Long-Chain Alkylthio Cyclodextrin Derivatives for Modulation of Quorum-Sensing-Based Bioluminescence in Aliivibrio fischeri Model System.

Quorum sensing (QS) allows bacteria to coordinate their activities by producing and detecting low-molecular-weight signal molecules based on population density, thereby controlling the infectivity of bacteria through various virulence factors. Quorum-sensing inhibition is a promising approach to tackle bacterial communication. Cyclodextrins (CDs) are a class of cyclic oligosaccharides that reversibly encapsulate the acyl chain of the signal molecules, thereby preventing their binding to receptors and interrupting bacterial communication. This results in the inhibition of the expression of various properties, including different virulence factors. To examine the potential quorum-quenching (QQ) ability of newly prepared cyclodextrin derivatives, we conducted short-term tests using Aliivibrio fischeri, a heterotrophic marine bacterium capable of bioluminescence controlled by quorum sensing. α- and ß-cyclodextrins monosubstituted with alkylthio moieties and further derivatized with quaternary ammonium groups were used as the test agents. The effect of these cyclodextrins on the quorum-sensing system of A. fischeri was investigated by adding them to an exponential growth phase of the culture and then measuring bioluminescence intensity, population growth, and cell viability. Our results demonstrate that the tested cyclodextrins have an inhibitory effect on the quorum-sensing system of A. fischeri. The inhibitory effect varies based on the length of the alkyl chain, with alkylthio substitution enhancing it and the presence of quaternary ammonium groups decreasing it. Our findings suggest that cyclodextrins can be a promising therapeutic agent for the treatment of bacterial infections.

Single-cell level LasR-mediated quorum sensing response of Pseudomonas aeruginosa to pulses of signal molecules.

Quorum sensing (QS) is a communication form between bacteria via small signal molecules that enables global gene regulation as a function of cell density. We applied a microfluidic mother machine to study the kinetics of the QS response of Pseudomonas aeruginosa bacteria to additions and withdrawals of signal molecules. We traced the fast buildup and the subsequent considerably slower decay of a population-level and single-cell-level QS response. We applied a mathematical model to explain the results quantitatively. We found significant heterogeneity in QS on the single-cell level, which may result from variations in quorum-controlled gene expression and protein degradation. Heterogeneity correlates with cell lineage history, too. We used single-cell data to define and quantitatively characterize the population-level quorum state. We found that the population-level QS response is well-defined. The buildup of the quorum is fast upon signal molecule addition. At the same time, its decay is much slower following signal withdrawal, and the quorum may be maintained for several hours in the absence of the signal. Furthermore, the quorum sensing response of the population was largely repeatable in subsequent pulses of signal molecules.

Pneumococcal competence is a populational health sensor driving multilevel heterogeneity in response to antibiotics.

Competence for natural transformation is a central driver of genetic diversity in bacteria. In the human pathogen Streptococcus pneumoniae, competence exhibits a populational character mediated by the stress-induced ComABCDE quorum-sensing (QS) system. Here, we explore how this cell-to-cell communication mechanism proceeds and the functional properties acquired by competent cells grown under lethal stress. We show that populational competence development depends on self-induced cells stochastically emerging in response to stresses, including antibiotics. Competence then propagates through the population from a low threshold density of self-induced cells, defining a biphasic Self-Induction and Propagation (SI&P) QS mechanism. We also reveal that a competent population displays either increased sensitivity or improved tolerance to lethal doses of antibiotics, dependent in the latter case on the competence-induced ComM division inhibitor. Remarkably, these surviving competent cells also display an altered transformation potential. Thus, the unveiled SI&P QS mechanism shapes pneumococcal competence as a health sensor of the clonal population, promoting a bet-hedging strategy that both responds to and drives cells towards heterogeneity.

A fungal metabolic regulator underlies infectious synergism during Candida albicans-Staphylococcus aureus intra-abdominal co-infection.

Candida albicans and Staphylococcus aureus are two commonly associated pathogens that cause nosocomial infections with high morbidity and mortality. Our prior and current work using a murine model of polymicrobial intra-abdominal infection (IAI) demonstrates that synergistic lethality is driven by Candida-induced upregulation of functional S. aureus α-toxin leading to polymicrobial sepsis and organ damage. In order to determine the candidal effector(s) mediating enhanced virulence, an unbiased screen of C. albicans transcription factor mutants was undertaken revealing that zcf13Δ/Δ fails to drive augmented α-toxin or lethal synergism during co-infection. A combination of transcriptional and phenotypic profiling approaches shows that ZCF13 regulates genes involved in pentose metabolism, including RBK1 and HGT7 that contribute to fungal ribose catabolism and uptake, respectively. Subsequent experiments reveal that ribose inhibits the staphylococcal agr quorum sensing system and concomitantly represses toxicity. Unlike wild-type C. albicans, zcf13Δ/Δ did not effectively utilize ribose during co-culture or co-infection leading to exogenous ribose accumulation and agr repression. Forced expression of RBK1 and HGT7 in the zcf13Δ/Δ mutant fully restores pathogenicity during co-infection. Collectively, our results detail the interwoven complexities of cross-kingdom interactions and highlight how intermicrobial metabolism impacts polymicrobial disease pathogenesis with devastating consequences for the host.

Exploring rose absolute and phenylethyl alcohol as novel quorum sensing inhibitors in Pseudomonas aeruginosa and Chromobacterium violaceum.

Inter-cellular signaling, referred to as quorum sensing (QS), regulates the production of virulence factors in numerous gram-negative bacteria, such as the human pathogens Pseudomonas aeruginosa and Chromobacterium violaceum. QS inhibition may provide an opportunity for the treatment of bacterial infections. This represents the initial study to examine the antibiofilm and antivirulence capabilities of rose absolute and its primary component, phenylethyl alcohol. QS inhibition was assessed by examining extracellular exopolysaccharide synthesis, biofilm development, and swarming motility in P. aeruginosa PAO1, along with violacein production in C. violaceum ATCC 12472. Molecular docking analysis was conducted to explore the mechanism by which PEA inhibits QS. Our results indicate that rose absolute and PEA caused decrease in EPS production (60.5-33.5%), swarming motility (94.7-64.5%), and biofilm formation (98.53-55.5%) in the human pathogen P. aeruginosa PAO1. Violacein production decreased by 98.1% and 62.5% with an absolute (0.5 v/v %) and PEA (2 mM). Moreover, the molecular docking analysis revealed a promising competitive interaction between PEA and AHLs. Consequently, this study offers valuable insights into the potential of rose absolute and PEA as inhibitors of QS in P. aeruginosa and C. violaceum.

Norwogonin aids in fighting MRSA-induced pneumonia by targeting agrAC to inhibit α-hemolysin production.

The increasing prevalence of infections related to methicillin-resistant Staphylococcus aureus (MRSA) necessitates the exploration of innovative therapeutic strategies that diverge from conventional antibiotic treatments. This is imperative to effectively combat resistance and manage these infections. The adoption of antivirulence strategies has emerged as a particularly promising avenue. This approach applies a heightened selective pressure on pathogens, thereby diminishing the likelihood of bacteria evolving resistance to antibiotics. In our pursuit of novel therapeutics for treating MRSA infections, we have focused on agents that inhibit the virulence of S. aureus without impeding its growth, aiming to minimize the development of drug resistance. α-Hemolysin, a critical virulence factor encoded by the hla gene, is a cytotoxin that forms pores in host cell membranes and plays a pivotal role in the progression of disease during bacterial infections. Herein, we identified that norwogonin could effectively inhibit Hla production via targeting agrAC, a crucial protein in quorum sensing, resulting in dose-dependent inhibition of hemolytic activity without suppressing S. aureus growth. In vitro assays illustrated that norwogonin decreased the thermal stability of agrAC, providing evidence of interaction between norwogonin and agrAC. Meanwhile, norwogonin alleviated Hla-mediated A549 cell damage and reduced lactate dehydrogenase release. In vivo studies suggested that norwogonin treatment blocked the establishment of a mouse model of pneumonia caused by S. aureus USA300. Notably, norwogonin enhanced the antibacterial potency of oxacillin. In conclusion, norwogonin is a promising candidate for treating S. aureus infections, offering a novel alternative to traditional antibiotics by targeting virulence factors and enhancing the efficacy of existing treatments.

1H-Pyrrole-2,5-dicarboxylic acid, a quorum sensing inhibitor from one endophytic fungus in Areca catechu L., acts as antibiotic accelerant against Pseudomonas aeruginosa.

Pseudomonas aeruginosa has already been stipulated as a "critical" pathogen, emphasizing the urgent need for researching and developing novel antibacterial agents due to multidrug resistance. Bacterial biofilm formation facilitates cystic fibrosis development and restricts the antibacterial potential of many current antibiotics. The capacity of P. aeruginosa to form biofilms and resist antibiotics is closely correlated with quorum sensing (QS). Bacterial QS is being contemplated as a promising target for developing novel antibacterial agents. QS inhibitors are a promising strategy for treating chronic infections. This study reported that the active compound PT22 (1H-pyrrole-2,5-dicarboxylic acid) isolated from Perenniporia tephropora FF2, one endophytic fungus from Areca catechu L., presents QS inhibitory activity against P. aeruginosa. Combined with gentamycin or piperacillin, PT22 functions as a novel antibiotic accelerant against P. aeruginosa. PT22 (0.50 mg/mL, 0.75 mg/mL, and 1.00 mg/mL) reduces the production of QS-related virulence factors, such as pyocyanin and rhamnolipid, and inhibits biofilm formation of P. aeruginosa PAO1 instead of affecting its growth. The architectural disruption of the biofilms was confirmed by visualization through scanning electron microscopy (SEM) and confocal laser scanning microscopy (CLSM). Real-time quantitative PCR (RT-qPCR) indicated that PT22 significantly attenuated the expression of QS-related genes followed by docking analysis of molecules against QS activator proteins. PT22 dramatically increased the survival rate of Galleria mellonella. PT22 combined with gentamycin or piperacillin presents significant inhibition of biofilm formation and eradication of mature biofilm compared to monotherapy, which was also confirmed by visualization through SEM and CLSM. After being treated with PT22 combined with gentamycin or piperacillin, the survival rates of G. mellonella were significantly increased compared to those of monotherapy. PT22 significantly enhanced the susceptibility of gentamycin and piperacillin against P. aeruginosa PAO1. Our results suggest that PT22 from P. tephropora FF2 as a potent QS inhibitor is a candidate antibiotic accelerant to combat the antibiotic resistance of P. aeruginosa.

Phenotypic memory in quorum sensing.

Quorum sensing (QS) is a regulatory mechanism used by bacteria to coordinate group behavior in response to high cell densities. During QS, cells monitor the concentration of external signals, known as autoinducers, as a proxy for cell density. QS often involves positive feedback loops, leading to the upregulation of genes associated with QS signal production and detection. This results in distinct steady-state concentrations of QS-related molecules in QS-ON and QS-OFF states. Due to the slow decay rates of biomolecules such as proteins, even after removal of the initial stimuli, cells can retain elevated levels of QS-associated biomolecules for extended periods of time. This persistence of biomolecules after the removal of the initial stimuli has the potential to impact the response to future stimuli, indicating a memory of past exposure. This phenomenon, which is a consequence of the carry-over of biomolecules rather than genetic inheritance, is known as "phenotypic" memory. This theoretical study aims to investigate the presence of phenotypic memory in QS and the conditions that influence this memory. Numerical simulations based on ordinary differential equations and analytical modeling were used to study gene expression in response to sudden changes in cell density and extracellular signal concentrations. The model examined the effect of various cellular parameters on the strength of QS memory and the impact on gene regulatory dynamics. The findings revealed that QS memory has a transient effect on the expression of QS-responsive genes. These consequences of QS memory depend strongly on how cell density was perturbed, as well as various cellular parameters, including the Fold Change in the expression of QS-regulated genes, the autoinducer synthesis rate, the autoinducer threshold required for activation, and the cell growth rate.

Effect of L-HSL on biofilm and motility of Pseudomonas aeruginosa and its mechanism.

Pseudomonas aeruginosa (P. aeruginosa) biofilm formation is a crucial cause of enhanced antibiotic resistance. Quorum sensing (QS) is involved in regulating biofilm formation; QS inhibitors block the QS signaling pathway as a new strategy to address bacterial resistance. This study investigated the potential and mechanism of L-HSL (N-(3-cyclic butyrolactone)-4-trifluorophenylacetamide) as a QS inhibitor for P. aeruginosa. The results showed that L-HSL effectively inhibited the biofilm formation and dispersed the pre-formed biofilm of P. aeruginosa. The production of extracellular polysaccharides and the motility ability of P. aeruginosa were suppressed by L-HSL. C. elegans infection experiment showed that L-HSL was non-toxic and provided protection to C. elegans against P. aeruginosa infection. Transcriptomic analysis revealed that L-HSL downregulated genes related to QS pathways and biofilm formation. L-HSL exhibits a promising potential as a therapeutic drug for P. aeruginosa infection. KEY POINTS: • Chemical synthesis of N-(3-cyclic butyrolactone)-4-trifluorophenylacetamide, named L-HSL. • L-HSL does not generate survival pressure on the growth of P. aeruginosa and can inhibit the QS system. • KEGG enrichment analysis found that after L-HSL treatment, QS-related genes were downregulated.

Biofilm formation in food industries: Challenges and control strategies for food safety.

Various pathogens have the ability to grow on food matrices and instruments. This grow may reach to form biofilms. Bacterial biofilms are community of microorganisms embedded in extracellular polymeric substances (EPSs) containing lipids, DNA, proteins, and polysaccharides. These EPSs provide a tolerance and favorable living condition for microorganisms. Biofilm formations could not only contribute a risk for food safety but also have negative impacts on healthcare sector. Once biofilms form, they reveal resistances to traditional detergents and disinfectants, leading to cross-contamination. Inhibition of biofilms formation and abolition of mature biofilms is the main target for controlling of biofilm hazards in the food industry. Some novel eco-friendly technologies such as ultrasound, ultraviolet, cold plasma, magnetic nanoparticles, different chemicals additives as vitamins, D-amino acids, enzymes, antimicrobial peptides, and many other inhibitors provide a significant value on biofilm inhibition. These anti-biofilm agents represent promising tools for food industries and researchers to interfere with different phases of biofilms including adherence, quorum sensing molecules, and cell-to-cell communication. This perspective review highlights the biofilm formation mechanisms, issues associated with biofilms, environmental factors influencing bacterial biofilm development, and recent strategies employed to control biofilm-forming bacteria in the food industry. Further studies are still needed to explore the effects of biofilm regulation in food industries and exploit more regulation strategies for improving the quality and decreasing economic losses.

Effects of chlorogenic acid-grafted-chitosan on biofilms, oxidative stress, quorum sensing and c-di-GMP in Pseudomonas fluorescens.

This study determined the inhibitory mechanism as well as anti-biofilm activity of chlorogenic acid-grafted-chitosan (CS-g-CA) against Pseudomonas fluorescens (P. fluorescens) in terms of biofilm content, oxidative stress, quorum sensing and cyclic diguanosine monophosphate (c-di-GMP) concentration, and detected the changes in the expression levels of related genes by quantitative real-time PCR (qRT-PCR). Results indicated that treatment with sub-concentrations of CS-g-CA for P. fluorescens led to reduce the biofilm size of large colonies, decrease the content of biofilm and extracellular polymers, weaken the motility and adhesion of P. fluorescens. Moreover, CS-g-CA resulted in higher ROS levels, diminished catalase activity (CAT), and increased superoxide dismutase (SOD) in P. fluorescens. CS-g-CA reduced the production of quorum-sensing signaling molecules (AHLs) and the concentration of c-di-GMP in bacteria. Genes for flagellar synthesis (flgA), the resistance to stress (rpoS and hfq), and pde (phosphodiesterases that degrade c-di-GMP) were significantly down-regulated as determined by RT-PCR. Overall, CS-g-CA leads to the accumulation of ROS in bacteria via P. fluorescens environmental resistance genes and decreases the activity of enzymes in the bacterial antioxidant system, and interferes with the production and reception of quorum-sensing signaling molecules and the synthesis of c-di-GMP in P. fluorescens, which regulates the generation of biofilms.

Quorum sensing mediated response mechanism of anammox consortia to anionic surfactant: Molecular simulation and molecular evidence.

The widespread use of surfactants raise challenges to biological wastewater treatment. Anaerobic ammonium oxidation (anammox) process has the potential to treat wastewater containing anionic surfactants, but the response of anammox consortia at the molecular level under long-term exposure is unclear. Using high-throughput sequencing and gene quantification, combined with molecular docking, the effect of sodium dodecyl sulfonate (SDS) on anammox consortia were investigated. Levels of reactive oxygen species (ROS) might be lower than the threshold of oxidative damage, while the increase of lactate dehydrogenase (LDH) represented the cell membrane damage. Decreased abundance of functional genes (hdh, hzsA and nirS) indicated the decrease of the anammox bacterial abundance. Trace amounts of N-acyl homoserine lactone (AHL, C6-HSL, C8-HSL and C12-HSL) contained in influent could induce endogenous quorum sensing (QS), which could regulate the correlation between functional bacteria to optimize the microbial community and strengthen the resistance of anammox consortia to SDS. In addition, the proliferation of disinfectant resistance genes might increase the environmental pathogenicity of sewage discharge. This work highlights the potential response mechanism of anammox consortium to surfactants and provides a universal microbial-friendly bioenhancement strategy based on QS.

Prunus persica leaves aqueous extract mediated biosynthesis of Ag nanoparticles and assessment of its anti-quorum sensing potential against Hafnia species.

Hafnia sp. was one of the specific spoilage bacteria in aquatic products, and the aim of the study was to investigate the inhibition ability of the silver nanoparticles (AgNPs) biosynthesis by an aqueous extract of Prunus persica leaves toward the spoilage-related virulence factors of Hafnia sp. The synthesized P-AgNPs were spherical, with a mean particle size of 36.3 nm and zeta potential of 21.8 ± 1.33 mV. In addition, the inhibition effects of P-AgNPs on the growth of two Hafnia sp. strains and their quorum sensing regulated virulence factors, such as the formation of biofilm, secretion of N-acetyl-homoserine lactone (AHLs), proteases, and exopolysaccharides, as well as their swarming and swimming motilities were evaluated. P-AgNPs had a minimum inhibitory concentration (MIC) of 64 µg ml-1 against the two Hafnia sp. strains. When the concentration of P-AgNPs was below MIC, it could inhibit the formation of biofilms by Hafnia sp at 8-32 µg ml-1, but it promoted the formation of biofilms by Hafnia sp at 0.5-4 µg ml-1. P-AgNPs exhibited diverse inhibiting effects on AHLs and protease production, swimming, and swarming motilities at various concentrations.

AI-2 quorum sensing-induced galactose metabolism activation in Streptococcus suis enhances capsular polysaccharide-associated virulence.

Bacteria utilize intercellular communication to orchestrate essential cellular processes, adapt to environmental changes, develop antibiotic tolerance, and enhance virulence. This communication, known as quorum sensing (QS), is mediated by the exchange of small signalling molecules called autoinducers. AI-2 QS, regulated by the metabolic enzyme LuxS (S-ribosylhomocysteine lyase), acts as a universal intercellular communication mechanism across gram-positive and gram-negative bacteria and is crucial for diverse bacterial processes. In this study, we demonstrated that in Streptococcus suis (S. suis), a notable zoonotic pathogen, AI-2 QS enhances galactose utilization, upregulates the Leloir pathway for capsular polysaccharide (CPS) precursor production, and boosts CPS synthesis, leading to increased resistance to macrophage phagocytosis. Additionally, our molecular docking and dynamics simulations suggest that, similar to S. pneumoniae, FruA, a fructose-specific phosphoenolpyruvate phosphotransferase system prevalent in gram-positive pathogens, may also function as an AI-2 membrane surface receptor in S. suis. In conclusion, our study demonstrated the significance of AI-2 in the synthesis of galactose metabolism-dependent CPS in S. suis. Additionally, we conducted a preliminary analysis of the potential role of FruA as a membrane surface receptor for S. suis AI-2.

Engineering a biomimicking strategy for discovering nonivamide-based quorum-sensing inhibitors for controlling bacterial infection.

The overuse of antibiotics over an extended period has led to increasing antibiotic resistance in pathogenic bacteria, culminating in what is now considered a global health crisis. To tackle the escalating disaster caused by multidrug-resistant pathogens, the development of new bactericides with new action mechanism is highly necessary. In this study, using a biomimicking strategy, a series of new nonivamide derivatives that feature an isopropanolamine moiety [the structurally similar to the diffusible signal factor (DSF) of Xanthomonas spp.] were prepared for serving as potential quorum-sensing inhibitors (QSIs). After screening and investigation of their rationalizing structure-activity relationships (SARs), compound A26 was discovered as the most optimal active molecule, with EC50 values of 9.91 and 7.04 µg mL-1 against Xanthomonas oryzae pv oryzae (Xoo) and Xanthomonas axonopodis pv. citri (Xac). A docking study showed that compound A26 exhibited robust interactions with Glu A: 161 of RpfF, which was strongly evidenced by fluorescence titration assay (KA value for Xoo RpfF-A26 = 104.8709 M-1). Furthermore, various bioassays showed that compound A26 could inhibit various bacterial virulence factors, including biofilm formation, extracellular polysaccharides (EPS), extracellular enzyme activity, DSF production, and swimming motility. In addition, in vivo anti-Xoo results showed that compound A26 had excellent control efficiency (curative activity: 43.55 %; protective activity: 42.56 %), surpassing that of bismerthiazol and thiodiazole copper by approximately 8.0%-37.3 %. Overall, our findings highlight a new paradigm wherein nonivamide derivatives exhibit potential in combating pathogen resistance issues by inhibiting bacterial quorum sensing systems though attributing to their new molecular skeleton, novel mechanisms of action, and non-toxic features.

Falcaria vulgaris extract: A mixture of quorum sensing inhibitors for controlling Pectobacterium carotovorum subsp. carotovorum.

A promising strategy to control bacterial diseases involves using Quorum Sensing Inhibitor (QSI) compounds. This study aimed to evaluate the potential of Falcaria vulgaris plant extract to combat the phytopathogenic Pectobacterium carotovorum subsp. carotovorum (Pcc) via its QSI activity. Using biosensors and Minimum Inhibitory Concentration (MIC) assays, the QSI and antimicrobial aspects of the extract were assessed. Furthermore, the effect of the extract on the reduction of tuber maceration in potatoes was examined. Subsequently, homology modeling based on LasR was conducted to analyze interactions between ligand 3-oxo-C8-AHL, and ExpR2 protein. Docking studies were performed on all extract compounds identified via Gas Chromatography-Mass Spectrometry (GC-MS) analysis. The extract effectively reduced maceration at sub-MIC concentrations across various pathogenic strains. Furthermore, Cyclopentadecanone, 2-hydroxy, showed more negative docking energy than the native ligand. Z,E-2,13-Octadecadien-1-ol showed energy equivalence to the native ligand. Additionally, this plant included certain compounds or their analogs that had previously been discovered as QSI compounds. These compounds included oleic acid, n-Hexadecanoic acid, cytidine, and linoleic acid, and they had energies that were comparable to that of the native ligand. In conclusion, the remarkable QSI property showed by this plant is likely attributed to a combination of compounds possessing this characteristic.

Unveiling bacterial communication with a MATLAB GUI implementing the diffusion-based quorum sensing model.

Bacteria employ quorum sensing as a remarkable mechanism for coordinating behaviors and communicating within their communities. In this study, we introduce a MATLAB Graphical User Interface (GUI) that offers a versatile platform for exploring the dynamics of quorum sensing. Our computational framework allows for the assessment of quorum sensing, the investigation of parameter dependencies, and the prediction of minimum biofilm thickness required for its initiation. A pivotal observation from our simulations underscores the pivotal role of the diffusion coefficient in quorum sensing, surpassing the influence of bacterial cell dimensions. Varying the diffusion coefficient reveals significant fluctuations in autoinducer concentration, highlighting its centrality in shaping bacterial communication. Additionally, our GUI facilitates the prediction of the minimum biofilm thickness necessary to trigger quorum sensing, a parameter contingent on the diffusion coefficient. This feature provides valuable insights into spatial constraints governing quorum sensing initiation. The interplay between production rates and cell concentrations emerges as another critical facet of our study. We observe that higher production rates or cell concentrations expedite quorum sensing, underscoring the intricate relationship between cell communication and population dynamics in bacterial communities. While our simulations align with mathematical models reported in the literature, we acknowledge the complexity of living organisms, emphasizing the value of our GUI for standardizing results and facilitating early assessments of quorum sensing. This computational approach offers a window into the environmental conditions conducive to quorum sensing initiation, encompassing parameters such as the diffusion coefficient, cell concentration, and biofilm thickness. In conclusion, our MATLAB GUI serves as a versatile tool for understanding the diverse aspects of quorum sensing especially for non-biologists. The insights gained from this computational framework advance our understanding of bacterial communication, providing researchers with the means to explore diverse ecological contexts where quorum sensing plays a pivotal role.

Liquid Interfacial Gating of Superhydrophobic Plasmonic Metal-Organic Frameworks for Three-in-One Separation, Enrichment, and Recognition in Bacterial Quorum Sensing.

Poor adsorption properties of nonadsorbing targets and competing adsorption of nontargets at a liquid interface always hamper the development of interface sensing techniques. There is a need to fabricate materials that are applicable to various interface assemblies and, meanwhile, could be employed as interfacial gating to improve the performance of interface sensing by separating, enriching, and recognizing targets at the liquid interface. Here, superhydrophobic zeolite imidazole frameworks-8@gold nanoparticles-1H,1H,2H,2H-perfluorodecanethiol (ZIF-8@GNPs-PFDT) with a static water contact angle (WCA) of 155° was constructed via electrostatic self-assembly and surface graft modification. The plasmonic metal-organic framework (PMOF) nanohybrid realized all-purpose self-assembly at air/liquid and liquid/liquid interfaces and also facilely assembled on the surface of liquid droplets, hydrogels, and foams. The self-assembled porous materials displayed the capability for separating, enriching, and recognizing analytes at various oil/water interfaces and thus could be used to adsorb nonadsorbing targets and block the competing adsorption of nontargets. The self-assembled ZIF-8@GNPs-PFDT structures were employed as a three-in-one interfacial gating to endow the excellent surface-enhanced Raman scattering (SERS) sensing capability and has become a promising tool for dye molecular analysis, oil/water separation, organic phase identification, and in situ cultivation and monitoring of bacterial quorum sensing (QS).

Designing and synthesizing peptide-based quorum sensing modulators.

Quorum sensing (QS) is a density-dependent bacterial communication system that uses small molecules as regulatory modulators. Synthetic changes to these molecules can up-or-down-regulate this system, leading to control of phenotypes, like competence and virulence factor production, that have implications in human health. In this chapter, a methodology for library design and screening of synthetic autoinducing peptides (AIPs) to uncover QS SARs is delineated. Additionally, procedures for the synthesis, purification and analysis of linear and cyclic AIPs are detailed. This includes solutions for potential synthetic challenges including diketopiperazine formation when using N-methyl amino acids and cyclization of peptides containing N-terminal cysteine residues. These procedures have and are currently being applied to develop potent QS modulators in Streptococcus pneumoniae, Bacillus cereus, Streptococcus gordonii and Lactiplantibacillus plantarum.

Effects of quorum sensing-interfering agents, including macrolides and furanone C-30, and an efflux pump inhibitor on nitrosative stress sensitivity in Pseudomonas aeruginosa.

Long-term administration of certain macrolides is efficacious in patients with persistent pulmonary Pseudomonas aeruginosa infection, despite how limited the clinically achievable concentrations are, being far below their MICs. An increase in the sub-MIC of macrolide exposure-dependent sensitivity to nitrosative stress is a typical characteristic of P. aeruginosa. However, a few P. aeruginosa clinical isolates do not respond to sub-MIC of macrolide treatment. Therefore, we examined the effects of sub-MIC of erythromycin (EM) on the sensitivity to nitrosative stress together with an efflux pump inhibitor (EPI) phenylalanine arginyl ß-naphthylamide (PAßN). The sensitivity to nitrosative stress increased, suggesting that the efflux pump was involved in inhibiting the sub-MIC of macrolide effect. Analysis using efflux pump-mutant P. aeruginosa revealed that MexAB-OprM, MexXY-OprM, and MexCD-OprJ are factors in reducing the sub-MIC of macrolide effect. Since macrolides interfere with quorum sensing (QS), we demonstrated that the QS-interfering agent furanone C-30 (C-30) producing greater sensitivity to nitric oxide (NO) stress than EM. The effect of C-30 was decreased by overproduction of MexAB-OprM. To investigate whether the increase in the QS-interfering agent exposure-dependent sensitivity to nitrosative stress is characteristic of P. aeruginosa clinical isolates, we examined the viability of P. aeruginosa treated with NO. Although treatment with EM could reduce cell viability, a high variability in EM effects was observed. Conversely, C-30 was highly effective at reducing cell viability. Treatment with both C-30 and PAßN was sufficiently effective against the remaining isolates. Therefore, the combination of a QS-interfering agent and an EPI could be effective in treating P. aeruginosa infections.