Biology subjects

Behnsen, J.

Publications and source records attributed to Behnsen, J..

9 recordsLinked to original sources

bioRxiv2025

Commensal Escherichia coli colonization triggers Peyer's patch development

The gut microbiota plays a pivotal role in shaping mucosal immunity, yet the specific microbes contributing to lymphoid tissue development remain poorly defined. Here, we identify Escherichia coli, a pioneer commensal bacterium, as a key driver of naive B cell accumulation in gut Peyers patches and lamina propria via a CXCR2-dependent mechanism. We show that E. coli promotes B cell recruitment through the production of curli amyloid fibers, which signal via Toll-like receptor 2 (TLR2). Notably, this effect extends beyond the neonatal period, revealing a broader temporal window for microbial modulation of mucosal immune development. These findings reveal a previously unrecognized role for a defined gut commensal bacterium and its molecular products in orchestrating the formation of gut-associated lymphoid tissue and B cell recruitment.

microbiology↗

bioRxiv2024

PgtE protease enables virulent Salmonella to evade C3-mediated serum and neutrophil killing

Non-typhoidal Salmonella serovars, such as Salmonella enterica serovar Typhimurium (STm), are a leading cause of inflammatory diarrhea in otherwise healthy individuals. Among children, the elderly, and immunocompromised individuals, STm can spread to systemic sites and cause potentially lethal bacteremia. Phagocytic cells and the immune complement system are pivotal to preventing the dissemination of STm. PgtE, an STm outer membrane protease, has been previously described to cleave over a dozen mammalian protein substrates in vitro, including complement protein C3. However, these activities have mostly been observed with mutant, avirulent strains with a truncated O-antigen that renders bacteria sensitive to complement killing. Here, we report that virulent STm utilizes PgtE to evade complement-mediated killing in vivo. The wild-type pathogen increases pgtE expression and PgtE proteolytic function within macrophages and in macrophage-like in vitro growth conditions, concomitant with physiologic O-antigen shortening in these environments. Furthermore, we found that wild-type STms resistance to complement-mediated serum and neutrophil killing is PgtE-dependent. We propose that PgtE promotes the systemic spread of STm by acting as a second line of defense against complement when STm escapes from a macrophage.

microbiology↗

bioRxiv2024

Amino acid competition shapes Acinetobacter baumannii gut carriage

Antimicrobial resistance is an urgent threat to human health. Asymptomatic colonization is often critical for persistence of antimicrobial-resistant pathogens. Gut colonization by the antimicrobial-resistant priority pathogen Acinetobacter baumannii is associated with increased risk of clinical infection. Ecological factors shaping A. baumannii gut colonization remain unclear. Here we show that A. baumannii and other pathogenic Acinetobacter evolved to utilize the amino acid ornithine, a non- preferred carbon source. A. baumannii utilizes ornithine to compete with the resident microbiota and persist in the gut in mice. Supplemental dietary ornithine promotes long-term fecal shedding of A. baumannii. By contrast, supplementation of a preferred carbon source--monosodium glutamate (MSG)-- abolishes the requirement for A. baumannii ornithine catabolism. Additionally, we report evidence for diet promoting A. baumannii gut carriage in humans. Together, these results highlight that evolution of ornithine catabolism allows A. baumannii to compete with the microbiota in the gut, a reservoir for pathogen spread.

microbiology↗

bioRxiv2024

Commensal Yeast Promotes Salmonella Typhimurium Virulence

Enteric pathogens engage in complex interactions with the host and the resident microbiota to establish gut colonization. Although mechanistic interactions between enteric pathogens and bacterial commensals have been extensively studied, whether and how commensal fungi affect pathogenesis of enteric infections remains largely unknown. Here we show that colonization with the common human gut commensal fungus Candida albicans worsened infections with the enteric pathogen Salmonella enterica serovar Typhimurium. Presence of C. albicans in the mouse gut increased Salmonella cecum colonization and systemic dissemination. We investigated the underlying mechanism and found that Salmonella binds to C. albicans via Type 1 fimbriae and uses its Type 3 Secretion System (T3SS) to deliver effector proteins into C. albicans. A specific effector, SopB, was sufficient to manipulate C. albicans metabolism, triggering increased arginine biosynthesis in C. albicans and the release of millimolar amounts of arginine into the extracellular environment. The released arginine, in turn, induced T3SS expression in Salmonella, increasing its invasion of epithelial cells. C. albicans deficient in arginine production was unable to increase Salmonella virulence in vitro or in vivo. In addition to modulating pathogen invasion, arginine also directly influenced the host response to infection. Arginine-producing C. albicans dampened the inflammatory response during Salmonella infection, whereas C. albicans deficient in arginine production did not. Arginine supplementation in the absence of C. albicans increased the systemic spread of Salmonella and decreased the inflammatory response, phenocopying the presence of C. albicans. In summary, we identified C. albicans colonization as a susceptibility factor for disseminated Salmonella infection, and arginine as a central metabolite in the cross-kingdom interaction between fungi, bacteria, and host.

microbiology↗

bioRxiv2024

IFI207, a young and fast-evolving protein, controls retroviral replication via the STING pathway

Mammalian AIM-2-like receptor (ALR) proteins bind nucleic acids and initiate production of type I interferons or inflammasome assembly, thereby contributing to host innate immunity. In mice, the Alr locus is highly polymorphic at the sequence and copy number level and we show here, is one of the most dynamic regions of the genome. One rapidly evolving gene within this region, Ifi207, was introduced to the Mus genome by gene conversion or an unequal recombination event a few million years ago. Ifi207 has a large, distinctive repeat region that differs in sequence and length among Mus species and even closely related inbred Mus musculus strains. We show that IFI207 controls MLV infection in vivo and that it plays a role in the STING-mediated response to cGAMP, dsDNA, DMXXA and MLV. IFI207 binds to STING and inclusion of its repeat region appears to stabilize STING protein. The Alr locus and Ifi207 provide a clear example of the evolutionary innovation of gene function, possibly as a result of host-pathogen co-evolution. IMPORTANCEThe Red Queen hypothesis predicts that the arms race between pathogens and the host may accelerate evolution of both sides, and therefore cause higher diversity in virulence factors and immune-related proteins, respectively (1). The Alr gene family in mice has undergone rapid evolution in the last few million years and includes the creation of two novel members, MndaL and Ifi207. Ifi207 in particular became highly divergent, with significant genetic changes between highly related inbred mice. IFI207 protein acts in the STING pathway and contributes to anti-retroviral resistance via a novel mechanism. The data show that under the pressure of host-pathogen coevolution in a dynamic locus, gene conversion and recombination between gene family members creates new genes with novel and essential functions that play diverse roles in biological processes.

immunology↗

bioRxiv2021

Salmonella enterica serovar Typhimurium chitinases modulate the intestinal glycome and promote small intestinal invasion.

Salmonella enterica serovar Typhimurium (Salmonella) is one of the leading causes of food-borne illnesses worldwide. To colonize the gastrointestinal tract, Salmonella produces multiple virulence factors that facilitate cellular invasion. Chitinases have been recently emerging as virulence factors for various pathogenic bacterial species and the Salmonella genome contains two annotated chitinases: STM0018 (chiA) and STM0233. However, the role of these chitinases during Salmonella pathogenesis is unknown. The putative chitinase STM0233 has not been studied previously and only limited data exists on ChiA. Chitinases typically hydrolyze chitin polymers, which are absent in vertebrates. However, chiA expression was detected in infection models and purified ChiA cleaved carbohydrate subunits present on mammalian surface glycoproteins, indicating a role during pathogenesis. Here, we demonstrate that expression of chiA and STM0233 is upregulated in the mouse gut and that both chitinases facilitate epithelial cell adhesion and invasion. Salmonella lacking both chitinases showed a 70% reduction in invasion of small intestinal epithelial cells in vitro. In a gastroenteritis mouse model, chitinase-deficient Salmonella strains were also significantly attenuated in the invasion of small intestinal tissue. This reduced invasion resulted in significantly delayed Salmonella dissemination to the spleen and the liver, but chitinases were not required for systemic survival. The invasion defect of the chitinase-deficient strain was rescued by the presence of wild-type Salmonella, suggesting that chitinases are secreted. By analyzing N-linked glycans of small intestinal cells, we identified specific N-acetylglucosamine-containing glycans as potential extracellular targets of Salmonella chitinases. This analysis also revealed differential abundance of Lewis X-containing glycans that is likely a result of host cell modulation due to the detection of Salmonella chitinases. Similar glycomic changes elicited by chitinase deficient strains indicate functional redundancy of the chitinases. Overall, our results demonstrate that Salmonella chitinases contribute to intestinal adhesion and invasion through modulation of the host glycome. Author SummarySalmonella Typhimurium infection is one of the leading causes of food-borne illnesses worldwide. In order for Salmonella to effectively cause disease, it has to invade the epithelial cells lining the intestinal tract. This invasion step allows Salmonella to replicate efficiently, causing further tissue damage and inflammation. In susceptible patients, Salmonella can spread past the intestines and infect peripheral organs. It is essential to fully understand the invasion mechanism used by Salmonella to design better treatments for infection. Here, we demonstrate that the two chitinases produced by Salmonella are involved in this invasion process. We show that Salmonella chitinases interact with surface glycans of intestinal epithelial cells and promote adhesion and invasion. Using a mouse infection model, we show that Salmonella chitinases are required for the invasion of the small intestine and enhance the dissemination of Salmonella to other organs. This study reveals an additional mechanism by which Salmonella invades and causes infection.

microbiology↗

bioRxiv2021

Proteus mirabilis employs a contact-dependent killing system against competing Enterobacteriaceae

Many bacterial species encode systems for interference competition with other microorganisms. Some systems are effective without contact (e.g. through secretion of toxins), while other systems (e.g. Type VI secretion system (T6SS)) require direct contact between cells. Here, we provide the initial characterization of a novel contact-dependent competition system for Proteus mirabilis. In neonatal mice, a commensal P. mirabilis strain apparently eliminated commensal Escherichia coli. We replicated the phenotype in vitro and showed that P. mirabilis efficiently reduced viability of several Enterobacteriaceae species, but not Gram-positive species or yeast cells. Importantly, P. mirabilis strains isolated from humans also killed E. coli. Reduction of viability occurred from early stationary phase to 24h of culture and was observed in shaking liquid media as well as on solid media. Killing required contact, but was independent of T6SS, the only contact-dependent killing system described for P. mirabilis. Expression of the killing system was regulated by osmolarity and components secreted into the supernatant. Stationary phase P. mirabilis culture supernatant itself did not kill but was sufficient to induce killing in an exponentially growing co-culture. In contrast, killing was largely prevented in media with low osmolarity. In summary, we provide the initial characterization of a potentially novel interbacterial competition system encoded in P. mirabilis. IMPORTANCEThe study of bacterial competition systems has received significant attention in recent years. These systems collectively shape the composition of complex ecosystems like the mammalian gut. They are also being explored as narrow-spectrum alternatives to specifically eliminate problematic pathogenic species. However, many competition systems that effectively work in vitro do not show strong phenotypes in the gut. Our study was informed by an observation in infant mice. Further in vitro studies confirmed that P. mirabilis was able to kill several Enterobacteriaceae species. This killing system is novel for P. mirabilis and might represent a new function of a known system or even a novel system, as the observed characteristics do not fit with described contact-dependent competition systems. Competition systems are frequently present in multiple Enterobacteriaceae species. If present or transferred into a probiotic, it might be used in the future to reduce blooms of pathogenic Enterobacteriaceae associated with disease.

microbiology↗

bioRxiv2020

Siderophore-mediated zinc acquisition enhances enterobacterial colonization of the inflamed gut.

Zinc is an essential cofactor for bacterial metabolism, and many Enterobacteriaceae express the zinc transporters ZnuABC and ZupT to acquire this metal in the host. Unexpectedly, the probiotic bacterium Escherichia coli Nissle 1917 exhibited appreciable growth in zinc-limited media even when these transporters were deleted. By utilizing in vitro and in vivo studies, as well as native spray metal infusion mass spectrometry and ion identity molecular networking, we discovered that Nissle utilizes yersiniabactin as a zincophore. Indeed, yersiniabactin enables Nissle to scavenge zinc in zinc-limited media, to resist calprotectin-mediated zinc sequestration, and to thrive in the inflamed gut. Moreover, we discovered that yersiniabactins affinity for iron or zinc changes in a pH-dependent manner, with higher affinity for zinc as the pH increased. Altogether, we demonstrate that siderophore metal affinity can be influenced by the local environment and reveal a mechanism of zinc acquisition available to many commensal and pathogenic Enterobacteriaceae.

microbiology↗

bioRxiv2020

Loss of PKCα increases arterial medial calcification in a uremic mouse model of chronic kidney disease

Arterial medial calcification is an independent risk factor for mortality in chronic kidney disease. We previously reported that knock-down of PKC expression increases high phosphate-induced mineral deposition by vascular smooth muscle cells in vitro. This new study tests the hypothesis that PKC regulates uremia-induced medial calcification in vivo. Female wild-type and PKC-/- mice underwent a two-stage subtotal nephrectomy and were fed a high phosphate diet for 8 weeks. X-ray micro computed tomography demonstrated that uremia-induced medial calcification was increased in the abdominal aorta and aortic arch of PKC-/- mice compared to wild-types. Blood urea nitrogen was also increased in PKC-/- mice compared to wild-types; there was no correlation between blood urea nitrogen and calcification in PKC-/- mice. Phosphorylated SMAD2 immunostaining was detected in calcified aortic arches from uremic PKC-/- mice; the osteogenic marker Runx2 was also detected in these areas. No phosphorylated SMAD2 staining were detected in calcified arches from uremic wild-types. PKC knock-down increased TGF-{beta}1-induced SMAD2 phosphorylation in vascular smooth muscle cells in vitro, whereas the PKC activator prostratin decreased SMAD2 phosphorylation. In conclusion, loss of PKC increases uremia-induced medial calcification. The PKC/TGF-{beta} signaling axis could therefore represent a new therapeutic target for arterial medial calcification in chronic kidney disease.

cell biology↗