Biology subjects

Marteyn, B. S.

Publications and source records attributed to Marteyn, B. S..

8 recordsLinked to original sources

bioRxiv2026

SigA forms amyloid fibrils and supports the competition of Shigella with the microbiota

Shigella sonnei is an enteropathogen that causes bacillary dysentery. During the first step of its virulence cycle, it must outcompete the resident microbiota to establish its own niche. Here we report that SigA, the sole SPATE (Serine Protease Autotransporter of Enterobacteriaceae) family member in S. sonnei, plays an indirect but central role in this process. A genome-wide analysis showed that the SPATE family includes SigA, Pic, SepA, and Sat. We demonstrated that SigA self-assembles into amyloid fibrils (F-SigA) independently of its protease activity. F-SigA remains associated with the S. sonnei surface in vitro and in vivo. Purified F-SigA fibrils have a diameter of 17.7 {+/-} 3.2 nm, and their amyloid organization was confirmed using specific markers and biochemical methods. F-SigA is secreted into the lumen in vivo and localizes to the surface of the colonic epithelium. We found that colicin E1 (ColE1) interacts with F-SigA amyloid fibrils, and that F-SigA-ColE1 complexes display antimicrobial activity that promotes S. sonnei competition with other bacteria. Because Pic, another Shigella SPATE, also forms amyloid fibrils, we anticipate that this virulence mechanism may be relevant across a wide range of Shigella strains and enterobacteria and may serve additional roles during the Shigella virulence cycle.

microbiology↗

bioRxiv2024

An unprecedented small RNA-riboswitch interaction controls expression of a bifunctional pump that is essential for Staphylococcus aureus infection

Maintaining manganese and iron homeostasis is critical for the human pathogen Staphylococcus aureus. To counteract metal-based host defense strategies (e.g., nutritional immunity, metal poisoning), S. aureus uses a combination of metal-sensing transcription factors and regulatory RNAs to maintain metal homeostasis. In this study, we uncovered an unprecedented interaction between a cis- and a trans-acting regulatory RNA controlling a conditionally essential gene, mntY, encoding a Mn efflux pump. This broadly conserved RNA-RNA interaction between a Fe-responsive sRNA and a Mn-sensing riboswitch allows the integration of Feand Mn-related stresses, notably encountered at the infection site, to fine-tune mntY expression. Remarkably, deletion of the mntY gene is strongly pleomorphic, causing growth defects, altering virulence factor expression, immune evasion, and survival during infection. We demonstrated that MntY is critical for the adaptation of S. aureus to both low and high Mn environments, due to its dual role in metalation of Mn-dependent exoenzymes and Mn detoxification. These findings point to MntY as a promising new therapeutic target to combat multidrug-resistant staphylococcal infections.

microbiology↗

bioRxiv2023

SPATEs promote the survival of Shigella to the plasma complement system upon hemorrhage and bacteremia

Shigella spp. are the causative agents of shigellosis, which remains a leading cause of death in children under the age of five. Shigellosis is characterized by fever and results in hemorrhagic diarrhea; in more severe cases, Shigella bacteremia has been reported. These clinical features strongly suggest that Shigella survive exposure to plasma, although this has not yet been studied at the molecular level. In this report, we confirmed in a guinea pig model of shigellosis that local hemorrhages were induced by S. flexneri 5a and S. sonnei, and we demonstrated that Shigella reached mucosal CD31+/CD34+ blood vessels during the late stages of infection and further disseminated in the bloodstream. These results confirmed the exposure of Shigella to plasma components within the hemorrhagic colonic mucosa and in the bloodstream. We demonstrated that all the tested Shigella strains survived plasma exposure in vitro, and we showed that Serine Protease Autotransporters of Enterobacteriaceae (SPATEs) are essential for Shigella dissemination within the colonic mucosa. We have confirmed that SPATEs are expressed and secreted in poorly oxygenated environments encountered by Shigella from hypoxic foci of infection to the bloodstream. We further demonstrated that SPATEs promoted Shigella survival in plasma, by cleaving complement component 3 (C3), thereby impairing complement system activation. We have shown here that the ability of Shigella to survive plasma exposure is a key factor in its virulence, both within primary foci and systemically. Significance StatementIn this study we aimed to better understand the significance of the ability of Shigella to survive plasma exposure, as we observed that non-pathogenic E. coli rapidly lysed upon exposure. Indeed, we reported that Shigella was already exposed to plasma components within the colonic mucosa, as we reported in a guinea pig model of shigellosis that hemorrhages were induced, that were associated with local diffusion of plasma components in the infected colonic mucosa. Shigella was obviously exposed to plasma during bacteremia. The ability of Shigella to survive in plasma has not been previously reported. Here we have shown, first, that Shigella was able to divide and grow in the presence of human plasma, and second, we found that SPATEs played a central role in this process by impairing with the activation of the complement system.

microbiology↗

bioRxiv2022

Neutrophils degranulate GAG-containing proteoglycofili, which block Shigella growth and degrade virulence factors

Summary paragraphNeutrophil degranulation plays a central role in their ability to kill pathogens but also to stimulate other immune cells1-3. Here we show that neutrophil degranulation, induced in hypoxia or upon Shigella infection in vitro and in vivo, leads to the release of polymers called neutrophil Proteoglycofili (PGF). PGF are mainly composed of granular proteins (myeloperoxidase, elastase, lactoferrin, cathelicidin, albumin) pre-stored in various types of granules, and chondroitin sulfate. PGF individual fibers have a diameter of 43.9 {+/-} 20.3 nm and. They secreted by viable neutrophils and do not contain DNA, as opposed to NETs which contains also granular proteins, chondroitin sulfate in addition to chromatin, released upon neutrophil disintegration and cell death. We demonstrated that PGF block the growth of Shigella and other bacteria and degrade Shigella virulence factors. The degradation of the chondroitin sulfate polymers with testes hyaluronidases destabilizes PGF ultrastructure and abolishes its antimicrobial activity. Our results provide novel insights in the neutrophil degranulation process and open new doors for the investigation of PGF contribution to cytokines concentration gradient formation and adaptive immune cells activation. Further investigations are required to better appreciate the importance of this "sterile blaster" in infectious or inflammatory diseases.

immunology↗

bioRxiv2020

Preventing neutrophil from oxygen exposure allows their basal state maintenance

Neutrophils are the most abundant circulating white blood cells and are central players of the innate immune response. During their lifecycle, neutrophils mainly evolve under low oxygen conditions (0.1 - 4% O2) to which they are well adapted. Neutrophils are atypical cells since they are mainly glycolytic, and highly susceptible to oxygen-exposure, which induces their activation and death, through mechanisms which remain currently elusive. Nevertheless, nearly all studies conducted on neutrophils are carried out under atmospheric oxygen (21%), corresponding to hyperoxic conditions. Here we investigated the impact of hyperoxia during neutrophil purification and culture on neutrophil viability, activation and cytosolic protein content. Neutrophil hyper-activation (CD62L shedding) is induced during culture under hyperoxic conditions (24h), compared to neutrophils cultured under anoxic conditions. In addition, we show that maintaining neutrophils in autologous plasma is the most suitable strategy to maintain their basal state. Our results show that manipulating neutrophils under hyperoxic conditions leads to the loss of ~100 cytosolic proteins during purification, while it does not lead to an immediate impact on neutrophils activation (CD11bhigh, CD54high, CD62Llow) or viability (DAPI+). We identified two clusters of proteins belonging to the cholesterol metabolism and to the complement and coagulation cascade pathways, which are highly susceptible to neutrophil oxygen-exposure during their purification. In conclusion, preserving neutrophil from oxygen-exposure during their manipulation - purification and culture- is recommended to avoid their experimental activation and for preserving a large set of cytosolic proteins from alteration.

immunology↗

bioRxiv2020

The ascorbate-deficient guinea pig model of shigellosis allows the study of the entire Shigella life cycle

Shigella spp. are the causative agents of bacillary dysentery or shigellosis, mainly in children living in developing countries. The study of Shigella entire life cycle in vivo and the evaluation of vaccine candidates protection efficacy have been hampered by the lack of a suitable animal model of infection (1). None of the ones evaluated so far (mouse, rabbit, guinea pig) allows to recapitulate shigellosis symptoms upon Shigella oral challenge. Historical reports suggest that dysentery and scurvy are both metabolic diseases associated with ascorbate-deficiency. Mammals which are susceptible to Shigella infection (humans, non-human primates and guinea pigs) are the lonely ones which are unable to synthesize ascorbate. We optimized a low-ascorbate diet to induce moderate ascorbate-deficiency but not scurvy in guinea pigs (Ascplasma conc.=1.6 M vs 36 M with optimal ascorbate supply). We demonstrated that moderate ascorbate-deficiency increases shigellosis severity during extended period of time (up to 48h) with all strains tested (Shigella flexneri 5a and 2a, Shigella sonnei). At late time-points, a massive influx of neutrophils was observed both within the disrupted colonic mucosa and in the luminal compartment, although Shigella remains able to disseminate deep into the organ to reach the sub-mucosal layer and the bloodstream. This new model of shigellosis opens new doors for the study both of Shigella infection strategy and innate and adaptive immune responses to Shigella infection. It may be also of a great interest to study the virulence of other pathogen for which no suitable animal model of infection is available (Vibrio cholerae, Yersinia pestis, Mycobacterium tuberculosis or Campylobacter jejuni, among others). SignificanceThe study of Shigella virulence cycle in vivo has been hampered by the lack of a suitable animal model, which would allow the colonic mucosa infection upon oral challenge. Based on historical reports and physiological aspects, it was suggested that ascorbate-deficiency may stand as a new dysentery risk-factor. To test this hypothesis, we set up a new ascorbate-deficient guinea pig model and demonstrated for the first time that the Shigella infectious process occurred for extended period of time (up to 48h) and demonstrated that shigellosis severity was higher in ascorbate-deficient animal. Ascorbate-deficient guinea pig model of infection may be used to assess the virulence of other pathogens for which no suitable animal model of infection is still lacking.

microbiology↗

bioRxiv2020

IlvY is an important regulator of Shigella infection in vitro and in vivo

Shigellosis results from oral ingestion of the Gram-negative bacteria Shigella, and symptoms include severe diarrhea and dysentery. In the absence of vaccines, small molecule antibacterial drugs have provided treatment options for shigellosis. However, Shigella drug resistance is rapidly emerging, and Shigella strains with resistance to both third-generation cephalosporins and azithromycin have been identified in Asia. A re-conceptualization is needed regarding the development of therapeutics that target bacterial pathogens in order to reduce resistance development and alteration of gut microbiota, which is depleted upon treatment with wide spectrum antibiotics, thereby increasing susceptibility to subsequent enteric infections. A more organism-specific approach is to develop agents targeting virulence factors such as toxins, adhesins, invasins, quorum sensing, and protein secretion systems. For Shigella, there is interest in targeting transcription factors essential for Shigella infection in vivo rather than specific effectors. Here we describe the importance of the Shigella transcription factor IlvY in Shigella virulence in vitro and in vivo. This work included the development of a novel, oral mouse model of Shigella infection with wild-type adult mice. Unlike previous models, mice do not require antibiotic pretreatment or diet modifications. This mouse model was used to demonstrate the importance of IlvY for Shigella in vivo survival and that deletion of ilvY impacts host responses to infection. These results illustrate that IlvY is a potential therapeutic target for the treatment of shigellosis. In addition, the novel mouse model provides an exciting new opportunity to investigate therapeutic efficacy against Shigella infection and host responses to infection.

microbiology↗

bioRxiv2020

Ascorbate maintains a low plasma low oxygen level

In human blood, oxygen is mainly transported by red blood cells. Accordingly, the oxygen level in plasma is expected to be limited, although it has not been quantified yet. Here, by developing dedicated methods and tools, we determined that human plasma pO2 = 8.4 mmHg (1.2% O2). Oxygen solubility in plasma was believed to be similar to water. Here we reveal that plasma has an additional ascorbate-dependent oxygen-reduction activity. Plasma oxygenation oxidizes ascorbate (49.5 M in fresh plasma vs <2 M in oxidized plasma) and abolishes this capacity, which is restored by ascorbate supplementation. We confirmed these results in vivo, showing that the plasma pO2 is significantly higher in ascorbate-deficient guinea pigs (plasma ascorbate < 2M), compared to control (plasma ascorbate > 15M). Plasma low oxygen level preserves the integrity of oxidation-sensitive components such as ubiquinol. Circulating leucocytes are well adapted to these conditions, since the abundance of their mitochondrial network is limited. These results shed a new light on the importance of oxygen exposure on leucocyte biological study, in regards with the reducing conditions they encounter in vivo; but also on the manipulation of blood products to improve their integrity and potentially improve transfusions efficacy. Key points

immunology↗