Regulation of Caenorhabditis elegans and Pseudomonas aeruginosa machinery during interactions

Subsequent infection differentially affects the proteome of Caenorhabditis elegans by abrogating the intestinal cell proliferation

With a wide range of bacterial infections growing, it has become a big challenge to the research field to combat the newly emerging diseases. Immuno-compromised patients are vulnerable to opportunistic infections. P. mirabilis, an opportunistic pathogen infects the nematode when the immune system is compromised. In the present study, the C. elegans was pre-exposed to S. aureus for a short term, and then consecutively infected with P. mirabilis. The primary infection caused by S. aureus makes the immune system of C. elegans vulnerable making it easy for P. mirabilis to colonize efficiently during subsequent exposure, thereby stimulating the immune system of the nematode. In this study, the C. elegans exposed to the pathogens (S. aureus 4 h/P. mirabilis 40 h and S. aureus 8 h/P. mirabilis 60 h time points) showed a substantial difference in the banding patterns of SDS-PAGE gel, when compared to their respective OP50 fed controls. 2-DE identified a total of 235 proteins from all the time points which had >2 fold regulation. The regulated protein spots were identified by MALDI-ToF/ToF analysis and one common protein CDC-25.1 was found to be regulated in all the comparative time points. CDC-25.1 seemed to down regulate during subsequent infection and up regulate in single infection. The transcriptomic regulation of cdc-25.1 also reflects the protein regulation. In addition to it, survival assay in cdc-25.1 mutant nematodes confirm the susceptibility of host during subsequent infection.

Lactic acid bacteria that activate immune gene expression in Caenorhabditis elegans can antagonise Campylobacter jejuni infection in nematodes, chickens and mice

BACKGROUND

Campylobacter jejuni is the major micro-bacillary pathogen responsible for human coloenteritis. Lactic acid bacteria (LAB) have been shown to protect against Campylobacter infection. However, LAB with a good ability to inhibit the growth of C. jejuni in vitro are less effective in animals and animal models, and have the disadvantages of high cost, a long cycle, cumbersome operation and insignificant immune response indicators. Caenorhabditis elegans is increasingly used to screen probiotics for their anti-pathogenic properties. However, no research on the use of C. elegans to screen for probiotic candidates antagonistic to C. jejuni has been conducted to date.

RESULTS

This study established a lifespan model of C. elegans, enabling the preselection of LAB to counter C. jejuni infection. A potential protective mechanism of LAB was identified. Some distinct LAB species offered a high level of protection to C. elegans against C. jejuni. The LAB strains with a high protection rate reduced the load of C. jejuni in C. elegans. The transcription of antibacterial peptide genes, MAPK and Daf-16 signalling pathway-related genes was elevated using the LAB isolates with a high protection rate. The reliability of the lifespan model of C. elegans was verified using mice and chickens infected with C. jejuni.

CONCLUSIONS

The results showed that different LAB had different abilities to protect C. elegans against C. jejuni. C. elegans provides a reliable model for researchers to screen for LAB that are antagonistic to C. jejuni on a large scale.

Proteomic analysis of Caenorhabditis elegans against Salmonella Typhi toxic proteins

Bacterial effector molecules are crucial infectious agents that can cause pathogenesis. In the present study, the pathogenesis of toxic Salmonella enterica serovar Typhi (S. Typhi) proteins on the model host Caenorhabditis elegans was investigated by exploring the host's regulatory proteins during infection through the quantitative proteomics approach. Extracted host proteins were analyzed using two-dimensional gel electrophoresis (2D-GE) and differentially regulated proteins were identified using MALDI TOF/TOF/MS analysis. Of the 150 regulated proteins identified, 95 were downregulated while 55 were upregulated. The interaction network of regulated proteins was predicted using the STRING tool. Most downregulated proteins were involved in muscle contraction, locomotion, energy hydrolysis, lipid synthesis, serine/threonine kinase activity, oxidoreductase activity, and protein unfolding. Upregulated proteins were involved in oxidative stress pathways. Hence, cellular stress generated by S. Typhi proteins in the model host was determined using lipid peroxidation as well as oxidant and antioxidant assays. In addition, candidate proteins identified via extract analysis were validated by western blotting, and the roles of several crucial molecules were analyzed in vivo using transgenic strains (myo-2 and col-19) and mutant (ogt-1) of C. elegans. To the best of our knowledge, this is the first study to report protein regulation in host C. elegans exposed to toxic S. Typhi proteins. It highlights the significance of p38 MAPK and JNK immune pathways.

A proteomic analysis of Caenorhabditis elegans mitochondria during bacterial infection

Mitochondria are involved in a variety of cellular metabolic processes and their functions are regulated by intrinsic and extrinsic stimuli. Recent studies have revealed functional diversity and importance of mitochondria in many cellular processes, including the innate immune response. This study evaluated the specific response and proteomic changes in host Caenorhabditis elegans mitochondria during Pseudomonas aeruginosa PAO1 infection. We performed an inclusive approach to determine the C. elegans mitochondria proteome. The protein fractions of mitochondria were analysed by tandem LC-MS/MS, 129 differentially regulated proteins were identified, indicating an involvement of various mitochondrial processes. The several known components of the oxidative phosphorylation (OXPHOS) machinery, the tricarboxylic acid (TCA) cycle, mitochondrial unfolded protein response (UPR^mt) and stable mitochondria-encoded proteins were found to be differentially expressed. Our results in-depth provide new horizons for mitochondria-associated protein functions and the classification of mitochondrial diseases during host-pathogen interaction.

Phillyrin is an effective inhibitor of quorum sensing with potential as an anti-Pseudomonas aeruginosa infection therapy

In the present study, we evaluated the antibacterial and anti-quorum sensing qualities of phillyrin. The minimum inhibitory concentration (MIC) of phillyrin with regard to Pseudomonas aeruginosa is 0.5 mg/ml. The production of virulence factors—such as rhamnolipid (>78.69%), pyocyanin (>85.94%), and elastase (>89.95%)—that affect the pathogenicity of the P. aeruginosa strain PAO1 apparently declined in the presence of 0.25 mg/ml phillyrin. Biofilm formation decreased by 84.48%. In a Caenorhabditis elegans–Pseudomonas aeruginosa infection model, diseased worms lived longer (63.33%) in a phillyrin-containing medium than in a drug-free medium, and the drug did not directly kill the pathogen. Therefore, the present work suggests that phillyrin has potential as an antimicrobial agent for the control of infectious pathogens.

O-GlcNAcylation confers protection against Staphylococcus aureus infection in Caenorhabditis elegans through ubiquitination

Glycosylation is one of the most prevalent post-translational modifications in biological systems. In Caenorhabditis elegans, O-GlcNAcylation has been shown to be actively involved in the regulation of dauer formation and detoxification of toxins secreted by invading pathogens. On this backdrop, the present study is focused on understanding the role of O-GlcNAcylation in C. elegans during Staphylococcus aureus infection using a gel based proteomic approach. Results of time course killing assays with wild-type and mutants of glycosylation and comparison of results revealed an increase in the survival of the C. elegans oga-1 mutant when compared to wild-type N2 and the ogt-1 mutant. Increased survival of C. elegans N2 upon S. aureus infection in the presence of O-(2-acetamido-2-deoxy-d-glucopyranosylidenamino) N-phenylcarbamate (PUGNAc-an OGA inhibitor) further confirmed the involvement of O-GlcNAcylation in protecting C. elegans from infection. The two-dimensional gel-based proteomic analysis of the control and S. aureus infected C. elegans oga-1 mutant followed by mass spectrometric identification of differentially expressed proteins has been carried out. The results revealed that key proteins involved in ubiquitination such as Cullin-1 (CUL-1), Cullin-3 (CUL-3), BTB and MATH domain-containing protein 15 (BATH-15), ubiquitin-conjugating enzyme E2 variant 3 (UEV-3) and probable ubiquitin-conjugating enzyme E2 7 (UBC-7) are upregulated. Real-time PCR analysis further confirms the upregulation of genes encoding the above-mentioned proteins which are involved in the ubiquitin-mediated pathways in C. elegans. In addition, treatment of C. elegans wild-type N2 and the oga-1 mutant with PUGNAc + suramin and suramin (an ubiquitination inhibitor), respectively has resulted in increased sensitivity to S. aureus infection. Hence, it is presumed that upregulation of proteins involved in the ubiquitination pathway could be the key regulatory mechanism responsible for the enhanced survival of the oga-1 mutant during S. aureus infection.

Lactobacillus casei triggers a TLR mediated RACK-1 dependent p38 MAPK pathway in Caenorhabditis elegans to resist Klebsiella pneumoniae infection

In the present study, the effect of Lactic Acid Bacteria (LAB) was investigated at the molecular level using the model organism Caenorhabditis elegans against Klebsiella pneumoniae. Out of the 13 LAB screened, Lactobacillus casei displayed excellent protective efficacy by prolonging the survival of K. pneumoniae-infected nematodes. Pretreatment with L. casei significantly decreased bacterial colonization and rescued K. pneumoniae-infected C. elegans from various physiological impairments. The concomitant upregulation of key immune genes that regulate the TLR, RACK-1 as well as the p38 MAPK pathway rather than the IIS and ERK pathway suggested that the plausible immunomodulatory mechanism of L. casei could be by triggering the TLR, RACK-1 and p38 MAPK pathway. Furthermore, the hyper-susceptibility of L. casei treated loss-of-function mutants of the tol-1, RACK-1 and p38 MAPK pathway (sek-1 and pmk-1) to K. pneumoniae infection and gene expression analysis suggested that L. casei triggered a TLR mediated RACK-1 dependent p38 MAPK pathway to increase host resistance and protect nematodes against K. pneumoniae infection.

l-Ascorbyl 2,6-dipalmitate inhibits biofilm formation and virulence in methicillin-resistant Staphylococcus aureus and prevents triacylglyceride accumulation in Caenorhabditis elegans

In the present study, the antibiofilm, antipathogenic and anticarotenogenic potential ofl-ascorbyl 2,6-dipalmitate (ADP) against methicillin-resistantStaphylococcus aureus(MRSA) has been evaluated.

Short term memory of Caenorhabditis elegans against bacterial pathogens involves CREB transcription factor

One of the key issues pertaining to the control of memory is to respond to a consistently changing environment or microbial niche present in it. Human cyclic AMP response element binding protein (CREB) transcription factor which plays a crucial role in memory has a homolog in C. elegans, crh-1. crh-1 appears to influence memory processes to certain extent by habituation of the host to a particular environment. The discrimination between the pathogen and a non-pathogen is essential for C. elegans in a microbial niche which determines its survival. Training the nematodes in the presence of a virulent pathogen (S. aureus) and an opportunistic pathogen (P. mirabilis) separately exhibits a different behavioural paradigm. This appears to be dependent on the CREB transcription factor. Here we show that C. elegans homolog crh-1 helps in memory response for a short term against the interacting pathogens. Following conditioning of the nematodes to S. aureus and P. mirabilis, the wild type nematodes exhibited a positive response towards the respective pathogens which diminished slowly after 2h. By contrast, the crh-1 deficient nematodes had a defective memory post conditioning. The molecular data reinforces the importance of crh-1 gene in retaining the memory of nematode. Our results also suggest that involvement of neurotransmitters play a crucial role in modulating the memory of the nematode with the assistance of CREB. Therefore, we elucidate that CREB is responsible for the short term memory response in C. elegans against bacterial pathogens.

Proteome analysis reveals translational inhibition of Caenorhabditis elegans enhances susceptibility to Pseudomonas aeruginosa PAO1 pathogenesis

Caenorhabditis elegans-Pseudomonas aeruginosa infection model is commonly used for pathogenesis studies over the decades. In the present study, upon exposure to the Pseudomonas aeruginosa PAO1, the 2D-PAGE was performed to examine the total proteins differences of C. elegans during the PAO1 infection at different time durations (12-48h). Also, the 2D-DIGE using the cyanine dyes were performed (48h) to identify the differentially regulated proteins against the PAO1 infection. Among the 19 short-listed proteins, 5 proteins were down-regulated and 14 proteins were up-regulated. Eukaryotic elongation factor-2 (EEF-2), a GTP binding protein involves in protein elongation process was down regulated during the pathogen infection. The 2D-PAGE analysis and MS data for the 12 and 24h infections identified the NDK-1 and other essential protein includes, ACS-18, ACT-1, GPD-3, GDH-1 and LBP-6 which are involved in important cellular homeostasis were down regulated. Validation studies using qPCR analysis for eef-2 and other selected genes, western blot analysis for EEF-2 and effect of host translational inhibition studies using Cycloheximide during PAO1 infection suggests that P. aeruginosa systematically restrains the function of host by arresting the expression of EEF-2 and thereby inhibiting protein translational events. Further, in silico analysis revealed the Exotoxin A could directly bind with the host EEF-2 and NDK-1 during the C. elegans- PAO1 interactions.

BIOLOGICAL SIGNIFICANCE

Model system, C. elegans facilitates the identification of virulence mechanisms during bacterial pathogenesis. Upon infection by the fungal and bacterial pathogens, the C. elegans system induces an array of transcriptional responses, including differential expression of effector/modulator genes that provide safeguard and fight against infection. However, the in-depth knowledge of host response by the pathogen at protein level remains unclear. Much of the studies were carried out only at the transcripts level and scarce reports are available at the protein level for the host-pathogen interaction studies. In order to provide few interesting clues at the protein level, the nematode, C. elegans was infected with the human pathogen P. aeruginosa and the response(s) of host was investigated at the protein level by 2D-DIGE analysis and further validation studies using qPCR and western blotting techniques. Our differential proteomics data suggest that translational inhibition as one of the patterns of pathogenesis in C. elegans during P. aeruginosa infection. Since many of the effectors identified through C. elegans are conserved in other systems including human, our data pave the way for understanding important regulatory pathways involved during bacterial pathogenesis that can be translated into higher eukaryotic organisms.

Changes in Caenorhabditis elegans immunity and Staphylococcal virulence factors during their interactions

The nematode Caenorhabditis elegans is used as a model system for the study of host-pathogen interactions. Lipoteichoic acid (LTA) is one of the major virulent and immunostimulatory components found in gram positive bacteria. The current study used LTA isolated from Staphylococcus aureus and pathogenic and non-pathogenic Staphylococcus epidermidis. The overall physiological assays revealed that LTA exposed C. elegans show a significant reduction in the life span, production of eggs and progenies. To understand the involvement of innate immune specific players at the mRNA level, the regulation of few candidate antimicrobial genes was studied during Staphylococcal LTA exposures. qPCR analysis indicated an upregulation of antimicrobial peptides during LTA exposures. To understand the involvement of LTA and other virulent genes during infection, the regulation of LTA synthase and a few virulence genes was monitored during host exposure. The qPCR analyses indicated the upregulation of ltaS and other virulence genes (atoxin, sak, ssaA and fbe) during infection. Ability of the pathogens to modify their internal machinery during host presence was monitored by Fourier transform infrared spectroscopy, electrochemical impedance spectroscopy and cyclic voltametric analyses. The FTIR results indicated distinct alterations of peaks from Staphylococcal LTA composition between control and the host exposed. Further, EIS and CV data displayed clear differences between the host exposed Staphylococcal samples compared to their respective unexposed controls. The pathogenic and non-pathogenic strains showed different types of regulations and interactions during host exposures. The observed modifications clearly suggest that the Gram positive pathogen changes its LTA production and possibly the structure to cause a severe pathogenic effect on an interacting host.

Alterations in Caenorhabditis elegans and Cronobacter sakazakii lipopolysaccharide during interaction

Lipopolysaccharide is one of the pathogen-associated molecular patterns of Gram-negative bacteria which are essential for its pathogenicity. Cronobacter sakazakii is an opportunistic, emergent pathogen, which infects and cause mortality in Caenorhabditis elegans. In this study, modifications in host and C. sakazakii LPS during infections were evaluated. The physiological assays revealed that LPS alone is sufficient to affect the host pharyngeal pumping rate, brood size and cause lethality. FTIR spectra of LPS revealed that C. sakazakii modifies its LPS to escape from the recognition of host immune system. These results indicate that LPS plays a key role in C. sakazakii pathogenicity. qPCR studies revealed that LPS modulated the expression of selected host immune (clec-60, clec-87, lys-7, ilys-3, F08G5.6, atf-7, scl-2, cpr-2) and aging-related genes (skn-1, clk-2, bra-2, age-1, bec-1, daf-16, daf-2). Moreover, it was confirmed that p38 MAPK pathway has a major role in host immune response against LPS-mediated challenges.

Modulation of Caenorhabditis elegans immune response and modification of Shigella endotoxin upon interaction

To analyze the pathogenesis at both physiological and molecular level using the model organism, Caenorhabditis elegans at different developmental stages in response to Shigella spp. and its pathogen associated molecular patterns such as lipopolysaccharide. The solid plate and liquid culture-based infection assays revealed that Shigella spp. infects C. elegans and had an impact on the brood size and pharyngeal pumping rate. LPS of Shigella spp. was toxic to C. elegans. qPCR analysis revealed that host innate immune genes have been modulated upon Shigella spp. infections and its LPS challenges. Non-destructive analysis was performed to kinetically assess the alterations in LPS during interaction of Shigella spp. with C. elegans. The modulation of innate immune genes attributed the surrendering of host immune system to Shigella spp. by favoring the infection. LPS appeared to have a major role in Shigella-mediated pathogenesis and Shigella employs a tactic behavior of modifying its LPS content to escape from the recognition of host immune system.

Phenol, 2,4-bis(1,1-dimethylethyl) of marine bacterial origin inhibits quorum sensing mediated biofilm formation in the uropathogen Serratia marcescens

Intercellular communication in bacteria (quorum sensing, QS) is an important phenomenon in disease dissemination and pathogenesis, which controls biofilm formation also. This study reports the anti-QS and anti-biofilm efficacy of seaweed Gracilaria gracilis associated Vibrio alginolyticus G16 against Serratia marcescens. Purification and mass spectrometric analysis revealed the active principle as phenol, 2,4-bis(1,1-dimethylethyl) [PD]. PD affected the QS regulated virulence factor production in S. marcescens and resulted in a significant (p < 0.05) reduction in biofilm (85%), protease (41.9%), haemolysin (69.9%), lipase (84.3%), prodigiosin (84.5%) and extracellular polysaccharide (84.62%) secretion without hampering growth, as evidenced by XTT [2,3-bis (2-methoxy-4-nitro-5-sulfophenyl)-2H-tetrazolium-5-carboxanilide] assay. qPCR analysis confirmed the down-regulation of the fimA, fimC, flhD and bsmA genes involved in biofilm formation. Apart from biofilm inhibition and disruption, PD increased the susceptibility of S. marcescens to gentamicin when administered synergistically, which opens another avenue for combinatorial therapy where PD can be used to enhance the efficacy of conventional antibiotics.

Analysis of Pseudomonas aeruginosa PAO1 lipid A changes during the interaction with model organism, Caenorhabditis elegans

Lipopolysaccharide (LPS) is the main surface constituent of Gram-negative bacteria. Lipid A, the hydrophobic moiety, outer monolayer of the outer cell membrane forms the major component of LPS. Immunogenic Lipid A is recognized by the innate immune system through the TLR 4/MD-2 complex. Pseudomonas aeruginosa PAO1, a Gram-negative bacterium is known to cause nosocomial infection and known for its adaptation to adverse environmental conditions. Pseudomonas aeruginosa can infect a broad host spectrum including Caenorhabditis elegans, a simple free living soil nematode. Here, we reveal that PAO1 modifies its Lipid A during the host interaction with C. elegans. The penta-acylated form of Lipid A was identified by using matrix assisted laser desorption ionization-time of flight analysis and the β-(1,6)-linked disaccharide of glucosamine with phosphate groups, 2 and 2' amide linked fatty acid chain and 3 and 3' ester linked fatty acids were investigated for the modification using the non destructive (1)H NMR, spin-lattice (T₁) relaxation measurement, differential scanning calorimetry. T₁ relaxation measurements showed that the 2 and 2' amide linked fatty acid chain, -CH in the glucosamine disaccharide of PAO1 lipid A, in an exposed host had a different spin lattice relaxation time compared to an unexposed host and the findings were reconfirmed using in vitro human corneal epithelial cells cell lines. Furthermore, scanning electron microscope and confocal laser scanning microscopy analysis revealed that the P. aeruginosa PAO1 biofilm formation was disturbed in the exposed host condition. The daf-12, daf-16, tol-1, pmk-1, ins-7 and ilys3 immune genes of C. elegans were examined with live bacterial and isolated lipid moiety infection and the expression was found to be highly specific. Overall, the present study revealed that PAO1 modified its 2 and 2' amide linked fatty acid chain in the lipid A of PAO1 LPS during the exposed host condition.

Effects of sequential infections of Caenorhabditis elegans with Staphylococcus aureus and Proteus mirabilis

Caenorhabditis elegans can be used to study the dynamics of polymicrobial infections, specifically those between Gram-positive and Gram-negative bacteria. With C. elegans, Proteus mirabilis acts as an opportunistic pathogen and does not kill this host. Hence, in the present study, C. elegans was immunochallenged by pre-infecting it with the pathogen Staphylococcus aureus in order to study the subsequent effect of P. mirabilis on the host. It was found that 12 hrs of S. aureus and 80 hrs of subsequent P. mirabilis infection significantly reduced the life span of exposed C. elegans by 80%. However, preinfection with S. aureus for 8 and 4 hrs reduced the life span of C. elegans by only 60 and 30%, respectively. Further, there was greater production of reactive oxygen species in the sequentially infected samples than in the S. aureus and P. mirabilis controls. Real time PCR analysis indicated regulation of candidate immune regulatory genes, lysozyme (lys-7), CUB-like proteins (F08G5.6), neuropeptide-like factors (nlp-29), transcription factors of mitogen-activated protein kinase (ATF-7) and daf-2-daf-16 (daf-16), insulin-like signaling pathways and C-type lectin (clec-60 and clec-87) family members during S. aureus and subsequent P. mirabilis-mediated infections, indicating possible roles of, and contributions by, the above factors during host immune responses against these sequential infections. The present findings demonstrate that S. aureus infections increase the vulnerability of the C. elegans host by subverting its immune system, which then permits the opportunistic pathogen P. mirabilis to be pathogenic to this host.

An evolutionarily conserved innate immunity protein interaction network

The innate immune response plays a critical role in fighting infection; however, innate immunity also can affect the pathogenesis of a variety of diseases, including sepsis, asthma, cancer, and atherosclerosis. To identify novel regulators of innate immunity, we performed comparative genomics RNA interference screens in the nematode Caenorhabditis elegans and mouse macrophages. These screens have uncovered many candidate regulators of the response to lipopolysaccharide (LPS), several of which interact physically in multiple species to form an innate immunity protein interaction network. This protein interaction network contains several proteins in the canonical LPS-responsive TLR4 pathway as well as many novel interacting proteins. Using RNAi and overexpression studies, we show that almost every gene in this network can modulate the innate immune response in mouse cell lines. We validate the importance of this network in innate immunity regulation in vivo using available mutants in C. elegans and mice.