Killing of Caenorhabditis elegans by Pseudomonas aeruginosa used to model mammalian bacterial pathogenesis

Molecular requirements for C. elegans transgenerational epigenetic inheritance of pathogen avoidance

Bacteria are Caenorhabditis elegans' food, and worms are naturally attracted to many bacteria, including pathogenic Pseudomonas, preferring PA14 over laboratory Escherichia coli (OP50). Despite this natural attraction to PA14, prior PA14 exposure causes the worms to instead avoid PA14. This behavioral switch can happen quickly - even within the duration of the choice assay. We show that accurate assessment of the animals' true first choice requires the use of a paralytic (azide) to trap the worms at their initial choice, preventing the switch from attraction to avoidance of PA14 within the assay period. We previously discovered that exposure of C. elegans to 25°C plate-grown PA14 at 20°C for 24 hr not only leads to PA14 avoidance, but also to four generations of naïve progeny avoiding PA14, while other PA14 paradigms only cause P0 and/or F1 avoidance. We also showed that the transgenerational (P0-F4) epigenetic avoidance is mediated by P11, a small RNA produced by PA14. P11 is both necessary and sufficient for TEI of learned avoidance. P11 is highly expressed in our standard growth conditions (25°C on surfaces), but not in other conditions, suggesting that the reported failure to observe F2-F4 avoidance is likely due to the absence of P11 expression in PA14 in the experimenters' growth conditions. Additionally, we tested ~35 genes for involvement in TEI of learned pathogen avoidance. The conservation of multiple components of this sRNA TEI mechanism across C. elegans strains and in multiple Pseudomonas species suggests that this TEI behavior is likely to be physiologically important in wild conditions.

Ferric Uptake Regulator Contributes to Pseudomonas donghuensis HYS-Induced Iron Metabolic Disruption in Caenorhabditis elegans

Iron is essential for vital biological processes, with its metabolism closely linked to host-pathogen interactions. Pseudomonas donghuensis HYS, with its superior iron uptake capacity, demonstrates pronounced virulence toward Caenorhabditis elegans. However, the virulence mechanisms remain unexplored. Ferric uptake regulator (Fur) regulates iron homeostasis and pathogenicity in bacteria, yet its role in HYS-mediated C. elegans pathogenesis requires systematic investigation. In this study, comparing the pathogenic processes of HYS and P. aeruginosa PA14 revealed that HYS causes stronger, irreversible toxicity via distinct mechanisms. Transcriptomics revealed that HYS infection disrupts C. elegans iron metabolism pathways, specifically iron transport, and iron-sulfur cluster utilization. Fur was identified as a pivotal regulator in HYS virulence and was indispensable for its colonization. Specifically, Fur was critical for disrupting nematode iron metabolism, as fur deletion eliminated this effect. While Fur regulated two HYS siderophores, neither of them mediated in the iron metabolism disruption of C. elegans. Screening identified Fur-regulated virulence factors to further investigate the function of Fur in HYS virulence, particularly alkaline proteases, and type II secretion system components. This study highlight that HYS can disrupt the iron metabolism pathway in C. elegans; Fur serves as a pivotal positive regulator in HYS-induced damage, particularly in disrupting iron metabolism through a siderophore-independent pathway. These findings expand the understanding of Pseudomonas pathogenicity and Fur-mediated virulence regulation.

hmuSTUV operon positively regulates the alginate gene cluster to mediate the pathogenicity of Pseudomonas donghuensis HYS

Pseudomonas donghuensis HYS is highly virulent to Caenorhabditis elegans, but with mechanistic details that are not fully understood. The hmuSTUV operon was reported to participate in the synthesis of heme in Pseudomonas. However, the exact role of the hmuSTUV operon in Pseudomonas virulence has not been elucidated. In this study, we report for the first time that the hmuSTUV operon in P. donghuensis HYS causes host virulence, and that hmuS was a key gene for the toxicity of this operon. Furthermore, RNA-seq data showed that hmuS deletion inhibited alginate gene expression, thereby inhibiting biofilm formation. The hmuSTUV operon and alginate gene cluster are conserved in Pseudomonas. By constructing mutant strains carrying GFP, we found that the hmuS deletion reduced colonisation of HYS to the host gut. Moreover, the expression of the alginate gene cluster was controlled by the construction of a L-arabinose-inducible promoter. hmuS positively regulated alginate gene cluster expression, mediating bacterial virulence against C. elegans. In addition, HYS originating from the East Lake of Wuhan City was more pathogenic to zebrafish than any other pathogenic Pseudomonas, through impairment of zebrafish neurodevelopment and locomotor ability, by colonizing to the zebrafish brain. In conclusion, the hmuSTUV operon positively regulated the alg gene cluster, thereby disabling bacterial biofilm formation and colonisation to mediate bacterial pathogenicity to the host. These novel findings revealed the critical interaction between the hmuSTUV operon and the alg gene cluster in the bacterial virulence of Pseudomonas, providing new insights into Pseudomonas pathogenicity.

Patterns of pathogenesis in innate immunity: insights from C. elegans

The cells in barrier tissues can distinguish pathogenic from commensal bacteria and target inflammatory responses only in the context of infection. As such, these cells must be able to identify pathogen infection specifically and not just the presence of an infectious organism, because many innocuous bacteria express the ligands that activate innate immunity in other contexts. Unravelling the mechanisms that underly this specificity, however, is challenging. Free-living nematodes, such as Caenorhabditis elegans, are faced with a similar dilemma, as they live in microorganism-rich habitats and eat bacteria as their source of nutrition. Nematodes lost canonical mechanisms of pattern recognition during their evolution and have instead evolved mechanisms to identify specific ligands or symptoms in the host that indicate active infection with an infectious microorganism. Here we review how C. elegans surveys for these patterns of pathogenesis to activate innate immune defences. Collectively, this work demonstrates that using C. elegans as an experimental platform to study host-pathogen interactions at barrier surfaces reveals primordial and fundamentally important principles of innate immune sensing in the animal branch of the tree of life.

Behavioral Cooperation or Conflict of Human Intestinal Roundworms and Microbiomes: A Bio-Activity Perspective

Human infections are greatly impacted by intestinal nematodes. These nematodes, which encompass the large roundworms, have a direct impact on human health and well-being due to their close cohabitation with the host's microorganisms. When nematodes infect a host, the microbiome composition changes, and this can impact the host's ability to control the parasites. We aimed to find out if the small intestinal roundworms produce substances that have antimicrobial properties and respond to their microbial environment, and if the immune and regulatory reactions to nematodes are altered in humans lacking gut microbes. There is no doubt that different nematodes living in the intestines can alter the balance of intestinal bacteria. Nonetheless, our knowledge about the parasite's influence on the gut microbiome remains restricted. The last two decades of study have revealed that the type of iron utilized can influence the activation of unique virulence factors. However, some roundworm proteins like P43, which makes up a large portion of the worm's excretory-secretory product, have an unknown role. This review explores how the bacterial iron regulatory network contributes to the adaptability of this opportunistic pathogen, allowing it to successfully infect nematodes in different host environments.

Sources of behavioral variability in C. elegans: Sex differences, individuality, and internal states

Animal behavior varies across different timescales. This includes rapid shifts in behavior as animals transition between states and long-term changes that develop throughout an organism's life. This review presents the contributions of sex differences, individuality, and internal states to behavioral variability in the roundworm Caenorhabditis elegans. Sex is determined by chromosome composition, which directs neuronal development through gene regulation and experience to shape dimorphic behaviors. Genetically identical individuals within the same sex and reared in the same conditions still display distinctive, long-lasting behavioral traits that are controlled by neuromodulatory systems. At all life stages, internal states within the individual, shaped by external factors like food and stress, modulate behavior over minutes to hours. The interplay between these factors gives rise to rich behavioral diversity in C. elegans. These factors impact behavior in a sequential manner, as genetic sex, individuality, and internal states influence behavior over progressively finer timescales.

Hyperpiliation, not loss of pilus retraction, reduces Pseudomonas aeruginosa pathogenicity

Type IVa pili (T4aP) are important virulence factors for many bacterial pathogens. Previous studies suggested that the retraction ATPase, PilT, modulates pathogenicity due to its critical role in pilus dynamics and twitching motility. Here we use a Caenorhabditis elegans slow-killing model to show that hyperpiliation, not loss of pilus retraction, reduces virulence of Pseudomonas aeruginosa strains PAK and PA14. Hyperactivating point mutations in the P. aeruginosa PilSR two-component system that controls transcription of the major pilin gene, pilA, increased levels of surface pili to the same extent as deleting pilT, without impairing twitching motility. These functionally hyperpiliated PilSR mutants had significant defects in pathogenicity that were rescued by deleting pilA or through disruption of hyperpiliation via deletion of the type III secretion system needle-length regulator, PscP. Hyperpiliated pilT deletion or pilO point mutants showed similar PilA-dependent impairments in virulence, validating the phenotype. Together, our data support a model where a surfeit of pili reduces virulence, potentially through the prevention of effective engagement of contact-dependent virulence factors. These findings suggest that the role of T4aP retraction in virulence should be revised.IMPORTANCEPseudomonas aeruginosa is a major contributor to hospital-acquired infections and particularly problematic due to its intrinsic resistance to many front-line antibiotics. Strategies to combat this and other important pathogens include the development of anti-virulence therapeutics. We show that the pathogenicity of P. aeruginosa is impaired when the amount of T4aP expressed on the cell surface increases, independent of the bacteria's ability to twitch. We propose that having excess T4aP on the cell surface may physically interfere with productive engagement of the contact-dependent type III secretion toxin delivery system. A better understanding of how T4aP modulate interaction of bacteria with target cells will improve the design of therapeutics targeting components involved in the regulation of T4aP expression and function to reduce the clinical burden of P. aeruginosa and other T4aP-expressing bacteria.

Reported transgenerational responses to Pseudomonas aeruginosa in Caenorhabditis elegans are not robust

We report our attempt to replicate reports of transgenerational epigenetic inheritance in Caenorhabditis elegans. Multiple laboratories report that C. elegans adults and their F1 embryos exposed to the pathogen Pseudomonas aeruginosa show pathogen aversion behavior and increased daf-7/TGFβ reporter gene expression. However, results from one group show persistence of both through the F4 generation. We failed to consistently detect either the avoidance response or elevated daf-7 expression beyond the F1 generation. We confirmed that the dsRNA transport proteins SID-1 and SID-2 are required for intergenerational (F1) inheritance of pathogen avoidance, but not for the F1 inheritance of elevated daf-7 expression. Reanalysis of RNA seq data provides additional evidence that this intergenerational inherited PA14 response may be mediated by small RNAs. The experimental methods are well-described, the source materials are readily available, including samples from the reporting laboratory, and we explored a variety of environmental conditions likely to account for lab-to-lab variability. None of these adjustments altered our results. We conclude that this example of transgenerational inheritance lacks robustness, confirm that the intergenerational avoidance response, but not the elevated daf-7p::gfp expression in F1 progeny, requires sid-1 and sid-2, and identify candidate siRNAs and target genes that may mediate this intergenerational response.

Neopterin extends C. elegans lifespan in an ATFS-1-dependent manner

Neopterin, a byproduct of tetrahydrobiopterin synthesis, is commonly used as a biomarker for immune system activation. In addition to its role in immune responses, neopterin levels are known to increase with age. Its impact on longevity, however, remains unclear. Here, we demonstrate that neopterin supplementation extends lifespan in Caenorhabditis elegans . Additionally, neopterin shows moderate activation of the mitochondrial unfolded protein response (UPR mt ), and that the neopterin-mediated lifespan extension is dependent on ATFS-1 , the primary transcription factor regulating UPR mt . These findings highlight the need for further investigation into the biological functions and health-promoting effects of neopterin.

Endosomal catabolism of phosphatidylinositol 4,5-bisphosphate is fundamental in building resilience against pathogens

Endosomes are characterized by the presence of various phosphoinositides that are essential for defining the membrane properties. However, the interplay between endosomal phosphoinositides metabolism and innate immunity is yet to be fully understood. Here, our findings highlight the evolutionary continuity of RAB-10/Rab10's involvement in regulating innate immunity. Upon infection of Caenorhabditis elegans with Pseudomonas aeruginosa, an increase in RAB-10 activity was observed in the intestine. Conversely, when RAB-10 was absent, the intestinal diacylglycerols (DAGs) decreased, and the animal's response to the pathogen was impaired. Further research revealed that UNC-16/JIP3 acts as an RAB-10 effector, facilitating the recruitment of phospholipase EGL-8 to endosomes. This leads to a decrease in endosomal phosphatidylinositol 4,5-bisphosphate (PI(4,5)P2) and an elevation of DAGs, as well as the activation of the PMK-1/p38 MAPK innate immune pathway. It is noteworthy that the dimerization of UNC-16 is a prerequisite for its interaction with RAB-10(GTP) and the recruitment of EGL-8. Moreover, we ascertained that the rise in RAB-10 activity, due to infection, was attributed to the augmented expression of LET-413/Erbin, and the nuclear receptor NHR-25/NR5A1/2 was determined to be indispensable for this increase. Hence, this study illuminates the significance of endosomal PI(4,5)P2 catabolism in boosting innate immunity and outlines an NHR-25-mediated mechanism for pathogen detection in intestinal epithelia.

Quiescent behavior in response to bacterial infection in C. elegans

Sickness behaviors serve an important role in recovery from infection. Using the WorMotel and a motivated displacement assay, we show that C. elegans engages in quiescent behavior following infection with Serratia marcesens , a bacterial pathogen. This quiescence is increased with increasing severity of the infection. Furthermore, we show this behavior is distinct from stress-induced sleep due to a lack of feeding quiescence and regulation by sleep-inducing neurons.

Pediococcus pentosaceus MZF16 Probiotic Strain Prevents In Vitro Cytotoxic Effects of Pseudomonas aeruginosa H103 and Prolongs the Lifespan of Caenorhabditis elegans

Pseudomonas aeruginosa is an opportunistic pathogenic bacterium, responsible for several life-threatening infections due to its multiple virulence factors and problematic multi-drug resistance, hence the necessity to find alternatives such as competitive probiotics. Pediococcus pentosaceus MZF16 is an LAB strain, isolated from traditional dried meat "Ossban", with high probiotic potential. Our study investigated the capacity of P. pentosaceus MZF16 to counteract P. aeruginosa H103 using several tests on intestinal cells (analysis of cytotoxicity, inflammation, adhesion/invasion) and on the in vivo Caenorhabditis elegans model. The effect of MZF16 on the quorum sensing of the pathogen was also examined. We found that P. pentosaceus MZF16 was able to reduce H103 cytotoxicity and inflammatory activity and prevented pathogen colonization and translocation across Caco-2/TC7 cells. MZF16 also exerted an anti-virulence effect by attenuating quorum-sensing (QS) molecules and pyoverdine production and extended C. elegans lifespan. The obtained results highlight the potential of P. pentosaceus MZF16 probiotic strain as an anti-Pseudomonas aeruginosa alternative and establish a basis for elucidating the mechanisms of P. pentosaceus MZF16 involved in countering P. aeruginosa virulence.

The Roles of Distinct Transcriptional Factors in the Innate Immunity of C. elegans

Deleterious molecules or factors produced by pathogens can hinder the normal physiological functioning of organisms. In response to these survival challenges, organisms rely on innate immune signaling as their first line of defense, which regulates immune-responsive genes and antimicrobial peptides to protect against pathogenic infections. These genes are under the control of transcription factors, which are known to regulate the transcriptional activity of genes after binding to their regulatory sequences. Previous studies have employed Caenorhabditis elegans as a host-pathogen interaction model to demonstrate the essential role of different transcription factors in the innate immunity of worms. In this review, we summarize the advances made regarding the functioning of distinct transcription factors in the innate immune response upon pathogen infection. Finally, we discuss the open questions in the field, whose resolutions have the potential to expand our understanding of the mechanisms underlying the innate immunity of organisms.

Quorum sensing regulation by the nitrogen phosphotransferase system in Pseudomonas aeruginosa

In the opportunistic pathogen Pseudomonas aeruginosa, the nitrogen-related phosphotransferase system (PTSNtr) influences multiple virulence behaviors. The PTSNtr is comprised of three enzymes: first PtsP, then the PtsO phosphocarrier, and the final PtsN phosphoacceptor. We previously showed that ptsP inactivation increases LasI-LasR quorum sensing, a system by which P. aeruginosa regulates genes in response to population density. LasI synthesizes a diffusible autoinducer that binds and activates the LasR receptor, which activates a feedback loop by increasing lasI expression. In this study, we examined the impact of the PTSNtr on quorum sensing. Disruption of ptsP increased the expression of some, but not all, tested quorum-controlled genes, including lasI, phzM (pyocyanin biosynthesis), hcnA (hydrogen cyanide biosynthesis), and, to a lesser extent, rsaL (quorum sensing regulator). Expression of these genes remained dependent on LasR and the autoinducer, whether provided endogenously or exogenously. Increased lasI expression in ΔptsP (or ΔptsO) cells was partly due to the presence of unphosphorylated PtsN, which alone was sufficient to elevate lasI expression. However, we observed residual increases in ΔptsP or ΔptsO cells even in the absence of PtsN, suggesting that PtsP and PtsO can regulate gene expression independent of PtsN. Indeed, genetically disrupting the PtsO phosphorylation site impacted gene expression in the absence of PtsN, and transcriptomic evidence suggested that PtsO and PtsN have distinct regulons. Our results expand our view of how the PTSNtr components function both within and apart from the classic phosphorylation cascade to regulate key virulence behaviors in P. aeruginosa.

An Artificial Neural Network for Image Classification Inspired by the Aversive Olfactory Learning Neural Circuit in Caenorhabditis elegans

This study introduces an artificial neural network (ANN) for image classification task, inspired by the aversive olfactory learning neural circuit in Caenorhabditis elegans (C. elegans). Although artificial neural networks (ANNs) have demonstrated remarkable performance in various tasks, they still encounter challenges including excessive parameterization, high training costs and limited generalization capabilities, etc. C. elegans, boasting a simple nervous system consisting of merely 302 neurons, is capable of exhibiting complex behaviors such as aversive olfactory learning. This research pinpoints key neural circuit related to aversive olfactory learning in C. elegans by means of behavioral experiment and high-throughput RNA sequencing, and then translates it into an architecture of ANN for image classification. Furthermore, other ANNs for image classification with different architectures are constructed for comparative performance analysis to underscore the advantages of the bio-inspired designed architecture. The results show that the ANN inspired by the aversive olfactory learning neural circuit in C. elegans attains higher accuracy, greater consistency and faster convergence rate in the image classification task, particularly when dealing with more complex classification challenges. This study not only demonstrates the potential of bio-inspired design in improving the capabilities of ANNs but also offers a novel perspective and methodology for future ANNs design.

Early life long-term exposure to aflatoxin B1 induces aging and alters innate immunity associated with SKN-1/Nrf2 in Caenorhabditis elegans

Aflatoxin B1 (AFB1), a known human carcinogen, represents the most toxic aflatoxin metabolite. Exposure to AFB1 causes increased oxidative stress and immunotoxicity, which are important factors contributing to aging. However, the role of AFB1-induced toxicity in altered innate immunity and aging remains largely unclear. The nematode Caenorhabditis elegans is a suitable model organism for studying aging and toxicology due to its well-studied molecular mechanisms and short life cycle. Effects of AFB1 at 1, 2.5, and 5 μM (312, 781, and 1561 μg/L) on growth, reproduction, and lifespan were examined. The Pseudomonas aeruginosa PA14 slow-killing assay was performed to investigate innate immunity, followed by studying the possible mechanisms using transgenic strains and qPCR analysis. The results showed that early life long-term AFB1 exposure (2.5 and 5 μM) delayed development, reduced reproduction, and shortened lifespan in C. elegans. Furthermore, in aged worms, AFB1 exposure caused a dose-dependent decrease in survival of C. elegans against P. aeruginosa PA14 infection. At adulthood day 4 in the presence of live Escherichia coli OP50, AFB1 (2.5 μM) significantly increased lipofuscin levels (a hallmark of aging) compared to adult day 0, whereas no increase in lipofuscin was observed in nematodes (adulthood day 4) fed with dead E. coli OP50. Additionally, the increased lipofuscin was abolished in the skn-1 mutant with either live or dead E. coli OP50. Furthermore, AFB1 suppressed intestinal SKN-1::GFP translocation. Two-way ANOVA analysis revealed that the activity of E. coli OP50 and AFB1 interactively affected the expression of genes: skn-1, gst-4, hsp-16.1, hsp-16.49, and hsp-70. Our findings highlight the role of AFB1-induced toxicity in altered innate immunity and aging through the involvement of the transcription factor SKN-1/Nrf2.

Modulation by NPY/NPF-like receptor underlies experience-dependent, sexually dimorphic learning

The evolutionary paths taken by each sex within a given species sometimes diverge, resulting in behavioral differences. Given their distinct needs, the mechanism by which each sex learns from a shared experience is still an open question. Here, we reveal sexual dimorphism in learning: C. elegans males do not learn to avoid the pathogenic bacteria PA14 as efficiently and rapidly as hermaphrodites. Notably, neuronal activity following pathogen exposure was dimorphic: hermaphrodites generate robust representations, while males, in line with their behavior, exhibit contrasting representations. Transcriptomic and behavioral analysis revealed that the neuropeptide receptor npr-5, an ortholog of the mammalian NPY/NPF-like receptor, regulates male learning by modulating neuronal activity. Furthermore, we show the dependency of the males' decision-making on their sexual status and demonstrate the role of npr-5 as a modulator of incoming sensory cues. Taken together, these findings illustrate how neuromodulators drive sex-specific behavioral plasticity in response to a shared experience.

Probiotics-sensing mechanism in neurons that initiates gut mitochondrial surveillance for pathogen defense

Animals constantly face microbial challenges, and microbe-mediated infection protection is crucial for host survival. Identifying specific bacteria and their interactions with host intracellular surveillance systems is important but challenging. Here, we develop a "probiotics" screening system that identifies Escherichia coli mutants, such as ΔymcB, which protect hosts from Pseudomonas aeruginosa PA14 infection by activating the mitochondrial unfolded protein response (UPRmt). Genetic screening reveals that MDSS-1, a neuronal transmembrane protein, is crucial for sensing ΔymcB and triggering intestinal UPRmt. MDSS-1 functions as a potential receptor in ASE neurons, detecting ΔymcB and transmitting signals through neuropeptides, GPCRs, Wnt signaling, and endopeptidase inhibitors to activate intestinal UPRmt and enhance protection. Constitutive activation of MDSS-1 in ASE neurons is sufficient to induce UPRmt and confer infection resistance. This study uncovers a neuron-intestine communication mechanism, where ASE neurons detect bacteria and modulate the intestinal mitochondrial surveillance system for host adaptation to pathogens.

Distinct mechanisms of non-autonomous UPRER mediated by GABAergic, glutamatergic, and octopaminergic neurons

The capacity to deal with stress declines during the aging process, and preservation of cellular stress responses is critical to healthy aging. The unfolded protein response of the endoplasmic reticulum (UPRER) is one such conserved mechanism, which is critical for the maintenance of several major functions of the ER during stress, including protein folding and lipid metabolism. Hyperactivation of the UPRER by overexpression of the major transcription factor, xbp-1s, solely in neurons drives lifespan extension as neurons send a neurotransmitter-based signal to other tissue to activate UPRER in a non-autonomous fashion. Previous work identified serotonergic, dopaminergic, and tyraminergic neurons in this signaling paradigm. To further expand our understanding of the neural circuitry that underlies the non-autonomous signaling of ER stress, we activated UPRER solely in glutamatergic, octopaminergic, and GABAergic neurons in C. elegans and paired whole-body transcriptomic analysis with functional assays. We found that UPRER-induced signals from glutamatergic neurons increased expression of canonical protein homeostasis pathways and octopaminergic neurons promoted pathogen response pathways; while minor, statistically significant changes were observed in lipid metabolism-related genes with GABAergic UPRER activation. These findings provide further evidence for the distinct role neuronal subtypes play in driving the diverse response to ER stress.

Nematode-bacteria interactions in bovine parasitic otitis

Bovine parasitic otitis poses challenges in diagnosis, treatment and involves various agents, such as bacteria, fungi, mites, and nematodes. This study focused on the nematodes and bacteria isolated from the auditory canals of dairy cattle. A total of twenty samples were collected from dairy cattle in two states of Brazil. The results showed that Metarhabditis freitasi and M. costai nematodes were identified in 75% of samples. Bacterial species from the ear, identified via mass spectrometry, revealed that different strains were present in 65% of the cattle. Mycoplasma spp. were identified in 45% of samples through molecular techniques. Gram-negative bacteria and Mycoplasma spp. were exclusively found in nematode-infected cattle. Furthermore, the bacteria exhibited resistance to multiple antimicrobial classes, and demonstrating multiresistance. Electron microscopy revealed biofilm aggregates on the cuticle of Metarhabditis spp., suggesting a potential role of these nematodes in bacterial migration and interaction with nervous tissue. Thirteen bacterial strains demonstrated biofilm formation ability, indicating their potential pathogenic role. This research highlights the persistent and complex nature of parasitic otitis, emphasizing the significant role of nematode-bacteria associations in its pathogenicity. The presence of resistant strains and biofilm formation underscores the challenges in managing the diagnosis and treatment of bovine parasitic otitis.

New tools to monitor Pseudomonas aeruginosa infection and biofilms in vivo in C. elegans

Introduction

Antimicrobial resistance is a growing health problem. Pseudomonas aeruginosa is a pathogen of major concern because of its multidrug resistance and global threat, especially in health-care settings. The pathogenesis and drug resistance of P. aeruginosa depends on its ability to form biofilms, making infections chronic and untreatable as the biofilm protects against antibiotics and host immunity. A major barrier to developing new antimicrobials is the lack of in vivo biofilm models. Standard microbiological testing is usually performed in vitro using planktonic bacteria, without representation of biofilms, reducing translatability. Here we develop tools to study both infection and biofilm formation by P. aeruginosa in vivo to accelerate development of strategies targeting infection and pathogenic biofilms.

Methods

Biofilms were quantified in vitro using Crystal Violet staining and fluorescence biofilm assays. For in vivo assays, C. elegans were infected with P. aeruginosa strains. Pathogenicity was quantified by measuring healthspan, survival and GFP fluorescence. Healthspan assays were performed using the WormGazerTM automated imaging technology.

Results

Using the nematode Caenorhabditis elegans and P. aeruginosa reporters combined with in vivo imaging we show that fluorescent P. aeruginosa reporters that form biofilms in vitro can be used to visualize tissue infection. Using automated tracking of C. elegans movement, we find that that the timing of this infection corresponds with a decline in health endpoints. In a mutant strain of P. aeruginosa lacking RhlR, a transcription factor that controls quorum sensing and biofilm formation, we find reduced capacity of P. aeruginosa to form biofilms, invade host tissues and negatively impact healthspan and survival.

Discussion

Our findings suggest that RhlR could be a new antimicrobial target to reduce P. aeruginosa biofilms and virulence in vivo and C. elegans could be used to more effectively screen for new drugs to combat antimicrobial resistance.

Adult single-nucleus neuronal transcriptomes of insulin signaling mutants reveal regulators of behavior and learning

Gene expression in individual neurons can change during development to adulthood and can have large effects on behavior. Additionally, the insulin/insulin-like signaling (IIS) pathway regulates many of the adult functions of Caenorhabditis elegans, including learning and memory, via transcriptional changes. We used the deep resolution of single-nucleus RNA sequencing to define the adult transcriptome of each neuron in wild-type and daf-2 mutants, revealing expression differences between L4 larval and adult neurons in chemoreceptors, synaptic genes, and learning/memory genes. We used these data to identify adult new AWC-specific regulators of chemosensory function that emerge upon adulthood. daf-2 gene expression changes correlate with improved cognitive functions, particularly in the AWC sensory neuron that controls learning and associative memory; behavioral assays of AWC-specific daf-2 genes revealed their roles in cognitive function. Combining technology and functional validation, we identified conserved genes that function in specific adult neurons to control behavior, including learning and memory.

Pseudomonas aeruginosa quorum sensing and biofilm attenuation by a di-hydroxy derivative of piperlongumine (PL-18)

Bacterial communication, Quorum Sensing (QS), is a target against virulence and prevention of antibiotic-resistant infections. 16 derivatives of Piperlongumine (PL), an amide alkaloid from Piper longum L., were screened for QS inhibition. PL-18 had the best QSI activity. PL-18 inhibited the lasR-lasI, rhlR-rhlI, and pqs QS systems of Pseudomonas aeruginosa. PL-18 inhibited pyocyanin and rhamnolipids that are QS-controlled virulence elements. Iron is an essential element for pathogenicity, biofilm formation and resilience in harsh environments, its uptake was inhibited by PL-18. Pl-18 significantly reduced the biofilm biovolume including in established biofilms. PL-18-coated silicon tubes significantly inhibited biofilm formation. The transcriptome study of treated P. aeruginosa showed that PL-18 indeed reduced the expression of QS and iron homeostasis related genes, and up regulated sulfur metabolism related genes. Altogether, PL-18 inhibits QS, virulence, iron uptake, and biofilm formation. Thus, PL-18 should be further developed against bacterial infection, antibiotic resistance, and biofilm formation.

Translation initiation or elongation inhibition triggers contrasting effects on Caenorhabditis elegans survival during pathogen infection

Diverse microbial pathogens are known to attenuate host protein synthesis. Consequently, the host mounts a defense response against protein translation inhibition, leading to increased transcript levels of immune genes. The seemingly paradoxical upregulation of immune gene transcripts in response to blocked protein synthesis suggests that the defense mechanism against translation inhibition may not universally benefit host survival. However, a comprehensive assessment of host survival on pathogens upon blockage of different stages of protein synthesis is currently lacking. Here, we investigate the impact of knockdown of various translation initiation and elongation factors on the survival of Caenorhabditis elegans exposed to Pseudomonas aeruginosa. Intriguingly, we observe opposing effects on C. elegans survival depending on whether translation initiation or elongation is inhibited. While translation initiation inhibition enhances survival, elongation inhibition decreases it. Transcriptomic studies reveal that translation initiation inhibition activates a bZIP transcription factor ZIP-2-dependent innate immune response that protects C. elegans from P. aeruginosa infection. In contrast, inhibiting translation elongation triggers both ZIP-2-dependent and ZIP-2-independent immune responses that, while effective in clearing the infection, are detrimental to the host. Thus, our findings reveal the opposing roles of translation initiation and elongation inhibition in C. elegans survival during P. aeruginosa infection, highlighting distinct transcriptional reprogramming that may underlie these differences.

IMPORTANCE

Several microbial pathogens target host protein synthesis machinery, potentially limiting the innate immune responses of the host. In response, hosts trigger a defensive response, elevating immune gene transcripts. This counterintuitive response can have either beneficial or harmful effects on host survival. In this study, we conduct a comprehensive analysis of the impact of knocking down various translation initiation and elongation factors on the survival of Caenorhabditis elegans exposed to Pseudomonas aeruginosa. Intriguingly, inhibiting initiation and elongation factors has contrasting effects on C. elegans survival. Inhibiting translation initiation activates immune responses that protect the host from bacterial infection, while inhibiting translation elongation induces aberrant immune responses that, although clear the infection, are detrimental to the host. Our study reveals divergent roles of translation initiation and elongation inhibition in C. elegans survival during P. aeruginosa infection and identifies differential transcriptional reprogramming that could underlie these differences.

SKN-1 activation during infection of Caenorhabditis elegans requires CDC-48 and endoplasmic reticulum proteostasis

During challenge of Caenorhabditis elegans with human bacterial pathogens such as Pseudomonas aeruginosa and Enterococcus faecalis, the elicited host response can be damaging if not properly controlled. The activation of Nrf (nuclear factor erythroid-related factor)/CNC (Cap-n-collar) transcriptional regulators modulates the response by upregulating genes that neutralize damaging molecules and promote repair processes. Activation of the C. elegans Nrf ortholog, SKN-1, is tightly controlled by a myriad of regulatory mechanisms, but a central feature is an activating phosphorylation accomplished by the p38 mitogen-activated kinase (MAPK) cascade. In this work, loss of CDC-48, an AAA+ ATPase, was observed to severely compromise SKN-1 activation on pathogen and we sought to understand the mechanism. CDC-48 is part of the endoplasmic reticulum (ER)-associated degradation (ERAD) complex where it functions as a remodeling chaperone enabling the translocation of proteins from the ER to the cytoplasm for degradation by the proteosome. Interestingly, one of the proteins retrotranslocated by ERAD, a process necessary for its activation, is SKN-1A, the ER isoform of SKN-1. However, we discovered that SKN-1A is not activated by pathogen exposure in marked contrast to the cytoplasmic-associated isoform SKN-1C. Rather, loss of CDC-48 blocks the antioxidant response normally orchestrated by SKN-1C by strongly inducing the unfolded protein response (UPRER). The data are consistent with the model of these 2 pathways being mutually inhibitory and support the emerging paradigm in the field of coordinated cooperation between different stress responses.

Cyclic di-GMP incorporates the transcriptional factor FleQ03 in Pseudomonas syringae MB03 to elicit biofilm-dependent resistance in response to Caenorhabditis elegans predation

Bacteria usually form biofilms as a defense mechanism against predation by bacterivorous nematodes. In this context, the second messenger c-di-GMP from the wild-type Pseudomonas syringae MB03 actuates the transcriptional factor FleQ03 to elicit biofilm-dependent nematicidal activity against Caenorhabditis elegans N2. P. syringae MB03 cells exhibited nematicidal activity and c-di-GMP content in P. syringae MB03 cells was increased after feeding to nematodes. Expression of a diguanylate cyclase (DGC) gene in P. syringae MB03 resulted in an increased c-di-GMP content, biofilm yield and nematicidal activity, whereas converse effects were obtained when expressing a phosphodiesterase (PDE) gene. Molecular docking and isothermal titration calorimetry assays verified the affinity activity between c-di-GMP and the FleQ03 protein. The disruption of the fleQ03 gene in P. syringae MB03, while increasing c-di-GMP content, significantly diminished both biofilm formation and nematicidal activity. Interestingly, P. syringae MB03 formed a full-body biofilm around the worms against predation, probably extending from the tail to the head, whereas it was not observed in the fleQ03 gene disrupted cells. Thus, we hypothesized that c-di-GMP incorporated FleQ03 to reinforce bacterial biofilm and biofilm-dependent pathogenicity in response to C. elegans predation, providing insights into a possible means of resisting bacterivorous nematodes by bacteria in natural ecosystems.

Reported transgenerational responses to Pseudomonas aeruginosa in C. elegans are not robust

Here we report our attempt to replicate reports of transgenerational epigenetic inheritance in Caenorhabditis elegans. Published results from multiple laboratories show that C. elegans adults and their F1 embryos exposed to the pathogen Pseudomonas aeruginosa show pathogen aversion behavior and a pathogen exposure-dependent increase in daf-7/TGFβ reporter gene expression. However, results from one group show persistence of the aversion behavior and elevated daf-7 expression in the F2, F3, and F4 generations. In contrast, we failed to consistently detect either the pathogen avoidance response or elevated daf-7 expression beyond the F1 generation. We did confirm that the dsRNA transport proteins SID-1 and SID-2 are required for the intergenerational (F1) inheritance of pathogen avoidance, but not for the F1 inheritance of elevated daf-7 expression. Furthermore, our reanalysis of RNA seq data provides additional evidence that this intergenerational inherited PA14 response may be mediated by small RNAs. The experimental methods are well-described, the source materials are readily available, including samples from the reporting laboratory, and we explored a variety of environmental conditions likely to account for lab-to-lab variability. None of these adjustments altered our results. We conclude that this example of transgenerational inheritance lacks robustness, confirm that the intergenerational avoidance response, but not the elevated daf-7p::gfp expression in F1 progeny, requires sid-1 and sid-2, and identify candidate siRNAs and target genes that may mediate this intergenerational response.

ASI-RIM neuronal axis regulates systemic mitochondrial stress response via TGF-β signaling cascade

Morphogens play a critical role in coordinating stress adaptation and aging across tissues, yet their involvement in neuronal mitochondrial stress responses and systemic effects remains unclear. In this study, we reveal that the transforming growth factor beta (TGF-β) DAF-7 is pivotal in mediating the intestinal mitochondrial unfolded protein response (UPRmt) in Caenorhabditis elegans under neuronal mitochondrial stress. Two ASI sensory neurons produce DAF-7, which targets DAF-1/TGF-β receptors on RIM interneurons to orchestrate a systemic UPRmt response. Remarkably, inducing mitochondrial stress specifically in ASI neurons activates intestinal UPRmt, extends lifespan, enhances pathogen resistance, and reduces both brood size and body fat levels. Furthermore, dopamine positively regulates this UPRmt activation, while GABA acts as a systemic suppressor. This study uncovers the intricate mechanisms of systemic mitochondrial stress regulation, emphasizing the vital role of TGF-β in metabolic adaptations that are crucial for organismal fitness and aging during neuronal mitochondrial stress.

Compressed sensing based approach identifies modular neural circuitry driving learned pathogen avoidance

An animal's survival hinges on its ability to integrate past information to modify future behavior. The nematode C. elegans adapts its behavior based on prior experiences with pathogen exposure, transitioning from attraction to avoidance of the pathogen. A systematic screen for the neural circuits that integrate the information of previous pathogen exposure to modify behavior has not been feasible because of the lack of tools for neuron type specific perturbations. We overcame this challenge using methods based on compressed sensing to efficiently determine the roles of individual neuron types in learned avoidance behavior. Our screen revealed that distinct sets of neurons drive exit from lawns of pathogenic bacteria and prevent lawn re-entry. Using calcium imaging of freely behaving animals and optogenetic perturbations, we determined the neural dynamics that regulate one key behavioral transition after infection: stalled re-entry into bacterial lawns. We find that key neuron types govern pathogen lawn specific stalling but allow the animal to enter nonpathogenic E. coli lawns. Our study shows that learned pathogen avoidance requires coordinated transitions in discrete neural circuits and reveals the modular structure of this complex adaptive behavioral response to infection.

Intestinal immunity in C. elegans is activated by pathogen effector-triggered aggregation of the guard protein TIR-1 on lysosome-related organelles

Toll/interleukin-1/resistance (TIR)-domain proteins with enzymatic activity are essential for immunity in plants, animals, and bacteria. However, it is not known how these proteins function in pathogen sensing in animals. We discovered that the lone enzymatic TIR-domain protein in the nematode C. elegans (TIR-1, homolog of mammalian sterile alpha and TIR motif-containing 1 [SARM1]) was strategically expressed on the membranes of a specific intracellular compartment called lysosome-related organelles. The positioning of TIR-1 on lysosome-related organelles enables intestinal epithelial cells in the nematode C. elegans to survey for pathogen effector-triggered host damage. A virulence effector secreted by the bacterial pathogen Pseudomonas aeruginosa alkalinized and condensed lysosome-related organelles. This pathogen-induced morphological change in lysosome-related organelles triggered TIR-1 multimerization, which engaged its intrinsic NAD+ hydrolase (NADase) activity to activate the p38 innate immune pathway and protect the host against microbial intoxication. Thus, TIR-1 is a guard protein in an effector-triggered immune response, which enables intestinal epithelial cells to survey for pathogen-induced host damage.

SHC-3: a previously unidentified C. elegans Shc family member functions in the insulin-like signaling pathway to enhance survival during L1 arrest

Shc (Src homologous and collagen) proteins function in many different signaling pathways where they mediate phosphorylation-dependent protein-protein interactions. These proteins are characterized by the presence of two phosphotyrosine-binding domains, an N-terminal PTB and a C-terminal SH2. We describe a previously unrecognized Caenorhabditis elegans Shc gene, shc-3 and characterize its role in stress response. Both shc-3 and shc-1 are required for long-term survival in L1 arrest and survival in heat stress, however, they do not act redundantly but rather play distinct roles in these processes. Loss of shc-3 did not further decrease survival of daf-16 mutants in L1 arrest, suggesting that like SHC-1, SHC-3 functions in the insulin-like signaling pathway. In the absence of SHC-3, DAF-16 nuclear entry and exit are slowed, suggesting that SHC-3 is required for rapid changes in DAF-16 signaling.

Lysosome-related organelle integrity suppresses TIR-1 aggregation to restrain toxic propagation of p38 innate immunity

Innate immunity in bacteria, plants, and animals requires the specialized subset of Toll/interleukin-1/resistance gene (TIR) domain proteins that are nicotinamide adenine dinucleotide (NAD+) hydrolases. Aggregation of these TIR proteins engages their enzymatic activity, but it is unknown how this protein multimerization is regulated. Here, we discover that TIR oligomerization is controlled to prevent immune toxicity. We find that p38 propagates its own activation in a positive feedback loop, which promotes the aggregation of the lone enzymatic TIR protein in the nematode C. elegans (TIR-1, homologous to human sterile alpha and TIR motif-containing 1 [SARM1]). We perform a forward genetic screen to determine how the p38 positive feedback loop is regulated. We discover that the integrity of the specific lysosomal subcompartment that expresses TIR-1 is actively maintained to limit inappropriate TIR-1 aggregation on the membranes of these organelles, which restrains toxic propagation of p38 innate immunity. Thus, innate immunity in C. elegans intestinal epithelial cells is regulated by specific control of TIR-1 multimerization.

A functional screen for ubiquitin regulation identifies an E3 ligase secreted by Pseudomonas aeruginosa

Ubiquitin signaling controls many aspects of eukaryotic biology, including targeted protein degradation and immune defense. Remarkably, invading bacterial pathogens have adapted secreted effector proteins that hijack host ubiquitination to gain control over host responses. These ubiquitin-targeted effectors can exhibit, for example, E3 ligase or deubiquitinase activities, often without any sequence or structural homology to eukaryotic ubiquitin regulators. Such convergence in function poses a challenge to the discovery of additional bacterial virulence factors that target ubiquitin. To overcome this, we have developed a workflow to harvest natively secreted bacterial effectors and functionally screen them for ubiquitin regulatory activities. After benchmarking this approach on diverse ligase and deubiquitinase activities from Salmonella Typhimurium, Enteropathogenic Escherichia coli, and Shigella flexneri, we applied it to the identification of a cryptic E3 ligase activity secreted by Pseudomonas aeruginosa. We identified an unreported P. aeruginosa E3 ligase, which we have termed Pseudomonas Ub ligase 1 (PUL-1), that resembles none of the other E3 ligases previously established in or outside of the eukaryotic system. Importantly, in an animal model of P. aeruginosa infection, PUL-1 ligase activity plays an important role in regulating virulence. Thus, our workflow for the functional identification of ubiquitin-targeted effector proteins carries promise for expanding our appreciation of how host ubiquitin regulation contributes to bacterial pathogenesis.

Serotonin deficiency from constitutive SKN-1 activation drives pathogen apathy

When an organism encounters a pathogen, the host innate immune system activates to defend against pathogen colonization and toxic xenobiotics produced. C. elegans employ multiple defense systems to ensure survival when exposed to Pseudomonas aeruginosa including activation of the cytoprotective transcription factor SKN-1/NRF2. Although wildtype C. elegans quickly learn to avoid pathogens, here we describe a peculiar apathy-like behavior towards PA14 in animals with constitutive activation of SKN-1, whereby animals choose not to leave and continue to feed on the pathogen even when a non-pathogenic and healthspan-promoting food option is available. Although lacking the urgency to escape the infectious environment, animals with constitutive SKN-1 activity are not oblivious to the presence of the pathogen and display the typical pathogen-induced intestinal distension and eventual demise. SKN-1 activation, specifically in neurons and intestinal tissues, orchestrates a unique transcriptional program which leads to defects in serotonin signaling that is required from both neurons and non-neuronal tissues. Serotonin depletion from SKN-1 activation limits pathogen defenses capacity, drives the pathogen-associated apathy behaviors and induces a synthetic sensitivity to selective serotonin reuptake inhibitors. Taken together, our work reveals interesting insights into how animals perceive environmental pathogens and subsequently alter behavior and cellular programs to promote survival.

Behavioral plasticity

Behavioral plasticity allows animals to modulate their behavior based on experience and environmental conditions. Caenorhabditis elegans exhibits experience-dependent changes in its behavioral responses to various modalities of sensory cues, including odorants, salts, temperature, and mechanical stimulations. Most of these forms of behavioral plasticity, such as adaptation, habituation, associative learning, and imprinting, are shared with other animals. The C. elegans nervous system is considerably tractable for experimental studies-its function can be characterized and manipulated with molecular genetic methods, its activity can be visualized and analyzed with imaging approaches, and the connectivity of its relatively small number of neurons are well described. Therefore, C. elegans provides an opportunity to study molecular, neuronal, and circuit mechanisms underlying behavioral plasticity that are either conserved in other animals or unique to this species. These findings reveal insights into how the nervous system interacts with the environmental cues to generate behavioral changes with adaptive values.

Characterization of natural product inhibitors of quorum sensing reveals competitive inhibition of Pseudomonas aeruginosa RhlR by ortho-vanillin

Quorum sensing (QS) is a cell-cell signaling system that enables bacteria to coordinate population density-dependent changes in behavior. This chemical communication pathway is mediated by diffusible N-acyl L-homoserine lactone signals and cytoplasmic signal-responsive LuxR-type receptors in Gram-negative bacteria. As many common pathogenic bacteria use QS to regulate virulence, there is significant interest in disrupting QS as a potential therapeutic strategy. Prior studies have implicated the natural products salicylic acid, cinnamaldehyde, and other related benzaldehyde derivatives as inhibitors of QS in the opportunistic pathogen Pseudomonas aeruginosa, yet we lack an understanding of the mechanisms by which these compounds function. Herein, we evaluate the activity of a set of benzaldehyde derivatives using heterologous reporters of the P. aeruginosa LasR and RhlR QS signal receptors. We find that most tested benzaldehyde derivatives can antagonize LasR or RhlR reporter activation at micromolar concentrations, although certain molecules also cause mild growth defects and nonspecific reporter antagonism. Notably, several compounds showed promising RhlR or LasR-specific inhibitory activities over a range of concentrations below that causing toxicity. ortho-Vanillin, a previously untested compound, was the most promising within this set. Competition experiments against the native ligands for LasR and RhlR revealed that ortho-vanillin can interact competitively with RhlR but not with LasR. Overall, these studies expand our understanding of benzaldehyde activities in the LasR and RhlR receptors and reveal potentially promising effects of ortho-vanillin as a small molecule QS modulator against RhlR.

IMPORTANCE

Quorum sensing (QS) regulates many aspects of bacterial pathogenesis and has attracted much interest as a target for anti-virulence therapies over the past 30 years, for example, antagonists of the LasR and RhlR QS receptors in Pseudomonas aeruginosa. Potent and selective QS inhibitors remain relatively scarce. However, natural products have provided a bounty of chemical scaffolds with anti-QS activities, but their molecular mechanisms are poorly characterized. The current study serves to fill this void by examining the activity of an important and wide-spread class of natural product QS modulators, benzaldehydes, and related derivatives, in LasR and RhlR. We demonstrate that ortho-vanillin can act as a competitive inhibitor of RhlR, a receptor that has emerged and may supplant LasR in certain settings as a target for P. aeruginosa QS control. The results and insights provided herein will advance the design of chemical tools to study QS with improved activities and selectivities.

Recent advances in the development of bacterial response regulators inhibitors as antibacterial and/or antibiotic adjuvant agent: A new approach to combat bacterial resistance

The number of new antibacterial agents currently being discovered is insufficient to combat bacterial resistance. It is extremely challenging to find new antibiotics and to introduce them to the pharmaceutical market. Therefore, special attention must be given to find new strategies to combat bacterial resistance and prevent bacteria from developing resistance. Two-component system is a transduction system and the most prevalent mechanism employed by bacteria to respond to environmental changes. This signaling system consists of a membrane sensor histidine kinase that perceives environmental stimuli and a response regulator which acts as a transcription factor. The approach consisting of developing response regulators inhibitors with antibacterial activity or antibiotic adjuvant activity is a novel approach that has never been previously reviewed. In this review we report for the first time, the importance of targeting response regulators and summarizing all existing studies carried out from 2008 until now on response regulators inhibitors as antibacterial agents or / and antibiotic adjuvants. Moreover, we describe the antibacterial activity and/or antibiotic adjuvants activity against the studied bacterial strains and the mechanism of different response regulator inhibitors when it's possible.

Antibiotics Trigger Host Innate Immune Response via Microbiota-Brain Communication in C. elegans

Besides their direct bactericidal effect, antibiotics have also been suggested to stimulate the host immune response to defend against pathogens. However, it remains unclear whether any antibiotics may stimulate the host immune response by affecting bacterial activity. In this study, reasoning that genetic mutations inhibit bacterial activities and, thereby, may mimic the effects of antibiotics, we performed genome-wide screening and identified 77 E. coli genes whose inactivation induces C. elegans cyp-14A4, representing an innate immune and detoxification response. Further analyses reveal that this host immune response can clearly be induced through either inactivating the E. coli respiratory chain via the bacterial cyoB mutation or using the antibiotic Q203, which is able to enhance host survival when encountering the pathogen Pseudomonas aeruginosa. Mechanistically, the innate immune response triggered by both the cyoB mutation and Q203 is found to depend on the host brain response, as evidenced by their reliance on the host neural gene unc-13, which is required for neurotransmitter release in head neurons. Therefore, our findings elucidate the critical involvement of the microbiota-brain axis in modulating the host immune response, providing mechanistic insights into the role of antibiotics in triggering the host immune response and, thus, facilitating host defense against pathogens.

SICKO: Systematic Imaging of Caenorhabditis Killing Organisms

Caenorhabditis elegans are an important model system for research on host-microbe interaction. Their rapid life cycle, short lifespan, and transparent body structure allow simple quantification of microbial load and the influence of microbial exposure on host survival. C. elegans host-microbe interaction studies typically examine group survival and infection severity at fixed timepoints. Here we present an imaging pipeline, Systematic Imaging of Caenorhabditis Killing Organisms (SICKO), that allows longitudinal characterization of microbes colonizing isolated C. elegans, enabling dynamic tracking of tissue colonization and host survival in the same animals. Using SICKO, we show that Escherichia coli or Pseudomonas aeruginosa gut colonization dramatically shortens C. elegans lifespan and that immunodeficient animals lacking pmk-1 are more susceptible to colonization but display similar colony growth relative to wild type. SICKO opens new avenues for detailed research into bacterial pathogenesis, the benefits of probiotics, and the role of the microbiome in host health.

Milk Fat Globule Membrane-Containing Protein Powder Promotes Fitness in Caenorhabditis elegans

Milk-derived peptides and milk fat globule membrane (MFGM) have gained interest as health-promoting food ingredients. However, the mechanisms by which these nutraceuticals modulate the function of biological systems often remain unclear. We utilized Caenorhabditis elegans to elucidate how MFGM-containing protein powder (MProPow), previously used in a clinical trial, affect the physiology of this model organism. Our results demonstrate that MProPow does not affect lifespan but promotes the fitness of the animals. Surprisingly, gene expression analysis revealed that MProPow decreases the expression of genes functioning on innate immunity, which also translates into reduced survival on pathogenic bacteria. One of the innate immunity-associated genes showing reduced expression upon MProPow supplementation is cpr-3, the homolog of human cathepsin B. Interestingly, knockdown of cpr-3 enhances fitness, but not in MProPow-treated animals, suggesting that MProPow contributes to fitness by downregulating the expression of this gene. In summary, this research highlights the value of C. elegans in testing the biological activity of food supplements and nutraceuticals. Furthermore, this study should encourage investigations into whether milk-derived peptides and MFGM mediate their beneficial effects through the modulation of cathepsin B expression in humans.

Neuronal GPCR NMUR-1 regulates energy homeostasis in response to pathogen infection

A key question in current immunology is how the innate immune system generates high levels of specificity. Our previous study in Caenorhabditis elegans revealed that NMUR-1, a neuronal G protein-coupled receptor homologous to mammalian receptors for the neuropeptide neuromedin U (NMU), regulates distinct innate immune responses to different bacterial pathogens. Here, by using quantitative proteomics and functional assays, we discovered that NMUR-1 regulates F1FO ATP synthase and ATP production in response to pathogen infection, and that such regulation contributes to NMUR-1-mediated specificity of innate immunity. We further demonstrated that ATP biosynthesis and its contribution to defense is neurally controlled by the NMUR-1 ligand CAPA-1 and its expressing neurons ASG. These findings indicate that NMUR-1 neural signaling regulates the specificity of innate immunity by controlling energy homeostasis as part of defense against pathogens. Our study provides mechanistic insights into the emerging roles of NMU signaling in immunity across animal phyla.

Bacteria are a major determinant of Orsay virus transmission and infection in Caenorhabditis elegans

The microbiota is a key determinant of the physiology and immunity of animal hosts. The factors governing the transmissibility of viruses between susceptible hosts are incompletely understood. Bacteria serve as food for Caenorhabditis elegans and represent an integral part of the natural environment of C. elegans. We determined the effects of bacteria isolated with C. elegans from its natural environment on the transmission of Orsay virus in C. elegans using quantitative virus transmission and host susceptibility assays. We observed that Ochrobactrum species promoted Orsay virus transmission, whereas Pseudomonas lurida MYb11 attenuated virus transmission relative to the standard laboratory bacterial food Escherichia coli OP50. We found that pathogenic Pseudomonas aeruginosa strains PA01 and PA14 further attenuated virus transmission. We determined that the amount of Orsay virus required to infect 50% of a C. elegans population on P. lurida MYb11 compared with Ochrobactrum vermis MYb71 was dramatically increased, over three orders of magnitude. Host susceptibility was attenuated even further in the presence of P. aeruginosa PA14. Genetic analysis of the determinants of P. aeruginosa required for attenuation of C. elegans susceptibility to Orsay virus infection revealed a role for regulators of quorum sensing. Our data suggest that distinct constituents of the C. elegans microbiota and potential pathogens can have widely divergent effects on Orsay virus transmission, such that associated bacteria can effectively determine host susceptibility versus resistance to viral infection. Our study provides quantitative evidence for a critical role for tripartite host-virus-bacteria interactions in determining the transmissibility of viruses among susceptible hosts.

Modeling Host-Pathogen Interactions in C. elegans: Lessons Learned from Pseudomonas aeruginosa Infection

Infections, such as that by the multiresistant opportunistic bacterial pathogen Pseudomonas aeruginosa, may pose a serious health risk, especially on vulnerable patient populations. The nematode Caenorhabditis elegans provides a simple organismal model to investigate both pathogenic mechanisms and the emerging role of innate immunity in host protection. Here, we review the virulence and infection strategies of P. aeruginosa and host defenses of C. elegans. We summarize the recognition mechanisms of patterns of pathogenesis, including novel pathogen-associated molecular patterns and surveillance immunity of translation, mitochondria, and lysosome-related organelles. We also review the regulation of antimicrobial and behavioral defenses by the worm's neuroendocrine system. We focus on how discoveries in this rich field align with well-characterized evolutionary conserved protective pathways, as well as on potential crossovers to human pathogenesis and innate immune responses.

Protocol for survival assay of Caenorhabditis elegans to Pseudomonas aeruginosa PA14 infection

The nematode Caenorhabditis elegans is a powerful model organism for studying the molecular and cellular mechanisms of innate immunity governed by the intestine. Here, we present a protocol to perform C. elegans survival assays to infection by the bacterial pathogen Pseudomonas aeruginosa PA14. Specifically, we describe steps for preparing C. elegans strains and PA14 bacteria for survival assays. This protocol will assist researchers to study genes involved in intestinal innate immunity and gut defense against pathogen infection. For complete details on the use and execution of this protocol, please refer to Liu et al.1 and Zheng et al.2.

Lysosomal dysfunction by inactivation of V-ATPase drives innate immune response in C. elegans

Pathogens target vacuolar ATPase (V-ATPase) to inhibit lysosomal acidification or lysosomal fusion, causing lysosomal dysfunction. However, it remains unknown whether cells can detect dysfunctional lysosomes and initiate an immune response. In this study, we discover that dysfunction of lysosomes caused by inactivation of V-ATPase enhances innate immunity against bacterial infections. We find that lysosomal V-ATPase interacts with DVE-1, whose nuclear localization serves as a proxy for the induction of mitochondrial unfolded protein response (UPRmt). The inactivation of V-ATPase promotes the nuclear localization of DVE-1, activating UPRmt and inducing downstream immune response genes. Furthermore, pathogen resistance conferred by inactivation of V-ATPase requires dve-1 and its downstream immune effectors. Interestingly, animals grow slower after vha RNAi, suggesting that the vha-RNAi-induced immune response costs the most energy through activation of DVE-1, which trades off with growth. This study reveals how dysfunctional lysosomes can trigger an immune response, emphasizing the importance of conserving energy during immune defense.

Veratryl Alcohol Attenuates the Virulence and Pathogenicity of Pseudomonas aeruginosa Mainly via Targeting las Quorum-Sensing System

Pseudomonas aeruginosa is an opportunistic pathogen that usually causes chronic infections and even death in patients. The treatment of P. aeruginosa infection has become more challenging due to the prevalence of antibiotic resistance and the slow pace of new antibiotic development. Therefore, it is essential to explore non-antibiotic methods. A new strategy involves screening for drugs that target the quorum-sensing (QS) system. The QS system regulates the infection and drug resistance in P. aeruginosa. In this study, veratryl alcohol (VA) was found as an effective QS inhibitor (QSI). It effectively suppressed the expression of QS-related genes and the subsequent production of virulence factors under the control of QS including elastase, protease, pyocyanin and rhamnolipid at sub-inhibitory concentrations. In addition, motility activity and biofilm formation, which were correlated with the infection of P. aeruginosa, were also suppressed by VA. In vivo experiments demonstrated that VA could weaken the pathogenicity of P. aeruginosa in Chinese cabbage, Drosophila melanogaster, and Caenorhabditis elegans infection models. Molecular docking, combined with QS quintuple mutant infection analysis, identified that the mechanism of VA could target the LasR protein of the las system mainly. Moreover, VA increased the susceptibility of P. aeruginosa to conventional antibiotics of tobramycin, kanamycin and gentamicin. The results firstly demonstrate that VA is a promising QSI to treat infections caused by P. aeruginosa.

PemB, a type III secretion effector in Pseudomonas aeruginosa, affects Caenorhabditis elegans life span

Pseudomonas aeruginosa is one of the leading nosocomial opportunistic pathogens causing acute and chronic infections. Among its main virulent factors is the Type III secretion system (T3SS) which enhances disease severity by delivering effectors to the host in a highly regulated manner. Despite its importance for virulence, only six T3SS-dependent effectors have been discovered so far. Previously, we identified two new potential effectors using a machine-learning algorithm approach. Here we demonstrate that one of these effectors, PemB, is indeed virulent. Using a live Caenorhabditis elegans infection model, we demonstrate this effector damages the integrity of the intestine barrier leading to the death of the host. Implementing a high-throughput assay using Saccharomyces cerevisiae, we identified several candidate proteins that interact with PemB. One of them, EFT1, has an ortholog in C. elegans (eef-2) and is also an essential gene and a well-known target utilized by different pathogens to induce toxicity to the worm. Accordingly, we found that by silencing the eef-2 gene in C. elegans, PemB could no longer induce its toxic effect. The current study further uncovers the complex machinery assisting P. aeruginosa virulence and may provide novel insight how to manage infection associated with this hard-to-treat pathogen.

Antagonism between neuropeptides and monoamines in a distributed circuit for pathogen avoidance

Pathogenic infection elicits behaviors that promote recovery and survival of the host. After exposure to the pathogenic bacterium Pseudomonas aeruginosa PA14, the nematode Caenorhabditis elegans modifies its sensory preferences to avoid the pathogen. Here, we identify antagonistic neuromodulators that shape this acquired avoidance behavior. Using an unbiased cell-directed neuropeptide screen, we show that AVK neurons upregulate and release RF/RYamide FLP-1 neuropeptides during infection to drive pathogen avoidance. Manipulations that increase or decrease AVK activity accelerate or delay pathogen avoidance, respectively, implicating AVK in the dynamics of avoidance behavior. FLP-1 neuropeptides drive pathogen avoidance through the G protein-coupled receptor DMSR-7, as well as other receptors. DMSR-7 in turn acts in multiple neurons, including tyraminergic/octopaminergic neurons that receive convergent avoidance signals from the cytokine DAF-7/transforming growth factor β. Neuromodulators shape pathogen avoidance through multiple mechanisms and targets, in agreement with the distributed neuromodulatory connectome of C. elegans.

Glycerol metabolism impacts biofilm phenotypes and virulence in Pseudomonas aeruginosa via the Entner-Doudoroff pathway

Pseudomonas aeruginosa is a ubiquitous bacterium and a notorious opportunistic pathogen that forms biofilm structures in response to many environmental cues. Biofilm formation includes attachment to surfaces and the production of the exopolysaccharide Pel, which is present in both the PAO1 and PA14 laboratory strains of P. aeruginosa. Biofilms help protect bacterial cells from host defenses and antibiotics and abet infection. The carbon source used by the cells also influences biofilm, but these effects have not been deeply studied. We show here that glycerol, which can be liberated from host surfactants during infection, encourages surface attachment and magnifies colony morphology differences. We find that glycerol kinase is important but not essential for glycerol utilization and relatively unimportant for biofilm behaviors. Among downstream enzymes predicted to take part in glycerol utilization, Edd stood out as being important for glycerol utilization and for enhanced biofilm phenotypes in the presence of glycerol. Thus, gluconeogenesis and catabolism of anabolically produced glucose appear to impact not only the utilization of glycerol but also glycerol-stimulated biofilm phenotypes. Finally, waxworm moth larvae and nematode infection models reveal that interruption of the Entner-Doudoroff pathway, but not abrogation of glycerol phosphorylation, unexpectedly increases P. aeruginosa lethality in both acute and chronic infections, even while stimulating a stronger immune response by Caenorhabditis elegans.IMPORTANCEPseudomonas aeruginosa, the ubiquitous environmental bacterium and human pathogen, forms multicellular communities known as biofilms in response to various stimuli. We find that glycerol, a common carbon source that bacteria can use for energy and biosynthesis, encourages biofilm behaviors such as surface attachment and colony wrinkling by P. aeruginosa. Glycerol can be derived from surfactants that are present in the human lungs, a common infection site. Glycerol-stimulated biofilm phenotypes do not depend on phosphorylation of glycerol but are surprisingly impacted by a glucose breakdown pathway, suggesting that it is glycerol utilization, and not its mere presence or cellular import, that stimulates biofilm phenotypes. Moreover, the same mutations that block glycerol-stimulated biofilm phenotypes also impact P. aeruginosa virulence in both acute and chronic animal models. Notably, a glucose-breakdown mutant (Δedd) counteracts biofilm phenotypes but shows enhanced virulence and stimulates a stronger immune response in Caenorhabditis elegans.

BMP signaling to pharyngeal muscle in the C. elegans response to a bacterial pathogen regulates anti-microbial peptide expression and pharyngeal pumping

Host response to pathogens recruits multiple tissues in part through conserved cell signaling pathways. In Caenorhabditis elegans, the bone morphogenetic protein (BMP) like DBL-1 signaling pathway has a role in the response to infection in addition to other roles in development and postdevelopmental functions. In the regulation of body size, the DBL-1 pathway acts through cell autonomous signal activation in the epidermis (hypodermis). We have now elucidated the tissues that respond to DBL-1 signaling upon exposure to two bacterial pathogens. The receptors and Smad signal transducers for DBL-1 are expressed in pharyngeal muscle, intestine, and epidermis. We demonstrate that expression of receptor-regulated Smad (R-Smad) gene sma-3 in the pharynx is sufficient to improve the impaired survival phenotype of sma-3 mutants and that expression of sma-3 in the intestine has no effect when exposing worms to bacterial infection of the intestine. We also show that two antimicrobial peptide genes - abf-2 and cnc-2 - are regulated by DBL-1 signaling through R-Smad SMA-3 activity in the pharynx. Finally, we show that pharyngeal pumping activity is reduced in sma-3 mutants and that other pharynx-defective mutants also have reduced survival on a bacterial pathogen. Our results identify the pharynx as a tissue that responds to BMP signaling to coordinate a systemic response to bacterial pathogens.