Biology subjects

Byndloss, M. X.

Publications and source records attributed to Byndloss, M. X..

7 recordsLinked to original sources

bioRxiv2026

Aspartate aminotransferase is required for Salmonella expansion in the inflamed gut via TCA anaplerosis

Aspartate represents an important proteogenic amino acid in all living organisms. Many microorganisms can produce aspartate through various biosynthetic processes, utilizing it for energy production and as a precursor for synthesizing other biomolecules, such as amino acids and nucleotides. The enteric pathogen Salmonella Typhimurium (S. Tm) has developed mechanisms to access aspartate as a nutrient source during expansion in the inflamed gut. However, how S. Tm deals with aspartate starvation during infection remains unknown. To address this knowledge gap, we interrogated Salmonellas reliance on the bi-directional aspartate aminotransferase encoded by aspC for growth in vitro and during host colonization using murine models of Salmonella infection. AspC can interconvert aspartate and the TCA intermediate oxaloacetate and is hypothesized to support S. Tm cellular demands for aspartate during starvation or support refueling of the TCA cycle via oxaloacetate synthesis. Herein, we find that loss of aspC results in a gut-specific S. Tm colonization defect that increases with the course of infection. Importantly, aspC is dispensable for S. Tm systemic colonization in CBA/J mice. Additionally, we report that loss of aspC results in a significant growth defect during respiration of inflammation-derived electron acceptors in vitro. Interruption of oxidative TCA cycle progression via TCA enzyme deletion or supplementation with TCA intermediates (e.g., oxaloacetate) abrogates the defect observed in {Delta}aspC S. Tm in vitro. Thus, suggesting the requirement for AspC to catabolize aspartate and support the TCA cycle during respiration. Altogether, we report that AspC plays a critical role in S. Tm pathogenesis in a gut-specific manner during inflammation through supporting energy generation.

microbiology↗

bioRxiv2025

Short-term alterations in dietary amino acids override host genetic susceptibility and reveal mechanisms of Salmonella Typhimurium small intestine colonization

In addition to individual genetics, environmental factors (e.g., dietary changes) may influence host susceptibility to gastrointestinal infection through unknown mechanisms. Herein, we developed a model in which CBA/J mice, a genetically resistant strain that tolerates intestinal colonization by the enteric pathogen Salmonella Typhimurium (S. Tm), rapidly succumb to infection after exposure to a diet rich in L-amino acids (AA). In mice, S. Tm-gastroenteritis is restricted to the large intestine (cecum), limiting their use to understand S. Tm small intestine (ileum) colonization, a feature of human Salmonellosis. Surprisingly, CBA mice fed AA diet developed ileitis with enhanced S. Tm ileal colonization. Using germ-free mice and ileal-fecal slurry transplant, we found diet-mediated S. Tm ileal expansion to be microbiota-dependent. Mechanistically, S. Tm relied on Fructosyl-asparagine utilization to expand in the ileum during infection. We demonstrate how AA diet overrides host genetics by altering the gut microbiotas ability to prevent S. Tm ileal colonization.

microbiology↗

bioRxiv2023

Nitrate-mediated luminal expansion of Salmonella Typhimurium is dependent on the ER stress protein CHOP

Salmonella Typhimurium is an enteric pathogen that employs a variety of mechanisms to exploit inflammation resulting in expansion in the intestinal tract, but host factors that contribute to or counteract the luminal expansion are not well-defined. Endoplasmic reticulum (ER) stress induces inflammation and plays an important role in the pathogenesis of infectious diseases. However, little is known about the contribution of ER stress-induced inflammation during Salmonella pathogenesis. Here, we demonstrate that the ER stress markers Hspa5 and Xbp1 are induced in the colon of S. Typhimurium infected mice, but the pro-apoptotic transcription factor Ddit3, that encodes for the protein CHOP, is significantly downregulated. S. Typhimurium-infected mice deficient for CHOP displayed a significant decrease in inflammation, colonization, dissemination, and pathology compared to littermate control mice. Preceding the differences in S. Typhimurium colonization, a significant decrease in Nos2 gene and iNOS protein expression was observed. Deletion of Chop decreased the bioavailability of nitrate in the colon leading to reduced fitness advantage of wild type S. Typhimurium over a napA narZ narG mutant strain (deficient in nitrate respiration). CD11b+ myeloid cells, but not intestinal epithelial cells, produced iNOS resulting in nitrate bioavailability for S. Typhimurium to expand in the intestinal tract in a CHOP-dependent manner. Altogether our work demonstrates that the host protein CHOP facilitates iNOS expression in CD11b+ cells thereby contributing to luminal expansion of S. Typhimurium via nitrate respiration. Author SummarySalmonella Typhimurium is a gastroenteric bacterium that replicates to large numbers within the gastrointestinal (GI) tract allowing for efficient host-to-host transmission. One strategy that allows Salmonella to expand in the GI tract is via nitrate respiration that is generated during Salmonella infections. Our results presented here provide more insight into the role of the host protein CHOP in the production of nitrate and the subsequent growth of Salmonella in the GI tract. CHOP expression is regulated within the unfolded protein response (UPR), an adaptive response pathway that is activated when cells are undergoing endoplasmic reticulum (ER) stress. ER stress has been implicated in several infectious and inflammatory diseases; however, little is known about the contribution of ER stress and the UPR during Salmonella infections. Here, we demonstrate that Chop is downregulated in mice infected with S. Typhimurium, and that mice deficient for CHOP have reduced bacterial numbers in the colon, suggesting that downregulation of Chop is a host response to resist intestinal colonization by Salmonella. Our results further show that CHOP contributes to increased expression of iNOS, responsible for nitrate production, thereby increasing the bioavailability of nitrate that allows for Salmonella growth. Altogether, our research provides a better understanding of the contribution of the ER stress protein CHOP in intestinal health and disease.

microbiology↗

bioRxiv2023

Iron acquisition by a commensal bacterium modifies host nutritional immunity during Salmonella infection

During intestinal inflammation, host nutritional immunity starves microbes of essential micronutrients such as iron. Pathogens scavenge iron using siderophores, which is counteracted by the host using lipocalin-2, a protein that sequesters iron-laden siderophores, including enterobactin. Although the host and pathogens compete for iron in the presence of gut commensal bacteria, the roles of commensals in nutritional immunity involving iron remain unexplored. Here, we report that the gut commensal Bacteroides thetaiotaomicron acquires iron in the inflamed gut by utilizing siderophores produced by other bacteria including Salmonella, via a secreted siderophore-binding lipoprotein termed XusB. Notably, XusB-bound siderophores are less accessible to host sequestration by lipocalin-2 but can be "re-acquired" by Salmonella, allowing the pathogen to evade nutritional immunity. As the host and pathogen have been the focus of studies of nutritional immunity, this work adds commensal iron metabolism as a previously unrecognized mechanism modulating the interactions between pathogen and host nutritional immunity.

microbiology↗

bioRxiv2023

Turicibacterales protect mice from severe Citrobacter rodentium infection

One of the major contributors to child mortality in the world is diarrheal diseases, with an estimated 800,000 deaths per year. Many pathogens are causative agents of these illnesses, including the enteropathogenic (EPEC) or enterohemorrhagic (EHEC) forms of Escherichia coli. These bacteria are characterized by their ability to cause attaching and effacing lesions in the gut mucosa. Although much has been learned about the pathogenicity of these organisms and the immune response against them, the role of the intestinal microbiota during these infections is not well characterized. Infection of mice with E. coli requires pre-treatment with antibiotics in most mouse models, which hinders the study of the microbiota in an undisturbed environment. Using Citrobacter rodentium as a murine model for attaching and effacing bacteria, we show that C57BL/6 mice deficient in granzyme B expression are highly susceptible to severe disease caused by C. rodentium infection. Although a previous publication from our group shows that granzyme B-deficient CD4+ T cells are partially responsible for this phenotype, in this report we present data demonstrating that the microbiota, in particular members of the order Turicibacterales, have an important role in conferring resistance. Mice deficient in Turicibacter sanguinis have increased susceptibility to severe disease. However, when these mice are co-housed with resistant mice, or colonized with T. sanguinis, susceptibility to severe infection is reduced. These results clearly suggest a critical role for this commensal in the protection against entero-pathogens.

microbiology↗

bioRxiv2022

Microbiota-derived aspartate drives pathogenic Enterobacteriaceae expansion in the inflamed gut

Inflammation boosts the availability of electron acceptors in the intestinal lumen creating a favorable niche for pathogenic Enterobacteriaceae. However, the mechanisms linking intestinal inflammation-mediated changes in luminal metabolites and pathogen expansion remain unclear. Here, we show that mucosal inflammation induced by Salmonella enterica serovar Typhimurium (S. Tm) infection and chemical colitis results in increased intestinal levels of the amino acid aspartate. The S. Tm and E. coli genomes encode an aspartate ammonia-lyase (aspA) which converts aspartate into fumarate, an alternative electron acceptor. S. Tm and pathogenic E. coli used aspA-dependent fumarate respiration for growth in the murine gut only during inflammation. Such growth advantage was abolished in the gut of germ-free mice. However, mono-association of gnotobiotic mice with members of the classes Bacteroidia and Clostridia restored the benefit of aspartate utilization to the pathogens. Our findings demonstrate the role of microbiota-derived amino acids in driving respiration-dependent Enterobacteriaceae expansion during colitis.

microbiology↗

bioRxiv2021

Salmonella Typhimurium uses anaerobic respiration to overcome propionate-mediated colonization resistance

The gut microbiota benefits the host by limiting enteric pathogen expansion (colonization resistance) partially via the production of inhibitory metabolites. Propionate, a short-chain fatty acid produced by microbiota members, is proposed to mediate colonization resistance against Salmonella enterica serovar Typhimurium (S. Tm). Here, we show that S. Tm overcomes the inhibitory effects of propionate by using it as a carbon source for anaerobic respiration. We determined that propionate metabolism provides an inflammation-dependent colonization advantage to S. Tm during infection. Such benefit was abolished in the intestinal lumen of Salmonella-infected germ-free mice. Interestingly, S. Tm propionate-mediated intestinal expansion was restored when germ-free mice were monocolonized with Bacteroides thetaiotaomicron (B. theta), a prominent propionate producer in the gut, but not when mice were monocolonized with a propionate production-deficient B. theta strain. Taken together, our results reveal a novel strategy used by S. Tm to mitigate colonization resistance by metabolizing microbiota-derived propionate.

microbiology↗