Pathogenic Bacteria Research Articles

Innate lymphoid cells, immune functional dynamics, epithelial parallels, and therapeutic frontiers in infections.

Innate lymphoid cells (ILCs) have emerged as pivotal players in the field of immunology, expanding our understanding of innate immunity beyond conventional paradigms. This comprehensive review delves into the multifaceted world of ILCs, beginning with their serendipitous discovery and traversing their ontogeny and heterogeneity. We explore the distinct subsets of ILCs unraveling their intriguing plasticity, which adds a layer of complexity to their functional repertoire. As we journey through the functional activities of ILCs, we address their role in immune responses against various infections, categorizing their interactions with helminthic parasites, bacterial pathogens, fungal infections, and viral invaders. Notably, this review offers a detailed examination of ILCs in the context of specific infections, such as Mycobacterium tuberculosis, Citrobacter rodentium, Clostridium difficile, Salmonella typhimurium, Helicobacter pylori, Listeria monocytogenes, Staphylococcus aureus, Pseudomonas aeruginosa, Influenza virus, Cytomegalovirus, Herpes simplex virus, and severe acute respiratory syndrome coronavirus 2. This selection aimed for a comprehensive exploration of ILCs in various infectious contexts, opting for microorganisms based on extensive research findings rather than considerations of virulence or emergence. Furthermore, we raise intriguing questions about the potential immune functional resemblances between ILCs and epithelial cells, shedding light on their interconnectedness within the mucosal microenvironment. The review culminates in a critical assessment of the therapeutic prospects of targeting ILCs during infection, emphasizing their promise as novel immunotherapeutic targets. Nevertheless, due to their recent discovery and evolving understanding, effectively manipulating ILCs is challenging. Ensuring specificity and safety while evaluating long-term effects in clinical settings will be crucial.

Lysine polyphosphate modifications contribute to virulence factors in Pseudomonas aeruginosa.

Inorganic polyphosphate (polyP) is a universally conserved polymer involved in various biological processes, but its role as a direct protein regulator remains largely unexplored. Lysine polyphosphate modification (KPM), a strong but non-covalent interaction between polyP and lysine-rich protein sequences, has not been functionally characterized until now. In this study, we present the first investigation into KPM's biological significance using Pseudomonas aeruginosa, a critical priority pathogen known for its antibiotic resistance and virulence. We identified two essential bacterial proteins, EngA and SrmB, as novel KPM targets. Through site-specific lysine deletions, we demonstrated that disrupting lysine-polyP interactions severely impairs biofilm formation and significantly reduces the production of key virulence factors, including pyoverdine and pyocyanin. These findings establish a direct functional link between polyP and bacterial pathogenicity mediated by KPM. Our results highlight KPM as a previously unrecognized regulatory mechanism critical for controlling bacterial virulence factors. This work uncovers the first functional role of KPM and its importance in regulating virulence phenotypes in a major human pathogen.IMPORTANCEPolyphosphate is commonly known for its roles in metabolism and stress response. How inorganic polyphosphate (polyP) facilitates bacterial virulence has remained largely elusive. This study reveals that lysine polyphosphate modification (KPM), a chemical interaction between polyP and lysine-rich proteins, is essential for bacterial survival and pathogenicity in P. aeruginosa, a harmful microbe responsible for difficult-to-treat infections. We discovered that disrupting KPM in key proteins impairs the bacteria's ability to form protective biofilms and produce harmful toxins. This previously unknown biological process links polyP to protein function in controlling bacterial virulence factors. Our findings open new possibilities for developing anti-virulence therapies aimed at reducing bacterial infections without promoting antibiotic resistance.

Altered Mental Status and First-Time Seizure in Teen With a Subacute Inguinal Mass.

A healthy 13-year-old boy who resides in rural Vermont presented after witnessed, generalized seizure-like activity for approximately 2minutes. He had been well until the development of right inguinal pain and rash 2weeks before presentation, which had progressed to a 5-cm irregular, red, tender, and raised area that was unresponsive to 5days of cephalexin. At the time of presentation, he was afebrile and hemodynamically stable and only responsive to localized stimuli. Initial laboratory evaluation, toxicology screening, and computed tomography of the head were all unremarkable. Ultrasonography of the inguinal lesion showed an abscess with subcutaneous edema and reactive lymphadenopathy. He did not have evidence of stroke or status epilepticus. Because of his persistent altered mental status, the patient was admitted to the pediatric intensive care unit, and pediatric infectious disease was consulted. A detailed history revealed he had extensive recent animal exposures that included bear, deer, dogs, chickens, and kittens. Cerebrospinal fluid (CSF) analysis showed 5 leukocytes (26% polymorphonuclear leukocyte), normal glucose, and slightly elevated protein. Video electroencephalogram demonstrated bilateral cerebral dysfunction, whereas the brain magnetic resonance imaging and magnetic resonance venogram scan results were normal. CSF culture and polymerase chain reaction results for bacterial and viral pathogens were negative. Fluid collected from the inguinal lesion showed neutrophils but no organisms. The following discussion describes this patient's full course, differential diagnoses, diagnostic workup with clinical reasoning, and final diagnosis.

Characterization and genome analysis of the novel virulent Burkholderia phage Bm1, which is active against pan-drug-resistant Burkholderia multivorans

The escalating challenges of antibiotic resistance in bacterial pathogens have necessitated the exploration of alternative therapeutic strategies. Among these, bacteriophage therapy has regained attention as a promising approach to combat multidrug-resistant bacteria. Bacteriophages are viruses that infect and lyse specific bacterial strains, making them attractive candidates for targeted antimicrobial treatment. Burkholderia multivorans, a Gram-negative bacterium, is known to cause opportunistic infections, particularly in individuals with a compromised immune system or with cystic fibrosis. The prevalence of antibiotic-resistant Burkholderia strains has raised concerns about treatment options. In this study, we characterized the Burkholderia phage Bm1, a virulent bacteriophage isolated from an environmental source. Electron microscopy revealed that Bm1 phage particles have myovirus morphology, with an icosahedral head of 72 nm in diameter and a contractile tail of 100 nm in length and 18 nm in width. The genome of phage Bm1 consists of a double-stranded DNA of 67,539 bp with a terminal repeat region at each end. Comparative analysis indicated that the closest relative of phage Bm1 is Burkholderia phage BCSR129, with a calculated VIRIDIC identity of 57.7%. The apparent absence of an integrase gene suggests that the Burkholderia phage Bm1 has a strictly lytic life cycle.

PelD is required downstream of c-di-GMP for host specialization of Pseudomonas lurida

BackgroundThe bacterial second messenger c-di-GMP is known to influence the formation of biofilms and thereby persistence of pathogenic and beneficial bacteria in hosts. A previous evolution experiment with Pseudomonas lurida MYb11, occasional symbiont of the nematode Caenorhabditis elegans, led to the emergence of host-specialized variants with elevated intracellular c-di-GMP. Thus far, the molecular underpinnings of c-di-GMP-mediated host specialization were unknown in this symbiosis. Therefore, the current study aimed at identifying candidate molecular processes by combining transcriptomic and functional genetic analyses.ResultsWe found that MYb11 host specialists differentially expressed genes related to attachment, motility and biofilm production, including pelD from the pel gene cluster. pelD deletion resulted in reduced intra-host competitive fitness, lower bacterial numbers in C. elegans and loss of biofilm biomass.ConclusionOur results identify pelD as a previously unknown key modulator of beneficial symbiont-host associations that acts downstream of c-di-GMP.

Recent advances in sugar-fatty acid esters and their analogs: antimicrobial properties, structural-functional relationships and potential mechanisms.

Sugar-fatty acid esters and their analogs (SFAEA) exhibit broad-spectrum antimicrobial activities. The article comprehensively outlined their inhibitory potential against key pathogenic and spoilage bacteria as well as fungal species. Antibacterial efficacy is quantitatively assessed using minimum inhibitory concentration (MIC), and antifungal activity is typically characterized by inhibition zones or mycelial growth inhibition rates. Research highlighted that sugar esters incorporating medium- to long-chain fatty acids, particularly those derived from sucrose, galactose, and mannose, demonstrated superior antibacterial properties. The lauric acid and myristic acid moieties were found to be exceptional compared to other length in the fatty acid portion. The chain length of the hydrophobic group, the glycosyl structure and the substitution level and type of the hydrophobic group in the sugar ester and other factors all have an impact on the antibacterial effect. It was found that the disruption of cell envelope, the generation of reactive oxygen species, the interactions with cytoplasmic contents and the influences on metabolic pathways were major reasons leading to cell death. Omics technologies and molecular docking also suggested some potential mechanisms. Additionally, future research directions regarding the application in food and mechanistic studies were presented.

The ArcAB two-component system is associated with the susceptibility of Aggregatibacter actinomycetemcomitans to superoxide and hydrogen peroxide.

Aggregatibacter actinomycetemcomitans is a Gram-negative facultative anaerobe and is associated with periodontal disease. This bacterium is exposed to environmental stresses, such as osmotic pressure, temperature shifts, pH shifts, and antimicrobial substances, including reactive oxygen species (ROS), in the human oral cavity. The bacterial two-component system ArcAB modulates gene expression in response to environmental changes, primarily by sensing oxygen pressure in several pathogens belonging to the γ-proteobacteria. It is also known to provide adaptation to ROS stress; however, its function in A. actinomycetemcomitans remains unclear. In this study, we found that the expression of sod, which encodes superoxide dismutase, was increased in the inactivated mutant of arcA, which encodes a response regulator. The mutant exhibited reduced susceptibility to superoxide and hydrogen peroxide (H2O2). Additionally, this strain showed reduced susceptibility to H2O2 from Streptococcus sanguinis and increased survival in macrophages. Since ArcB is the cognate histidine kinase of ArcA, the inactivated mutant of arcB was analyzed for its phenotypes. The arcB mutant exhibited reduced susceptibility to superoxide and H2O2. Compared to wild type, the phosphorylation level of ArcA in the arcB mutant was decreased. These results suggest that the ArcA response regulator receives phosphate groups from ArcB histidine kinase and negatively regulates the expression of sod, thereby affecting bacterial survival in response to ROS produced by oral commensals and host immune cells.IMPORTANCEAggregatibacter actinomycetemcomitans is an oral pathogen that is known to be a highly virulent periodontal pathogen, showing strong adherence to periodontal tissue and toxin production, which leads to aggressive periodontitis. This bacterium is associated not only with oral infections but also with systemic infections, such as infective endocarditis and brain abscesses. Therefore, elucidating the adaptation mechanisms of this bacterium is important for human health. Bacterial two-component systems (TCSs) have been studied as attractive targets for elucidating bacterial fitness and pathogenicity in the host. This study characterized a TCS in A. actinomycetemcomitans, ArcAB, which is associated with susceptibility to ROS produced by host cells or oral commensals. Our findings provide insights into the bacterial adaptation mechanism against oxidative stress, which is crucial for understanding the survival strategies of the periodontal pathogen.

Correction to “Self‐Thermophoretic Nanoparticles Enhance Intestinal Mucus Penetration and Reduce Pathogenic Bacteria Interception in Colorectal Cancer”

Correction to “Self‐Thermophoretic Nanoparticles Enhance Intestinal Mucus Penetration and Reduce Pathogenic Bacteria Interception in Colorectal Cancer”

Orally Administered ZnxCeyO2/Se Hydrogel with Effective Antioxidant Activity for Treating Inflammatory Bowel Disease by Inhibiting Ferroptosis.

Oxidative stress leads to intestinal barrier damage, which induces immune responses to occur and further promotes oxidative stress exacerbating inflammatory bowel disease (IBD). In this work, the multifunctional ZnxCeyO2/Se (ZCSO) nanozyme wrapped with acid-resistant calcium alginate hydrogel designed for oral administration is prepared. The ZCSO nanozyme can promote the activation of the Nrf2 oxidative stress pathway, then significantly improve the efficiency of scavenging reactive oxygen species (ROS) and up-regulate the protein expression of glutathione peroxidase 4 (GPx4), which is closely related to the inhibition of ferroptosis. In addition, the ZCSO nanozyme inhibiting the growth of some pathogenic bacteria proliferating due to oxidative stress shows a positive regulation of the intestinal flora and reduces the secretion of pro-inflammatory factors and the levels of inflammatory macrophages, achieving the significant preventive and delayed therapeutic effect of colitis mice. Consequently, the distinctive properties of ZCSO nanozyme render it a promising candidate for the treatment of IBD by effectively scavenging ROS, thereby interrupting the detrimental cycle between oxidative stress and immune response, ultimately promoting the proliferation of epithelial cells to reestablish the integrity of the intestinal mucosal barrier.

Characterization and therapeutic potential of phage vB_Eco_ZCEC08 against multidrug-resistant uropathogenic Escherichia coli

BackgroundUrinary tract infections (UTIs) caused by antibiotic-resistant bacteria have become a significant public health concern. The increasing ineffectiveness of antibiotics has led to a renewed focus on investigating other strategies, such as bacteriophages, to target specific pathogenic bacteria and prevent future resistance.ResultsThis study reports the isolation and characterization of bacteriophage vB_Eco_ZCEC08 targeting uropathogenic Escherichia coli (UPEC). Phage vB_Eco_ZCEC08 is morphologically a non-contractile tailed phage that exhibits strong lytic activity against UPEC with a short latent period of less than 15 min and a lysis time of 20 min to produce a high burst of around 900 phage particles per host cell. vB_Eco_ZCEC08 phage activity demonstrated exceptional stability against temperature [-80–60 ̊C], pH [2, 3, 4, 5, 6, 7, 8, 9, 10–11], UV exposure and incubation in artificial human urine. The phage effectively reduced UPEC counts over a range of infection rates, with MOI 1 the most effective, and which resulted in the limited emergence of phage-insensitive bacteria. A whole-genome study of the 47.926 bp vB_Eco_ZCEC08 phage identified one tRNA gene and 84 predicted genes. Comparative genomics and phylogenetic analysis suggest that the vB_Eco_ZCEC08 phage belongs to the same genus as the Salmonella phage vB_SenS_ST1 but represents a new species. Phage vB_Eco_ZCEC08 showed minimal cytotoxicity against human urinary bladder cancer and skin fibroblast cell lines.ConclusionvB_Eco_ZCEC08 phage demonstrates strong selective lytic activity against UPEC in the absence of any lysogenic behavior. These properties coupled with inherent physiochemical stability and low cytotoxicity support the development of vB_Eco_ZCEC08 as an alternative treatment for multidrug-resistant UPEC.

Identification of Chlortetracycline Hydrochloride as a Antibacterial Compound Against Pseudomonas syringae pv. tomato DC3000 Through Natural Products Library Screening.

Pseudomonas syringae (P. syringae) can infect over 50 different crops worldwide, causing significant economic losses, and it is one of the major bacterial pathogens affecting global crops. Currently, there are no effective control strategies for bacterial leaf spot disease caused by P. syringae. In this study, a high-throughput screening of 1680 natural products was conducted to evaluate their antibacterial effects. Microbial-derived compounds such as Polymyxin B sulfate (1), Methacycline hydrochloride (2), Tetracycline hydrochloride (3), Chlortetracycline hydrochloride (4), Demeclocycline hydrochloride (5), and Doxycycline hyclate (6) exhibited strong antibacterial activity against Pseudomonas syringae pv. tomato DC3000 (Pst DC3000), with inhibition rates exceeding 60%. Further research revealed that compound 4 had a minimum inhibitory concentration of 0.4μM. After 12h of treatment with 12.8μM of compound 4, bacterial killing efficiency reached 98%. Moreover, compound 4 effectively inhibited the occurrence of bacterial leaf spot disease. In conclusion, this study suggests that microbial-derived natural products hold great potential as effective bactericides against Pst DC3000, providing a new approach for the control of bacterial leaf spot disease.

Pseudomonas aeruginosa as a model bacterium in antiphage defense research.

Bacteriophages, or phages, depend on their bacterial hosts for proliferation, leading to a coevolutionary relationship characterized by on-going arms races, where bacteria evolve diverse antiphage defense systems. The development of in silico methods and high-throughput screening techniques has dramatically expanded our understanding of bacterial antiphage defense systems, enormously increasing the known repertoire of the distinct mechanisms across various bacterial species. These advances have revealed that bacterial antiphage defense systems exhibit a remarkable level of complexity, ranging from highly conserved to specialized mechanisms, underscoring the intricate nature of bacterial antiphage defense systems. In this review, we provide a concise snapshot of antiphage defense research highlighting two preponderantly commandeered approaches and classification of the known antiphage defense systems. A special focus is placed on the model bacterial pathogen, Pseudomonas aeruginosa in antiphage defense research. We explore the complexity and adaptability of these systems, which play crucial roles in genome evolution and adaptation of P. aeruginosa in response to an arsenal of diverse phage strains, emphasizing the importance of this organism as a key emerging model bacterium in recent antiphage defense research.

Host population dynamics influence Leptospira spp. transmission patterns among Rattus norvegicus in Boston, Massachusetts, US.

Leptospirosis (caused by pathogenic bacteria in the genus Leptospira) is prevalent worldwide but more common in tropical and subtropical regions. Transmission can occur following direct exposure to infected urine from reservoir hosts, or a urine-contaminated environment, which then can serve as an infection source for additional rats and other mammals, including humans. The brown rat, Rattus norvegicus, is an important reservoir of Leptospira spp. in urban settings. We investigated the presence of Leptospira spp. among brown rats in Boston, Massachusetts and hypothesized that rat population dynamics in this urban setting influence the transportation, persistence, and diversity of Leptospira spp. We analyzed DNA from 328 rat kidney samples collected from 17 sites in Boston over a seven-year period (2016-2022); 59 rats representing 12 of 17 sites were positive for Leptospira spp. We used 21 neutral microsatellite loci to genotype 311 rats and utilized the resulting data to investigate genetic connectivity among sampling sites. We generated whole genome sequences for 28 Leptospira spp. isolates obtained from frozen and fresh tissue from some of the 59 positive rat kidneys. When isolates were not obtained, we attempted genomic DNA capture and enrichment, which yielded 14 additional Leptospira spp. genomes from rats. We also generated an enriched Leptospira spp. genome from a 2018 human case in Boston. We found evidence of high genetic structure among rat populations that is likely influenced by major roads and/or other dispersal barriers, resulting in distinct rat population groups within the city; at certain sites these groups persisted for multiple years. We identified multiple distinct phylogenetic clades of L. interrogans among rats that were tightly linked to distinct rat populations. This pattern suggests L. interrogans persists in local rat populations and its transportation is influenced by rat population dynamics. Finally, our genomic analyses of the Leptospira spp. detected in the 2018 human leptospirosis case in Boston suggests a link to rats as the source. These findings will be useful for guiding rat control and human leptospirosis mitigation efforts in this and other similar urban settings.

Listeria monocytogenes requires phosphotransferase systems to facilitate intracellular growth and virulence.

The metabolism of bacterial pathogens is exquisitely evolved to support virulence in the nutrient-limiting host. Many bacterial pathogens utilize bipartite metabolism to support intracellular growth by splitting carbon utilization between two carbon sources and dividing flux to distinct metabolic needs. For example, previous studies suggest that the professional cytosolic pathogen Listeria monocytogenes (L. monocytogenes) utilizes glycerol and hexose phosphates (e.g., Glucose-6-Phosphate) as catabolic and anabolic carbon sources in the host cytosol, respectively. However, the role of this putative bipartite metabolism in L. monocytogenes virulence has not been fully assessed. Here, we demonstrate that when L. monocytogenes is unable to consume either glycerol (ΔglpD/ΔgolD), hexose phosphates (ΔuhpT), or both (ΔglpD/ΔgolD/ΔuhpT), it is still able to grow in the host cytosol and is 10- to 100-fold attenuated in vivo suggesting that L. monocytogenes consumes alternative carbon source(s) in the host. An in vitro metabolic screen using BioLog's phenotypic microarrays unexpectedly demonstrated that WT and PrfA* (G145S) L. monocytogenes, a strain with constitutive virulence gene expression, use phosphotransferase system (PTS) mediated carbon sources. These findings contrast with the existing metabolic model that cytosolic L. monocytogenes expressing PrfA does not use PTS mediated carbon sources. We next demonstrate that two independent and universal phosphocarrier proteins (PtsI [EI] and PtsH [HPr]), essential for the function of all PTS, are critical for intracellular growth and virulence in vivo. Constitutive virulence gene expression using a PrfA* (G145S) allele in ΔglpD/ΔgolD/ΔuhpT and ΔptsI failed to rescue in vivo virulence defects suggesting phenotypes are due to metabolic disruption and not virulence gene regulation. Finally, in vivo attenuation of ΔptsI and ΔptsH was additive to ΔglpD/ΔgolD/ΔuhpT, suggesting that hexose phosphates and glycerol and PTS mediated carbon source are relevant metabolites. Taken together, these studies indicate that PTS are critical virulence factors for the cytosolic growth and virulence of L. monocytogenes.

Mapping the ultrastructural topology of the corynebacterial cell surface.

Corynebacterium glutamicum is a diderm bacterium extensively used in the industrial-scale production of amino acids. Corynebacteria belong to the bacterial family Mycobacteriaceae, which is characterized by a highly unusual cell envelope with an outer membrane consisting of mycolic acids, called mycomembrane. The mycomembrane is further coated by a surface (S-)layer array in C. glutamicum, making this cell envelope highly distinctive. Despite the biotechnological significance of C. glutamicum and biomedical significance of mycomembrane-containing pathogens, ultrastructural and molecular details of its distinctive cell envelope remain poorly characterized. To address this, we investigated the cell envelope of C. glutamicum using electron cryotomography and cryomicroscopy of focused ion beam-milled single and dividing cells. Our cellular imaging allowed us to map the different components of the cell envelope onto the tomographic density. Our data reveal that C. glutamicum has a variable cell envelope, with the S-layer decorating the mycomembrane in a patchy manner. We further isolated and resolved the structure of the S-layer at 3.1 Å-resolution using single particle electron cryomicroscopy. Our structure shows that the S-layer of C. glutamicum is composed of a hexagonal array of the PS2 protein, which interacts directly with the mycomembrane via an anchoring segment containing a coiled-coil motif. Bioinformatic analyses revealed that the PS2 S-layer is sparsely yet exclusively present within the Corynebacterium genus and absent in other genera of the Mycobacteriaceae family, suggesting distinct evolutionary pathways in the development of their cell envelopes. Our structural and cellular data collectively provide a topography of the unusual C. glutamicum cell surface, features of which are shared by many pathogenic and microbiome-associated bacteria, as well as by several industrially significant bacterial species.

Development of a rapid diagnostic method for Dickeya dadantii, the bacterial canker pathogen of peach, using loop-mediated isothermal amplification (LAMP).

Given that accurate diagnosis of bacterial canker in peach trees that cause rapid death is difficult based on disease symptoms alone, a rapid genetic diagnosis technique is required. In this study, we aimed to develop a rapid and efficient method to identify Dickeya dadantii, the causative agent, using the loop-mediated isothermal amplification (LAMP) method. Two types of DNA were extracted from the thin cambium slices of peach tree trunks and branches. Purified DNA was obtained using a commercial kit. Crude DNA was boiled and diluted with the Tris-HCl buffer. Then, 119 peach tree cambium samples were analyzed to detect D. dadantii using the previously reported polymerase chain reaction method and newly designed LAMP primers. Notably, LAMP exhibited equivalent or superior positivity rates compared to polymerase chain reaction for both DNA types, particularly crude DNA. Additionally, D. dadantii was detected in the resin formed on the peach tree trunks and branches. Overall, the developed method shows potential for the non-invasive diagnosis of infections and mitigation of infection risk for effective fruit tree management.

The microbial regulation spectrum of metformin in patients with type 2 diabetes: An individual-based meta-analysis of 1431 participants.

Gut microbiota plays a significant role in metformin efficacy and therapeutic response. However, different studies have often produced some inconsistent outcomes. To gain a more comprehensive understanding of the transformation of gut microbiota in person with diabetes and the subsequent modifications following metformin intervention. Seven databases were searched from the inception of each database up to October 30, 2024. The raw sequence reads of nine available datasets were downloaded from the National Center for Biotechnology Information (NCBI). The process of selecting and assessing papers for this study was meticulously managed by two authors, working independently to screen and evaluate each publication. For the data extraction phase, a standardized form was employed, capturing critical details. Metformin significantly boosts the presence of Akkermansia and short-chain fatty acid (SCFA)-producing bacteria, such as Pseudobutyrivibrio, Oribacterium and Anaerotruncus, and simultaneously diminishes pathogenic bacteria including Enterobacillus, Gemmobacter, Shinella, Klebsiella and Enterocloster. In addition, Bifidobacterium and Blautia were increased in T2D patients but restored to near normal levels by metformin, and this alteration is regional specific. Our analysis delivers more concrete evidence regarding the shifts in gut microbiota following metformin treatment, significantly enriching our understanding of the interplay between gut microbiome dynamics and the management of T2D.

An anticipatory mechanism that enhances cooperative behaviors of quorum sensing mutants of Pseudomonas aeruginosa.

Social interactions substantially influence the dynamics and functions of microbial communities. Cooperative behaviors serve to benefit populations, yet they are often exploited by cheating cells, thus creating a conflict between individuals in the microbial population. However, the underlying mechanisms by which cooperative behaviors are stabilized are incompletely elucidated. Here, we used quorum sensing (QS) as a model of cooperation, and functionally studied QS regulator LasR variant strains in the context of cooperative behaviors. We found that a LasR228 variant strain, bearing a non-conserved substitution in LasR, exhibited minimal LasR-dependent phenotypes. However, the function of this LasR228 variant strain was restored by inactivation of the transcriptional repressor PsdR, and the phenotypes of this variant strain were similar to the parental strain. Furthermore, we illustrate a post-transcriptional regulatory mechanism responsible for the activation of the LasR228 variant. Unlike LasR228, the PsdR-null-LasR228 strain demonstrated cooperative behaviors in competition with the LasR-null strain. Since psdR mutations precede the emergence of LasR variants in the evolution of P. aeruginosa using casein broth, this PsdR-mediated cooperative mechanism serves as an anticipatory control against potential cheating LasR variant strains. Additionally, our cell-killing assay showed that the cooperative PsdR-null-LasR228 strain was associated with increased bacterial pathogenicity to eukaryotic host cells. In conclusion, our study reveals the functional plasticity of LasR variants, which can be modulated by secondary mutations, affecting cooperation and conflict within populations. Our identification of a novel cooperative molecular mechanism offers insight into the maintenance of cooperation within microbial communities.

Proteomic characterization of Mycobacterium tuberculosis subjected to carbon starvation.

Mycobacterium tuberculosis (Mtb) is the causative agent of tuberculosis (TB), the leading cause of infectious disease-related deaths worldwide. TB infections present on a spectrum from active to latent disease. In the human host, Mtb faces hostile environments, such as nutrient deprivation, hypoxia, and low pH. Under these conditions, Mtb can enter a dormant, but viable, state characterized by a lack of cell replication and increased resistance to antibiotics. Dormant Mtb poses a major challenge to curing infections and eradicating TB globally. We subjected Mtb mc26020 (ΔlysA and ΔpanCD), a double auxotrophic strain, to carbon starvation (CS), a culture condition that induces growth stasis and mimics environmental conditions associated with dormancy in vivo. We provide a detailed analysis of the proteome in CS compared to replicating samples. We observed extensive proteomic reprogramming, with 36% of identified proteins significantly altered in CS. Many enzymes involved in oxidative phosphorylation and lipid metabolism were retained or more abundant in CS. The cell wall biosynthetic machinery was present in CS, although numerous changes in the abundance of peptidoglycan, arabinogalactan, and mycolic acid biosynthetic enzymes likely result in pronounced remodeling of the cell wall. Many clinically approved anti-TB drugs target cell wall biosynthesis, and we found that these enzymes were largely retained in CS. Lastly, we compared our results to those of other dormancy models and propose that CS produces a physiologically distinct state of stasis compared to hypoxia in Mtb.IMPORTANCETuberculosis is a devastating human disease that kills over 1.2 million people a year. This disease is caused by the bacterial pathogen Mycobacterium tuberculosis (Mtb). Mtb excels at surviving in the human host by entering a non-replicating, dormant state. The current work investigated the proteomic changes that Mtb undergoes in response to carbon starvation, a culture condition that models dormancy. The authors found broad effects of carbon starvation on the proteome, with the relative abundance of 37% of proteins significantly altered. Protein changes related to cell wall biosynthesis, metabolism, and drug susceptibility are discussed. Proteins associated with a carbon starvation phenotype are identified, and results are compared to other dormancy models, including hypoxia.

Antimicrobial activities and beta-lactamase inhibitory property of actinomycetes from Atlas forest soils in Northeastern Algeria.

Actinomycetes bacteria are an inexhaustible natural source of secondary metabolites with diverse antimicrobial activities. In the current study, screening based on antimicrobial activity of the cell-free supernatant (CFS) of 23 actinomycetes isolates from Atlas forest soils in Northeastern Algeria was performed against ten human bacterial pathogens and Candida albicans ATCC 10231 strain. Among them, three isolates AM138DZ, AM141DZ and AM183DZ showed antagonistic effects towards indicator pathogens. The isolate AM183AZ exhibited strong activities against Staphylococcus aureus ATCC 6538, C. albicans ATCC 10231, clinical strains Esherichia coli BLSE and Salmonella spp. BLSE. The isolates AM141AZ and AM138AZ displayed high antimicrobial activity towards C. albicans 10231. Interestingly, the CFS of AM138DZ and AM141DZ combined with amoxicillin inhibited β-lactamase activity from Klebsiella pneumoniae ATCC 700603, an extended-spectrum β-lactamase producing strain. The ethyl acetate extracts of the three isolates displayed a large spectrum of antimicrobial activity against all pathogens tested. Analysis of their contents by UPLC-ESI-MS/MS revealed the identification of 16 to 18 compounds, among them 5 flavonoids, 6 organic acids and 2 phenols. Overall, flavonoids (such as rutin, chrysin, quercetin and catechin) were the major compounds detected in the three extracts. Depending on the isolate, other notable compounds were detected at significant levels: β-caroten, salicin and salycilic acid. Molecular identification of the three isolates using 16S rRNA sequence homology suggested that these isolates should be assigned as Streptomyces flavogriseus AM138DZ, Streptomyces felleus AM141DZ, and Streptomyces rubiginosohelvolus AM183DZ strains. Our study provides a promising natural alternative source of antimicrobials and β-lactamase inhibitors in particular.