable to the extended shape of cellulose.

Absence of gut microbiota reduces neonatal survival and exacerbates liver disease in Cyp2c70-deficient mice with a human-like bile acid composition.

Mice with deletion of Cyp2c70 have a human-like bile acid composition, display age- and sex-dependent signs of hepatobiliary disease and can be used as a model to study interactions between bile acids and the gut microbiota in cholestatic liver disease. In the present study, we rederived Cyp2c70-/- mice as germ-free (GF) and colonized them with a human or a mouse microbiota to investigate whether the presence of a microbiota can be protective in cholangiopathic liver disease associated with Cyp2c70-deficiency. GF Cyp2c70-/- mice showed reduced neonatal survival, liver fibrosis, and distinct cholangiocyte proliferation. Colonization of germ-free breeding pairs with a human or a mouse microbiota normalized neonatal survival of the offspring, and particularly colonization with mouse microbiota from a conventionally raised mouse improved the liver phenotype at 6-10 weeks of age. The improved liver phenotype in conventionalized (CD) Cyp2c70-/- mice was associated with increased levels of tauro-ursodeoxycholic acid (TUDCA) and UDCA, resulting in a more hydrophilic bile acid profile compared with GF and humanized Cyp2c70-/- mice. The hydrophobicity index of biliary bile acids of CD Cyp2c70-/- mice was associated with changes in gut microbiota, liver weight, liver transaminases, and liver fibrosis. Hence, our results indicate that neonatal survival of Cyp2c70-/- mice seems to depend on the establishment of a gut microbiota at birth, and the improved liver phenotype in CD Cyp2c70-/- mice may be mediated by a larger proportion of TUDCA/UDCA in the circulating bile acid pool and/or by the presence of specific bacteria.

Chlorovirus PBCV-1 protein A064R has three of the transferase activities necessary to synthesize its capsid protein N-linked glycans.

Paramecium bursaria chlorella virus-1 (PBCV-1) is a large double-stranded DNA (dsDNA) virus that infects the unicellular green alga Chlorella variabilis NC64A. Unlike many other viruses, PBCV-1 encodes most, if not all, of the enzymes involved in the synthesis of the glycans attached to its major capsid protein. Importantly, these glycans differ from those reported from the three domains of life in terms of structure and asparagine location in the sequon of the protein. Previous data collected from 20 PBCV-1 spontaneous mutants (or antigenic variants) suggested that the a064r gene encodes a glycosyltransferase (GT) with three domains, each with a different function. Here, we demonstrate that: domain 1 is a ß-l-rhamnosyltransferase; domain 2 is an α-l-rhamnosyltransferase resembling only bacterial proteins of unknown function, and domain 3 is a methyltransferase that methylates the C-2 hydroxyl group of the terminal α-l-rhamnose (Rha) unit. We also establish that methylation of the C-3 hydroxyl group of the terminal α-l-Rha is achieved by another virus-encoded protein A061L, which requires an O-2 methylated substrate. This study, thus, identifies two of the glycosyltransferase activities involved in the synthesis of the N-glycan of the viral major capsid protein in PBCV-1 and establishes that a single protein A064R possesses the three activities needed to synthetize the 2-OMe-α-l-Rha-(1→2)-ß-l-Rha fragment. Remarkably, this fragment can be attached to any xylose unit.

Structural Determination and Chemical Synthesis of the N-Glycan from the Hyperthermophilic Archaeon Thermococcus kodakarensis.

Asparagine-linked protein glycosylations (N-glycosylations) are one of the most abundant post-translational modifications and are essential for various biological phenomena. Herein, we describe the isolation, structural determination, and chemical synthesis of the N-glycan from the hyperthermophilic archaeon Thermococcus kodakarensis. The N-glycan from the organism possesses a unique structure including myo-inositol, which has not been found in previously characterized N-glycans. In this structure, myo-inositol is highly glycosylated and linked with a disaccharide unit through a phosphodiester. The straightforward synthesis of this glycan was accomplished through diastereoselective phosphorylation and phosphodiester construction by SN 2 coupling. Considering the early divergence of hyperthermophilic organisms in evolution, this study can be expected to open the door to approaching the primitive function of glycan modification at the molecular level.

Promoter-Controlled Synthesis and Conformational Analysis of Cyclic Mannosides up to a 32-mer.

Cyclodextrins are widely used as carriers of small molecules for drug delivery owing to their remarkable host properties and excellent biocompatibility. However, cyclic oligosaccharides with different sizes and shapes are limited. Cycloglycosylation of ultra-large bifunctional saccharide precursors is challenging due to the constrained conformational spaces. Herein we report a promoter-controlled cycloglycosylation approach for the synthesis of cyclic α-(1→6)-linked mannosides up to a 32-mer. Cycloglycosylation of the bifunctional thioglycosides and (Z)-ynenoates was found to be highly dependent on the promoters. In particular, a sufficient amount of a gold(I) complex played a key role in the proper preorganization of the ultra-large cyclic transition state, providing a cyclic 32-mer polymannoside, which represents the largest synthetic cyclic polysaccharide to date. NMR experiments and a computational study revealed that the cyclic 2-mer, 4-mer, 8-mer, 16-mer, and 32-mer mannosides adopted different conformational states and shapes.

N-glycans from Paramecium bursaria chlorella virus MA-1D: Re-evaluation of the oligosaccharide common core structure.

Paramecium bursaria chlorella virus MA-1D is a chlorovirus that infects Chlorella variabilis strain NC64A, a symbiont of the protozoan Paramecium bursaria. MA-1D has a 339-kb genome encoding ca. 366 proteins and 11 tRNAs. Like other chloroviruses, its major capsid protein (MCP) is decorated with N-glycans, whose structures have been solved in this work by using nuclear magnetic spectroscopy and matrix-assisted laser desorption ionization-time of flight mass spectrometry along with MS/MS experiments. This analysis identified three N-linked oligosaccharides that differ in the nonstoichiometric presence of three monosaccharides, with the largest oligosaccharide composed of eight residues organized in a highly branched fashion. The N-glycans described here share several features with those of the other chloroviruses except that they lack a distal xylose unit that was believed to be part of a conserved core region for all the chloroviruses. Examination of the MA-1D genome detected a gene with strong homology to the putative xylosyltransferase in the reference chlorovirus PBCV-1 and in virus NY-2A, albeit mutated with a premature stop codon. This discovery means that we need to reconsider the essential features of the common core glycan region in the chloroviruses.

Peptidoglycan from Akkermansia muciniphila MucT: chemical structure and immunostimulatory properties of muropeptides.

Akkermansia muciniphila is an intestinal symbiont known to improve the gut barrier function in mice and humans. Various cell envelope components have been identified to play a critical role in the immune signaling of A. muciniphila, but the chemical composition and role of peptidoglycan (PG) remained elusive. Here, we isolated PG fragments from A. muciniphila MucT (ATCC BAA-835), analyzed their composition and evaluated their immune signaling capacity. Structurally, the PG of A. muciniphila was found to be noteworthy due of the presence of some nonacetylated glucosamine residues, which presumably stems from deacetylation of N-acetylglucosamine. Some of the N-acetylmuramic acid (MurNAc) subunits were O-acetylated. The immunological assays revealed that muropeptides released from the A. muciniphila PG could both activate the intracellular NOD1 and NOD2 receptors to a comparable extent as muropeptides from Escherichia coli BW25113. These data challenge the hypothesis that non-N-acetylattion of PG can be used as a NOD-1 evasion mechanism. Our results provide new insights into the diversity of cell envelope structures of key gut microbiota members and their role in steering host-microbiome interactions.