Bacterial Quorum-sensing Systems Research Articles

Regulation of quorum sensing for the manipulation of conjugative transfer of antibiotic resistance genes in wastewater treatment system

The emergence and transmission of antibiotic resistance genes (ARGs) through plasmid-mediated conjugation has become a significant worldwide public health threat. Biofilms are widely recognized as the primary reservoirs for ARGs, providing favorable conditions for horizontal gene transfer. Quorum sensing (QS) plays a critical role in bacterial biofilm formation, which further influences the spread of bacterial resistance. In this study, we examined the effects of vanillin, a QS inhibitor (QSI), at subinhibitory concentrations (sub-MICs) ranging from 0 – 0.1 g/L, on the transfer of ARGs between Escherichia coli and Pseudomonas aeruginosa. Our findings indicated that vanillin at sub-MICs inhibited the conjugative transfer frequency of the RP4 plasmid. This inhibition was supported by the downregulation of plasmid transfer genes. The suppression of conjugation can mainly be attributed to the inhibition of biofilm formation, the synthesis of extracellular polymeric substances (EPS), and the secretion of virulence factors, all of which are regulated by the bacterial QS system. On the other hand, the levels of ROS and cell membrane permeability were not primary explanations for this phenomenon. Furthermore, vanillin also reduced the conjugative transfer frequency of ARGs in wastewater effluent, providing a potential approach to alleviate bacterial resistance in water environments. These findings underscore the regulatory role of QSI in controlling ARGs transfer and have significant implications for manipulating the dissemination of bacterial resistance in the environment.

Hibiscus tiliaceus ethanolic leaf extract modulates quorum sensing-facilitated virulence factors

Abstract. Husnah M, Suhartono S, Ismail YS. 2023. Hibiscus tiliaceus ethanolic leaf extract modulates quorum sensing-facilitated virulence factors. Biodiversitas 24: 5962-5971. Bacterial pathogenicity and infections are often associated with the presence of virulence factors generated mostly through quorum-sensing (QS) mechanisms. Therefore, QS suppression is considered an effective strategy for combatting pathogens. Many studies to search for new anti-QS agents, particularly those of plant origin, have been intensively conducted. Hibiscus tiliaceus L. is one of the medicinal plants exhibiting various pharmacological activities including antibacterial potential; however, the study regarding its effects on bacterial QS systems has not been reported. Therefore, this study aimed to investigate the potency of Hibiscus tiliaceus ethanolic leaf extract (HELE) as a modulating agent against Chromobacterium violaceum ATCC122472, Staphylococcus aureus ATCC 29213, and Pseudomonas aeruginosa PA01. The extract was obtained through maceration and phytochemical screening was carried out by GC-MS. To evaluate antibacterial and anti-QS potentials of HELE, minimum inhibitory concentration (MIC); minimum bactericidal concentration (MBC); growth inhibition rate; disc diffusion; and inhibition of violacein, pyocyanin, swarming motility, and biofilm formation were assayed. Statistical analysis was performed using SPPS software and Analysis of Varian (ANOVA) was employed to determine significant differences between the control and treatment groups. Phytochemical screening revealed the presence of 16 different compounds in HELE, represented predominantly by diterpenoids (phytol), fatty acids (palmitic acid and oleic acid), and p-Tolualdehyde. MIC was found at 10 mg/mL against both C. violaceum ATCC122472 and S. aureus ATCC 29213, and 160 mg/mL against P. aeruginosa PA01. The MBC for the first two bacteria was 20 mg/mL, whereas that against P. aeruginosa PA01 remains to be determined. HELE was able to suppress the production of violacein, pyocyanin, and swarming motility at sub-MIC concentrations, highlighting the anti-QS potential of the extract. HELE at sub-MICs was found to stimulate biofilm formation, whereas at 2 x MIC exhibited an inhibitory effect. These findings justified that HELE might serve as a promising candidate not only as a future QS-inhibitory but also as a concentration-dependent QS-modulating agent.

Potential role of AgNPs within wastewater in deteriorating sludge floc structure and settleability during activated sludge process: Filamentous bacteria and quorum sensing

Excellent sludge floc structure and settleability are essential to maintain the process stability and excellent effluent quality during the activated sludge process. The underlying effect of silver nanoparticles (AgNPs) within wastewater on sludge floc structure and settleability is still unclear. The potential role of AgNPs in promoting filamentous bacterial proliferation and deteriorating sludge floc structure and settleability based on quorum sensing (QS) were investigated in this study. The results indicated that N-acyl homoserine lactose (AHL) concentration sharply increased from 23.56 to 108.41 ng/g VSS in the sequencing batch reactor with 1 mg/L AgNPs. AgNPs strengthened communication between filamentous bacteria, which triggered the filamentous bacterial QS system involving the synthetic gene hdtS and sensing genes traR and lasR. Filamentous bacterial proliferation was promoted by the triggered QS via positively regulating its cell cycle progression including chromosomal replication and divisome formation. In addition, extracellular protein production was obviously increased from 43.56 to 97.91 mg/g VSS through QS by regulating arginine and tyrosine secretion during filamentous bacterial proliferation under 1 mg/L AgNPs condition, which led to an increase in the negative charge and hydrophily at the cell surface. AgNPs resulted in an obvious increase in the surface energy barrier (WT) between bacteria. The change in the physicochemical properties of extracellular polymeric substance (EPS) induced by QS among filamentous bacteria obviously inhibited bacterial aggregation between filamentous bacteria and floc-forming bacteria under AgNPs condition, thus resulting in serious deterioration of the sludge floc structure and settleability. This study provided new insights into the microcosmic mechanism for the effect of AgNPs on sludge floc structure and settleability.

Biofilm inhibition based on controlling the transmembrane transport and extracellular accumulation of quorum sensing signals

The regulation of bacterial quorum sensing (QS) has been used to inhibit biofouling in wastewater treatment plants and the formation of biofilms. In contrast to traditional QS regulation strategies, this study aimed to obstruct the transmembrane transport process of QS signals to decrease their extracellular accumulation. Three phytochemicals, astragaloside IV, eugenol, and baicalin were selected, their effects on biofilm formation by Pseudomonas aeruginosa PA14 were studied, and the mechanisms determined. The inhibition efficiency of biofilm formation by 50 mg/L astragaloside IV, 1 mg/L eugenol, and 1 mg/L baicalin were 37%, 26%, and 26%, respectively. Confocal laser scanning microscopy and analysis of extracellular polymeric substances indicated that the three inhibitors affected the structure and composition of the biofilms. Furthermore, bacterial motility and a variety of QS-related virulence factors were suppressed by the inhibitor treatment due to changes in bacterial QS. Notably, the three inhibitors all decreased the extracellular concentration of the QS signaling molecule 3-oxo-C12-homoseine lactone by affecting the function of efflux pump MexAB-OprM. This indirectly interfered with the bacterial QS system and thus inhibited biofilm formation. In conclusion, this study revealed the inhibitory effects and inhibition mechanism of three phytochemicals on efflux pump and QS of P. aeruginosa and realized the inhibition on biofilm formation. We update the efflux pump inhibitor library and provide a new way for biofilm contamination control.

Recent advances on the regulation of bacterial biofilm formation by herbal medicines.

Biofilm formation is a fundamental part of life cycles of bacteria which affects various aspects of bacterial-host interactions including the development of drug resistance and chronic infections. In clinical settings, biofilm-related infections are becoming increasingly difficult to treat due to tolerance to antibiotics. Bacterial biofilm formation is regulated by different external and internal factors, among which quorum sensing (QS) signals and nucleotide-based second messengers play important roles. In recent years, different kinds of anti-biofilm agents have been discovered, among which are the Chinese herbal medicines (CHMs). CHMs or traditional Chinese medicines have long been utilized to combat various diseases around the world and many of them have the ability to inhibit, impair or decrease bacterial biofilm formation either through regulation of bacterial QS system or nucleotide-based second messengers. In this review, we describe the research progresses of different chemical classes of CHMs on the regulation of bacterial biofilm formation. Though the molecular mechanisms on the regulation of bacterial biofilm formation by CHMs have not been fully understood and there are still a lot of work that need to be performed, these studies contribute to the development of effective biofilm inhibitors and will provide a novel treatment strategy to control biofilm-related infections.

Quorum Quenching-Mediated Biofilm Mitigation on Functionalized Ultrafiltration Membranes via Atom Transfer Radical Polymerization

Quorum sensing (QS) critically affects biofilm formation during membrane filtration, which can be manipulated for membrane biofouling mitigation. This study demonstrates a quorum quenching strategy for combating membrane biofouling by functionalizing poly(vinylidene fluoride) (PVDF) membranes via atom transfer radical polymerization of a QS inhibitor, vanillin. Poly(vanillin) brushes are successfully grafted on the membrane surface, which is verified by extensive membrane characterization. The effective biofilm inhibition ability and mitigation mechanism of poly(vanillin) brushes are evaluated by analyzing the QS-related gene expression and acyl-homoserine lactone (AHL) signal molecule concentrations. We show that poly(vanillin) brushes can inhibit the bacterial QS system and decrease the AHL concentration to mitigate membrane biofouling. In dynamic filtration experiments, the vanillin-grafted PVDF membrane exhibits a 50% increase in stable flux compared to that of the pristine PVDF membrane. Our results provide an alternate strategy for mitigating membrane biofouling by regulating the bacterial QS system via inhibitor-functionalized membranes.

Computational and Biological Evaluation of β-Adrenoreceptor Blockers as Promising Bacterial Anti-Virulence Agents.

Bacterial resistance to antibiotics is an increasing public health threat as it has the potential to affect people at any stage of life, as well as veterinary. Various approaches have been proposed to counteract the bacterial resistance development. Tackling bacterial virulence is one of the most promising approaches that confer several merits. The bacterial virulence is mainly regulated by a communication system known as quorum sensing (QS) system. Meanwhile, bacteria can sense the adrenergic hormones and eavesdrops on the host cells to establish their infection, adrenergic hormones were shown to enhance the bacterial virulence. In this study, β-adrenoreceptor blockers were proposed not only to stop bacterial espionage on our cells but also as inhibitors to the bacterial QS systems. In this context, a detailed in silico study has been conducted to evaluate the affinities of twenty-two β-blockers to compete on different structural QS receptors. Among the best docked and thermodynamically stable β-blockers; atenolol, esmolol, and metoprolol were subjected to further in vitro and in vivo investigation to evaluate their anti-QS activities against Chromobacterium violaceum, Pseudomonas aeruginosa and Salmonella typhimurium. The three tested β-blockers decreased the production of QS-controlled C. violaceum, and the formation of biofilm by P. aeruginosa and S. typhimurium. Additionally, the tested β-blockers down-regulated the P. aeruginosa QS-encoding genes and S. typhimurium sensor kinase encoding genes. Furthermore, metoprolol protected mice against P. aeruginosa and S. typhimurium. Conclusively, these investigated β-blockers are promising anti-virulence agents antagonizing adrenergic hormones induced virulence, preventing bacterial espionage, and blocking bacterial QS systems.

Neuroprotective effects of 2-heptyl-3-hydroxy-4-quinolone in HT22 mouse hippocampal neuronal cells

The neuroprotective activity of 2-heptyl-3-hydroxy-4(1H)-quinolone (compound 1) was evaluated using the neurotoxicity of glutamate in the HT22 cell line. Compound 1, known as a signal molecule of the bacterial quorum-sensing system, protects neuronal cells from glutamate-induced neurotoxicity by inhibiting cellular Ca2+ uptake and glutamate-triggered ROS accumulation. MAPK signaling pathway inhibition by compound 1 was evaluated by immunoblotting the phosphorylation status of the proteins. Furthermore, pro-apoptotic protein levels and AIF translocation to the nucleus were found to be reduced by compound 1. In conclusion, compound 1 showed neuroprotective effects by inhibiting apoptotic neuronal cell death.

Bacterial Quorum-Sensing Systems and Their Role in Intestinal Bacteria-Host Crosstalk.

Quorum-sensing (QS) system is a rapidly developing field in which we are gradually expanding our understanding about how bacteria communicate with each other and regulate their activities in bacterial sociality. In addition to collectively modifying bacterial behavior, QS-related autoinducers may also be embedded in the crosstalk between host and parasitic microbes. In this review, we summarize current studies on QS in the intestinal microbiome field and its potential role in maintaining homeostasis under physiological conditions. Additionally, we outline the canonical autoinducers and their related QS signal-response systems by which several pathogens interact with the host under pathological conditions, with the goal of better understanding intestinal bacterial sociality and facilitating novel antimicrobial therapeutic strategies.

Evaluating the effect of antibiotics sub-inhibitory dose on Pseudomonas aeruginosaquorum sensing dependent virulence and its phenotypes.

The opportunistic Pseudomonas aeruginosa virulence controlled by quorum sensing (QS) also identified as, cell-cell communication. QS system is organized by the LasI-LasR and the RhlI-RhlR components. Provided that QS tends to perform a key role in virulence gene expression and host defence function, QS inhibitors have been proposed as potential antipseudomonal therapies. Sub-inhibitory concentrations (sub-MIC) of antibiotics, although having biostatic effect on bacteria, but can interfere with bacterial QS system and virulence. This research aimed to examine the impact of sub-MIC of azithromycin, imipenem, cefepime and piperacillin/tazobactam on the QS-dependent virulence including pyocyanin and biofilm production, haemolysin, protease and DNase in P. aeruginosa wildtype and mutant strains; transcriptional-regulator (ΔLasR), autoinducer synthesis protein (ΔLasI), transcriptional-regulator (ΔRhlR), protease precursor (ΔLasA) and double regulators mutants (ΔLasR/RhlR). The growth of all strains showed similar pattern, however, in presence of antibiotics significant growth variation was observed among mutant strains when compared to wild type strain. Antimicrobial activity tested by agar diffusion method of all antibiotics on all strains were used to compare the zones of therapeutic and sub-MIC doses showing a significant difference in the inhibition zone. QS-dependant virulence as biofilm, pyocyanin, protease, haemolysin and DNase production showed significant variation on all strains compared to wild type in response to antibiotics used at sub-MIC doses. In conclusion well known antibiotics can be used in sub-MIC doses to decrease the virulence of P. aeruginosa in addition to overcoming the major side effect of the high doses and the occurrence of resistance.

Evaluation of quorum-sensing inhibitory effects of extracts of three traditional medicine plants with known antibacterial properties.

Today an alternative approach to control bacterial infections is the use of natural and traditional plant compounds to interfere with their quorum-sensing (QS) systems. In this study, antibacterial and anti-QS sensing activity of Syzygium aromaticum, Dionysia revoluta Boiss. and Eucalyptus camaldulensis Dehnh. were evaluated. These plants are local to the Middle East region and have since ancient times been used for their antibacterial activity. Plant compounds were extracted with n-hexane, methanol and 96% ethanol mixed solvent. Antibacterial activity of this herbal extracts against five Gram-negative and Gram-positive bacteria were assessed. The effective sub–minimum inhibitory concentration (MIC) of this extract on bacterial QS systems were investigated by a violacein quantification assay in the Chromobacterium violaceum CV026 biosensor strain, inhibition of exogenously QS signal molecules in Aeromonas veronii bv. Sobria strain BC88 and Pseudomonas aeruginosa isolated from a patient with cystic fibrosis in vitro. Results found that Syzygium aromaticum 0.39 to 0.048 mg/mL, Dionysia revoluta Boiss. 3.1 to 0.39 mg/mL and E. camaldulensis 0.78 to 0.097 mg/mL showed anti-QS activities by reducing the violacein formation depletion of QS signals produced in A. veronii and P. aeruginosa at sub-MICs. Regarding the anti-QS effects of these herbal extracts, their effective components may be candidates for use in combating bacterial infections at sub-MICs.

Role of plant compounds in the modulation of the conjugative transfer of pRet42a.

One of the most studied mechanisms involved in bacterial evolution and diversification is conjugative transfer (CT) of plasmids. Plasmids able to transfer by CT often encode beneficial traits for bacterial survival under specific environmental conditions. Rhizobium etli CFN42 is a Gram-negative bacterium of agricultural relevance due to its symbiotic association with Phaseolus vulgaris through the formation of Nitrogen-fixing nodules. The genome of R. etli CFN42 consists of one chromosome and six large plasmids. Among these, pRet42a has been identified as a conjugative plasmid. The expression of the transfer genes is regulated by a quorum sensing (QS) system that includes a traI gene, which encodes an acyl-homoserine lactone (AHL) synthase and two transcriptional regulators (TraR and CinR). Recently, we have shown that pRet42a can perform CT on the root surface and inside nodules. The aim of this work was to determine the role of plant-related compounds in the CT of pRet42a. We found that bean root exudates or root and nodule extracts induce the CT of pRet42a in the plant rhizosphere. One possibility is that these compounds are used as nutrients, allowing the bacteria to increase their growth rate and reach the population density leading to the activation of the QS system in a shorter time. We tested if P. vulgaris compounds could substitute the bacterial AHL synthesized by TraI, to activate the conjugation machinery. The results showed that the transfer of pRet42a in the presence of the plant is dependent on the bacterial QS system, which cannot be substituted by plant compounds. Additionally, individual compounds of the plant exudates were evaluated; among these, some increased and others decreased the CT. With these results, we suggest that the plant could participate at different levels to modulate the CT, and that some compounds could be activating genes in the conjugation machinery.

Phenazines as potential biomarkers of Pseudomonas aeruginosa infections: synthesis regulation, pathogenesis and analytical methods for their detection.

Infectious diseases are still a worldwide important problem. This fact has led to the characterization of new biomarkers that would allow an early, fast and reliable diagnostic and targeted therapy. In this context, Pseudomonas aeruginosa can be considered one of the most threatening pathogens since it causes a wide range of infections, mainly in patients that suffer other diseases. Antibiotic treatment is not trivial given the incidence of resistance processes and the fewer new antibiotics that are placed on the market. With this scenario, relevant quorum sensing (QS) molecules that regulate the secretion of virulence factors and biofilm formation can play an important role in diagnostic and therapeutic issues. In this review, we have focused our attention on phenazines, as possible new biomarkers. They are pigmented metabolites that are produced by diverse bacteria, characterized for presenting unique redox properties. Phenazines are involved in virulence, competitive fitness and are an essential component of the bacterial QS system. Here we describe their role in bacterial pathogenesis and we revise phenazine production regulation systems. We also discuss phenazine levels previously reported in bacterial isolates and in clinical samples to evaluate them as putative good candidates to be used as P. aeruginosa infection biomarkers. Moreover we deeply go through all analytical techniques that have been used for their detection and also new approaches are discussed from a critical point. Graphical abstract.

Effects of Natural Products on Bacterial Communication and Network-Quorum Sensing.

Quorum sensing (QS) has emerged as a research hotspot in microbiology and medicine. QS is a regulatory cell communication system used by bacterial flora to signal to the external environment. QS influences bacterial growth, proliferation, biofilm formation, virulence factor production, antibiotic synthesis, and environmental adaptation. Through the QS system, natural products can regulate the growth of harmful bacteria and enhance the growth of beneficial bacteria, thereby improving human health. Herein, we review advances in the discovery of natural products that regulate bacterial QS systems.

Molecular Mechanisms of Phosphate Stress Activation of Pseudomonas aeruginosa Quorum Sensing Systems.

The hierarchical quorum sensing (QS) systems of Pseudomonas aeruginosa, consisting of las, pqs, and rhl, coordinate the expression of bacterial virulence genes. Previous studies showed that under phosphate deficiency conditions, two-component regulatory system PhoRB could activate various genes involved in cytotoxicity through modulation of QS systems, but the mechanism by which PhoR/PhoB influences QS remains largely unknown. Here, we provide evidence that among the key QS regulatory genes in P. aeruginosa, rhlR, pqsA, mvfR, and lasI were activated by the response regulator PhoB under phosphate-depleted conditions. We show that PhoB is a strong competitor against LasR and RsaL for binding to the promoter of lasI and induces significant expression of lasI, rhlR, and mvfR. However, expression of lasI, encoding the signal 3-oxo-C12-HSL, was increased only marginally under the same phosphate-depleted conditions. This seeming inconsistency was attributed to the induction of pvdQ, which encodes an enzyme for degradation of 3-oxo-C12-HSL signal molecules. Taken together, the results from this study demonstrate that through the two-component regulatory system PhoR/PhoB, phosphate depletion stress could influence the QS network by modulating several key regulators, including lasI, rhlR, mvfR, and pvdQ The findings highlight not only the potency of the PhoR/PhoB-mediated bacterial stress response mechanism but also the plasticity of the P. aeruginosa QS systems in coping with the changed environmental conditions.IMPORTANCE It is not fully understood how phosphate deficiency could influence the virulence of Pseudomonas aeruginosa through modulation of the bacterial QS systems. This report presents a systemic investigation on the impact of phosphate depletion on the hierarchy of quorum sensing systems of P. aeruginosa The results showed that phosphate stress could have an extensive impact on the QS networks of this bacterial pathogen. Among the 7 QS regulatory genes representing the 3 sets of QS systems tested, 4 were significantly upregulated by phosphate depletion stress through the PhoR/PhoB two-component regulatory system, especially the upstream QS regulatory gene lasI We also present evidence that the response regulator PhoB was a strong competitor against the las regulators LasR and RsaL for the lasI promoter, unveiling the mechanistic basis of the process by which phosphate stress could modulate the bacterial QS systems.

Plant-Microbial Interactions Involving Quorum Sensing Regulation

Quorum Sensing (QS) is a mechanism of bacterial intercellular communication that depends on their population density. QS activates the expression of hundreds of bacterial genes, many of which play an important role in plant-bacterial interactions. This review summarizes the latest achievements in the research of bacterial QS signaling in plant-microbial interactions. The review focuses specifically on the best-studied QS systems, i.e., those of gram-negative bacteria which involve N-acyl-homoserine lactones (AHL). The effects of AHL and AHL-producing bacteria on plant growth, development, and defense responses are considered. Signaling functions of plant metabolites which regulate QS-dependent behavior of associated microbiota via the activation or inhibition of bacterial QS systems are described. Possible degradation pathways of AHL in the rhizosphere are also considered. Practical applications of QS regulation for plant protection are discussed.

Pheromone peptide cOB1 from native Enterococcus faecalis forms amyloid‐like structures: A new paradigm for peptide pheromones

Pheromone peptides are an important component of bacterial quorum-sensing system. The pheromone peptide cOB1 (VAVLVLGA) of native commensal Enterococcus faecalis has also been identified as an antimicrobial peptide (AMP) and reported to kill the prototype clinical isolate strain of E. faecalis V583. In this study, the pheromone peptide cOB1 has shown to form amyloid-like structures, a characteristic which is never reported for a pheromone peptide so far. With in silico analysis, the peptide was predicted to be highly amyloidogenic. Further, under experimental conditions, cOB1 formed aggregates displaying characteristics of amyloid structures such as bathochromic shift in Congo red absorbance, enhancement in thioflavin T fluorescence, and fibrillar morphology under transmission electron microscopy. This novel property of pheromone peptide cOB1 may have some direct effects on the binding of the pheromone to the receptor cells and subsequent conjugative transfer, making this observation more important for the therapeutics, dealing with the generation of virulent and multidrug-resistant pathogenic strains.

Virtual screening for quorum-sensing inhibitors of Pseudomonas fluorescens P07 from a food-derived compound database.

Pseudomonas fluorescens are important psychrotrophic food spoilage bacteria that are frequently detected in dairy, meat and aquatic products. Quorum sensing (QS) is an intercellular communication and gene regulation mechanism that enables bacteria to monitor their cell densities and regulate a variety of physiological processes. Hence, targeting the bacterial QS system might be a feasible approach to improve food quality and safety by regulating the spoilage caused by P. fluorescens. In this study, we screened a food-derived three-dimensional (3D) compound database to search for potential QS inhibitors (QSIs) with higher security. The 3D structures of LuxI- and LuxR-type proteins of P. fluorescens P07 were used as targets to screen for QSIs. A total of 25 compounds with high docking scores were tested for their anti-QS activities by indicator strains. The results show that 19 compounds possessed anti-QS activities. Among them, (+)-catechin had the strongest anti-QS activity. The results show that (+)-catechin significantly inhibited the production of extracellular enzymes, swimming motility, biofilm formation, acyl-homoserine lactones and extracellular polymeric substances (EPSs) of P. fluorescens P07. The inhibitory mechanism of (+)-catechin on the QS system of P. fluorescens P07 was discussed in the context of molecular docking analysis and real-time quantitative PCR (RT-qPCR). Virtual screening was useful in finding novel QSIs with high security of P. fluorescens P07 from a food-derived 3D compound database. The high hit rate suggested that foods are rich sources of QSIs, and have great potential for exploration. The modelled LuxI- and LuxR-type proteins could be used as targets to discover P. fluorescens P07 QSIs. (+)-catechin, (-)-epicatechin, propyl gallate, hesperidin and lycopene which were identified as potent QSIs, and may be applied in food preservation and biofilm elimination.

A novel quorum-sensing controlled Type I Effector of Pseudomonas aeruginosa, TesG, suppresses host immune response during chronic infection

Abstract Pseudomonas aeruginosa is a versatile gram-negative pathogen with intricate intracellular regulatory networks that are responsible for a variety of acute and chronic diseases. The survival strategy of this microorganism during pathogenic process especially in causing chronic infections still remains largely elusive. By using in situ RNA-sequencing, here we show that P. aeruginosa undergoes a large-scale transcriptional reprogramming during lung infection. Specifically, more genes of the TCA cycle, oxidative phosphorylation, nucleotide metabolism, T3SS, and two-component system were up-regulated in acute lung infection, while more genes of lipid metabolism, amino acid metabolism, ABC transporters, the T6SS, the QS system, and biofilm formation were up-regulated in chronic lung infection. Notably, a novel virulence factor TesG (PA4141), which is dominated by the vital quorum sensing (QS) system and secreted by the adjacent type I secretion system, can suppress host inflammatory response and remarkably facilitate the development of chronic lung infection. TesG enters alveolar macrophages by clathrin-mediated endocytosis and therefore suppress subsequent adhesion and phagocytosis, as well as the secretion of cytokines and chemokines of macrophages. Mechanically, TesG can bind to and inhibit the activity of eukaryotic small GTPase RhoA by blocking the junction of RhoA with the Rho-guanine nucleotide exchange factor PDZ-RhoGEF. Overall, the characterization of TesG in our current study reveals a new functional aspect of bacterial QS system during host-pathogen interaction, and may open a new avenue for further mechanistic study of chronic respiratory disease and the development of antibacterial therapy.

English

Many pathogenic bacteria produce virulence factors controlled by a mechanism of regulation named quorum sensing (QS). Inhibition of bacterial QS system is a more recent therapeutic approach to counterbalance the emergence of multi-drug resistant bacteria. This study aimed to assess the abilities of methanol extract from Guiera senegalensis galls and its isolated compound methyl gallate to quench the quorum sensing system. Methanol extract from galls of G. senegalensis at the concentration of 100 µg/ml demonstrated significant inhibitory effect on pyocyanin and violacein production respectively in Pseudomonas aeruginosa PAO1 and Chromobacterium violaceum CV026. Colum chromatography and recycling High Performance Liquid Chromatography (HPLC) of methanol extract from galls of G. senegalensis led to the isolation of one active quorum quenching compound. Different spectroscopic methods (MS and NMR) were used to elucidate the structure of this isolated compound as being the methyl gallate (MG). Methyl gallate at the final concentration of 12.5 µg/ml demonstrated good anti-QS activity by inhibiting violacein and pyocyanin production. Its low molecular weight and the capacity to interfere with the mechanism of QS make methyl gallate, an interesting candidate for development of drugs as an alternative to antibiotics to combat bacterial resistance. Key words: Guiera senegalensis, methyl gallate, Pseudomonas aeruginosa PAO1, quorum sensing.