Magnetite-facilitated AHL-mediated quorum sensing enhances nitrate removal and mitigates nitrous oxide emissions in constructed wetlands under polycyclic aromatic hydrocarbons stress.

Streptococcus constellatus inhabits the healthy human gastrointestinal tract and oral microbiome; however, the incidence of this species becoming opportunistically pathogenic has increased in recent decades. S. constellatus has the potential to cause severe pyogenic infections requiring combination antibiotic therapy or surgical intervention. Some virulence processes in S. constellatus, such as genetic competence, are regulated through quorum sensing (QS), facilitated by its 16-mer competence stimulating peptide (CSP). Several target residues on the CSP molecule were identified that can be mutated to enhance the peptide activity and/or lead to competitive inhibition of the competence regulon QS circuitry, thereby modulating related pathogenic phenotypes. Using a rational design approach, second-generation peptide analog libraries were designed and screened, resulting in optimization of a competitive QS inhibitor, CSP-D1AI4AM6A, with an IC50 of 38.3 nM. Overall, this work provides a rational framework upon which novel QS modulators can be designed to attenuate virulence processes in this opportunistic pathogen.

AI-2-mediated quorum sensing marks the ecological transition from collective cooperation to individual survival during Daqu storage.

Industrial processing of lactic acid bacteria (LAB) frequently exposes cells to acute low-temperature stress during frozen handling, cold-chain transport, and pre-lyophilization stabilization. These short-term freezing events disrupt membrane integrity and reduce the viability of LAB, including Lactiplantibacillus plantarum, compromising product quality and functional performance. This study evaluated whether activating the endogenous quorum sensing pathway could enhance biofilm development and improve tolerance to acute freezing stress (-20 °C, 2 days) in L. plantarum JB1. Compared with the wild type, the activity of the signaling molecule AI-2 in the dual-plasmid strain increased by 2.31- to 3.40-fold from 4 to 24 h, peaking at 8 h, while the expression level of the luxS gene increased by 50.83-fold. Biofilm formation reached its peak at 24 h, maximum biofilm formation increased by 2.47-fold relative to the wild type, and the expression level of the luxS gene increased by 27.64-fold compared with the wild type. Hydrophobicity increased 1.88-fold, from 38.6% (wild type) to 72.4%. After freezing, the viable cell counts of the dual-plasmid strain increased by 15.02-fold compared to the wild type. Live/dead fluorescence staining further confirmed enhanced cryotolerance, with the quorum sensing (QS)-activated strain exhibiting a higher live cell proportion and reduced membrane-damaged cells relative to the wild type across all sampling points, with the live/dead ratio increasing 1.95- to 10.67-fold. Activation of the LuxS/AI-2 QS pathway increased AI-2 activity, surface hydrophobicity, and biofilm biomass in L. plantarum JB1. These enhancements translated into improved tolerance to acute freezing, with higher viable counts and superior membrane integrity. © 2026 Society of Chemical Industry.

The QseB/QseC two-component system modulates virulence, motility, and outer membrane vesicles biogenesis in Salmonella enteritidis.

Multilayer microbial framework of aerobic granule microecosystems: Integrating community ecology, genetic networks, and enhancement strategies.

Multifaceted metabolic engineering of Streptomyces hygroscopicus for milbemycins overproduction.

Microbial physiological responses to dense aggregates formation on micron-sized porous carrier: Roles of electron transfer and quorum sensing in enhanced nitrogen removal from high-ammonia wastewater.

Anti-quorum-sensing activity of Plectranthus aliciae in multispecies Cutibacterium acnes-Staphylococcus epidermidis systems.

Orthogonal quorum sensing circuits enable dynamic regulation in Escherichia coli.

Streptococcus thermophilus S-3 is an industrial dairy fermentation species, which can modulate growth and metabolism through quorum sensing (QS). However, the regulatory mechanisms governing high-density bacterial proliferation remain elusive in S. thermophilus S-3. This study focuses on Rgg, a quorum sensing-associated transcription factor, examining its regulatory role in high-density growth dynamics. Three Rgg putative transcriptional regulators (orf383, orf447, and orf1010) in S. thermophilus S-3 were identified, and their evolutionary conservation and conserved DNA-binding domains were characterized, supporting their predicted role in transcriptional regulation of high-density growth. Phenotypic analysis showed that the S-3Δ447 mutant exhibited 30.9% lower maximum optical density and 68.8% lower viability than wild-type strains. Transcriptomic profiling revealed Rgg-dependent dysregulation: 209 upregulated/272 downregulated genes at 7 h, 82 downregulated/20 upregulated at 12 h, and 25 upregulated/33 downregulated at 20 h. KEGG pathway analysis highlighted enrichment in ABC transporters and amino/nucleotide sugar metabolic. Notably, oppC/oppD downregulation disrupted SHP-Rgg binding, impairing oligopeptide signaling. Furthermore, ganP/ganQ suppression reduced lactose uptake capacity and ultimately suppressed cellular proliferation. Conversely, artP upregulation promoted arginine catabolism preference, effectively compensating for observed growth deficiencies. This study elucidated the regulatory role of rgg genes in the high-cell-density growth of S. thermophilus S-3. Rgg coordinates high-density cell proliferation through the dual regulation of peptide-mediated QS initiation and carbon-nitrogen metabolic flux reprogramming. © 2026 Society of Chemical Industry.

The removal mechanisms and novel strategies of antibiotic resistance genes in anaerobic sludge digestion: Insight into microbial metabolic regulation.

Hexanoic acid inhibits in vitro growth and biofilm formation in Xanthomonas vesicatoria and Xanthomonas euvesicatoria.

The quorum-sensing (QS) system plays a crucial role in regulating the virulence of the Ralstonia solanacearum species complex (RSSC). It is controlled by the phcBSR operon and phcA genes. PhcQ may contribute to the activation of PhcA and regulates the expression of QS-dependent genes. Here, we genetically demonstrate that PhcQ functions as a key component of the QS regulatory pathway by maintaining the protein stability of PhcA in R. pseudosolanacearum OE1-1. Deletion of phcQ significantly increased the expression of genes encoding the type III secretion system but decreased the expression of genes for the synthesis of exopolysaccharide, consistent with that of PhcA. The phcQ mutants exhibited enhanced growth at early stages and retained weak virulence on tobacco plants, although they are nonvirulent on tomato plants. Using an overexpression system, we positioned PhcQ downstream of PhcB and upstream of PhcA in the QS regulatory cascade. PhcQ did not affect phcA transcription, while proteomic analysis and western blot revealed that PhcQ maintains PhcA protein stability, with PhcA protein levels reduced to approximately 41% in phcQ mutants. Further structural analysis revealed a disordered tail within the C-terminus of PhcA that is dispensable for PhcA function yet critical for protein stability. Using bimolecular fluorescence complementation and GST pull-down assay, we demonstrated that PhcQ binds directly to PhcA both invitro and in planta, and deletion of this C-terminus tail impaired their binding affinity. These findings reveal a novel regulatory mechanism where PhcQ binds to PhcA and maintains its protein stability to ensure proper QS-dependent gene regulation in RSSC.

Cinnamon essential oil (CEO), one of volatile plant compounds, exhibits potent inhibitory effects on bacterial growth. Pseudomonas tolaasii (P. tolaasii) is the primary spoilage bacterium that causes the decay of Agaricus bisporus. This study investigated the effects of cinnamon essential oil (CEO) on quorum sensing (QS) and biofilm formation in Pseudomonas tolaasii. Whole-genome analysis revealed 102 QS-related genes and their association with 10 virulence protein clusters. AHL signaling molecules (C4-HSL, C6-HSL, C8-HSL, and 3-Oxo-C10-HSL) were identified using biosensor methods and LC-MS/MS. CEO significantly inhibited virulence factor secretion, including protease, elastase, and rhamnolipid. It also reduced swarming and swimming motility by 77.21% and 71.38%, respectively, and effectively suppressed biofilm formation by lowering bacterial viscosity and surface hydrophobicity. At a concentration of 0.4 μL/mL, CEO reduced biofilm formation by 40.89% within 24h, as measured by the crystal violet method. Microscopic and FTIR analysis confirmed CEO's effect on biofilm and extracellular polymer secretion. Thus, it may serve as a novel type of anti-biofilm agent.

Revealing the role of quorum sensing molecules in the treatment of kitchen waste with composite bacterial agents: Performance, mechanisms, and scale-up verification.

Membrane fouling is a major impediment to the widespread application of membrane bioreactors (MBRs) for water treatment. In recent years, the electro-conductive membrane bioreactor (E-MBR) has demonstrated efficacy in mitigating membrane fouling. The application of a negative potential to the electro-conductive membrane promotes electrostatic repulsion, effectively displacing negatively charged extracellular polymeric substances (EPS) away from the membrane surface. However, given the established vital role of quorum sensing (QS) in membrane fouling development, the interference of the negative potential on QS-mediated EPS secretion and biofilm formation has been largely overlooked. Herein, we found that the negative potential applied to the electro-conductive membrane could effectively suppress the QS process, thereby inducing the in situ quorum quenching (QQ) effect. The application of negative potential significantly reduced the levels of the signal molecule C14-HSL as well as EPS. Metagenomic analysis indicated that the relative abundance of the "signal transduction mechanism" pathway was suppressed, and the functional genes encoding C14-HSL receptor proteins belonging to "LuxR family" was downregulated in the cake layer of E-MBR. Density functional theory calculations and molecular dynamics simulation results revealed that the application of negative potential enhanced the electrostatic repulsion between the membrane and C14-HSL and induced the conformational changes of the LuxR protein, which synergistically induced the in situ QQ effect. This study provides a novel perspective on the antifouling mechanism in E-MBR.

Development of antimicrobial resistance in bacteria is a major concern. The study of quorum sensing (QS), the bacterial communication system that coordinates important events in an infection, opens a new avenue for treating infections. QS helps in biofilm formation which acts as a physical barrier and alters the microenvironment which traps the molecules or slows down the antibiotic diffusion making them less effective. Since the standard drugs are not very effective against bacteria anymore, demand for the discovery of other alternatives arises. Phytochemicals extracted from commonly used plants like Coleus amboinicus, known to have antimicrobial properties, can be used to develop novel drugs against quorum sensing and hence suppress bacterial infection. Here, we have identified a set of phytochemicals from C. amboinicus whose drug-like properties were predicted using SwissADME and their interactions with the targets involved in QS in Pseudomonas aeruginosa, Vibrio harveyi and Chromobacterium violaceum were studied by performing molecular docking using PyRx software. Beta-amyrin, chrysoeriol and apigenin were found to be the top scored molecules with docking scores of -9.3, -11.3, and - 11.1kcal/mol respectively, and were considered for molecular dynamics simulation using GROMACS software. This was followed by in vitro tests such as Agar well diffusion, Scanning electron microscopy, Pyocyanin assay and Crystal violet assay. Erythromycin was used as the standard drug and as a positive control to validate the results. Based on both in vitro and in silico studies, the phytochemicals from C. amboinicus have the potential to be inhibitors of quorum sensing targets. These findings are preliminary and should be interpreted as hypotheses to be tested experimentally rather than as established mechanisms.

Serratia sp. are opportunistic Gram-negative bacteria capable of forming robust biofilms and expressing a wide range of quorum sensing (QS)-regulated virulence factors, including motility, protease secretion, and prodigiosin production. The rise of multidrug-resistant strains has emphasized the urgent need for alternative therapeutic strategies targeting bacterial virulence rather than viability. In this context, nonsteroidal anti-inflammatory drugs (NSAIDs) such as ketoprofen have emerged as potential quorum-quenching agents. This study explores the antivirulence activity of ketoprofen against Serratia sp. through a combination of in-vitro phenotypic assays and an advanced in-silico framework. In-vitro assays demonstrated that sub-inhibitory concentrations of ketoprofen significantly impair key virulence traits. Ketoprofen exhibited up to 90.68% inhibition of initial bacterial adhesion and disrupted mature biofilms, reducing biomass by up to 79.1%. Furthermore, motility assays revealed profound inhibition of both swimming and swarming behaviors, alongside a 100% suppression of protease activity and a 60.4% reduction in prodigiosin production, without exerting direct bactericidal effects. To elucidate the molecular basis of this competitive antagonism, an integrative computational approach was deployed. Deep learning-driven molecular docking (GNINA) revealed that ketoprofen targets the LuxR-type QS receptor SmaR with exceptional and reproducible affinity (mean Vina affinity of -9.51kcal/mol), vastly outperforming natural acyl-homoserine lactone (AHL) autoinducers. Kinetic stability was validated through 5 ns vacuum molecular dynamics (MD), followed by 100 ns explicit solvent MD simulations in independent replicates. The trajectories confirmed remarkable positional retention of the ligand (Ligand RMSD ~ 0.08-0.16nm) within the binding pocket. Rigorous MM/PBSA free energy calculations on the equilibrated trajectories yielded highly favorable binding free energies (ΔG ranging from - 19.90 to -30.11kcal/mol), driven by massive enthalpic contributions (ΔH up to -34.20kcal/mol) and a persistent network engaging 10 to 14 key interacting residues. Overall, these findings demonstrate that ketoprofen acts as a highly stable "molecular plug", effectively outcompeting endogenous AHL signals to lock the SmaR receptor in an inactive state. This highlights ketoprofen's immense potential as a repurposed antivirulence agent for combating biofilm-associated and multidrug-resistant Serratia infections.

ABSTRACTThe AHL (acyl‐homoserine lactone)‐mediated quorum‐sensing (QS) regulatory mechanism is ubiquitously distributed in gram‐negative pathogens. In Dickeya oryzae, N‐(3‐oxo‐hexanoyl)‐L‐homoserine lactone (OHHL), synthesised by ExpIEcz, regulates bacterial swimming motility and virulence. However, the role of its putative cognate receptor ExpREcz has not yet been characterised. In this study, we showed that deletion of expREcz alone did not cause significant changes in various phenotypes associated with D. oryzae physiology and pathogenesis. However, in the absence of a functional OHHL synthase ExpIEcz, ExpREcz was a potent repressor modulating the production of cellulases, polygalacturonases and zeamines, biofilm formation and pathogenicity of D. oryzae EC1, and it was a positive regulator modulating bacterial swimming motility. Further analysis showed that the regulatory activity of ExpREcz was abolished by OHHL, and that the QS signal might relieve the regulation of ExpREcz by interacting with two conserved AHL‐binding residues of ExpREcz. Moreover, we found that ExpREcz repressed its own expression through a region in the 5′ noncoding region of expREcz that lacks a canonical lux box. These findings suggest that the mechanism may enable D. oryzae to relieve ExpREcz suppression and initiate infection at high cell density when the QS signal reaches a threshold level.