The type III secretion injectisome

The crystal structure of the toxin EspC from enteropathogenic Escherichia coli reveals the mechanism that governs host cell entry and cytotoxicity

Enteropathogenic E. coli (EPEC) is a significant cause of diarrhea, leading to high infant mortality rates. A key toxin produced by EPEC is the EspC autotransporter, which is regulated alongside genes from the locus of enterocyte effacement (LEE), which collectively result in the characteristic attaching and effacing lesions on the intestinal epithelium. In this study, we present the crystal structure of the EspC passenger domain (αEspC) revealing a toxin comprised a serine protease attached to a large β-helix with additional subdomains. Using various modified EspC expression constructs, alongside type III secretion system-mediated cell internalization assays, we dissect how the αEspC structural features enable toxin entry into the intestinal epithelium to cause cell cytotoxicity.

Evaluating the protective effects of Aurodox in a murine model of Shiga toxin-producing Escherichia coli

Shiga Toxin-Producing E. coli (STEC) are a group of acute small intestine pathogens responsible for foodborne outbreaks of bloody diarrhoea. The expression of Shiga toxins (Stx) carried by STEC can initiate Haemolytic Uremic Syndrome (HUS), a major cause of acute renal failure in children. Here, we investigate the anti-virulence potential of Aurodox - a natural product of Streptomyces goldiniensis. Previously, we have shown that Aurodox downregulates the expression of the T3SS, inhibiting epithelial cell colonisation in vitro. Here, we use the Citrobacter rodentium DBS770 (Cr Stx2dact) model of STEC infection to demonstrate that Aurodox protects mice against Citrobacter rodentium-associated colonic hyperplasia and Stx-mediated renal injury. Given antibiotic-associated dysbiosis of the gut is associated with inflammation and the emergence of opportunistic pathogens, we examined the effect of Aurodox on the faecal bacteriome. We show that although the microbial community is altered following Aurodox treatment, changes are distinct from those associated with traditional antibiotic therapies.

Not just passengers: effectors contribute to the assembly of the type VI secretion system as structural building blocks

Protein secretion systems are critical macromolecular machines employed by bacteria to interact with diverse environments and hosts during their life cycle. Cytosolically produced protein effectors are translocated across at least one membrane to the outside of the cells or directly into target cells. In most secretion systems, these effectors are mere passengers in unfolded or folded states. However, the type VI secretion system (T6SS) stands out as a powerful contractile device that requires some of its effectors as structural components. This review aims to provide an updated view of the diverse functions of effectors, especially focusing on their roles in T6SS assembly, the implications for T6SS engineering, and the potential of recently developed T6SS models to study effector-T6SS association.

Salmonella Typhimurium persistently infects host via its effector SseJ-induced PHB2-mediated mitophagy

Despite decades of research on effective methods to resist Salmonella enterica serovar Typhimurium (S. Typhimurium) pathogenicity, the mechanisms of S. Typhimurium-host interactions have not been fully determined. S. Typhimurium is characterized as an important zoonosis in public health worldwide because of its endemicity, high morbidity, and difficulty in applying control and prevention measures. Herein, we introduce a novel bacterial factor, secretion system effector J (SseJ), and its interactive host protein, PHB2 (prohibitin 2). We explored whether SseJ affected S. Typhimurium replication and survival in the host. S. Typhimurium infection caused severe mitochondrial damage and mitophagy, which facilitated S. Typhimurium proliferation in cells. S. Typhimurium SseJ activated the PINK1 (PTEN induced kinase 1)-PRKN (parkin RBR E3 ubiquitin protein ligase)-autophagosome-dependent mitophagy pathway, aided by the mitophagy receptor PHB2, for bacterial survival and persistent infection. Moreover, suppression of mitophagy alleviated the pathogenicity of S. Typhimurium. In conclusion, S. Typhimurium infection could be antagonized by targeting the SseJ-PHB2-mediated host mitochondrial autophagy pathway.Abbreviation: ACTB: actin beta; BafA1: bafilomycin A1; CCCP: carbonyl cyanide m-chlorophenyl hydrazone; co-IP: co-immunoprecipitation; CFU: colony-forming units; COX4/COXIV: cytochrome c oxidase subunit 4; CQ: chloroquine; hpi: h post-bacterial infection; MAP1LC3B/LC3B: microtubule associated protein 1 light chain 3 beta; Mdivi-1:mitophagy inhibitor mitochondrial division inhibitor 1; MFN2: mitofusin 2; MG132: z-leu-leu-leucinal; MOI: multiplicity of infection; mtDNA: mitochondrial DNA; PBS: phosphate-buffered saline; PGAM5: PGAM family member 5, mitochondrial serine/threonine protein phosphatase; PHB2: prohibitin 2; PINK1: PTEN induced kinase 1; qPCR: quantitative real-time reverse transcription PCR; Roc-A: Rocaglamide A; PRKN/Parkin: parkin RBR E3 ubiquitin protein ligase; SCVs: Salmonella-containing vacuoles; siRNA: small interfering RNA; SPI-2: Salmonella pathogenicity island 2; SseJ: secretion system effector J; S. Typhimurium: Salmonella enterica serovar Typhimurium; S.T-ΔSseJ: SseJ gene-deleted Salmonella Typhimurium strains; S.T-CΔSseJ: SseJ-complemented Salmonella Typhimurium strains; WT: wild-type.

YmoA functions as a molecular stress sensor in Yersinia

Pathogenic bacteria sense and respond to environmental fluctuations, a capability essential for establishing successful infections. The YmoA/Hha protein family are conserved transcription regulators in Enterobacteriaceae, playing a critical role in these responses. Specifically, YmoA in Yersinia adjusts the expression of virulence-associated traits upon temperature shift. Still, the molecular mechanisms transducing environmental signals through YmoA remain elusive. Our study employs nuclear magnetic resonance spectroscopy, biological assays and RNA-seq analysis to elucidate these mechanisms. We demonstrate that YmoA undergoes structural fluctuations and conformational dynamics in response to temperature and osmolarity changes, correlating with changes in plasmid copy number, bacterial fitness and virulence function. Notably, chemical shift analysis identifies key roles of a few specific residues and of the C-terminus region in sensing both temperature and salt-driven switch. These findings demonstrate that YmoA acts as a central stress sensor in Yersinia, fine-tuning virulence gene expression and balancing metabolic trade-offs.

Lawsonia intracellularis T3SS effector LI0758, an Rce1 ortholog, activates MAPK and NF-κB signaling in mammalian cells

Lawsonia intracellularis, a Gram-negative obligate intracellular bacterium causing porcine proliferative enteropathy, possesses a type III secretion system (T3SS), yet only a handful of its substrates have been experimentally characterized. In this study, we identify that LI0758 can be secreted by the Yersinia T3SS, which suppresses yeast growth and activates mitogen-activated protein kinase (MAPK) and nuclear factor-kappa B (NF-κB) signaling pathway in mammalian cells. Bioinformatics analyses indicate that LI0758 is an ortholog of Rce1, a eukaryotic CAAX protein endoprotease, sharing a similar subcellular localization on the endoplasmic reticulum (ER). While displaying unique activity in the yeast a-factor reporter system, LI0758 restores Ras2 localization in Rce1Δ mutant strains, implying functional similarity. Our findings underscore LI0758's pivotal role in activating MAPK pathways and suggest its potential to modulate the localization and function of host CAAX proteins. Further investigation holds promise for elucidating novel bacteria-host interaction mechanisms and fostering the development of innovative therapies against proliferative enteritis.

Sulforaphane Is Not Only a Food Supplement: It Diminishes the Intracellular Survival and Colonization of Salmonella enterica

Sulforaphane is a main bioactive component in several edible cruciferous vegetables. It acquires several benefits to health in addition to its considered antibacterial and antivirulence activities. Herein, we aimed at evaluating the antivirulence activity of sulforaphane against the worldwide clinically important enteric pathogen Salmonella enterica serovar Typhimurium. The influence of sulforaphane on bacterial adhesion, invasion, biofilm formation, and intracellular replication was assayed. Additionally, the effect of sulforaphane on the type III secretion system (TTSS) in S. enterica was quantified. The outcome of the combination with different antibiotics was assessed, and an in vivo protection assay was conducted to assess the influence on S. enterica pathogenesis. The results showed the significant antibiofilm activity of sulforaphane at subinhibitory effect in addition to its significant reduction in bacterial invasion and intracellular replication inside the host cells. The in vivo findings emphasized the decreased capacity of S. enterica to induce pathogenesis in the presence of sulforaphane. Our finding attributed these antivirulence activities to the interference of sulforaphane with TTSS-type II and the downregulation of its encoding genes. In a nutshell, the edible cruciferous vegetable bioactive sulforaphane is a safe adjunct therapy that can be administrated alongside traditional antibiotics for treating clinically significant enteric pathogens as S. enterica.

Light-Controlled Secretion and Injection of Proteins into Eukaryotic Cells by Optogenetic Control of the Bacterial Type III Secretion System

Gram-negative bacteria can use the type III secretion system (T3SS) to inject effector proteins into eukaryotic target cells. In this chapter, we describe the application of a light-controlled T3SS, based on the targeted sequestration of an essential dynamic T3SS component with the help of optogenetic interaction switches. This method enables to control the secretion or injection into eukaryotic cells for a wide range of protein cargos with high temporal and spatial precision.

Characterization of tailocins of Pragia fontium 24613 and the tailocin loci within the family Budviciaceae

Tailocins are nano-scale phage tail-like protein complexes that can mediate antagonistic interactions between closely related bacterial species. While the capacity to produce R-type tailocin was found widely across Gammaproteobacteria, the production of F-type tailocins seems comparatively rare. In this study, we examined the freshwater isolate, Pragia fontium 24613, which can produce both R- and F-type tailocins. We investigated their inhibition spectrum, focusing on clinically relevant enterobacteria, and identified the associated tailocin gene cluster. Transmission electron microscopy confirmed that inactivation of the tape measure protein within the tailocin cluster disrupted R-tailocin production. Comparative analysis of Budviciaceae gene clusters showed high conservation of R-type tailocin genes, whereas F-type tailocin genes were found in only a few species, with little conservation. Our findings indicate a high prevalence of bacteriocin production among underexplored Enterobacteriales species. Detected tailocins showed potential as antimicrobials targeting clinically significant pathogens.

The big chill: Growth of in situ structural biology with cryo-electron tomography

In situ structural biology with cryo-electron tomography (cryo-ET) and subtomogram averaging (StA) is evolving as a major method to understand the structure, function, and interactions of biological molecules in cells in a single experiment. Since its inception, the method has matured with some stellar highlights and with further opportunities to broaden its applications. In this short review, I want to provide a personal perspective on the developments in cryo-ET as I have seen it for the last ~20 years and outline the major steps that led to its success. This perspective highlights cryo-ET with my eyes as a junior researcher and my view on the present and past developments in hardware and software for in situ structural biology with cryo-ET.

Genomic Insight into Zoonotic and Environmental Vibrio vulnificus: Strains with T3SS2 as a Novel Threat to Public Health

Vibrio vulnificus is a significant opportunistic pathogen with the highest fatality rate among foodborne microbes. However, due to a lack of comprehensive surveillance, the characteristics of isolates in China remain poorly understood. This study analyzed 60 strains of V. vulnificus isolated from diverse sources in Shanghai, including shellfish, crabs, shrimps, throat swabs of migratory birds, as well as seafood farming water and seawater. Identification of the genotypes was performed using PCR, and cytotoxicity was determined using an LDH assay. DNA was sequenced using Illumina NovaSeq followed by a bioinformatic analysis. The results demonstrated that a majority of the strains belonged to the 16S rRNA B-vcgC genotype. All strains carried five antibiotic resistance genes (ARGs), with some strains carrying over ten ARGs, mediating resistance to multiple antibiotics. Five strains possessed a highly abundant effector delivery system, which further investigations revealed to be a type III secretion system II (T3SS2), marking the first description of T3SS2 in V. vulnificus. Phylogenetic analysis indicated that it belonged to a different genetic lineage from T3SS2α and T3SS2β of V. parahaemolyticus. Bacteria with T3SS2 sequences were concentrated in coastal areas and mostly within the genus Vibrio in the global prevalence survey. Our study provides essential baseline information for non-clinical V. vulnificus and discovers the existence of T3SS2 in several strains which may be more virulent, thereby posing a new threat to human health.

The polyadenylase PAPI is required for virulence plasmid maintenance in pathogenic bacteria

Many species of pathogenic bacteria harbor critical plasmid-encoded virulence factors, and yet the regulation of plasmid replication is often poorly understood despite playing a critical role in plasmid-encoded gene expression. Human pathogenic Yersinia, including the plague agent Y. pestis and its close relative Y. pseudotuberculosis, require the type III secretion system (T3SS) virulence factor to subvert host defense mechanisms and colonize host tissues. The Yersinia T3SS is encoded on the IncFII plasmid for Y ersinia virulence (pYV). Several layers of gene regulation enables a large increase in expression of Yersinia T3SS genes at mammalian body temperature. Surprisingly, T3SS expression is also controlled at the level of gene dosage. The number of pYV molecules relative to the number of chromosomes per cell, referred to as plasmid copy number, increases with temperature. The ability to increase and maintain elevated pYV plasmid copy number, and therefore T3SS gene dosage, at 37°C is important for Yersinia virulence. In addition, pYV is highly stable in Yersinia at all temperatures, despite being dispensable for growth outside the host. Yet how Yersinia reinforces elevated plasmid replication and plasmid stability remains unclear. In this study, we show that the chromosomal gene pcnB encoding the polyadenylase PAP I is required for regulation of pYV plasmid copy number (PCN), maintenance of pYV in the bacterial population outside the host, robust T3SS activity, and Yersinia virulence in a mouse infection model. Likewise, pcnB/PAP I is also required for robust expression of the Shigella flexneri virulence plasmid-encoded T3SS. Furthermore, Yersinia and Shigella pcnB/PAP I is required for maintaining normal PCN of model antimicrobial resistance (AMR) plasmids whose replication is regulated by sRNA, thereby increasing antibiotic resistance by ten-fold. These data suggest that pcnB/PAP I contributes to the spread and stabilization of virulence and AMR plasmids in bacterial pathogens, and is essential in maintaining the gene dosage required to mediate plasmid-encoded traits. Importantly pcnB/PAP I has been bioinformatically identified in many species of bacteria despite being studied in only a few species to date. Our work highlights the potential importance of pcnB/PAP I in antibiotic resistance, and shows for the first time that pcnB/PAP I reinforces PCN and virulence plasmid stability in natural pathogenic hosts with a direct impact on bacterial virulence.

Intestinal Lymphatic Biology, Drug Delivery, and Therapeutics: Current Status and Future Directions

Historically, the intestinal lymphatics were considered passive conduits for fluids, immune cells, dietary lipids, lipid soluble vitamins, and lipophilic drugs. Studies of intestinal lymphatic drug delivery in the late 20th century focused primarily on the drugs' physicochemical properties, especially high lipophilicity, that resulted in intestinal lymphatic transport. More recent discoveries have changed our traditional view by demonstrating that the lymphatics are active, plastic, and tissue-specific players in a range of biological and pathological processes, including within the intestine. These findings have, in turn, inspired exploration of lymph-specific therapies for a range of diseases, as well as the development of more sophisticated strategies to actively deliver drugs or vaccines to the intestinal lymph, including a range of nanotechnologies, lipid prodrugs, and lipid-conjugated materials that "hitchhike" onto lymphatic transport pathways. With the increasing development of novel therapeutics such as biologics, there has been interest in whether these therapeutics are absorbed and transported through intestinal lymph after oral administration. Here we review the current state of understanding of the anatomy and physiology of the gastrointestinal lymphatic system in health and disease, with a focus on aspects relevant to drug delivery. We summarize the current state-of-the-art approaches to deliver drugs and quantify their uptake into the intestinal lymphatic system. Finally, and excitingly, we discuss recent examples of significant pharmacokinetic and therapeutic benefits achieved via intestinal lymphatic drug delivery. We also propose approaches to advance the development and clinical application of intestinal lymphatic delivery strategies in the future. SIGNIFICANCE STATEMENT: This comprehensive review details the understanding of the anatomy and physiology of the intestinal lymphatic system in health and disease, with a focus on aspects relevant to drug delivery. It highlights current state-of-the-art approaches to deliver drugs to the intestinal lymphatics and the shift toward the use of these strategies to achieve pharmacokinetic and therapeutic benefits for patients.

Cold-water coral mortality under ocean warming is associated with pathogenic bacteria

Cold-water corals form vast reefs that are highly valuable habitats for diverse deep-sea communities. However, as the deep ocean is warming, it is essential to assess the resilience of cold-water corals to future conditions. The effects of elevated temperatures on the cold-water coral Lophelia pertusa (now named Desmophyllum pertusum) from the north-east Atlantic Ocean were experimentally investigated at the holobiont level, the coral host, and its microbiome. We show that at temperature increases of + 3 and + 5 °C, L. pertusa exhibits significant mortality concomitant with changes in its microbiome composition. In addition, a metagenomic approach revealed the presence of gene markers for bacterial virulence factors suggesting that coral death was due to infection by pathogenic bacteria. Interestingly, different coral colonies had different survival rates and, colony-specific microbiome signatures, indicating strong colony-specific variability in their response to warming waters. These results suggest that L. pertusa can only survive a long-term temperature increase of < 3 °C. Therefore, regional variations in deep-sea temperature increase should be considered in future estimates of the global distribution of cold-water corals.

Unravelling the Roles of Bacterial Nanomachines Bistability in Pathogens' Life Cycle

Bacterial nanomachines represent remarkable feats of evolutionary engineering, showcasing intricate molecular mechanisms that enable bacteria to perform a diverse array of functions essential to persist, thrive, and evolve within ecological and pathological niches. Injectosomes and bacterial flagella represent two categories of bacterial nanomachines that have been particularly well studied both at the molecular and functional levels. Among the diverse functionalities of these nanomachines, bistability emerges as a fascinating phenomenon, underscoring their dynamic and complex regulation as well as their contribution to shaping the bacterial community behavior during the infection process. In this review, we examine two closely related bacterial nanomachines, the type 3 secretion system, and the flagellum, to explore how the bistability of molecular-scale devices shapes the bacterial eco-pathological life cycle.

RNase-mediated reprogramming of Yersinia virulence

RNA degradation is an essential process that allows bacteria to regulate gene expression and has emerged as an important mechanism for controlling virulence. However, the individual contributions of RNases in this process are mostly unknown. Here, we tested the influence of 11 potential RNases in the intestinal pathogen Yersinia pseudotuberculosis on the expression of its type III secretion system (T3SS) and associated effectors (Yops) that are encoded on the Yersinia virulence plasmid. We found that exoribonuclease PNPase and endoribonuclease RNase III inhibit T3SS and yop gene transcription by repressing the synthesis of LcrF, the master activator of Yop-T3SS. Loss of both RNases led to an increase in lcrF mRNA levels. Our work indicates that PNPase exerts its influence via YopD, which accelerates lcrF mRNA degradation. Loss of RNase III, on the other hand, results in the downregulation of the CsrB and CsrC RNAs, thereby increasing the availability of active CsrA, which has been shown previously to enhance lcrF mRNA translation and stability. This CsrA-promoted increase of lcrF mRNA translation could be supported by other factors promoting the protein translation efficiency (e.g. IF-3, RimM, RsmG) that were also found to be repressed by RNase III. Transcriptomic profiling further revealed that Ysc-T3SS-mediated Yop secretion leads to global reprogramming of the Yersinia transcriptome with a massive shift of the expression from chromosomal to virulence plasmid-encoded genes. A similar reprogramming was also observed in the RNase III-deficient mutant under non-secretion conditions. Overall, our work revealed a complex control system where RNases orchestrate the expression of the T3SS/Yop machinery on multiple levels to antagonize phagocytic uptake and elimination by innate immune cells.

A Burkholderia cenocepacia-like environmental isolate strongly inhibits the plant fungal pathogen Zymoseptoria tritici

Fungal phytopathogens cause significant reductions in agricultural yields annually, and overusing chemical fungicides for their control leads to environmental pollution and the emergence of resistant pathogens. Exploring natural isolates with strong antagonistic effects against pathogens can improve our understanding of their ecology and develop new treatments for the future. We isolated and characterized a novel bacterial strain associated with the species Burkholderia cenocepacia, termed APO9, which strongly inhibits Zymoseptoria tritici, a commercially important pathogenic fungus causing Septoria tritici blotch in wheat. Additionally, this strain exhibits inhibitory activity against four other phytopathogens. We found that physical contact plays a crucial role for APO9's antagonistic capacity. Genome sequencing of APO9 and biosynthetic gene cluster (BGC) analysis identified nine classes of BGCs and three types of secretion systems (types II, III, and IV), which may be involved in the inhibition of Z. tritici and other pathogens. To identify genes driving APO9's inhibitory activity, we screened a library containing 1,602 transposon mutants and identified five genes whose inactivation reduced inhibition efficiency. One such gene encodes for a diaminopimelate decarboxylase located in a terpenoid biosynthesis gene cluster. Phylogenetic analysis revealed that while some of these genes are also found across the Burkholderia genus, as well as in other Betaproteobacteria, the combination of these genes is unique to the Burkholderia cepacia complex. These findings suggest that the inhibitory capacity of APO9 is complex and not limited to a single mechanism, and may play a role in the interaction between various Burkholderia species and various phytopathogens within diverse plant ecosystems.

IMPORTANCE

The detrimental effects of fungal pathogens on crop yields are substantial. The overuse of chemical fungicides contributes not only to environmental pollution but also to the emergence of resistant pathogens. Investigating natural isolates with strong antagonistic effects against pathogens can improve our understanding of their ecology and develop new treatments for the future. We discovered and examined a unique bacterial strain that demonstrates significant inhibitory activity against several phytopathogens. Our research demonstrates that this strain has a wide spectrum of inhibitory actions against plant pathogens, functioning through a complex mechanism. This plays a vital role in the interactions between plant microbiota and phytopathogens.

Haemolysins are essential to the pathogenicity of deep-sea Vibrio fluvialis

Vibrio fluvialis is an emerging foodborne pathogen that produces VFH (Vibrio fluvialis hemolysin) and δVFH (delta-Vibrio fluvialis hemolysin). The function of δVFH is unclear. Currently, no pathogenic V. fluvialis from deep sea has been reported. In this work, a deep-sea V. fluvialis isolate (V13) was examined for pathogenicity. V13 was most closely related to V. fluvialis ATCC 33809, a human isolate, but possessed 262 unique genes. V13 caused lethal infection in fish and induced pyroptosis involving activation of the NLRP3 inflammasome, caspase 1 (Casp1), and gasdermin D (GSDMD). V13 defective in VFH or VFH plus δVFH exhibited significantly weakened cytotoxicity. Recombinant δVFH induced NLRP3-Casp1-GSDMD-mediated pyroptosis in a manner that depended on K+ efflux and intracellular Ca2+ accumulation. δVFH bound several plasma membrane lipids, and these bindings were crucial for δVFH cytotoxicity. Together these results provided new insights into the function of δVFH and the virulence mechanism of V. fluvialis.

Design and Synthesis of Mandelic Acid Derivatives for Suppression of Virulence via T3SS against Citrus Canker

Citrus canker, a highly contagious bacterial disease caused by Xanthomonas citri subsp. citri (Xcc), poses a substantial threat to citrus crops, leading to serious reductions in fruit yield and economic losses. Most commonly used bactericides against Xcc lead to the rapid development of resistant subpopulations. Therefore, it is imperative to create novel drugs, such as type III secretion system (T3SS) inhibitors, that specifically target bacterial virulence factors rather than bacterial viability. In our study, we designed and synthesized a series of mandelic acid derivatives including 2-mercapto-1,3,4-thiazole. Seven substances were found to reduce the level of transcription of hpa1 without affecting bacterial viability. In vivo bioassays indicated that compound F9 significantly inhibited hypersensitive response and pathogenicity. RT-qPCR assays showed that compound F9 visibly suppressed the expression of Xcc T3SS-related genes as well as citrus canker susceptibility gene CsLOB1. Furthermore, the combination with compound F9 and quorum-quenching bacteria HN-8 can also obviously alleviate canker symptoms.

Antimicrobials: An update on new strategies to diversify treatment for bacterial infections

Ninety-five years after Fleming's discovery of penicillin, a bounty of antibiotic compounds have been discovered, modified, or synthesised. Diversification of target sites, improved stability and altered activity spectra have enabled continued antibiotic efficacy, but overwhelming reliance and misuse has fuelled the global spread of antimicrobial resistance (AMR). An estimated 1.27 million deaths were attributable to antibiotic resistant bacteria in 2019, representing a major threat to modern medicine. Although antibiotics remain at the heart of strategies for treatment and control of bacterial diseases, the threat of AMR has reached catastrophic proportions urgently calling for fresh innovation. The last decade has been peppered with ground-breaking developments in genome sequencing, high throughput screening technologies and machine learning. These advances have opened new doors for bioprospecting for novel antimicrobials. They have also enabled more thorough exploration of complex and polymicrobial infections and interactions with the healthy microbiome. Using models of infection that more closely resemble the infection state in vivo, we are now beginning to measure the impacts of antimicrobial therapy on host/microbiota/pathogen interactions. However new approaches are needed for developing and standardising appropriate methods to measure efficacy of novel antimicrobial combinations in these contexts. A battery of promising new antimicrobials is now in various stages of development including co-administered inhibitors, phages, nanoparticles, immunotherapy, anti-biofilm and anti-virulence agents. These novel therapeutics need multidisciplinary collaboration and new ways of thinking to bring them into large scale clinical use.

Function of Burkholderia pseudomallei RpoS and RpoN2 in bacterial invasion, intracellular survival, and multinucleated giant cell formation in mouse macrophage cell line

Melioidosis, a human infectious disease with a high mortality rate in many tropical countries, is caused by the pathogen Burkholderia pseudomallei (B. pseudomallei). The function of the B. pseudomallei sigma S (RpoS) transcription factor in survival during the stationary growth phase and conditions of oxidative stress is well documented. Besides the rpoS, bioinformatics analysis of B. pseudomallei genome showed the existence of two rpoN genes, named rpoN1 and rpoN2. In this study, by using the mouse macrophage cell line RAW264.7 as a model of infection, the involvement of B. pseudomallei RpoS and RpoN2 in the invasion, intracellular survival leading to the reduction in multinucleated giant cell (MNGC) formation of RAW264.7 cell line were illustrated. We have demonstrated that the MNGC formation of RAW264.7 cell was dependent on a certain number of intracellular bacteria (at least 5 × 104). In addition, the same MNGC formation (15%) observed in RAW264.7 cells infected with either B. pseudomallei wild type with multiplicity of infection (MOI) 2 or RpoN2 mutant (∆rpoN2) with MOI 10 or RpoS mutant (∆rpoS) with MOI 100. The role of B. pseudomallei RpoS and RpoN2 in the regulation of type III secretion system on bipB-bipC gene expression was also illustrated in this study.

Pilotins are mobile T3SS components involved in assembly and substrate specificity of the bacterial type III secretion system

In animal pathogens, assembly of the type III secretion system injectisome requires the presence of so-called pilotins, small lipoproteins that assist the formation of the secretin ring in the outer membrane. Using a combination of functional assays, interaction studies, proteomics, and live-cell microscopy, we determined the contribution of the pilotin to the assembly, function, and substrate selectivity of the T3SS and identified potential new downstream roles of pilotin proteins. In absence of its pilotin SctG, Yersinia enterocolitica forms few, largely polar injectisome sorting platforms and needles. Accordingly, most export apparatus subcomplexes are mobile in these strains, suggesting the absence of fully assembled injectisomes. Remarkably, while absence of the pilotin all but prevents export of early T3SS substrates, such as the needle subunits, it has little effect on secretion of late T3SS substrates, including the virulence effectors. We found that although pilotins interact with other injectisome components such as the secretin in the outer membrane, they mostly localize in transient mobile clusters in the bacterial membrane. Together, these findings provide a new view on the role of pilotins in the assembly and function of type III secretion injectisomes.

Lawsonia intracellularis flagellin protein LfliC stimulates NF-κB and MAPK signaling pathways independently of TLR5 interaction

Lawsonia intracellularis, a Gram-negative obligate intracellular bacterium and etiologic agent of porcine proliferative enteropathy, was observed to have a long, single, and unipolar flagellum. Bacterial flagellar filament comprises thousands of copies of the protein flagellin (FliC), and has been reported to be recognized by Toll-like receptor (TLR5) to activate the NF-κB and MAPK signaling pathways, thereby inducing the expression of proinflammatory genes. Recently, two L. intracellularis flagellin proteins, LfliC and LFliC, were reported to be involved in bacterial-host interaction and immune response. Here, to further explore the role of LfliC in proinflammatory response, we purified LfliC, and found that its exposure could activate NF-κB signaling pathway in both HEK293T and IPI-FX cells, as well as activate MAPK p38 and ERK1/2 in HEK293T cells but not in IPI-FX cells. However, our yeast two-hybrid and co-immunoprecipitation assay results revealed that LfliC has no interaction with the porcine TLR5 ECD domain though it harbors the conserved D1-like motif required for the interaction. Moreover, LfliC was identified as a substrate of the virulence-associated type III secretion system (T3SS) by using the heterologous Y. enterocolitica system. Transient expression of LfliC also activated the NF-κB and MAPK signaling pathway in HEK293T cells. Collectively, our results suggest that both the exposure and expression of L. intracellularis LfliC can induce the NF-κB and MAPK signaling pathway in mammalian cells. Our findings may provide important implications and resources for the development of diagnostic tools or vaccines and dissection of the pathogenesis of L. intracellularis.

Identification and bioinformatic analysis of invA gene of Salmonella in free range chicken

Abstract Salmonella is a serious cause of the health issues in human and animal worldwide. Salmonella has been isolated from different biological samples and it considers as the key role in induction of inflammation of gastrointestinal tract which in turn cause diarrhoea in different species. To further understand the involvement of Salmonella in contaminating and infecting fresh eggs and meat of free-range chicken. This study aimed to establish the microbiological and molecular detections of Salmonella in the cloaca of the free-range chicken and to identify predicted biological functions using Kyoto Encyclopedia of Gene and Genomic (KEGG) pathways and protein-protein interaction. Cloacal swabs were collected from free range chicken raised in the local farm in Duhok city. The isolates were cultured and biochemical test performed using XLD and TSI, respectively. Molecular detection and functional annotation of invA gene was carried out using Conventional PCR and bioinformatics approaches. The present study found that Salmonella was detected in 36 out of 86 samples using microbiological methods. To confirm these findings, invA gene was utilised and 9 out of 36 Salmonella isolates have shown a positive signal of invA by agarose gel. In addition, bioinformatic analysis revealed that invA gene was mainly associated with bacterial secretion processes as well as their KEGG terms and Protein-Protein Interaction were involved in bacterial invasion and secretion pathways. These findings suggested that invA gene plays important role in regulating colonization and invasion processes of Salmonella within the gut host in the free range chicken.

Primary architecture and energy requirements of Type III and Type IV secretion systems

Many pathogens use Type III and Type IV protein secretion systems to secrete virulence factors from the bacterial cytosol into host cells. These systems operate through a one-step mechanism. The secreted substrates (protein or nucleo-protein complexes in the case of Type IV conjugative systems) are guided to the base of the secretion channel, where they are directly delivered into the host cell in an ATP-dependent unfolded state. Despite the numerous disparities between these secretion systems, here we have focused on the structural and functional similarities between both systems. In particular, on the structural similarity shared by one of the main ATPases (EscN and VirD4 in Type III and Type IV secretion systems, respectively). Interestingly, these ATPases also exhibit a structural resemblance to F1-ATPases, which suggests a common mechanism for substrate secretion. The correlation between structure and function of essential components in both systems can provide significant insights into the molecular mechanisms involved. This approach is of great interest in the pursuit of identifying inhibitors that can effectively target these systems.

Characterization of translocon proteins in the type III secretion system of Lawsonia intracellularis

Lawsonia intracellularis, the etiologic agent of proliferative enteropathy (PE), is an obligate intracellular Gram-negative bacterium possessing a type III secretion system (T3SS), which enables the pathogen to translocate effector proteins into targeted host cells to modulate their functions. T3SS is a syringe-like apparatus consisting of a base, an extracellular needle, a tip, and a translocon. The translocon proteins assembled by two hydrophobic membrane proteins can form pores in the host-cell membrane, and therefore play an essential role in the function of T3SS. To date, little is known about the T3SS and translocon proteins of L. intracellularis. In this study, we first analyzed the conservation of the T3S apparatus between L. intracellularis and Yersinia, and characterized the putative T3S hydrophobic major translocon protein LI1158 and minor translocon protein LI1159 in the L. intracellularis genome. Then, by using Yersinia pseudotuberculosis as a surrogate system, we found that the full-length LI1158 and LI1159 proteins, but not the putative class II chaperone LI1157, were secreted in a - Ca2+ and T3SS-dependent manner and the secretion signal was located at the N terminus (aa 1-40). Furthermore, yeast-two hybrid experiments revealed that LI1158 and LI1159 could self-interact, and LI1159 could interact with LI1157. However, unlike CPn0809 and YopB, which are the major hydrophobic translocon proteins of the T3SS of C. pneumoniae and Yersinia, respectively, full-length LI1158 was non-toxic to both yeast and Escherichia coli cells, but full-length LI1159 showed certain toxicity to E. coli cells. Taken together, despite some differences from the findings in other bacteria, our results demonstrate that LI1158 and LI1159 may be the translocon proteins of L. intracellularis T3SS, and probably play important roles in the translocation of effector proteins at the early pathogen infection stage.

A self-amplifying RNA vaccine provides protection in a murine model of bubonic plague

Mice were immunized with a combination of self-amplifying (sa) RNA constructs for the F1 and V antigens of Yersinia pestis at a dose level of 1 μg or 5 μg or with the respective protein sub-units as a reference vaccine. The immunization of outbred OF1 mice on day 0 and day 28 with the lowest dose used (1 μg) of each of the saRNA constructs in lipid nanoparticles protected 5/7 mice against subsequent sub-cutaneous challenge on day 56 with 180 cfu (2.8 MLD) of a 2021 clinical isolate of Y. pestis termed 10-21/S whilst 5/7 mice were protected against 1800cfu (28MLD) of the same bacteria on day 56. By comparison, only 1/8 or 1/7 negative control mice immunized with 10 μg of irrelevant haemagglutin RNA in lipid nanoparticles (LNP) survived the challenge with 2.8 MLD or 28 MLD Y. pestis 10-21/S, respectively. BALB/c mice were also immunized with the same saRNA constructs and responded with the secretion of specific IgG to F1 and V, neutralizing antibodies for the V antigen and developed a recall response to both F1 and V. These data represent the first report of an RNA vaccine approach using self-amplifying technology and encoding both of the essential virulence antigens, providing efficacy against Y. pestis. This saRNA vaccine for plague has the potential for further development, particularly since its amplifying nature can induce immunity with less boosting. It is also amenable to rapid manufacture with simpler downstream processing than protein sub-units, enabling rapid deployment and surge manufacture during disease outbreaks.

Innovative Strategy for the Control of Citrus Canker: Inhibitors Targeting the Type III Secretion System of Xanthomonas citri Subsp. citri

To find potential type III secretion system (T3SS) inhibitors against citrus canker caused by Xanthomonas citri subsp. citri (Xcc), a new series of 5-phenyl-2-furan carboxylic acid derivatives stitched with 2-mercapto-1,3,4-thiadiazole were designed and synthesized. Among the 30 compounds synthesized, 14 compounds significantly inhibited the promoter activity of a harpin gene hpa1. Eight of the 14 compounds did not affect the growth of Xcc, but significantly reduced the hypersensitive response (HR) of tobacco and decreased the pathogenicity of Xcc on citrus plants. Subsequent studies have demonstrated that these inhibitory molecules effectively suppress the T3SS of Xcc and significantly impair the pathogen's ability to subvert citrus immunity, resulting in a reduction in the level of disease progression. As a result, our work has identified a series of potentially attractive agents for the control of citrus canker.

The evolution of intramitochondriality in Midichloria bacteria

Midichloria spp. are intracellular bacterial symbionts of ticks. Representatives of this genus colonise mitochondria in the cells of their hosts. To shed light on this unique interaction we evaluated the presence of an intramitochondrial localization for three Midichloria in the respective tick host species and generated eight high-quality draft genomes and one closed genome, showing that this trait is non-monophyletic, either due to losses or multiple acquisitions. Comparative genomics supports the first hypothesis, as the genomes of non-mitochondrial symbionts are reduced subsets of those capable of colonising the organelles. We detect genomic signatures of mitochondrial tropism, including the differential presence of type IV secretion system and flagellum, which could allow the secretion of unique effectors and/or direct interaction with mitochondria. Other genes, including adhesion molecules, proteins involved in actin polymerisation, cell wall and outer membrane proteins, are only present in mitochondrial symbionts. The bacteria could use these to manipulate host structures, including mitochondrial membranes, to fuse with the organelles or manipulate the mitochondrial network.

Phosphoprotein phosphatase activity positively regulates oligomeric pyrin to trigger inflammasome assembly in phagocytes

IMPORTANCE

Pyrin, a unique cytosolic receptor, initiates inflammatory responses against RhoA-inactivating bacterial toxins and effectors like Yersinia's YopE and YopT. Understanding pyrin regulation is crucial due to its association with dysregulated inflammatory responses, including Familial Mediterranean Fever (FMF), linked to pyrin gene mutations. FMF mutations historically acted as a defense mechanism against plague. Negative regulation of pyrin through PKN phosphorylation is well established, with Yersinia using the YopM effector to promote pyrin phosphorylation and counteract its activity. This study highlights the importance of phosphoprotein phosphatase activity in positively regulating pyrin inflammasome assembly in phagocytic cells of humans and mice. Oligomeric murine pyrin has S205 phosphorylated before inflammasome assembly, and this study implicates the dephosphorylation of murine pyrin S205 by two catalytic subunits of PP2A in macrophages. These findings offer insights for investigating the regulation of oligomeric pyrin and the balance of kinase and phosphatase activity in pyrin-associated infectious and autoinflammatory diseases.

Roles of host SUMOylation in bacterial pathogenesis

Bacteria frequently interfere with the post-translational modifications of host cells to facilitate their survival and growth after invasion. SUMOylation, a reversible post-translational modification process, plays an important role in biological life activities. In addition to being critical to host cell metabolism and survival, SUMOylation also regulates gene expression and cell signal transmission. Moreover, SUMOylation in eukaryotic cells can be used by a variety of bacterial pathogens to advance bacterial invasion. In this minireview, we focused on the role and mechanism of host SUMOylation in the pathogenesis of six important clinical bacterial pathogens (Listeria monocytogenes, Shigella flexneri, Salmonella Typhimurium, Klebsiella pneumoniae, Staphylococcus aureus, and Escherichia coli). Taken together, this review provided new insights for understanding the unique pathogen-host interaction based on host SUMOylation and provided a novel perspective on the development of new strategies to combat bacterial infections in the future.

A single filament biomechanical study of the enteropathogenic Escherichia coli Type III secretion system reveals a high elastic aspect ratio

Type III secretion systems (T3SSs) are syringe-like protein complexes used by some of the most harmful bacterial pathogens to infect host cells. While the T3SS filament, a long hollow conduit that bridges between bacteria and host cells, has been characterized structurally, very little is known about its physical properties. These filaments should endure shear and normal stresses imposed by the viscous mucosal flow during infection within the intestinal tract. We used atomic force microscopy (AFM) to probe the longitudinal and radial mechanical response of individual T3SS filaments by pulling on filaments extending directly from bacterial surfaces and later pressing into filaments that were detached from the bacteria. The measured longitudinal elastic moduli were higher by about two orders of magnitude than the radial elastic moduli. These proportions are commensurate with the role of the T3SS filament, which requires horizontal flexibility while maintaining its structural integrity to withstand intense stresses during infection.

Engineering Agrobacterium tumefaciens with a Type III Secretion System to Express Type III Effectors

Plants elicit defense responses when exposed to pathogens, which partly contribute to the resistance of plants to Agrobacterium tumefaciens-mediated transformation. Some pathogenic bacteria have sophisticated mechanisms to counteract these defense responses by injecting Type III effectors (T3Es) through the Type III secretion system (T3SS). By engineering A. tumefaciens to express T3SS to deliver T3Es, we suppressed plant defense and enhanced plant genetic transformation. Here, we describe the optimized protocols for mobilization of T3SS-expressing plasmid to engineer A. tumefaciens to deliver proteins through T3SS and fractionation of cultures to study proteins from pellet and supernatants to determine protein secretion from engineered A. tumefaciens.

Pseudomonas syringae Type III Secretion Protein HrpP Manipulates Plant Immunity To Promote Infection

The bacterial plant pathogen Pseudomonas syringae deploys a type III secretion system (T3SS) to deliver effector proteins into plant cells to facilitate infection, for which many effectors have been characterized for their interactions. However, few T3SS Hrp (hypersensitive response and pathogenicity) proteins from the T3SS secretion apparatus have been studied for their direct interactions with plants. Here, we show that the P. syringae pv. tomato DC3000 T3SS protein HrpP induces host cell death, suppresses pattern-triggered immunity (PTI), and restores the effector translocation ability of the hrpP mutant. The hrpP-transgenic Arabidopsis lines exhibited decreased PTI responses to flg22 and elf18 and enhanced disease susceptibility to P. syringae pv. tomato DC3000. Transcriptome analysis reveals that HrpP sensing activates salicylic acid (SA) signaling while suppressing jasmonic acid (JA) signaling, which correlates with increased SA accumulation and decreased JA biosynthesis. Both yeast two-hybrid and bimolecular fluorescence complementation assays show that HrpP interacts with mitogen-activated protein kinase kinase 2 (MKK2) on the plant membrane and in the nucleus. The HrpP truncation HrpP1-119, rather than HrpP1-101, retains the ability to interact with MKK2 and suppress PTI in plants. In contrast, HrpP1-101 continues to cause cell death and electrolyte leakage. MKK2 silencing compromises SA signaling but has no effect on cell death caused by HrpP. Overall, our work highlights that the P. syringae T3SS protein HrpP facilitates effector translocation and manipulates plant immunity to facilitate bacterial infection. IMPORTANCE The T3SS is required for the virulence of many Gram-negative bacterial pathogens of plants and animals. This study focuses on the sensing and function of the T3SS protein HrpP during plant interactions. Our findings show that HrpP and its N-terminal truncation HrpP1-119 can interact with MKK2, promote effector translocation, and manipulate plant immunity to facilitate bacterial infection, highlighting the P. syringae T3SS component involved in the fine-tuning of plant immunity.

Brevundimonas brasiliensis sp. nov.: a New Multidrug-Resistant Species Isolated from a Patient in Brazil

To increase knowledge on Brevundimonas pathogens, we conducted in-depth genomic and phenotypic characterization of a Brevundimonas strain isolated from the cerebrospinal fluid of a patient admitted in a neonatal intensive care unit. The strain was identified as a member of the genus Brevundimonas based on Vitek 2 system results and 16S rRNA gene sequencing and presented a multidrug resistance profile (MDR). Several molecular and biochemical tests were used to characterize and identify the species for in-depth results. The draft genome assembly of the isolate has a total length of 3,261,074 bp and a G+C of 66.86%, similar to other species of the genus. Multilocus sequence analysis, Type (Strain) Genome Server, digital DNA-DNA hybridization, and average nucleotide identity confirmed that the Brevundimonas sp. studied represents a distinct species, for which we propose the name Brevundimonas brasiliensis sp. nov. In silico analysis detected antimicrobial resistance genes (AMRGs) mediating resistance to β-lactams (penP, blaTEM-16, and blaBKC-1) and aminoglycosides [strA, strB, aac(6')-Ib, and aac(6')-Il]. We also found AMRGs encoding the AcrAB efflux pump that confers resistance to a broad spectrum of antibiotics. Colistin and quinolone resistance can be attributed to mutation in qseC and/or phoP and GyrA/GyrB, respectively. The Brevundimonas brasiliensis sp. nov. genome contained copies of type IV secretion system (T4SS)-type integrative and conjugative elements (ICEs); integrative mobilizable elements (IME); and Tn3-type and IS3, IS6, IS5, and IS1380 families, suggesting an important role in the development and dissemination of antibiotic resistance. The isolate presented a range of virulence-associated genes related to biofilm formation, adhesion, and invasion that can be relevant for its pathogenicity. Our findings provide a wealth of data to hinder the transmission of MDR Brevundimonas and highlight the need for monitoring and identifying new bacterial species in hospital environments. IMPORTANCE Brevundimonas species is considered an opportunistic human pathogen that can cause multiple types of invasive and severe infections in patients with underlying pathologies. Treatment of these pathogens has become a major challenge because many isolates are resistant to most antibiotics used in clinical practice. Furthermore, there are no consistent therapeutic results demonstrating the efficacy of antibacterial agents. Although considered a rare pathogen, recent studies have provided evidence of the emergence of Brevundimonas in clinical settings. Hence, we identified a novel pathogenic bacterium, Brevundimonas brasiliensis sp. nov., that presented a multidrug resistance (MDR) profile and carried diverse genes related to drug resistance, virulence, and mobile genetic elements. Such data can serve as a baseline for understanding the genomic diversity, adaptation, evolution, and pathogenicity of MDR Brevundimonas.

Drug repositioning: doxazosin attenuates the virulence factors and biofilm formation in Gram-negative bacteria

The resistance development is an increasing global health risk that needs innovative solutions. Repurposing drugs to serve as anti-virulence agents is suggested as an advantageous strategy to diminish bacterial resistance development. Bacterial virulence is controlled by quorum sensing (QS) system that orchestrates the expression of biofilm formation, motility, and virulence factors production as enzymes and virulent pigments. Interfering with QS could lead to bacterial virulence mitigation without affecting bacterial growth that does not result in bacterial resistance development. This study investigated the probable anti-virulence and anti-QS activities of α-adrenoreceptor blocker doxazosin against Proteus mirabilis and Pseudomonas aeruginosa. Besides in silico study, in vitro and in vivo investigations were conducted to assess the doxazosin anti-virulence actions. Doxazosin significantly diminished the biofilm formation and release of QS-controlled Chromobacterium violaceum pigment and virulence factors in P. aeruginosa and P. mirabilis, and downregulated the QS encoding genes in P. aeruginosa. Virtually, doxazosin interfered with QS proteins, and in vivo protected mice against P. mirabilis and P. aeruginosa. The role of the membranal sensors as QseC and PmrA was recognized in enhancing the Gram-negative virulence. Doxazosin downregulated the membranal sensors PmR and QseC encoding genes and could in silico interfere with them. In conclusion, this study preliminary documents the probable anti-QS and anti-virulence activities of doxazosin, which indicate its possible application as an alternative or in addition to antibiotics. However, extended toxicological and pharmacological investigations are essential to approve the feasible clinical application of doxazosin as novel efficient anti-virulence agent. KEY POINTS: • Anti-hypertensive doxazosin acquires anti-quorum sensing activities • Doxazosin diminishes the virulence of Proteus mirabilis and Pseudomonas aeruginosa • Doxazosin could dimmish the bacterial espionage.

Calcium-responsive plasmid copy number regulation is dependent on discrete YopD domains in Yersinia pseudotuberculosis

Yersinia pathogenicity depends mainly on a Type III Secretion System (T3SS) responsible for translocating effector proteins into the eukaryotic target cell cytosol. The T3SS is encoded on a 70 kb, low copy number virulence plasmid, pYV. A key T3SS regulator, YopD, is a multifunctional protein and consists of discrete modular domains that are essential for pore formation and translocation of Yop effectors. In Y. pseudotuberculosis, the temperature-dependent plasmid copy number increase that is essential for elevated T3SS gene dosage and virulence is also affected by YopD. Here, we found that the presence of intracellular YopD results in increased levels of the CopA-RNA and CopB, two inhibitors of plasmid replication. Secretion of YopD leads to decreased expression of copA and copB, resulting in increased plasmid copy number. Moreover, using a systematic mutagenesis of YopD mutants, we demonstrated that the same discrete modular domains important for YopD translocation are also necessary for both the regulation of plasmid copy number as well as copA and copB expression. Hence, Yersinia has evolved a mechanism coupling active secretion of a plasmid-encoded component of the T3SS, YopD, to the regulation of plasmid replication. Our work provides evidence for the cross-talk between plasmid-encoded functions with the IncFII replicon.

Effector Identification in Plant Pathogens

Effectors play a central role in determining the outcome of plant-pathogen interactions. As key virulence proteins, effectors are collectively indispensable for disease development. By understanding the virulence mechanisms of effectors, fundamental knowledge of microbial pathogenesis and disease resistance have been revealed. Effectors are also considered double-edged swords because some of them activate immunity in disease resistant plants after being recognized by specific immune receptors, which evolved to monitor pathogen presence or activity. Characterization of effector recognition by their cognate immune receptors and the downstream immune signaling pathways is instrumental in implementing resistance. Over the past decades, substantial research effort has focused on effector biology, especially concerning their interactions with virulence targets or immune receptors in plant cells. A foundation of this research is robust identification of the effector repertoire from a given pathogen, which depends heavily on bioinformatic prediction. In this review, we summarize methodologies that have been used for effector mining in various microbial pathogens which use different effector delivery mechanisms. We also discuss current limitations and provide perspectives on how recently developed analytic tools and technologies may facilitate effector identification and hence generation of a more complete vision of host-pathogen interactions. [Formula: see text] Copyright © 2023 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

The peanut root exudate increases the transport and metabolism of nutrients and enhances the plant growth-promoting effects of burkholderia pyrrocinia strain P10

BACKGROUND

Burkholderia pyrrocinia strain P10 is a plant growth-promoting rhizobacterium (PGPR) that can substantially increase peanut growth. However, the mechanisms and pathways involved in the interaction between B. pyrrocinia P10 and peanut remain unclear. To clarify complex plant-PGPR interactions and the growth-promoting effects of PGPR strains, the B. pyrrocinia P10 transcriptome changes in response to the peanut root exudate (RE) were elucidated and the effects of RE components on biofilm formation and indole-3-acetic acid (IAA) secretion were analyzed.

RESULTS

During the early interaction phase, the peanut RE enhanced the transport and metabolism of nutrients, including carbohydrates, amino acids, nitrogen, and sulfur. Although the expression of flagellar assembly-related genes was down-regulated, the expression levels of other genes involved in biofilm formation, quorum sensing, and Type II, III, and VI secretion systems were up-regulated, thereby enabling strain P10 to outcompete other microbes to colonize the peanut rhizosphere. The peanut RE also improved the plant growth-promoting effects of strain P10 by activating the expression of genes associated with siderophore biosynthesis, IAA production, and phosphorus solubilization. Additionally, organic acids and amino acids were identified as the dominant components in the peanut RE. Furthermore, strain P10 biofilm formation was induced by malic acid, oxalic acid, and citric acid, whereas IAA secretion was promoted by the alanine, glycine, and proline in the peanut RE.

CONCLUSION

The peanut RE positively affects B. pyrrocinia P10 growth, while also enhancing colonization and growth-promoting effects during the early interaction period. These findings may help to elucidate the mechanisms underlying complex plant-PGPR interactions, with potential implications for improving the applicability of PGPR strains.

Plant-exuded chemical signals induce surface attachment of the bacterial pathogen Pseudomonas syringae

Many plant pathogenic bacteria suppress host defenses by secreting small molecule toxins or immune-suppressing proteins into host cells, processes that likely require close physical contact between pathogen and host. Yet, in most cases, little is known about whether phytopathogenic bacteria physically attach to host surfaces during infection. Here we report that Pseudomonas syringae pv. tomato strain DC3000, a Gram-negative bacterial pathogen of tomato and Arabidopsis, attaches to polystyrene and glass surfaces in response to chemical signals exuded from Arabidopsis seedlings and tomato leaves. We characterized the molecular nature of these attachment-inducing signals and discovered that multiple hydrophilic metabolites found in plant exudates, including citric acid, glutamic acid, and aspartic acid, are potent inducers of surface attachment. These same compounds were previously identified as inducers of P. syringae genes encoding a type III secretion system (T3SS), indicating that both attachment and T3SS deployment are induced by the same plant signals. To test if surface attachment and T3SS are regulated by the same signaling pathways, we assessed the attachment phenotypes of several previously characterized DC3000 mutants, and found that the T3SS master regulator HrpL was partially required for maximal levels of surface attachment, whereas the response regulator GacA, a negative regulator of T3SS, negatively regulated DC3000 surface attachment. Together, our data indicate that T3SS deployment and surface attachment by P. syringae may be co-regulated by the same host signals during infection, possibly to ensure close contact necessary to facilitate delivery of T3SS effectors into host cells.

Yersinia enterocolitica in Crohn’s disease

Increasing attention is being paid to the unique roles gut microbes play in both physiological and pathological processes. Crohn’s disease (CD) is a chronic, relapsing, inflammatory disease of the gastrointestinal tract with unknown etiology. Currently, gastrointestinal infection has been proposed as one initiating factor of CD. Yersinia enterocolitica, a zoonotic pathogen that exists widely in nature, is one of the most common bacteria causing acute infectious gastroenteritis, which displays clinical manifestations similar to CD. However, the specific role of Y. enterocolitica in CD is controversial. In this Review, we discuss the current knowledge on how Y. enterocolitica and derived microbial compounds may link to the pathogenesis of CD. We highlight examples of Y. enterocolitica-targeted interventions in the diagnosis and treatment of CD, and provide perspectives for future basic and translational investigations on this topic.

The WxxxE proteins in microbial pathogenesis

Effector proteins secreted by pathogens modulate various host cellular processes and help in bacterial pathogenesis. Some of these proteins, injected by enteric pathogens via Type Three Secretion System (T3SS) were grouped together based on a conserved signature motif (WxxxE) present in them. The presence of WxxxE motif is not limited to effectors released by enteric pathogens or the T3SS but has been detected in non-enteric pathogens, plant pathogens and in association with Type II and Type IV secretion systems. WxxxE effectors are involved in actin organization, inflammation regulation, vacuole or tubule formation, endolysosomal signalling regulation, tight junction disruption, and apoptosis. The WxxxE sequence has also been identified in TIR [Toll/interleukin-1 (IL-1) receptor] domains of bacteria and host. In the present review, we have focussed on the established and predicted functions of WxxxE effectors secreted by several pathogens, including enteric, non-enteric, and plant pathogens.

Yersinia interactions with regulated cell death pathways

Cell death in response to infection is conserved across all kingdoms of life. In metazoans, cell death upon bacterial infection is primarily carried out by the cysteine and aspartate protease and receptor-interacting serine/threonine protein kinase families. The Gram-negative bacterial genus Yersinia includes pathogens that cause disease in humans and other animals ranging from plague to gastrointestinal infections. Pathogenic Yersiniae express a type-III secretion system (T3SS), which translocates effectors that disrupt phagocytosis and innate immune signaling to evade immune defenses and replicate extracellularly in infected tissues. Blockade of innate immune signaling, disruption of the actin cytoskeleton, and the membrane-disrupting activity of the T3SS translocon pore, are all sensed by innate immune cells. Here, we discuss recent advances in understanding the pathways that regulate Yersinia-induced cell death, and how manipulation of these cell death pathways over the course of infection promotes bacterial dissemination or host defense.

Exploring the Microbial Community and Functional Characteristics of the Livestock Feces Using the Whole Metagenome Shotgun Sequencing

The foodborne illness is the important public health concerns, and the livestock feces are known to be one of the major reservoirs of foodborne pathogens. Also, it was reported that 45.5% of foodborne illness outbreaks have been associated with the animal products contaminated with the livestock feces. In addition, it has been known that the persistence of a pathogens depends on many potential virulent factors including the various virulent genes. Therefore, the first step to understanding the public health risk of livestock feces is to identify and describe microbial communities and potential virulent genes that contribute to bacterial pathogenicity. We used the whole metagenome shotgun sequencing to evaluate the prevalence of foodborne pathogens and to characterize the virulence associated genes in pig and chicken feces. Our data showed that the relative abundance of potential foodborne pathogens, such as Bacillus cereus was higher in chickens than pigs at the species level while the relative abundance of foodborne pathogens including Campylobacter coli was only detected in pigs. Also, the microbial functional characteristics of livestock feces revealed that the gene families related to "Biofilm formation and quorum sensing" were highly enriched in pigs than chicken. Moreover, the variety of gene families associated with "Resistance to antibiotics and toxic compounds" were detected in both animals. These results will help us to prepare the scientific action plans to improve awareness and understanding of the public health risks of livestock feces.

Targeting bacterial pathogenesis by inhibiting virulence-associated Type III and Type IV secretion systems

Infections caused by Gram-negative pathogens pose a major health burden. Both respiratory and gastrointestinal infections are commonly associated with these pathogens. With the increase in antimicrobial resistance (AMR) over the last decades, bacterial infections may soon become the threat they have been before the discovery of antibiotics. Many Gram-negative pathogens encode virulence-associated Type III and Type IV secretion systems, which they use to inject bacterial effector proteins across bacterial and host cell membranes into the host cell cytosol, where they subvert host cell functions in favor of bacterial replication and survival. These secretion systems are essential for the pathogens to cause disease, and secretion system mutants are commonly avirulent in infection models. Hence, these structures present attractive targets for anti-virulence therapies. Here, we review previously and recently identified inhibitors of virulence-associated bacterial secretions systems and discuss their potential as therapeutics.

The Missing Pieces: The Role of Secretion Systems in Campylobacter jejuni Virulence

Campylobacter jejuni is likely the most common bacterial cause of gastroenteritis worldwide, responsible for millions of cases of inflammatory diarrhea characterized by severe abdominal cramps and blood in the stool. Further, C. jejuni infections are associated with post-infection sequelae in developed countries and malnutrition and growth-stunting in low- and middle-income countries. Despite the increasing prevalence of the disease, campylobacteriosis, and the recognition that this pathogen is a serious health threat, our understanding of C. jejuni pathogenesis remains incomplete. In this review, we focus on the Campylobacter secretion systems proposed to contribute to host-cell interactions and survival in the host. Moreover, we have applied a genomics approach to defining the structural and mechanistic features of C. jejuni type III, IV, and VI secretion systems. Special attention is focused on the flagellar type III secretion system and the prediction of putative effectors, given that the proteins exported via this system are essential for host cell invasion and the inflammatory response. We conclude that C. jejuni does not possess a type IV secretion system and relies on the type III and type VI secretion systems to establish a niche and potentiate disease.

Pseudomonas aeruginosa Cytotoxins: Mechanisms of Cytotoxicity and Impact on Inflammatory Responses

Pseudomonas aeruginosa is one of the most virulent opportunistic Gram-negative bacterial pathogens in humans. It causes many acute and chronic infections with morbidity and mortality rates as high as 40%. P. aeruginosa owes its pathogenic versatility to a large arsenal of cell-associated and secreted virulence factors which enable this pathogen to colonize various niches within hosts and protect it from host innate immune defenses. Induction of cytotoxicity in target host cells is a major virulence strategy for P. aeruginosa during the course of infection. P. aeruginosa has invested heavily in this strategy, as manifested by a plethora of cytotoxins that can induce various forms of cell death in target host cells. In this review, we provide an in-depth review of P. aeruginosa cytotoxins based on their mechanisms of cytotoxicity and the possible consequences of their cytotoxicity on host immune responses.

Molecular Detection of Virulence Factors in Salmonella serovars Isolated from Poultry and Human Samples

Salmonellosis is a common infectious disease in humans caused by Salmonella spp., which in recent years has shown an increase in its incidence, with products of avian origin being a common source of transmission. To present a successful infective cycle, there are molecular mechanisms such as virulence factors that provide characteristics that facilitate survival, colonization, and damage to the host. According to this, the study aims to characterize the virulence factors of Salmonella spp. strains isolated from broilers (n = 39) and humans (n = 10). The presence of 24 virulence genes was evaluated using end-point PCR. All the strains of Salmonella spp. isolated from broiler chickens revealed presence of 7/24 (29, 16%) virulence genes (lpfA, csgA, sitC, sipB, sopB, sopE, and sivH). Regarding the strains isolated from cases of gastroenteritis in humans, all strains contained (14/24, 58, 33%) virulence genes (lpfA, csgA, pagC, msgA, spiA, sitC, iroN, sipB, orgA, hilA, sopB, sifA, avrA, and sivH). In summary, the presence of virulence genes in different strains of Salmonella isolated from broilers and humans could be described as bacteria with potential pathogenicity due to the type and number of virulence genes detected. These findings are beneficial for the pathogenic monitoring of Salmonella in Colombia.

Nanomaterials against intracellular bacterial infection: from drug delivery to intrinsic biofunction

Fighting intracellular bacteria with strong antibiotics evading remains a long-standing challenge. Responding to and regulating the infectious microenvironment is crucial for treating intracellular infections. Sophisticated nanomaterials with unique physicochemical properties exhibit great potential for precise drug delivery towards infection sites, along with modulating infectious microenvironment via their instinct bioactivity. In this review, we first identify the key characters and therapeutic targets of intracellular infection microenvironment. Next, we illustrate how the nanomaterials physicochemical properties, such as size, charge, shape and functionalization affect the interaction between nanomaterials, cells and bacteria. We also introduce the recent progress of nanomaterial-based targeted delivery and controlled release of antibiotics in intracellular infection microenvironment. Notably, we highlight the nanomaterials with unique intrinsic properties, such as metal toxicity and enzyme-like activity for the treatment of intracellular bacteria. Finally, we discuss the opportunities and challenges of bioactive nanomaterials in addressing intracellular infections.