Quorum Sensing Genes Research Articles

Palmitoleic acid inhibits Pseudomonas aeruginosa quorum sensing activation and protects lungs from infectious injury

BackgroundUnsaturated fatty acids targeting quorum sensing (QS) system have shown potential application in reducing bacterial virulence. We aim to investigate the effect of palmitoleic acid (PMA) on P. aeruginosa QS activation, and its impact on infection-induced lung injury.MethodsThe influence of PMA on QS signaling molecule (3OC12-HSL and C4-HSL) concentrations, pyocyanin production, and QS gene transcription levels were examined in wildtype PAO1 culture. The roles of PMA in reducing infection-induced injury were assessed in human bronchial epithelial BEAS-2B cells and mouse lung infection models, respectively. PMA levels and QS signaling molecule concentrations were tested in the bronchoalveolar lavage fluid (BALF) of bronchiectasis patients with first-time detection of P. aeruginosa infection.ResultsPMA administration dose-dependently suppressed the expression of QS signaling molecules, pyocyanin, and QS genes during the logarithmic stage of bacterial growth. In BEAS-2B cells, PMA-treated PAO1 filtrates significantly reduced cell apoptosis and expression of IL-8 and IL-6. In mouse lung infection models, prophylactically oral administration of PMA significantly downregulated the expression of P. aeruginosa QS signals and QS genes (lasR, rhlR, rhlI, lasB, rhlA, phzA1, phnA) in lungs, and relieved neutrophilic airway inflammation. Finally, PMA levels were negatively correlated with the concentrations of both 3OC12-HSL and C4-HSL in BALF of bronchiectasis patients, and positively correlated with their forced vital capacity (FVC) and forced expiratory volume in the first second (FEV1.0).ConclusionOur findings show that PMA inhibits P. aeruginosa QS activation and protects lungs from injury caused by bacterial virulence. Hence, PMA may serve as a potential anti-QS agent against P. aeruginosa infection and would help to alleviate lung injury in bronchiectasis patients.

N-acyl-homoserine-lactones as a critical factor for biofilm formation during the initial adhesion stage in drinking water distribution systems.

The N-acyl-homoserine-lactone (AHLs)-mediated quorum sensing (QS) system is crucial for the coordination of microbial behaviors within communities. However, the levels of AHLs in biofilms in drinking water distribution systems (DWDSs) and their impact on biofilm formation remain poorly understood. Herein, we simulated DWDSs via biofilm reactors to explore the presence and influence of AHLs during the initial stages of biofilm formation on pipe walls. Glass, polypropylene random copolymer (PP-R) and stainless steel (SS) were used as the coupon materials and the three parallel experimental groups were set up and named accordingly. The glass material is considered to form biofilms only minimally and is therefore used as a negative control. By day 30, the concentration of AHLs in biofilm phase in both PP-R group and SS group reached 1200-1800 ng/L. The predominant AHLs were C6-HSL, C8-HSL, and C10-HSL, with a significant positive correlation between AHLs and biofilm biomass. Metagenomic analysis revealed that microbes exhibiting significant differences among the three groups all demonstrated notable correlations with AHLs. Subsequent analysis of QS genes revealed that the genes associated with AHLs biosynthesis and QS receptors were more abundant in the PP-R and SS groups with biofilm formation. Additionally, we analyzed the abundance of genes related to cell motility, transmembrane transport, tricarboxylic acid cycle, and genetic information synthesis. The co-occurrence network indicates that these processes exhibit a strong correlation with QS genes. This study demonstrates the pivotal role of AHLs in microbial communication during the initial stages of biofilm formation in DWDSs and indicates that the regulatory pathways and mechanisms of AHLs may vary under different environmental conditions.

Native Medicinal Plants and Their Effects on Anti-biofilm and Anti-quorum Sensing Activity

Background: Pseudomonas aeruginosa is an opportunistic pathogen with a high mortality rate, particularly among immunocompromised patients. The increase in antibiotic resistance in P. aeruginosa isolates from clinical samples has prompted researchers to seek alternative ways to reduce the pathogenicity of this microorganism. Targeting quorum sensing (QS) presents a promising approach for limiting infections caused by this bacterium. Objectives: This study aimed to evaluate mechanisms for reducing QS and controlling bacterial growth using various medicinal plants. Methods: In this study, the anti-QS effects of seven plant extracts—thyme (Thymus vulgaris), chamomile (Matricaria chamomilla), sumac (Rhus coriaria), ginger (Zingiber officinale), lemon balm (Melissa officinalis), rosehip (Echinacea angustifolia), and marshmallow (Althaea officinalis)—were investigated against P. aeruginosa. A total of 180 P. aeruginosa clinical isolates were examined. High-performance liquid chromatography (HPLC) was then used to detect phenolic compounds and flavonoids in the seven extracts. The presence of quorum-sensing genes (lasR, rhlR, and rhlI) was also evaluated. In addition, pyocyanin quantification, swarming motility assays, and biofilm formation assays were conducted with the herbal extracts. Results: The HPLC analysis results were determined based on relative times and peak areas, revealing specific peaks at different points. Molecular methods confirmed the presence of QS genes, including LasI (54%), lasR (34%), rhlR (12%), and rhlI (4%), which were used in anti-QS screening. Expression of the LasI gene decreased in P. aeruginosa strains treated with herbal extracts compared to untreated strains. Notably, Thymus vulgaris extract demonstrated the strongest inhibition, reducing violacein production by 70.5%, suppressing pyocyanin by 94%, and inhibiting swarming motility and biofilm formation by 80.3%. Conclusions: This study demonstrated that herbal extracts influence virulence factors and gene expression, particularly targeting the las gene, in P. aeruginosa isolates. We recommend further research on the extraction and identification of active ingredients, which may hold potential as therapeutic agents.

Effect of the quorum sensing signal molecule auto-inducer-2 on fermentation performance of Lactobacillus delbrueckii subsp. Bulgaricus DPUL-F36

Fermented milk is a typically product of co-fermentation by a variety of lactic acid bacteria (LAB). Quorum sensing (QS), as an intercellular communication mechanism of bacteria, may serve as a key factor influencing the quality of fermented milk. In this study, the fermentation performance of Lactobacillus delbrueckii subsp. bulgaricus DPUL-F36 were evaluated after supplementation with auto-inducer-2 (AI-2). The protein-protein interaction network (PPIN) was used to retrieve the interactions between QS genes and four major metabolic pathway genes. The expression of luxS gene in DPUL-F36 may affect amino acid metabolism, carbohydrate metabolism and cell wall formation. The key differential metabolites were identified by metabolomics analysis. A variety of amino acids including L-Glutamic, L-Tryptophan, L-Threonine, L-Histidine and L-Glutamine were found to be up-regulated in response to the addition of AI-2. Malic acid and succinate gradually accumulate in the tricarboxylic acid cycle. The consumption of citric acid increased with the fermentation process. In terms of rheological and texture characteristics of fermented milk, addition of AI-2 could effectively improve its shear stress resistance, firmness and index of viscosity. Our research provided a theoretical basis for improving the fermentation performance of DPUL-F36 strains, and support for the screening of excellent composite starter culture.

New insights into biofouling worsening induced by salinity stress in membrane bioreactor: Response of quorum sensing system and its regulation role

Severe worsening of biofouling under salinity stress remains one of the biggest hinderances to membrane bioreactor (MBR) treating saline wastewaters and other membrane technologies applied in saline conditions e.g. seawater desalination. The underlying influential mechanism of salinity stress on biofouling was firstly investigated from the perspective of quorum sensing (QS); Response of QS to salinity stress and its role in regulating biofouling behavior were clarified. Results showed that high salinity stress (over 20 g/L of NaCl) greatly stimulated QS activity, acyl-homoserine lactones (AHLs) were increased by over 200 % and 300 % in mixed liquor and cake layer, respectively; C4-OXO-HSL, C8-OXO-HSL, C10-OXO-HSL and C12-OXO-HSL became the dominant AHLs and showed strong correlations (R2＞0.95) with changes of fouling tendency and extracellular polymeric substances (EPS) characteristics. Metagenomic sequencing further revealed that balance between QS and quorum quenching (QQ) was broken when salinity was over 20 g/L; QS related bacteria and genes were significantly enriched, meanwhile QQ related bacteria and genes were radically suppressed. QS enhancing (by exogenous AHLs) and suppressing experiments (by vanillin) collectively verified the critical regulation role that QS played in biofouling worsening under high salinity stress (mainly via altering EPS characteristics); More importantly, it was demonstrated that suppressing the highly activated QS under high salinity stress was a feasible way to curb the worsening of biofouling. Present study provided new insights into biofouling worsening induced by high salinity stress in MBR; Also, the findings could help to understand biofouling phenomenon in other membrane processes facing salinity stress.

Identification and Validation of Garlic (Allium sativum) Metabolites as Quorum Sensing Inhibitors of Bacillus cereus Targeting the PlcR Receptor: An In Silico and In Vitro Study.

This study aimed to investigate the influence of garlic metabolites on the quorum sensing (QS) of Bacillus cereus, a foodborne pathogen that controls its main virulence factor through QS. The QS signal receptor PlcR of B. cereus was targeted by molecular docking with 82 garlic metabolites to identify the most potent QS inhibitors. Five metabolites, quercetin, kaempferol, luteolin, flavone, and rutin, were selected for further evaluation of their impacts on the growth, toxin production, and virulence of B. cereus in vitro. The expression levels of key QS genes were also measured to verify their anti-QS ability. The results revealed that quercetin reduced enterotoxin production by B. cereus but did not affect the QS process at the transcriptional level; flavone and rutin in garlic interfered with the QS of B. cereus by competing with the autoinducing peptide (AIP) PapR7 for the PlcR binding site, resulting in decreased enterotoxin secretion and hemolysis without altering the bacterial growth. Interestingly, luteolin and kaempferol in garlic acted as AIP analogs and bound to PlcR to stimulate the QS process and virulence. Furthermore, kaempferol, luteolin, flavone, and rutin had distinct or opposite interactions with PapR7 at the Gln237 or Tyr275 residues of PlcR, which determined the suppression or enhancement of the QS process. The findings suggested that flavone and rutin were effective compounds to inhibit the QS process in garlic and could be used as alternative methods to control B. cereus.

Polidocanol inhibits Enterococcus faecalis virulence factors by targeting fsr quorum sensing system

BackgroundThe wide spread of antimicrobial resistance in Enterococcus faecalis is a critical global concern, leading to increasingly limited treatment options. The fsr quorum sensing (QS) plays a critical role in the pathogenicity of E. faecalis, allowing bacteria to coordinate gene expression and regulate many virulence factors. Therefore, fsr QS of E. faecalis represents a potential therapeutic target that provides an effective strategy to treat antibiotic-resistant infections induced by E. faecalis.MethodsIn this study, distribution of different virulence factors including, gelatinase, protease, cell surface hydrophobicity and biofilm formation in sixty clinical isolates of Enterococcus faecalis was investigated. Sixty-six compounds were tested for their activity against fsr QS. The minimal inhibitory concentration of the tested compounds was evaluated using the microbroth dilution method. The effect of sub-inhibitory concentrations of the tested compounds on fsr QS was investigated using the gelatinase assay method. Additionally, the effect of potential QS inhibitor on the virulence factors was estimated. Quantitative real-time PCR was used to investigate the effect of the potential inhibitor on fsr QS related genes (fsrB-fsrC) and (gelE-sprE) and virulence associated genes including, asa1 and epbA.ResultsThe assessment of polidocanol activity against the fsr QS system was demonstrated by studying its effect on gelatinase production in E. faecalis clinical isolates. Sub-lethal concentrations of polidocanol showed a significant reduction in gelatinase and protease production by 54% to 70% and 64% to 85%, respectively. Additionally, it significantly reduced biofilm formation (P < 0.01) and interrupted mature biofilm at concentrations of ½, 1 × and 2 × MIC. Furthermore, polidocanol significantly decreased cell surface hydrophobicity (P < 0.01). Polidocanol at ½ MIC showed a significant reduction in the expression of QS genes including fsrB, fsrC, gelE and sprE by 57% to 97% without affecting bacterial viability. Moreover, it reduced the expression of virulence associated genes (asa1 and epbA) (P < 0.01).ConclusionPolidocanol appears to be a promising option for treating of E. faecalis infections by targeting the fsr QS system and exhibiting anti-biofilm activity.

Resistance patterns, virulence determinants, and biofilm genes of multidrug-resistant Pseudomonas aeruginosa isolated from fish and fish handlers

Pseudomonas aeruginosa (P. aeruginosa) is an opportunistic bacterium that is widely distributed in aquatic environments and causes major economic losses in fish and public health hazards.This study aimed to identify the occurrence of P. aeruginosa in samples collected from fish and fish handlers, and to investigate the antimicrobial susceptibility, virulence determinants, and biofilm genes of P. aeruginosa isolates. A total of 276 samples were cross-sectionally collected from Nile tilapia (53), Golden grey mullet (52), Mediterranean horse mackerel (50), Striped red mullet (71), and fish handlers (50) at five different retail fish markets in Damietta Governorate, Egypt. Pseudomonas species (spp.) were biochemically identified in 57.9% of the total examined samples. Peudomonas aeruginosa were the most prevalent species isolated from the fish and human samples via PCR technique. Peudomonas aeruginosa isolates exhibited full resistance (100%) to tobramycin (TOB), gentamicin (CN), and colistin (CL), with a high level of susceptibility (88.5%) to imipenem (IPM) using the disk diffusion method. Most P. aeruginosa isolates (84.6%) exhibited drug resistance, with 61.5% were multidrug resistance (MDR) and 23.1% were extensive drug resistance (XDR). Most isolates had at least four virulence-associated genes (lasB, toxA, exoU, and oprL) and three biofilm genes (psIA, peIA, and lasR) by using uniplex PCR. The lasI, and rhlR Quorum Sensing (QS) genes were identified in 84.6% and 61.5% in the examined P. aeruginosa isolates, respectively. The highest mortality rate in Nile tilapia experimentally infected with P. aeruginosa isolate encoding most of virulent genes. Multivariate analyses revealed high heterogeneity among the examined isolates. This study revealed the emergence of virulent and drug resistant P. aeruginosa isolates in fish, poses high risks to consumers and food. Thus, strict hygienic measures should be considered when catching, handling, and storing fish, in addition to the routine application of antimicrobial susceptibility testing.

Effects of exogenous signaling molecules on anaerobic sludge digestion: Quorum sensing and antibiotic resistance genes

Regulating quorum sensing (QS) signaling molecules could improve wastewater treatment but might increase antibiotic resistance. This study investigated the effects of exogenous C6-HSL on anaerobic sludge under oxytetracycline stress, with a focus on antibiotic resistance genes (ARGs) and the QS response. The results revealed that exogenous oxytetracycline increased the copy number of ARGs by more than 68.8 %. It also facilitated a 3.04-fold increase in the concentration of signaling molecules and increased the abundance of QS genes. Further addition of the C6-HSL accelerated oxytetracycline degradation, and reduced its residual concentration by 70.9 %, alleviating oxytetracycline stress on microbial communities, and correspondingly reducing stress release from AHL by 75.4 %. Importantly, this did not exacerbate antibiotic resistance, with no significant difference (p > 0.05) in the ARG abundance. These findings may provide valuable insights into the relationship between QS process and antibiotic resistance.

Comparison of Virulence and Quorum Sensing Gene Expression between Planktonic and Biofilm Cells of Legionella pneumophila

Abstract Legionella pneumophila is a waterborne bacterium that has a life cycle consisting of a transmissive phase in which free-living cells spread in the external environment, and a replicative phase with cells multiplying within biofilms. The transition from one phase to another is regulated by the bacterium’s quorum sensing system. As this system also regulates virulence, laboratory cultures of L. pneumophila were used to compare the different expressions of virulence and quorum sensing genes in planktonic and biofilm cells using RT-qPCR assays. The results showed a down regulation of the icmK gene in biofilm cells but only insignificant differences in the expression of 10 other genes associated with filamentation, conjugation, adherence and motility. The two quorum sensing genes examined, lpg1057 and lpg2731, differed in their expression profiles in planktonic and biofilm cells. While their expression in planktonic cells increased from day 10 until day 15 of incubation, their expression in biofilm cells steadily declined after 10 days of incubation. This decrease in quorum sensing gene expression was shown to be associated with a decrease in cell density in the biofilm, thus suggesting that the trigger for the transition from the replicative phase to the transmissive phase is likely to be nutrient depletion in the biofilm.

Fatty acid synthesis promoted by PA1895-1897 operon delays quorum sensing activation in Pseudomonas aeruginosa

PA1895-1897 is a quorum sensing (QS) operon regulated by the anti-activator LuxR homologue QscR in Pseudomonas aeruginosa. We aimed to investigate its impact on bacterial metabolism, and whether it contributes to the delayed QS activation. We performed liquid chromatograph-mass spectrometer-based metabolomics using wildtype PAO1, PA1895-1897-knockout mutant, and mutant with pJN105.PA1895-1897 overexpression vector. The impact of metabolites on QS signaling molecule (3OC12-HSL and C4-HSL) concentrations, pyocyanin production, and QS gene (lasR, lasI, rhlR, and rhlI) expression was examined. Metabolomics analysis found that fatty acid biosynthesis had the highest fold enrichment among all metabolic pathways in PA1895-1897-overexpressed mutants. Among these enriched fatty acids, palmitoleic acid and acetic acid were the predominantly abundant ones that significantly affected by PA1895-1897 operon. When different doses of exogenous palmitoleic acid or acetic acid were added to the cultures of PA1895-1897 knockout mutants, their levels of 3OC12-HSL, C4-HSL, and pyocyanin were decreased in a dose-dependent manner. High doses of palmitoleic acid and acetic acid suppressed the mRNA expression of lasR, rhlR, and rhlI. Inhibition of fatty acid biosynthesis increased the production of 3OC12-HSL, C4-HSL, and pyocyanin in PA1895-1897-overexpressed cultures. Our data suggest that fatty acid synthesis is promoted by PA1895-1897 operon, and contributes the delayed expression of QS phenotypes, furthering the understanding about the regulation of bacterial QS activation.

ZnO nanoparticle engineered Pseudomonas aeruginosa SOA1 towards enhanced Rhamnolipid production

Rhamnolipids, the potential biosurfactants, have widespread applications in pharmaceutics, food, and agriculture fields. However, its low biosynthesis efficiency limits surfactant industrialization. In this study, different nanoparticles (NPs) were immobilized over Pseudomonas aeruginosa (SOA1) and targeted towards increased rhamnolipids production by increasing the secretion (key step of rhamnolipids biosynthesis). It was observed that, upon adding ZnO NPs (4.0 g/L), rhamnolipids titer increased 4.87 times (from 4.1 to 19.98 g/L) in the 10 L bioreactor. This is due to an increment in the expression of the gene (present in the rhamnolipids biosynthesis process) with the introduction of ZnO NPs to SOA1. Further, with ZnO NPs, few rhamnolipid biosynthesis genes (rhlA and rhlB) were significantly upregulated. In contrast, the rhamnose biosynthetic genes (rmlA, rmlC, and algC) were down regulated during the early and late exponential growth phases as studied in Quantitative real-time PCR. The biosurfactant generation is regulated by quorum-sensing genes, which exhibit a hierarchical expression profile. Specifically, in the early log phase (ZnO NPs cultivation), the last gene was elevated, but both pqsE and rhlI were stimulated in the late log phase. This experiment paves a new path toward improving the biosynthesis of microbial metabolites via. NPs engineering.

HPLC-PDA Analysis of Polyacetylene Glucosides from Launaea capitata and Their Antibacterial and Antibiofilm Properties against Klebsiella pneumoniae.

Background/Objectives: Bacterial resistance and virulence are challenges in treating bacterial infections, especially in Klebsiella pneumoniae. Plants of the Launaea Cass. genus are used traditionally to address a variety of diseases, including infections, but the potential bioactive compounds are unknown. Our goals were to verify the potential contribution of two major polyacetylene glycosides isolated from our previous study, (3S,6E,12E)-6,12-tetradecadiene-8,10-diyne-1-ol 3-O-β-D-glucopyranoside (1) and bidensyneoside A (syn. gymnasterkoreaside A) [(3R,8E)-3-hydroxy-8-decene-4,6-diyn-1-yl β-D-glucopyranoside] (2), to the anti-infective properties of Launaea capitata and to develop a dependable HPLC method for their quantification; Methods: On a panel of K. pneumoniae clinical isolates, the antibacterial action of 1, 2, and the methanol extract of the whole L. capitata plant were evaluated by broth microdilution assay, while their antibiofilm action was evaluated by the crystal violet assay. qRT-PCR investigated luxS, mrkA, wzm, and wbbm genes that encode biofilm formation and quorum sensing (QS). The antibacterial activity of 1 was revealed by employing mice infection. Chromatographic separation was conducted using isocratic elution on a Hypersil BDS C18 column using a photodiode array (PDA) detector; Results: Compound 1 showed antibacterial activity with MIC values of 16-128 µg/mL. It remarkably reduced strong and moderate biofilm-forming bacterial isolates from 84.21% to 42.1% compared with the extract (68.42%) and 2 (78.95%). Compound 1 also downregulated the QS genes, luxS, mrkA, wzm, and wbbm, and exhibited in vivo antibacterial action through the enhancement of the histological construction of the liver and spleen, decreased TNF-α immunoreaction, bacterial burden, and the inflammatory mediators IL-1β and IL-6. A successful HPLC-PDA approach was developed to separate the binary mixture of 1 and 2 in less than 10 min with high sensitivity, with detection limits down to 0.518 and 0.095 µg/mL for 1 and 2, respectively; Conclusions: Compound 1 exhibited remarkable antibacterial and antibiofilm properties and may contribute to the anti-infectious traditional uses of L. capitata, meriting further clinical studies and serving as a reliable quality control biomarker for the plant.

Clinical, phenotypic characterization and genomic analysis of the mucoid Acinetobacter baumannii from a teaching hospital

BackgroundAcinetobacter baumannii (A. baumannii) has become a significant nosocomial pathogen globally over the past decade due to the increasing prevalence of antibiotic-resistant isolates. The formation of the mucoid phenotype is a crucial adaptive defense response to external pressure, but the clinical, phenotypic and genotypic characteristics and their relationship with sequence types (ST) and K locus (KL) types remain unclear. MethodsIn this study, we screened a total of 736 A. baumannii isolates, from which we identified and characterized 13 mucoid isolates. The study explored the clinical characteristics of patients with mucoid isolates, investigated the mucoid phenotype, performed capsule observation, quantified capsule production, and assessed antimicrobial susceptibility. Subsequently, whole-genome sequencing (WGS) was used to analyze the sequence types (ST), loci for capsular polysaccharide (KL), antibiotic resistance genes, virulence genes, and core-genome single-nucleotide polymorphisms (SNPs). Additionally, the virulence of all mucoid strains was evaluated through serum resistance assay, biofilm-forming assay, and Galleria mellonella survival assay. ResultsAll mucoid A. baumannii isolates were found to be encapsulated and extremely drug-resistant. Among patients infected with these isolates, 92.3 % had pulmonary infections, and the 30-day mortality rate was 61.5 %. The analysis revealed that not all strains are highly virulent. Whole-genome sequencing (WGS) identified the sequence types as ST136, ST208, ST381, ST195, and ST281, and the capsular types as KL77, KL7, KL33, KL2, and KL3. The ST208 and KL7 isolates exhibited higher virulence and greater biofilm formation, with KL7 isolates also showing higher capsule production. Despite these differences, no significant variations in virulence genes were observed among the mucoid isolates, except for biofilm-associated and quorum-sensing genes. The highly virulent ST208/KL7 strains (AB276, AB313, and AB552) lacked biofilm-associated genes (csuA/BABCDE), indicating these genes do not directly cause differences in biofilm formation. ConclusionThe mucoid A. baumannii isolates were extensively drug-resistant, and infections caused by these isolates could lead to higher mortality. However, not all strains had high virulence, with variations likely related to specific sequence types (ST) and K locus (KL) types.

Programmable Bacteria with Dynamic Virulence Modulation System for Precision Antitumor Immunity.

Engineered bacteria-mediated antitumor approaches have been proposed as promising immunotherapies for cancer. However, the off-target bacterial toxicity narrows the therapeutic window. Living microbes will benefit from their controllable immunogenicity within tumors for safer antitumor applications. In this study, a genetically encoded microbial activation strategy is reported that uses tunable and dynamic expression of surface extracellular polysaccharides to improve bacterial biocompatibility while retaining therapeutic efficacy. Based on screening of genes associated with Salmonella survival in macrophages, a novel attenuated Salmonella chassis strain AIS (htrA gene-deficient) highly enriched in tumors after administration and rapidly cleared from normal organs are reported. Subsequently, an engineered bacterial strain, AISI-H, is constructed based on the AIS strain and an optimized quorum-sensing regulatory system. The AISI-H strain can achieve recovery of dynamic tumor-specific bacterial virulence through a novel HTRA-RCSA axis-based and quorum-sensing synthetic gene circuit-mediated increase in extracellular polysaccharide content. These strains act "off" in normal organs to avoid unwanted immune activation and "on" in tumors for precise tumor suppression in mice. The AISI-H strain shows significant tumor inhibition and potent activation of anticancer immunity in a melanoma mouse model. The AISI-H strain exhibits excellent biocompatibility. This bacterial regulation strategy expands the applications of microbe-based antitumor therapeutics.

Metabolic activities of marine ammonia-oxidizing archaea orchestrated by quorum sensing.

Ammonia-oxidizing archaea (AOA) play crucial roles in marine carbon and nitrogen cycles by fixing inorganic carbon and performing the initial step of nitrification. Evaluation of carbon and nitrogen metabolism popularly relies on functional genes such as amoA and accA. Increasing studies suggest that quorum sensing (QS) mainly studied in biofilms for bacteria may serve as a universal communication and regulatory mechanism among prokaryotes; however, this has yet to be demonstrated in marine planktonic archaea. To bridge this knowledge gap, we employed a combination of metabolic activity markers (amoA, accA, and grs) to elucidate the regulation of AOA-mediated nitrogen, carbon processes, and their interactions with the surrounding heterotrophic population. Through co-transcription investigations linking metabolic markers to potential key QS genes, we discovered that QS molecules could regulate AOA's carbon, nitrogen, and lipid metabolisms under different conditions. Interestingly, specific AOA ecotypes showed a preference for employing distinct QS systems and a distinct QS circuit involving a typical population. Overall, our data demonstrate that QS orchestrates nitrogen and carbon metabolism, including the exchange of organic metabolites between AOA and surrounding heterotrophic bacteria, which has been previously overlooked in marine AOA research.

Cilostazol is a promising anti-pseudomonal virulence drug by disruption of quorum sensing

Resistance to antibiotics is a critical growing public health problem that desires urgent action to combat. To avoid the stress on bacterial growth that evokes the resistance development, anti-virulence agents can be an attractive strategy as they do not target bacterial growth. Quorum sensing (QS) systems play main roles in controlling the production of diverse virulence factors and biofilm formation in bacteria. Thus, interfering with QS systems could result in mitigation of the bacterial virulence. Cilostazol is an antiplatelet and a vasodilator FDA approved drug. This study aimed to evaluate the anti-virulence activities of cilostazol in the light of its possible interference with QS systems in Pseudomonas aeruginosa. Additionally, the study examines cilostazol’s impact on the bacterium’s ability to induce infection in vivo, using sub-inhibitory concentrations to minimize the risk of resistance development. In this context, the biofilm formation, the production of virulence factors and influence on the in vivo ability to induce infection were assessed in the presence of cilostazol at sub-inhibitory concentration. Furthermore, the outcome of combination with antibiotics was evaluated. Cilostazol interfered with biofilm formation in P. aeruginosa. Moreover, swarming motility, biofilm formation and production of virulence factors were significantly diminished. Histopathological investigation revealed that liver, spleen and kidney tissues damage was abolished in mice injected with cilostazol-treated bacteria. Cilostazol exhibited a synergistic outcome when used in combination with antibiotics. At the molecular level, cilostazol downregulated the QS genes and showed considerable affinity to QS receptors. In conclusion, Cilostazol could be used as adjunct therapy with antibiotics for treating Pseudomonal infections. This research highlights cilostazol’s potential to combat bacterial infections by targeting virulence mechanisms, reducing the risk of antibiotic resistance, and enhancing treatment efficacy against P. aeruginosa. These findings open avenues for repurposing existing drugs, offering new, safer, and more effective infection control strategies.

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.

Production of the siderophore lysochelin in rich media through maltose-promoted high-density growth of Lysobacter sp. 3655.

Siderophores are produced by bacteria in iron-restricted conditions. However, we found maltose could induce the biosynthesis of the siderophore lysochelin in Lysobacter sp. 3655 in rich media that are not compatible with siderophore production. Maltose markedly promoted cell growth, with over 300% increase in cell density (OD600) when LB medium was added with maltose (LBM). While lysochelin was not detectable when OD600 in LBM was below 5.0, the siderophore was clearly produced when OD600 reached 7.5 and dramatically increased when OD600 was 15.0. Coincidently, the transcription of lysochelin biosynthesis genes was remarkably enhanced following the increase of OD600. Conversely, the iron concentration in the cell culture dropped to 1.2 μM when OD600 reached 15.0, which was 6-fold lower than that in the starting medium. Moreover, mutants of the maltose-utilizing genes (orf2677 and orf2678) or quorum-sensing related gene orf644 significantly lowered the lysochelin yield. Transcriptomics analysis showed that the iron-utilizing/up-taking genes were up-regulated under high cell density. Accordingly, the transcription of lysochelin biosynthetic genes and the yield of lysochelin were stimulated when the iron-utilizing/up-taking genes were deleted. Finally, lysochelin biosynthesis was positively regulated by a TetR regulator (ORF3043). The lysochelin yield in orf3043 mutant decreased to 50% of that in the wild type and then restored in the complementary strain. Together, this study revealed a previously unrecognized mechanism for lysochelin biosynthetic regulation, by which the siderophore could still be massively produced in Lysobacter even grown in a rich culture medium. This finding could find new applications in large-scale production of siderophores in bacteria.

Cyclic di-peptide Cyclo (L-Phe-L-Pro) mitigates the quorum-sensing mediated virulence in Salmonella typhi and biofilm formation in poultry and plastic system

Salmonella typhi is a predominant foodborne pathogen, posing a significant threat to food quality and safety through typhoid outbreaks. Quorum sensing (QS) and its pathways are crucial for typhoid antigen regulation and S. typhi-mediated spoilage and pathogenesis. Therefore, this study intends to identify secondary metabolites from extracts of 15 bacterial isolates sourced from wild Mangifera indica (mango) brine pickles as novel anti-QS agents against S. typhi. Cell-free supernatants (CFS) of 15 bacterial isolates from fermented mango brine pickles were assessed and identified for anti-QS positive metabolites using GC-MS. Anti-QS metabolite was tested on early and mature biofilms, as well as violacein inhibition, EPS, cellular adherence, motility, antibiotics, and immune resistance of S. typhi. Gene expression and in-silico studies were also conducted to validate the compound's efficacy. The results depicted that among the 15 isolates, Bacillus subtilis P89 exhibited potent anti-QS properties. Gas chromatography-mass spectrometry (GC-MS) analysis identified twelve potential quorum-sensing inhibiting compounds, with Cyclo (L-Phenylalanine-L-Proline) (CPP) demonstrating the maximum anti-QS activity against S. typhi. CPP disrupted the pathogen's early and mature biofilms, reducing exo-polymeric substance production, cell hydrophobicity, and motility at sub-lethal concentrations. It also enhanced the immune response against S. typhi and improved traditional efficacy. Real-time qPCR analyses revealed CPP's modulation of essential quorum-sensing regulatory genes. Molecular docking studies indicated competitive binding of CPP with the SdiA receptor. CPP inhibited S. typhi biofilm formation on chicken skin, plastics, and eggshells. To our knowledge, this study is the first to highlight CPP's potential in food and clinical environments to combat S. typhi via quorum sensing-based mechanisms.