The hierarchy quorum sensing network in Pseudomonas aeruginosa

Multifaceted quorum-sensing inhibiting activity of 3-(Benzo[d][1,3]dioxol-4-yl)oxazolidin-2-one mitigates Pseudomonas aeruginosa virulence

As antibiotic resistance escalates into a global health crisis, novel therapeutic approaches against infectious diseases are in urgent need. Pseudomonas aeruginosa, an adaptable opportunistic pathogen, poses substantial challenges in treating a range of infections. The quorum-sensing (QS) system plays a pivotal role in orchestrating the production of a large set of virulence factors in a cell density-dependent manner, and the anti-virulence strategy targeting QS may show huge potential. Here, we present a comprehensive investigation into the potential of the synthesized compound 3-(benzo[d][1,3]dioxol-4-yl)oxazolidin-2-one (OZDO, C10H9NO4) as a QS inhibitor to curb the virulence of P. aeruginosa. By employing an integrated approach encompassing in silico screening, in vitro and in vivo functional identification, we elucidated the multifaceted effects of OZDO. Molecular docking predicted that OZDO interfered with three core regulatory proteins of P. aeruginosa QS system. Notably, OZDO exhibited significant inhibition on the production of pyocyanin, rhamnolipid and extracellular proteases, biofilm formation, and cell motilities of P. aeruginosa. Transcriptomic analysis and quantitative real-time PCR displayed the down-regulation of QS-controlled genes in OZDO-treated PAO1, reaffirming the QS-inhibition activity of OZDO. In vivo assessments using a Caenorhabditis elegans-infection model demonstrated OZDO mitigated P. aeruginosa pathogenicity, particularly against the hypervirulent strain PA14. Moreover, OZDO in combination with polymyxin B and aztreonam presented a promising avenue for innovative anti-infective therapy. Our study sheds light on the multifaceted potential of OZDO as an anti-virulence agent and its significance in combating P. aeruginosa-associated infections.

Design, synthesis and activity evaluation of dithiocarbamate-based L-homoserine lactone derivatives as Gram-negative bacteria quorum sensing inhibitors

Pseudomonas aeruginosa (P. aeruginosa) is an important Gram-negative opportunistic pathogen that uses quorum sensing to regulate its virulence and biofilm development, which contributes to its pathogenicity and drug resistance. As a result, focusing on the virulence and pathogenicity of P. aeruginosa through quorum sensing (QS) is considered a possible target for anti-infective therapy. In this work, we discovered new quorum-sensing inhibitors derived from the structural modification of the dithiocarbamate-based l-homoserine lactone derivatives library and the target compound (10p) demonstrated significant inhibitory activity against PAO1 biofilm (inhibition rate: 86.76 %), pyocyanin (68.05 %), rhamnolipid (34.56 %), LasA protease (61.01 %) and a low inhibitory on elastase production (6.59 %) at 60 μM. Moreover, compound 10p effectively attenuated P. aeruginosa motility, such as swimming (42.85 %) and swarming (72 %), and demonstrated no toxicity in vitro. The result indicates that compound 10p may serve as a promising new antibacterial synergist option for treating P. aeruginosa infections.

Two cinnamic acid derivatives as inhibitors of Pseudomonas aeruginosa las and pqs quorum-sensing systems: Impact on biofilm formation and virulence factors

INTRODUCTION

Quorum sensing (QS) is a bacterial communication mechanism that regulates gene expression, playing a crucial role in various physiological processes. Interfering with this signalling pathway is a promising strategy to control bacterial pathogenicity and virulence.

OBJECTIVES

This study evaluated the potential of two cinnamic acid derivatives, ferulic and sinapic acids, to inhibit the las and pqs systems in Pseudomonas aeruginosa. Their effects on biofilm architecture, virulence factor production and bacterial motility were also investigated.

METHODS

Bioreporter strains and bioluminescence-based assays were used to evaluate the modulation of QS-activity by cinnamic acid-type phenolic acids. In addition, in silico docking analysis was performed to validate the binding interactions of the cinnamic acid derivatives with QS-receptors. The biofilm architecture was analysed by optical coherence tomography, and virulence factors production (pyoverdine, pyocyanin, total proteases, lipases, gelatinases and siderophores) and motility were measured by absorbance measurement and plate agar method.

RESULTS

Ferulic and sinapic acids at 1000 µg mL-1 inhibited the las and pqs systems by 90 % and 80 %, respectively. The N-3-oxododecanoyl-homoserine lactone production was reduced by 70 % (6.25 µg mL-¹). In silico analysis demonstrated that cinnamic acid derivatives exhibited comparable interactions and higher docking scores than reference ligands and inhibitors. Biofilm thickness decreased from 96 µm to 11 µm, and virulence factors and swarming motility were significantly impaired. The comparable anti-QS activity of cinnamic acid derivatives suggests that the additional methoxy group in sinapic acid does not directly contribute to its anti-QS effect.

CONCLUSION

Ferulic and sinapic acids compromised the biofilm architecture and virulence of P. aeruginosa through QS inhibition.

PqsR-specific quorum sensing inhibitors targeting Pseudomonas aeruginosa: current advances and future directions

The emergence of multidrug-resistant (MDR) Pseudomonas aeruginosa is driven by diverse resistance mechanisms, including quorum sensing (QS) and biofilm formation. QS regulates virulence, antibiotic tolerance, efflux pumps, and biofilm development, enhancing the pathogen's adaptability. Among QS systems, the Pseudomonas quinolone signal regulator (PqsR) plays a central role in controlling virulence and biofilm-associated genes. This review critically examines the PqsR-regulated network and highlights the potential of PqsR inhibitors to reduce pathogenicity. Disrupting QS instead of targeting bacterial viability can enhance antibiotic efficacy, making this combinatorial approach a promising strategy to combat MDR P. aeruginosa.

Naringenin as a Potent Natural Biofilm Inhibitor of Pseudomonas aeruginosa in Diabetic Foot Ulcers Through lasR Competitive Inhibition

Chronic non-healing foot ulcers are a major complication in diabetic patients, contributing to significant morbidity and mortality. Microorganisms in these wounds form biofilms, conferring greater virulence and enhanced protection from antibiotics. Hence, we examined naringenin, and other natural compounds like chlorofuranone, 4-nitropyridine N-oxide, and quercetin as a positive control against the major pathogenic organism that forms biofilm in foot ulcers. Here, we focused on Pseudomonas aeruginosa, which produces high levels of biofilm in diabetic foot ulcers. Naringenin (47.10 µg/ml for PA21; 124.7 µg/ml for PA333) and other natural compounds were tested for their ability to inhibit biofilm formation and virulence in vitro, and their effect on biofilm-associated gene expression was studied. The biofilm inhibitory mechanism of naringenin was elucidated using in silico analysis and in vitro reporter gene assay. In vitro biofilm assays, confocal and scanning electron microscopy showed that natural compounds effectively inhibited biofilm, without causing cell death. Treatment with these compounds significantly altered the expression of genes associated with quorum sensing in P. aeruginosa, such as lasR, pslA, algA, gacS, and pelA. Naringenin decreased the production of major virulence factors in P. aeruginosa. Molecular docking showed that naringenin exhibited the strongest binding affinity to LasR, and the same was validated by reporter gene assay using plasmid pSB1142 indicating its role as a competitive inhibitor in the las quorum sensing system in P. aeruginosa. The findings of this study could be extrapolated to in vivo diabetic wound infection models to help optimize the use of naringenin in effective biofilm control for better wound management in diabetic patients.

PqsE adapts the activity of the Pseudomonas aeruginosa quorum-sensing transcription factor RhlR to both autoinducer concentration and promoter sequence identity

Pseudomonas aeruginosa is an opportunistic human pathogen that poses a significant health threat. Many pathogenic behaviors of P. aeruginosa are under control of the bacterial cell-cell communication system known as quorum sensing (QS). One of the QS master regulators, RhlR, is a receptor/transcription factor that not only relies on binding of its canonical ligand, N-butyrylhomoserine lactone (C4-HSL), but additionally requires a protein-protein interaction with the enzyme, PqsE. We constructed heterologous reporter strains in Escherichia coli that allow measurements of the reliance of RhlR on C4-HSL and/or PqsE binding for the ability to activate transcription of three RhlR-regulated genes: rhlA (PqsE independent), phzM (PqsE dependent), and azeB (PqsE inhibited). Analogous assays measuring activation of the three genes in P. aeruginosa were performed, and the patterns observed correlated tightly with the heterologous reporter assays. These results confirm that the binding of PqsE to RhlR is able to fine-tune RhlR transcription factor activity in a promoter-specific manner and prove that this ability is independent of other factors present in P. aeruginosa.IMPORTANCEPseudomonas aeruginosa is an opportunistic human pathogen that can cause fatal infections. There exists an urgent need for new, effective antimicrobial agents to combat P. aeruginosa. The PqsE-RhlR protein-protein interaction is essential for P. aeruginosa to be able to make toxins, form biofilms, and infect host organisms. In this study, we use both non-native models in Escherichia coli and measurements of gene expression/toxin production in P. aeruginosa to show that the PqsE-RhlR interaction enables fine-tuned gene expression and a heightened ability of P. aeruginosa to adapt to external conditions. These findings will be highly valuable as continued efforts are made to design inhibitors of the PqsE-RhlR interaction and test them as potential antimicrobial agents against P. aeruginosa infections.

Chromatographic fingerprinting and antibiofilm effect of Ziziphus jujuba fraction on Pseudomonas aeruginosa

Pseudomonas aeruginosa represents a critical global health threat, particularly affecting immunocompromised individuals, as well as patients with wounds and burn injuries. The increasing prevalence of multidrug-resistant (MDR) P. aeruginosa strains has significantly reduced the efficacy of conventional antimicrobial therapies, underscoring the urgent need for new, effective therapeutic alternatives. Plant-derived secondary metabolites have emerged as promising candidates due to their diverse bioactivities and favorable safety profiles. This study investigated the antimicrobial and anti-virulence potential of purified aqueous fractions of Ziziphus jujuba (ZJ) seeds against MDR P. aeruginosa clinical isolates. LC-ESI-MS/MS-MRM fingerprinting identified 33 compounds, including five predominant phenolics: 3,4-dihydroxybenzoic acid, gallic acid, syringic acid, chlorogenic acid, and ferulic acid. One hundred clinical isolates were evaluated for antibiotic sensitivity and biofilm-forming ability. The ZJ fraction exhibited potent antibacterial activity, with a minimum inhibitory concentration (MIC) of 1.56 mg/ml and significantly inhibited biofilm formation by approximately 70%. Additionally, quantitative real-time PCR showed a marked downregulation the key quorum-sensing genes lasI (45%), rhlI (42%), and rhlR (34%) (p ≤ 0.05). These findings reveal, for the first time, that the aqueous fraction of Z. jujuba seeds not only inhibits bacterial proliferation, but also attenuates biofilm formation and virulence gene expression in MDR-P. aeruginosa. These results highlight the potential of ZJ fraction as a promising plant-based antimicrobial agent. Further in vivo investigations and mechanistic studies are warranted to validate its clinical applicability and therapeutic efficacy.

Assessment of furobenzopyran from Ammi visnaga in disrupting Pseudomonas aeruginosa biofilms and suppressing associated virulence factors

Ammi visnaga, an herbal plant containing the furobenzopyran derivative (khellin) with therapeutic effects, remains unexplored for its potential to disrupt the biofilm formation and suppress the virulence factors mediated through the Las quorum-sensing system in Pseudomonas aeruginosa. The current study investigates the efficacy of khellin in inhibiting biofilm formation, suppressing biofilm-associated virulence factors at sub-minimum inhibitory concentration (sub-MIC) levels of ≤9 μg/mL, and its interactions with LasR are evaluated through molecular docking and dynamics simulation. In-silico analysis using the 'aBiofilm' web tool predicted a strong antibiofilm potential for khellin, with no prior reports of such activity. This prediction was supported by confocal laser scanning microscopy, which demonstrated significant biofilm inhibition at 9 μg/mL, along with noticeable microbial distortion. Further assessments showed that sub-MIC levels of khellin effectively reduced biofilm-associated virulence factors, including swimming and swarming motility, rhamnolipid content, cell surface hydrophobicity, alginate, and exopolysaccharide production, in a dose-dependent manner, though the extent of inhibition varied among these factors. Molecular docking analysis yielded a score of -7.285 kcal/mol, indicating a favorable binding, and 'Molecular Mechanics Generalized Born Surface Area' binding free energy of -28.32 kcal/mol confirms a stable and energetically favorable interaction with the target protein. The stability of the khellin-protein complex was validated through a 100 ns molecular dynamics simulation using the 'Optimized Potentials for Liquid Simulations-All Atom' force field model. Results of root mean square deviation, root mean square fluctuation, radius of gyration, intramolecular hydrogen bonds, molecular surface area, solvent accessible surface area, and polar surface area confirmed that khellin maintained stable interactions throughout the simulation. These findings suggest khellin as a potential candidate for treating Pseudomonas-associated biofilm infections and provide strong evidence that khellin may function as a quorum-sensing inhibitor of the P.aeruginosa's LasR protein.

Therapeutic potential of celastrol in bacterial infections: Current research advancements and future perspectives

Drug-resistant bacterial infections and their associated inflammatory diseases constitute a deadly threat to global health. Celastrol is one of the main effective components extracted from the traditional Chinese medicine Tripterygium wilfordii Hook.F (TWHF). An increasing number of researchers have been focusing on the pharmacological properties of celastrol in the context of bacterial infection and associated inflammatory complications. This paper presents a comprehensive review of the pharmacological activity and mechanisms of celastrol in the treatment of bacterial infectious diseases. Celastrol has been demonstrated to possess a range of antibacterial, anti-biofilm, anti-virulence and synergistic antibacterial properties with antibiotics, mediated through diverse molecular mechanisms. Several potential targets of celastrol, such as Δ1-Pyrroline-5-Carboxylate Dehydrogenase (P5CDH), Filamenting temperature-sensitive mutant Z (FtsZ), and GdpP, have been identified. By acting on these proteins, celastrol can disrupt bacterial structure (e.g., cell walls and membranes), inhibit macromolecular synthesis (protein, RNA, and DNA), and interfere with metabolic pathways. Furthermore, celastrol exerts dual immunomodulatory effects against bacterial infections through the coordinated regulation of host-pathogen interactions: by suppressing critical bacterial virulence factors staphyloxanthin (STX) and chemotaxis inhibitory protein of S. aureus (CHIPS) to counteract immune evasion mechanisms, while simultaneously activating nuclear respiratory factor 1 (Nrf1), nuclear factor kappa-B (NF-κB), mitogen-activated protein kinase (MAPK), and various signaling pathways of host immune cells to attenuate infection-induced hyperinflammatory responses and immunocyte-derived tissue damage. Finally, a review and discussion of the therapeutic potential of celastrol is presented, with particular attention to its future development as an effective therapeutic agent for treating diseases associated with bacterial infections.

Bio-informed synthesis of marine-sourced indole derivatives: suppressing gram-negative bacteria biofilm and virulence

Biofilms cling to surfaces to form complex architectures allowing their bacterial creators to acquire multidrug resistance and claiming countless lives worldwide. Therefore, finding novel compounds that affect virulence and biofilm-forming capacity of resistant pathogenic bacteria is imperative. Recently, we identified indole-based compounds that possess anti-biofilm properties in coral-associated bacteria. We succeeded in efficiently synthesizing two of these compounds, 1,1'-bisindole (NN) and 2,3-dihydro-2,2'-bisindole (DIV). They were found to attenuate biofilms of gram-negative bacterial pathogens, including Pseudomonas aeruginosa and Acinetobacter baumannii. Combining these compounds with the antibiotic tobramycin resulted in significant biofilm inhibition, particularly in the eradication of mature P. aeruginosa biofilms. Both of the bisindole derivatives, suppressed a number of bacterial virulence factors, reduced bacterial adhesion, and improved survival rates in infected Caenorhabditis elegans and human lung epithelial cell models. Transcriptome analyses of the bacteria treated with these compounds revealed that NN repressed or upregulated 307 genes when compared to untreated P. aeruginosa. These bacteria-derived molecules act in resistance-quenching and are potentially important candidates for inclusion in treatment protocols. The use of compounds that prevent the biofilm from accumulating the high cell densities critical to its structural and functional maintenance represents significant progress in the management of bacterial persistence. Therefore, a possible clinical implementation of these innovative compounds holds a promising future.

Inhibitors of the PqsR Quorum-Sensing Receptor Reveal Differential Roles for PqsE and RhlI in Control of Phenazine Production

Pseudomonas aeruginosa is a leading cause of hospital-acquired infections and it is resistant to many current antibiotic therapies, making development of new antimicrobial treatments imperative. The cell-to-cell communication process called quorum sensing controls P. aeruginosa pathogenicity. Quorum sensing relies on the production, release, and group-wide detection of extracellular signal molecules called autoinducers. Quorum sensing enables bacteria to synchronize group behaviors. P. aeruginosa possesses multiple quorum-sensing systems that control overlapping regulons, including some required for virulence and biofilm formation. Interventions that target P. aeruginosa quorum-sensing receptors are considered a fruitful avenue to pursue for new therapeutic advances. Here, we developed a P. aeruginosa strain that carries a bioluminescent reporter fused to a target promoter that is controlled by two P. aeruginosa quorum-sensing receptors. The receptors are PqsR, which binds and responds to the autoinducer called PQS (2-heptyl-3-hydroxy-4(1H)-quinolone) and RhlR, which binds and responds to the autoinducer called C4-HSL (C4-homoserine lactone). We used this reporter strain to screen >100,000 compounds with the aim of identifying inhibitors of either or both the PqsR and RhlR quorum-sensing receptors. We report results for 30 PqsR inhibitors from this screen. All of the identified compounds inhibit PqsR with IC50 values in the nanomolar to low micromolar range and they are readily docked into the autoinducer binding site of the PqsR crystal structure, suggesting they function competitively. The majority of hits identified are not structurally related to previously reported PqsR inhibitors. Recently, RhlR was shown to rely on the accessory protein PqsE for full function. Specifically, RhlR controls different subsets of genes depending on whether or not it is bound to PqsE, however, the consequences of differential regulation on the quorum-sensing output response have not been defined. PqsR regulates pqsE. That feature of the system enabled us to exploit our new set of PqsR inhibitors to show that RhlR requires PqsE to activate the biosynthetic genes for pyocyanin, a key P. aeruginosa virulence factor, while C4-HSL is dispensable. These results highlight the promise of inhibition of PqsR as a possible P. aeruginosa therapeutic to suppress production of factors under RhlR-PqsE control.

Analysing the integrated quorum sensing system its potential role in Pseudomonas aeruginosa pathogenesis

Since its discovery, Quorum Sensing (QS), a form of bacterial communication, has been the focus of numerous studies aimed at unravelling the mechanisms behind this intricate process. Bacterial QS relies on releasing low molecular weight signals known as autoinducers (AIs). When these AIs reach a threshold concentration, they activate coordinated genetic expression of pathogenic and bacterial survival mechanisms. Pseudomonas aeruginosa's QS has been extensively studied due to its incidence and clinical significance in a wide range of human infections. Several decades ago, three QS systems, named Las, Rhl, and Pqs, were identified and have since then become the focus of numerous research studies and the target of innovative diagnostic and therapeutic strategies. However, a fourth QS-related system was more recently proposed that it has been the subject of debate. Named "integrated quorum sensing" (Iqs), interconnects the previously mentioned systems with the phosphate stress response. The associated AI has been identified as 2-(2-hydroxyphenyl)-thiazole-4-carbaldehyde, also known as IQS. This discovery has sparked a controversial discussion about its biosynthetic origin and whether it truly functions as an intercellular communication system. In this review, we critically discuss the different hypotheses, and its biological relevance while presenting key findings of the Iqs system.

Pseudomonas aeruginosa biofilm: treatment strategies to combat infection

Pseudomonas aeruginosa is an opportunistic human pathogenic bacterium that is a common cause of both acute and chronic infections. Multidrug-resistant P. aeruginosa poses a significant challenge to antibiotics and therapeutic approaches due to its pathogenicity, virulence, and biofilm-forming ability mediated by quorum sensing. Understanding the pathogenic mechanisms is essential for developing potential drug targets. In this regard, strategies aimed at combating the targeted inhibition of virulence, quorum sensing pathways, secretion systems, biofilm-associated two-component systems, and signalling system regulators (such as c-di-GMP) associated with biofilm formation are critical. Several new antimicrobial agents have been developed using these strategies, including antimicrobial peptides, bacteriophages, nanoantibiotics, photodynamics, and natural products, which are considered promising therapeutic tools. In this review, we address the concept of biofilms, their regulation, and recent treatment strategies to target P. aeruginosa, a clinically significant pathogen known for biofilm formation.

Diversity-Oriented Synthesis and Antibiofilm Evaluation of Furan-2-Carboxamides

A diversity-oriented collection of furan-2-carboxamides with antibiofilm activity against P. aeruginosa is reported. The design involved the bioisosteric replacement of the labile furanone ring by a furan-2-carboxamide moiety to explore its influence on biological activity. After evaluation, carbohydrazides and triazoles showed significant antibiofilm activity, and 4b resulted in the most remarkable compound (58 % inhibition). Furthermore, treating P. aeruginosa with three active carboxamides reduced some virulence factors (pyocyanin and proteases), confirming the anti-quorum sensing properties of the derivatives and suggesting LasR as a plausible target. Molecular docking proposed that carbohydrazides share a similar binding mode to related furanones inside LasR with an excellent docking score, while higher derivatives diminished in silico affinity.

Arsenic-induced modulation of virulence and drug resistance in Pseudomonas aeruginosa

Arsenic contamination of water sources, whether from natural or industrial origins, represents a significant risk to human health. However, its impact on waterborne pathogens remains understudied. This research explores the effects of arsenic exposure on the opportunistic pathogen Pseudomonas aeruginosa, a bacterium found in diverse environments. The arsenic exposure at concentrations of 0.12-20 mg/L As(III) resulted in rapid growth arrest of P. aeruginosa. Moreover, arsenic exposure significantly reduced the production of key virulence factors such as elastase (by 1.48- to 9.24-fold), pyocyanin, and flagella while increasing siderophore and extracellular polysaccharide production (by 1.44-1.75 and 1.36-2.59 times, respectively). Proteomic analysis revealed that both low (0.12 mg/L) and high (1.2 mg/L) As(III) levels activated an antioxidant defense response, with upregulation of Fnr-2, TrxB2, and Ohr. Furthermore, arsenic-induced the overexpression of multidrug resistance efflux proteins MexAB-OprM, MexCD-OprJ, and MexEF-OprN. At the same time, proteins associated with quorum sensing (QS), type III secretion system (T3SS), pyocyanin biosynthesis, and flagellar assembly were downregulated. In vitro assays confirmed that arsenic reduced bacterial virulence and significantly enhanced survival and proliferation under antibiotic treatment. These results indicate that arsenic exposure modulates the virulence and antibiotic resistance of P. aeruginosa, raising concerns about the public health risks posed by the convergence of arsenic-contaminated water and multidrug-resistant bacteria.

Sweeteners affect biofilm formation and virulence gene expression in Pseudomonas aeruginosa PAO1

Pseudomonas aeruginosa is an opportunistic pathogen able to form biofilms, contributing to its virulence. With the increasing use of sweeteners in various foods, understanding their influence on bacterial behavior is critical. This study investigated the virulence of P. aeruginosa PAO1 exposed to sweeteners (erythritol, stevia, fructose, coconut sugar, cane sugar, demerara). Sweeteners didn't affect growth rates. Erythritol stimulated biofilm (100 µg/mL, 159.98% formation), while 10 µg/mL of coconut sugar, cane sugar, and demerara promoted lower levels (∼70% formation). Erythritol stimulated exopolysaccharides production but reduced biofilm eDNA. Stevia, fructose, and coconut sugar increased the expression of lasI, lasR, rhlI, rhlR, pqsA, mvfR, and pvdF. HPLC analysis confirmed sucrose as the major sugar in demerara, coconut and cane sugar. Erythritol stimulated biofilm and some virulence genes expression, while other sweeteners' effects varied. Cane sugar was a biofilm inhibitor with a limited gene expression effect. The sweeteners' impact on microorganisms is diverse and should be further investigated.

Inhibitory effects of reumycin produced by Streptomyces sp. TPMA0082 on virulence factors of Pseudomonas aeruginosa

Pseudomonas aeruginosa is an opportunistic human pathogen that causes a wide range of infections. The increasing multidrug-resistance of P. aeruginosa poses a critical challenge for medical care. P. aeruginosa employs virulence factors and biofilms to establish infections in humans and protect itself from environmental stress or antibiotics. These factors are regulated by a quorum sensing mechanism involving multiple regulatory systems that act interdependently through signaling molecules. Therefore, interference with quorum sensing systems can suppress the pathogenicity of P. aeruginosa. In this study, quorum sensing inhibitors were explored from secondary metabolites derived from 111 strains of actinomycetes by targeting the las system, which is thought to be upstream of the quorum sensing cascade in P. aeruginosa. As a result, reumycin was isolated from the culture broth of Streptomyces sp. TPMA0082. Reumycin, a molecule containing a pyrimidotriazine ring, inhibited the binding of the autoinducer to the LasR receptor in the las system, thereby suppressing the production of P. aeruginosa virulence factors, including pyocyanin, rhamnolipids, elastase, motility, and biofilms, without affecting bacterial growth. Toxoflavin, a reumycin derivative with a methyl group at the N1 position, exhibited strong antibacterial activity. Fervenulin, a reumycin derivative with a methyl group at the N8 position, had a negative impact on the logarithmic growth phase of the bacteria and exhibited lower inhibitory activity against virulence factor production compared to reumycin. These findings suggest that the position and number of methyl groups attached to the pyrimidotriazine structure significantly influence its biological activity, exerting distinct effects on quorum sensing inhibition and antibacterial activity.

Biofilm inhibition of multidrug-resistant Pseudomonas aeruginosa using green-synthesized silver nanoparticles and colistin

We aimed to investigate the synergistic effects of colistin and green-synthesized silver nanoparticles on the biofilm formation and expression of Quorum Sensing regulated and related genes in clinical isolates of P. aeruginosa. Ten clinical P. aeruginosa isolates collected from patients with burn wound infections were investigated. The antibiotic sensitivity pattern of the isolates was determined using disk diffusion and microbroth dilution tests. The silver nanoparticles (AgNPs) were synthesized using propolis and characterized. The microtiter plate method and scanning electron microscopy (SEM) were used to evaluate the synergistic effects of colistin and silver nanoparticles combination (AgNPs@CL) on the inhibition of biofilm formation. The effect of AgNPs@CL on the expression of genes controlled by QS was evaluated using RT-PCR. All isolates were strong biofilm formers. Confronting AgNPs@CL, all isolates were either synergistic or additive and effectively decrease the minimum inhibitory concentration (MIC) and minimum biofilm inhibitory concentration (MBIC) values of Carbapenem-Resistant P. aeruginosa (CRPA) isolates. The SEM analysis corroborated the enhanced biofilm inhibition observed with the combined treatment compared to individual AgNPs or colistin treatments. When exposed to AgNPs@CL, the expression levels of lasI, lasR, rhlI, rhlR, pelA, and pslA genes significantly decreased in P. aeruginosa ATCC 27,853 and clinical isolate No. #354, which displayed synergistic activity. In contrast, with additive activity, clinical isolate No. #30 showed no significant decrease. Targeting critical components of QS could effectively inhibit biofilm production. The results of our study suggest AgNPs@CL as an auxiliary to antibiotic therapy.

Regulatory roles of an sRNA derived from the 5´ UTR and sequence internal to lapA in Pseudomonas aeruginosa PAO1

Several key virulence factors of Pseudomonas aeruginosa are regulated by quorum-sensing systems, small noncoding RNAs (sRNAs), and environmental stress, leading to a high mortality rate. Our previous studies indicated that the alkaline phosphatase LapA regulated P. aeruginosa PAO1 biofilm formation in a chronic wound model established with ex vivo porcine skin explants. Notably, one particular sRNA located upstream of the lapA gene was highly expressed in the model. Therefore, the sRNA was further characterized via northern blotting and rapid amplification of cDNA ends. The results revealed that the sRNA we named LapS is 197 nucleotides in length and is derived from the 5´ UTR and sequence internal to the lapA gene. Next, LapS mutation, overexpression, and complementation strains were constructed from the PAO1 strain, and phenotypic experiments associated with lapA were performed and compared with those of the ΔlapA and wild-type strains. The results indicated that LapS is involved in regulating swarming motility, rhamnolipid and alkaline phosphatase production, las/rhl quorum-sensing systems, and biofilm formation by controlling the level of lapA mRNA under phosphate-depleted conditions. Therefore, this LapS-lapA signaling cascade is beneficial for balancing the virulence regulation of P. aeruginosa. Additionally, an in vitro study indicated that LapS directly and post-transcriptionally regulated at least one unlinked gene, putA, which encodes bifunctional proline dehydrogenase, a virulence factor of P. aeruginosa. Collectively, our findings reveal a previously unstudied regulatory sRNA and advance the understanding of the roles of sRNAs in the pathogenicity of P. aeruginosa.

IMPORTANCE

Pseudomonas aeruginosa is a common nosocomial pathogen that contains hundreds of virulence factors regulated by quorum-sensing systems and environmental stress. Small noncoding RNAs (sRNAs) involved in virulence regulation have been identified in P. aeruginosa. Recently, several potential sRNAs were identified in P. aeruginosa using transcriptome sequencing. However, some of these novel sRNAs have been functionally characterized. In this study, a previously uncharacterized sRNA, LapS, in P. aeruginosa PAO1 was identified as a novel sRNA. LapS is involved in regulating swarming motility, rhamnolipid production, and alkaline phosphatase production during phosphate-depleted stress by controlling the level of lapA mRNA. Furthermore, LapS deletion also reduced the mortality rate of Caenorhabditis elegans in a fast-kill assay. Additionally, LapS directly suppressed PutA, a virulence factor of P. aeruginosa. This study highlights the role of LapS in modulating P. aeruginosa virulence during phosphate-depleted stress.

New Insights into the Mediation of Biofilm Formation by Three Core Extracellular Polysaccharide Biosynthesis Pathways in Pseudomonas aeruginosa

Pseudomonas aeruginosa biofilms, driven by extracellular polysaccharides (EPSs), exacerbate pathogenicity and drug resistance, posing critical threats to public health. While EPS biosynthesis pathways are central to biofilm formation, their distinct contributions and regulatory dynamics remain incompletely understood. Here, we systematically dissect the roles of three core EPS pathways-Psl, Pel, and alginate-in biofilm architecture and function using multi-omics approaches. Key findings reveal Psl as the dominant regulator of biofilm elasticity and thickness, with its deletion disrupting chemotaxis, quorum sensing, and 3',5'-Cyclic GMP (c-di-GMP)/amino acid metabolism. Pel redundantly enhances biofilm biomass, but elevates flagellar synthesis efficiency when Psl is absent. Alginate exhibited negligible transcriptional or metabolic influence on biofilms. These insights clarify hierarchical EPS contributions and highlight Psl as a priority target for therapeutic strategies to dismantle biofilm-mediated resistance.

Comparative Genomics of Rhamnolipid Synthesis and Monoaromatic Hydrocarbon Tolerance Genes in Environmental Pseudomonas aeruginosa strains

Background

Bioremediation faces several compounds to recover oil spilled ecosystem. The BTEX (benzene, toluene, ethylbenzene, and xylene) are toxic hydrocarbons requiring efficient microbial degradation for bioremediation. Pseudomonas aeruginosa can degrade hydrocarbons through emulsification ( rhl genes) and tolerance ( mla genes). However, genomic organization of these systems in environmental P. aeruginosa strains remains unclear. This study aimed to investigate the rhl and mla systems in six strains isolated from hydrocarbon-contaminated sites in Peru.

Methods

Six Pseudomonas aeruginosa strains were evaluated in this study. Each strain were able to degrade hydrocarbon and tolerate heavy metals. DNA extraction, sequencing, and quality-controlled assembly, functional genome annotation was performed using BAKTA. Comparative analysis included high-quality Pseudomonas genomes from RefSeq, with ANI metrics. A phylogenetic tree was built from core gene alignment, revealed evolutionary connections and was visualized with iTOL.

Results

The assembled genomes ranged from 5.6 to 6.0 Mbp with ~66% GC content. All the strains were confirmed as P. aeruginosa by ANI; placing them within Clade 1 alongside environmental and clinical strains. Pangenome analysis identified 3,544 core genes and a diverse accessory genome. All strains had rhlABRI genes in a conserved 3'-5' orientation. Most of them contained duplicated rhlB gene, except C1BHIC5 strain. However, rhlG varied in position and orientation, it was often near rhlC, with C1BHIC5 also displaying an exception in rhlG orientation.100% of strains presented mla system, associated with toluene tolerance, with two copies of mlaA, mlaFEDC, and mlaEFD genes arranged with high synteny but variable orientations. In comparison to Pseudomonas putida, where mla genes are positioned between murA and ppcD with an additional toluene tolerance gene ( ttg2D).

Conclusions

In conclusion, the presence of the rhlABC genes and the BTEX tolerance genes in all of the analyzed strains allowed us to understand the great ability of P. aeruginosa to survive in polluted environments.

Quorum sensing inhibitors (QSIs): a patent review (2019-2023)

INTRODUCTION

The collective behavior of bacteria is regulated by Quorum Sensing (QS), in which bacteria release chemical signals and express virulence genes in a cell density-dependent manner. Quorum Sensing inhibitors (QSIs) are a large class of natural and synthetic compounds that have the potential to competitively inhibit the Quorum Sensing (QS) systems of several pathogens blocking their virulence mechanisms. They are considered promising compounds to deal with antimicrobial resistance, providing an opportunity to develop new drugs against these targets.

AREAS COVERED

The present review represents a comprehensive analysis of patents and patent applications available on Espacenet and Google Patent, from 2019 to 2023 referring to the therapeutic use of Quorum Sensing inhibitors.

EXPERT OPINION

Unlike classical antibiotics, which target the basic cellular metabolic processes, QSIs provide a promising alternative to attenuating virulence and pathogenicity without putting selective pressure on bacteria. The general belief is that QSIs pose no or little selective pressure on bacteria since these do not affect their growth. To date, QSIs are seen as the most promising alternative to traditional antibiotics. The next big step in this area of research is its succession to the clinical stage.

Transcriptional response study of auto inducer-2 regulatory system in Escherichia coli harboring blaNDM

BACKGROUND

The emergence of carbapenem resistance in gram-negative bacteria such as Escherichia coli is one of the world's most urgent public health problems. E. coli, which encounter a diverse range of niches in host can rapidly adapt to the changes in surrounding environment by coordinating their behavior via production, release and detection of signal molecules called autoinducers through a cell density dependent communication system known as quorum sensing. Here, in this study we investigated whether imipenem, and acyl homoserine lactone quorum sensing signal molecules influence the transcriptional response within lsr and lsrRK operon which are associated with auto inducer-2 mediated quorum sensing in E. coli. Two E. coli isolates carrying blaNDM were treated with 10% SDS for 20 consecutive days, resulting in the successful elimination of the blaNDM encoding plasmid from one isolate. Plasmid was extracted from the isolate and was transformed into recipient E. coli DH5α by electroporation. The native type, plasmid-cured type, transformant, and E. coli DH5α were allowed to grow under eight different inducing conditions and the transcriptional responses of lsr and lsrRK operons were studied by quantitative real-time PCR method.

RESULTS

The findings of this study highlight the distinct effects of imipenem and AHL on the transcriptional responses of the lsrB,lsrR, and lsrK genes in native type, plasmid cured type, transformant, and E. coli DH5α.

CONCLUSION

This study provides a basis for further research to elucidate different inducing conditions including antibiotics and autoinducers that could switch on the quorum sensing circuit in carbapenem non-susceptible E. coli, one of the world's most urgent public health threats.

Observational Study of Microbial Colonization and Infection in Neurological Intensive Care Patients Based on Electronic Health Records

Background/Objectives: Patients with central nervous system injuries who are hospitalized in intensive care units (ICUs) are at high risk for nosocomial infections. Limited data are available on the incidence and patterns of microbial colonization and infection in this patient population. Methods: To fill this gap, we performed an electronic health record-based study of 1614 chronic patients with brain injury admitted to the ICU from 2017 to 2023. Results: Among the infectious complications, pneumonia was the most common (n = 879; 54.46%). Sepsis was diagnosed in 54 patients, of whom 46 (85%) were diagnosed with pneumonia. The only pathogen that showed an association with the development of pneumonia and sepsis in colonized patients was Pseudomonas aeruginosa (pneumonia: p = 7.2 × 10-9; sepsis: p = 1.7 × 10-5). Bacterial isolates from patients with and without pneumonia did not differ in pathogen titer or dynamics, but patients with monomicrobial culture were more likely to develop pneumonia than patients with polymicrobial culture (1 vs. 2 pathogens, p = 0.014; 1 + 2 pathogens vs. 3 + 4 pathogens, p = 2.8 × 10-6), although the pathogen titer was lower in monoculture than in polyculture. Bacterial isolates from all patients and all culture sites showed high levels of multidrug resistance (Gram-negative bacteria: 88-100%; Gram-positive bacteria: 48-97%), with no differences in multidrug-resistant organism (MDRO) colonization and infection rates. Conclusions: Our results highlight the high burden of MDROs in neurological ICUs and provide novel ecosystem-based insights into mono- and polymicrobial colonization and infection development. These findings may be useful for developing strategies to protect against infections.

Synthesis, Cytotoxic Activity, Antiquorum Sensing Effect, Docking and Md Simulation of Novel 1,3-Disubstituted 2-Mercapto-1H-Benzo[D]Imidazolium Chlorides

A series of benzimidazolium chlorides (2a-c) and their corresponding 2-mercapto derivatives (3a-c) were proficiently synthesized and analyzed by NMR and LC-MS spectra. The in vitro cytotoxic assay demonstrated that some synthesized compounds were active on the cancer cell lines. The binding potential of the most active three compounds to topoisomerase II alpha (topo2α) was explored to unveil the possible mode of action for the cytotoxic activity. The binding potential was examined through molecular docking. The stability of compound-enzyme complexes from docking was investigated through molecular dynamics (MD) simulation. The docking study revealed that the three compounds (3a-c) showed the ability to bind to the enzyme. However, the binding strength of compounds was weaker than that of the standard drug, doxorubicin. The MD simulation analysis demonstrated that compounds 3a and 3b gave relatively stable complexes with the enzyme and thus they would remain inside the binding pocket during the simulation period. Furthermore, the pharmacokinetic properties of the relatively active compounds were computed in silico. The computation disclosed that all of compounds exhibited drug-like properties. It is worth mentioning that all of them were found to be nontoxic. In furtherance, the inhibitory effect of compounds (3a-c) on the quorum sensing system was inspected using the biomonitor strains Chromobacterium violaceum 026, Chromobacterium. violaceum VIR07 and Pseudomonas aeruginosa PAO1. In this regard, we focused on the appraisal of the virulence factors, including pyocyanin, elastase, and biofilm formation that are created by P. aeruginosa PAO1 as the source of infectious diseases. As a result, it was determined that all examined compounds displayed statistically significant inhibition effects, and the highest activity was observed on elastase production with an inhibition rate of 84-86%.

Exploring Marine natural products as potential Quorum sensing inhibitors by targeting the PqsR in Pseudomonas aeruginosa: Virtual screening assisted structural dynamics study

Antibiotic resistance is a critical global health issue, and Pseudomonas aeruginosa is a particularly challenging pathogen. This gram-negative bacterium is notorious for its high virulence and resistance to antimicrobial agents, making it a leading cause of nosocomial infections, significantly impacting public health. The adaptability and multidrug resistance of P. aeruginosa exacerbate treatment difficulties, resulting in increased morbidity and mortality rates worldwide. Consequently, targeting bacterial quorum sensing (QS) systems is a promising strategy for the development of novel antimicrobial compounds against this resilient pathogen. In this study, a structure-based virtual screening (SBVS) approach was employed to identify marine natural products (MNPs) as potential lead molecules targeting the biofilm-forming PqsR protein of P. aeruginosa. A total of ~37,000 MNPs were initially evaluated and ranked based on docking scores using high-throughput virtual screening (HTVS), Standard Precision (SP), and Extra Precision (XP) methods. Ten lead molecules (five from the CMNPD database and five from the MNPD database) were shortlisted based on their docking scores (<-10.0 kcal/mol) and binding free energy values (MM-GBSA ΔG <-40 kcal/mol). Their drug-likeness profiles were assessed using stringent criteria in the QikProp module of Schrödinger, and their chemical reactivity was evaluated through density functional theory (DFT) calculations. The structural and energetic interactions between the identified MNPs and the PqsR-binding pocket were validated through molecular dynamics simulations (MDS) and binding free energy (BFE) calculations. Structural dynamic analyses revealed that the MNP-bound PqsR complexes demonstrated stable interactions within the binding pocket, with hydrophobic residues such as L208, I236, and I263 playing a crucial role in maintaining stability. Among the identified MNPs, CMNPD14329, CMNPD23880, MNPD13399, and MNPD13725 emerged as promising lead molecules for further research. These candidates can serve as foundations for developing structural analogs with enhanced binding affinities for PqsR and other biofilm-forming proteins. Further experimental validation is essential to confirm the therapeutic potential of these identified MNPs.

The Role of Yinqiao Powder in Modulating Pseudomonas aeruginosa Biofilm and Virulence Factors

Purpose

It is now understood that the primary challenges in treating Pseudomonas aeruginosa (P. aeruginosa) infections are the secretion of multiple virulence factors, the formation of biofilm, and the emergence of multi-drug resistance. Small regulatory RNAs (sRNAs) and quorum sensing (QS) play an important role in regulating bacterial biofilms and multiple virulence factors, presenting potential targets for novel anti-P. aeruginosa therapies. Yinqiao Powder has demonstrated inhibitory activity against various bacteria and viruses. The objective of this study was to elucidate the precise mechanism of Yinqiao Powder's impact on P. aeruginosa virulence and to ascertain its clinical utility.

Methods

First, the effects of Yinqiao Powder on various virulence factors of P. aeruginosa were assessed through virulence phenotype experiments, including biofilm formation assay, pyocyanin production assay, rhamnolipid assay, and motility assay. Then, a cytotoxicity assay was used to evaluate the effect of P. aeruginosa treated by Yinqiao Powder on cells. Finally, an RT-qPCR assay was used to detect the effects of Yinqiao Powder on QS system and virulence-related gene expression.

Results

This study revealed that sub-minimum inhibitory concentration (sub-MIC) levels of Yinqiao Powder significantly inhibit biofilm formation, swarming motility, pyocyanin and rhamnolipid production in a dose-dependent manner. The cytotoxicity assay also confirmed that Yinqiao Powder weakened the cytotoxicity of P. aeruginosa. Furthermore, Yinqiao Powder was found to modulate the P. aeruginosa sRNA-QS-virulence network. Specifically, it repressed the lasI, the rhlI, and sRNA P27 while upregulating sRNA PhrD. Additionally, the phzA and pqsA genes, associated with pyocyanin and rhamnolipid/biofilm regulation, respectively, were repressed by Yinqiao Powder.

Conclusion

Yinqiao Powder effectively inhibits QS system-related regulatory genes, sRNAs, biofilm formation, swarming motility, pyocyanin and rhamnolipid production at specific concentrations. These results support the potential of Yinqiao Powder as a quorum-sensing inhibitor.

Spatial transcriptomics identifies novel Pseudomonas aeruginosa virulence factors

To examine host-pathogen interactions, we leveraged a dual spatial transcriptomics approach that simultaneously captures the expression of Pseudomonas aeruginosa genes alongside the entire host transcriptome using a murine model of ocular infection. This method revealed differential pathogen- and host-specific gene expression patterns in infected corneas, which generated a unified transcriptional map of infection. By integrating these data, we developed a predictive ridge regression model trained on images from infected tissues. The model achieved an R2 score of 0.923 in predicting bacterial burden distributions and identifying novel biomarkers associated with disease severity. Among iron acquisition pathogen-specific gene transcripts that showed significant enrichment at the host-pathogen interface, we discovered the novel virulence mediator PA2590, which was required for bacterial virulence. This study therefore highlights the power of combining bacterial and host spatial transcriptomics to uncover complex host-pathogen interactions and identify potentially druggable targets.

Chronic suppurative otitis media: disrupted host-microbial interactions and immune dysregulation

Recent research has uncovered new mechanisms that disrupt the balance between the host and microbes in the middle ear, potentially leading to dysbiosis and chronic suppurative otitis media (CSOM). Dysbiotic microbial communities, including core pathogens such as persister cells, are recognized for displaying cooperative virulence. These microbial communities not only evade the host's immune defenses but also promote inflammation that leads to tissue damage. This leads to uncontrolled disorder and pathogen proliferation, potentially causing hearing loss and systemic complications. In this discussion, we examine emerging paradigms in the study of CSOM that could provide insights into other polymicrobial inflammatory diseases. Additionally, we underscore critical knowledge gaps essential for developing a comprehensive understanding of how microbes interact with both the innate and adaptive immune systems to trigger and maintain CSOM.

Potential roles of quorum quenching in microbial aggregates during wastewater treatment

Quorum sensing-regulated microbial behaviors often negatively impact wastewater treatment, leading to issues such as biofouling in membrane bioreactors, filamentous bulking, and resistance gene transfer. Quorum quenching, which counteracts quorum sensing, offers a promising strategy to mitigate these problems. This review aims to highlight overlooked perspectives for its application in microbial aggregates during wastewater treatment. First, the review examines the quorum sensing network present in microbial aggregates and the regulatory role of different quorum sensing systems in bacterial function and behavior during wastewater treatment. The discussions cover hierarchical, parallel, and competitive quorum sensing systems to clarify the interactions among these pathways. A precise quorum quenching strategy is proposed to enhance efficiency based on the type of quorum sensing regulation. Additionally, a bridge is established between the physiological characteristics of quorum quenching bacteria and process parameters to achieve process control over bacterial function and behavior during wastewater treatment.

Quorum Sensing: Not Just a Bridge Between Bacteria

The study of quorum sensing (QS) has gained critical importance, offering insights into bacterial and microorganism communication. QS, regulated by autoinducers, synchronizes collective bacterial behaviors across diverse chemical signals and target genes. This review highlights innovative approaches to regulating QS, emphasizing the potential of quorum quenching and QS inhibitors to mitigate bacterial pathogenicity. These strategies have shown promise in aquaculture and plant resistance, disrupting QS pathways to combat infections. QS also provides opportunities for developing biosensors for early disease detection and preventing biofilm formation, which is critical to overcoming antimicrobial resistance. The applications of QS extend to cancer therapy, with targeted drug delivery systems utilizing QS mechanisms. Advancements in QS regulation, such as the use of nanomaterials, hydrogels, and microplastics, provide novel methods to modulate QS systems. This review explores the latest developments in QS, recognizing its significance in controlling bacterial behavior and its broad impacts on human health and disease management. Integrating these insights into therapeutic strategies and diagnostics represents a pivotal opportunity for medical progress.

Targeting Pseudomonas aeruginosa PAO1 pathogenicity: The role of Glycyrrhiza glabra in inhibiting virulence factors and biofilms

Pseudomonas aeruginosa (P. aeruginosa) is a Gram-negative opportunistic pathogen posing serious risks to immunocompromised individuals due to its virulence factors and biofilm formation. This study evaluated the efficacy of methanol extract of Glycyrrhiza glabra (G. glabra) in mitigating P. aeruginosa PAO1 pathogenesis through in-vitro assays, including Minimum Inhibitory Concentration (MIC), biofilm assay, growth curve analysis, pyocyanin quantification, and molecular docking. The extract inhibited PAO1 growth at 5 mg/mL and demonstrated significant antibiofilm activity at sub-MIC levels, reducing biofilm formation by 50.22 %, 22.13 %, and 11.53 % at concentrations of 1.25 mg/mL, 0.625 mg/mL, and 0.312 mg/mL, respectively. Pyocyanin production was also significantly suppressed. Molecular docking revealed that 4-(4-Trifluoromethyl-benzoylamino)-benzoic acid and betulinic acid, identified in the extract, exhibited strong binding affinities (-6.4 kcal/mol and -6.9 kcal/mol) to the QS regulator 7XNJ. These findings underscore the potential of G. glabra as an antipathogenic agent against P. aeruginosa, warranting further investigation into its clinical applications.

Exploring daidzein dimethyl ether from Albizzia lebbeck as a novel quorum sensing inhibitor against Pseudomonas aeruginosa: Insights from in vitro and in vivo studies

Infections of multidrug-resistant pathogens including Pseudomonas aeruginosa, cause a high risk of mortality in immunocompromised patients and underscore the need for novel natural antibacterial drugs. In this study, common phytochemicals prevalent in fruits and vegetables have been demonstrated for their ability to inhibit quorum sensing (QS) in Pseudomonas aeruginosa PAO1 (PA). Ten compounds were screened virtually by molecular docking, among which, daidzein dimethyl ether originally from Albizzia lebbeck showed the most significant inhibitory effect on the formation of biofilm and the accumulation of virulence factors, including elastase, pyocyanin and rhamnolipid in PA. Further, both qRT-PCR analysis of key QS components including LasR in PA and luminescence detection of LasR as a reporter in a heterologous system revealed that daidzein dimethyl ether at 10 µM significantly inhibited the transcription of lasR and its downstream targeting genes. At the same time, MD simulations also showed that daidzein dimethyl ether could reduce the stability of LasR. Furthermore, the protective effect of daidzein dimethyl ether against PA infection was demonstrated using zebrafish infection model. It was found to reduce significantly the inflammation in the PA-infected zebrafish and increase their survival rate by inhibiting prominently the accumulation of reactive oxygen species (ROS) and reducing fish mortality in PA-infected zebrafish larvae. Additionally, open field tests suggested that PA-infected zebrafish were observed with impaired swimming behaviour, but daidzein dimethyl ether-treatment rescued zebrafish from such swimming abnormalities. Histopathological analysis revealed that zebrafish treated with both PA and daidzein dimethyl ether showed obvious integrity in intestine tissues, compared to those with only PA treatment. This study firstly demonstrated the preventive advantages of daidzein dimethyl ether in an animal model against PA infection. It is worthwhile to explore further its potential therapeutic intervention as an antimicrobial agent.

Quorum Sensing Coordinates Carbon and Nitrogen Metabolism to Optimize Public Goods Production in Pseudomonas fluorescens 2P24

The coordination of public and private goods production is essential for bacterial adaptation to environmental changes. Quorum sensing (QS) regulates this balance by mediating the trade-off between the communal benefits of "public goods," such as siderophores and antibiotics, and the individual metabolic needs fulfilled by "private goods," such as intracellular metabolites utilized for growth and survival. Pseudomonas fluorescens 2P24 harbors a LasI/LasR-type QS system, MupI/MupR, which regulates mupirocin production through signaling molecules. This study explores how QS coordinates carbon and nitrogen metabolism to optimize the production of key secondary metabolites, including 2,4-diacetylphloroglucinol (2,4-DAPG), mupirocin, and siderophores, which serve as public goods. Loss of QS disrupts this balance by enhancing the Krebs cycle, denitrification, pyruvate anaplerosis, and ammonium assimilation, lead to halted 2,4-DAPG and mupirocin synthesis and increased siderophore production. In the absence of QS, elevated siderophore production compensates for iron acquisition, ensuring rapid cellular growth. Under nutrient-limited or high cell density conditions, MupR regulates carbon and nitrogen fluxes to sustain public goods production. These findings highlight QS as a key environmental sensor that fine-tunes resource allocation, bacterial fitness, and adaptation to ecological and nutritional conditions, suggesting the potential for QS-targeted approaches to enhance antibiotic production and agricultural sustainability.

The Role of Quorum Sensing in Phage Lifecycle Decision: A Switch Between Lytic and Lysogenic Pathways

Phages, the most abundant and diverse lifeforms on Earth, require strict parasitism for survival. During infection, temperate phages integrate both intracellular and extracellular host information to decide between lysis and lysogeny for replication. While various environmental and physiological factors influence the lysis-lysogeny decision, recent insights into phage-bacterium interactions reveal phages' ability to communicate with and influence bacteria, leveraging the host's quorum sensing system or small molecular signals. This article provides a succinct overview of current research advancements in this field, enhancing our understanding of phage-host dynamics and providing insights into bacteria's multicellular behavior in antiviral defense.

c-di-GMP phosphodiesterase ProE interacts with quorum sensing protein PqsE to promote pyocyanin production in Pseudomonas aeruginosa

The universal bacterial second messenger bis-(3'-5')-cyclic dimeric guanosine monophosphate (c-di-GMP) plays critical roles in regulating a variety of bacterial functions such as biofilm formation and virulence. The metabolism of c-di-GMP is inversely controlled by diguanylate cyclases (DGCs) and phosphodiesterases (PDEs). Recently, increasing studies suggested that the protein-protein interactions between DGCs/PDEs and their partners appear to be a common way to achieve specific regulation. In this work, we showed that the PDE ProE can interact with PQS quorum sensing protein PqsE to regulate pyocyanin production in Pseudomonas aeruginosa. Our bacterial two-hybrid assay demonstrated that ProE directly interacts with PqsE, and isothermal titration calorimetry and surface plasmon resonance assay further confirmed that the binding affinity of ProE with PqsE is at micromolar level. Both ProE and PqsE negatively regulate intracellular c-di-GMP levels. Furthermore, our transcriptomic study showed that co-expression of ProE and PqsE significantly changes the gene expression profiles in P. aeruginosa, especially with increased expression of pyocyanin genes, and the qPCR and phenotypic results confirmed the transcriptome data. Taken together, our study suggested that the interaction between ProE and PqsE plays a critical role in regulation of pyocyanin production and highlights the importance of protein-protein interaction mediated c-di-GMP signaling in P. aeruginosa.IMPORTANCEc-di-GMP is pivotal in orchestrating various bacterial functions. In Pseudomonas aeruginosa, the nuanced balance of intracellular c-di-GMP is maintained by approximately 41 diguanylate cyclases (DGCs) and phosphodiesterases (PDEs). Emerging studies indicate that the c-di-GMP metabolic DGCs and PDEs may be involved in the signal transduction process by directly binding to the target protein, thus influencing downstream function. Despite their known importance, the precise functions of these proteins, especially their interacting partners, remain unclear. In this study, we identified that PQS quorum sensing system protein PqsE is a binding partner of c-di-GMP phosphodiesterase ProE; further analysis suggested that the ProE specifically interacts with PqsE to promote pyocyanin production. Our study extended the regulatory mechanism of the c-di-GMP signal transduction and quorum sensing in governing bacterial physiology.

Reprofiling lamivudine as an antibiofilm and anti-pathogenic agent against Pseudomonas aeruginosa

Resistance to antibiotics is a critical growing public health problem that needs urgent action to combat. To avoid the stress on bacterial growth that evokes the development of resistance, anti-virulence agents can be an attractive strategy as they do not target bacterial growth. There are FDA approved drugs have been screened for their anti-virulence activities. Lamivudine (LAM) is a synthetic nucleoside analogue used as an antiretroviral in treatment of HIV and can be used in treatment of HBV. The present study aimed to assess the anti-virulence activities of LAM against a clinically important pathogen Pseudomonas aeruginosa. The LAM's antibiofilm and anti-virulence activities were evaluated. The impact of LAM on the quorum sensing (QS) systems which control the production of these virulence factors was assessed virtually and by quantification of the expression of QS-encoding genes. Furthermore, in vivo mice protection assay was conducted to attest the LAM's anti-pathogenic activity. The current findings elaborated the promising anti-pathogenic and anti-QS activities of LAM. LAM interfered with biofilm formation in P. aeruginosa PAO1 strain. Moreover, swarming motility and production of pyocyanin and protease were significantly diminished. At the molecular level, LAM downregulated the QS-encoding genes LasI, LasR, RhlR, PqsA and PqsR. Additionally, the detailed in silico docking and molecular simulation studies showed the considered high LAM's ability to bind and hinder the QS receptors in the P. aeruginosa. In an agreement with in vitro and in silico, the in vivo results showed the LAM full protection of mice against P. aeruginosa. In conclusion, LAM could be repurposed to be employed as adjunct therapy with traditional antibiotics for treating serious pseudomonal infections.

Thermodynamic modeling of RsmA - mRNA interactions capture novel direct binding across the Pseudomonas aeruginosa transcriptome

Pseudomonas aeruginosa (PA) is a ubiquitous, Gram-negative, bacteria that can attribute its survivability to numerous sensing and signaling pathways; conferring fitness due to speed of response. Post-transcriptional regulation is an energy efficient approach to quickly shift gene expression in response to the environment. The conserved post-transcriptional regulator RsmA is involved in regulating translation of genes involved in pathways that contribute to virulence, metabolism, and antibiotic resistance. Prior high-throughput approaches to map the full regulatory landscape of RsmA have estimated a target pool of approximately 500 genes; however, these approaches have been limited to a narrow range of growth phase, strain, and media conditions. Computational modeling presents a condition-independent approach to generating predictions for binding between the RsmA protein and highest affinity mRNAs. In this study, we improve upon a two-state thermodynamic model to predict the likelihood of RsmA binding to the 5' UTR sequence of genes present in the PA genome. Our modeling approach predicts 1043 direct RsmA-mRNA binding interactions, including 457 novel mRNA targets. We then perform GO term enrichment tests on our predictions that reveal significant enrichment for DNA binding transcriptional regulators. In addition, quorum sensing, biofilm formation, and two-component signaling pathways were represented in KEGG enrichment analysis. We confirm binding predictions using in vitro binding assays, and regulatory effects using in vivo translational reporters. These reveal RsmA binding and regulation of a broader number of genes not previously reported. An important new observation of this work is the direct regulation of several novel mRNA targets encoding for factors involved in Quorum Sensing and the Type IV Secretion system, such as rsaL and mvaT. Our study demonstrates the utility of thermodynamic modeling for predicting interactions independent of complex and environmentally-sensitive systems, specifically for profiling the post-transcriptional regulator RsmA. Our experimental validation of RsmA binding to novel targets both supports our model and expands upon the pool of characterized target genes in PA. Overall, our findings demonstrate that a modeling approach can differentiate direct from indirect binding interactions and predict specific sites of binding for this global regulatory protein, thus broadening our understanding of the role of RsmA regulation in this relevant pathogen.

Phenazine Scaffolds as a Potential Allosteric Inhibitor of LasR Protein in Pseudomonas aeruginosa

Millions of individuals suffer from chronic infections caused by bacterial biofilms, resulting in significant loss of life. Pseudomonas aeruginosa stands out as a major culprit in causing such chronic infections, largely due to its antibiotic resistance. This pathogen poses a considerable threat in healthcare settings, particularly to critically ill and immunocompromised patients. The persistence of chronic and recurrent bacterial infections is often attributed to bacterial biofilms. Therefore, there is an urgent need to discover novel small molecules capable of efficiently eliminating biofilms independent of bacterial growth. In this project, an in silico drug discovery approach was employed to identify nine halogenated-phenazine compounds as allosteric inhibitors of the LasR protein. The LasR is a key transcription factor that triggers other quorum-sensing systems and plays a crucial role in biofilm formation and activation of virulence genes. By inhibiting LasR, specifically targeting its allosteric site, the dimerization of LasR and subsequent biofilm formation could be prevented. Molecular docking and simulations, coupled with binding energy calculations, identified five compounds with potential as anti-biofilm agents. These compounds exhibited higher binding affinities to the distal site, suggesting their structural capability to interact with allosteric site residues of the LasR protein. Based on these findings, it is proposed that these compounds could serve as promising leads for the treatment of biofilm and quorum-sensing-related infections.

Inhibitors of the PqsR Quorum-Sensing Receptor Reveal Differential Roles for PqsE and RhlI in Control of Phenazine Production

Pseudomonas aeruginosa is a leading cause of hospital-acquired infections and it is resistant to many current antibiotic therapies, making development of new anti-microbial treatments imperative. The cell-to-cell communication process called quorum sensing controls P. aeruginosa pathogenicity. Quorum sensing relies on the production, release, and group-wide detection of extracellular signal molecules called autoinducers. Quorum sensing enables bacteria to synchronize group behaviors. P. aeruginosa possesses multiple quorum-sensing systems that control overlapping regulons, including those required for virulence and biofilm formation. Interventions that target P. aeruginosa quorum-sensing receptors are considered a fruitful avenue to pursue for new therapeutic advances. Here, we developed a P. aeruginosa strain that carries a bioluminescent reporter fused to a target promoter that is controlled by two P. aeruginosa quorum-sensing receptors. The receptors are PqsR, which binds and responds to the autoinducer called PQS (2-heptyl-3-hydroxy-4(1H)-quinolone) and RhlR, which binds and responds to the autoinducer called C4-HSL (C4-homoserine lactone). We used this reporter strain to screen >100,000 compounds with the aim of identifying inhibitors of either or both the PqsR and RhlR quorum-sensing receptors. We report results for 30 PqsR inhibitors from this screen. All of the identified compounds inhibit PqsR with IC50 values in the nanomolar to low micromolar range and they are readily docked into the autoinducer binding site of the PqsR crystal structure, suggesting they function competitively. The majority of hits identified are not structurally related to previously reported PqsR inhibitors. Recently, RhlR was shown to rely on the accessory protein PqsE for full function. Specifically, RhlR controls different subsets of genes depending on whether it is bound to PqsE or to C4-HSL, however, the consequences of differential regulation on the quorum-sensing output response have not been defined. PqsR regulates pqsE. That feature of the system enabled us to exploit our new set of PqsR inhibitors to show that RhlR requires PqsE to activate the biosynthetic genes for pyocyanin, a key P. aeruginosa virulence factor, while C4-HSL is dispensable. These results highlight the promise of inhibition of PqsR as a possible P. aeruginosa therapeutic to suppress production of factors under RhlR-PqsE control.

Innovative application of ceftriaxone as a quorum sensing inhibitor in Pseudomonas aeruginosa

Pseudomonas aeruginosa is a Gram-negative bacterium that has the potential to induce various healthcare-related infections through its array of virulence factors. The control of virulence factor expression is mainly regulated by a communication process among cells called quorum sensing (QS). Blocking QS could be a viable tactic to suppress virulence factors and reduce pathogenicity without impacting bacterial growth. This approach has the potential to significantly decrease the multiple drug resistance emergence. In this study, we explored the impact of ceftriaxone (CRO), which is a commonly used β-lactam antibiotic, and its metal derivatives on the QS system and virulence factors of both standard strains and clinical isolates of P. aeruginosa. The quorum sensing inhibitory (QSI) activity of CRO and ceftriaxone Nickel complex (CRON) was evaluated. The minimum inhibitory concentration (MIC) was determined and the effect of sub-MICs of CRO and CRON was assessed on P. aeruginosa strains virulence factors. CRO and CRON effectively suppressed the virulence factors of P. aeruginosa strains at sub-MICs, without altering bacterial viability. Additionally, a molecular docking investigation was carried out to identify potential mechanisms of QSI. CRO and CRON exhibited high ICM scores, potentially displacing natural ligands when interacting with LasR, LasI, and PqsR receptors.

Regulation of the H1 Type VI Secretion System by the Transcriptional Regulator NfxB in Pseudomonas aeruginosa

The type VI secretion system (T6SS) is a widely distributed molecular apparatus found in most Gram-negative bacteria. Studies show that T6SSs have functions in bacterial virulence, inter- and intra-bacterial competition, and environmental adaptation. Pseudomonas aeruginosa, an opportunistic pathogen, harbors three T6SS gene clusters that perform diverse roles in clinical infection. Herein, using DNA affinity chromatography of the H1-T6SS promoter, the fluoroquinolone antibiotic resistance regulator NfxB was identified. Further studies demonstrated that NfxB negatively regulates the expression of H1-T6SS by directly binding to its promoter region. T6SS expression and effector secretion are regulated by the fluoroquinolone antibiotic via NfxB, which enhances inter-bacterial competition in the complex bacterial ecology. Meanwhile, the deletion of nfxB alters carbenicillin resistance through an unknown pathway. This study provides new insights into the regulation of T6SS by environmental signals, and it provides data support for antibiotic resistance and inter-bacterial competition due to T6SSs.

Regulatory role of PA3299.1 small RNA in Pseudomonas aeruginosa biofilm formation via modulation of algU and mucA expression

Small RNAs (sRNAs) have emerged as key regulators of transcriptional factors and components within regulatory networks that govern bacterial biofilm formation. This study aimed to explore the regulatory role of the PA3299.1 sRNA in controlling biofilm formation in P. aeruginosa. Results showed that PA3299.1 expression was significantly elevated in both substratum-attached and colony biofilms compared to planktonic growth. Further investigation revealed that strains overexpressing PA3299.1 exhibited enhanced biofilm formation, while its deletion resulted in a substantial reduction in biofilm development. PA3299.1 was found to regulate the expression of AlgU and MucA, the sigma and anti-sigma factors, integral to the biofilm developmental network. In summary, this research identifies PA3299.1 as a critical regulator of biofilm formation and potentially a contributor to the pathogenicity of P. aeruginosa, that could help to develop new therapeutic strategies to manage biofilm-associated infections.

A plasmid-encoded inactive toxin-antitoxin system MtvT/MtvA regulates plasmid conjugative transfer and bacterial virulence in Pseudomonas aeruginosa

Plasmid-encoded toxin-antitoxin (TA) systems are known for their role in plasmid maintenance via post-segregational killing. Here, we identified an inactive type II TA system, MtvT/MtvA (MtvTA), encoded on the conjugative plasmid pPAD8 from the clinical Pseudomonas aeruginosa strain PAD8. Despite its annotation as a toxin, MtvT exhibited no detectable toxicity in our assays. Interestingly, the deletion of the MtvTA significantly increased the transfer efficiency of pPAD8 from PAD8 to P. aeruginosa strain PAO1. Functional assays revealed that the MtvTA complex negatively regulates plasmid transfer by binding to the promoters of dot/icm system genes. In addition, pPAD8ΔmtvTA attenuated the pathogenicity of the host strain compared to pPAD8, highlighting a regulatory role for MtvTA in virulence. Mechanistically, the MtvTA complex positively regulates the type III and type VI secretion systems and pyocyanin biosynthesis by directly binding to the promoters of exsA and rsmY/rsmZ and indirectly influencing lasI expression, respectively. These findings provide new insights into the regulatory roles of an inactive plasmid-encoded TA system, expanding our understanding of the interplay between plasmids and their bacterial hosts.

Quorum sensing regulation by the nitrogen phosphotransferase system in Pseudomonas aeruginosa

In the opportunistic pathogen Pseudomonas aeruginosa, the nitrogen-related phosphotransferase system (PTSNtr) influences multiple virulence behaviors. The PTSNtr is comprised of three enzymes: first PtsP, then the PtsO phosphocarrier, and the final PtsN phosphoacceptor. We previously showed that ptsP inactivation increases LasI-LasR quorum sensing, a system by which P. aeruginosa regulates genes in response to population density. LasI synthesizes a diffusible autoinducer that binds and activates the LasR receptor, which activates a feedback loop by increasing lasI expression. In this study, we examined the impact of the PTSNtr on quorum sensing. Disruption of ptsP increased the expression of some, but not all, tested quorum-controlled genes, including lasI, phzM (pyocyanin biosynthesis), hcnA (hydrogen cyanide biosynthesis), and, to a lesser extent, rsaL (quorum sensing regulator). Expression of these genes remained dependent on LasR and the autoinducer, whether provided endogenously or exogenously. Increased lasI expression in ΔptsP (or ΔptsO) cells was partly due to the presence of unphosphorylated PtsN, which alone was sufficient to elevate lasI expression. However, we observed residual increases in ΔptsP or ΔptsO cells even in the absence of PtsN, suggesting that PtsP and PtsO can regulate gene expression independent of PtsN. Indeed, genetically disrupting the PtsO phosphorylation site impacted gene expression in the absence of PtsN, and transcriptomic evidence suggested that PtsO and PtsN have distinct regulons. Our results expand our view of how the PTSNtr components function both within and apart from the classic phosphorylation cascade to regulate key virulence behaviors in P. aeruginosa.

Enhancement of aerobic sludge granulation by quorum sensing signaling molecules mediated by biomimetic bacterial extracellular vesicles

The addition of exogenous quorum sensing signaling molecules to the activated sludge system enables rapid sludge granulation. However, signaling molecules exposed to the environment are easily degraded, and their quorum sensing effects cannot be maintained in the long term. Therefore, they must be frequently added, which leads to an increase in operational costs. In this study, signaling molecules, acylated homoserine lactones (AHLs), were packaged into biomimetic bacterial extracellular vesicles-lipid vesicles (AHLs@ZZT), and the mediating role of lipid vesicles for AHLs was utilized to improve the utilization efficiency of signaling molecules. The results show that packaging of AHLs into vesicles slowed down the release of AHLs and protected them from degradation by porcine renal acylase. Moreover, the chemical properties of lipid vesicles are similar to the structure of bacterial cell walls, making it easier for the packaged AHLs to bind to target bacteria, thereby generating more EPS and accelerating the aggregation of microorganisms. After adding the lipid vesicles loaded with AHLs into the activated sludge system, the sludge granulation process was accelerated. Furthermore, the frequency of AHLs@ZZT addition was reduced by three times compared to that of unpackaged AHLs, resulting in a granular sludge with a smoother and denser surface. High-throughput sequencing of the sludge genome in the system indicated that adding AHLs@ZZT could promote microbial diversity and enrich functional microorganisms. Three-dimensional fluorescence spectra further revealed that the tryptophan and tyrosine proteins in extracellular polymeric substances secreted by these microorganisms facilitated sludge granulation. In summary, the lipid vesicle-mediated signaling molecular strategy can promote the rapid formation of granular sludge and maintain the long-term stability of the granular sludge structure, representing an economic and feasible regulation strategy.

RhlR-mediated cooperation in cystic fibrosis-adapted isolates of Pseudomonas aeruginosa

Pseudomonas aeruginosa uses quorum sensing (QS) to regulate the expression of dozens of genes, many of which encode shared products, called "public goods." P. aeruginosa possesses two complete acyl-homoserine lactone (AHL) QS circuits: the LasR-I and RhlR-I systems. Canonically, these systems are hierarchically organized: RhlR-I activity depends on LasR-I activation. However, in contrast to laboratory strains, isolates from people with cystic fibrosis can engage in AHL QS using only the transcription factor RhlR. In these isolates, RhlR regulates AHL QS and the production of secreted public goods, such as the exoprotease elastase, which are accessible to both producing and non-producing cells. When P. aeruginosa strains that use LasR to regulate elastase production are grown on casein as the sole carbon and energy source, LasR-null mutant "cheaters" commonly arise in populations due to a selective growth advantage. We asked if these social dynamics might differ in "RhlR cooperators": populations that use RhlR, not LasR, to regulate public goods. We passaged RhlR cooperators from several genetic backgrounds in casein broth. We found that cheaters emerged among most RhlR cooperators. However, in one isolate background, E90, RhlR-null mutants were dramatically outcompeted by RhlR cooperators. In this background, the mechanism by which RhlR mutants are outcompeted by RhlR cooperators is AHL-dependent and occurs in stationary phase but is not the same as previously described "policing" mechanisms. Our data suggest that cheating, or the lack thereof, does not explain the lack of RhlR mutants observed in most infection environments.IMPORTANCEQuorum sensing (QS) mutants arise in a variety of populations of bacteria, but mutants of the gene encoding the transcription factor RhlR in Pseudomonas aeruginosa appear to be infrequent. Our work provides insight on the mechanisms through which RhlR-mediated cooperation is maintained in a LasR-null population of P. aeruginosa. Characterizing the selective pressure(s) that disfavor mutations from occurring in RhlR may enhance our understanding of P. aeruginosa evolution in chronic infections and potentially guide the development of therapeutics targeting the RhlR-I QS circuit.

Dual RNA sequencing of a co-culture model of Pseudomonas aeruginosa and human 2D upper airway organoids

Pseudomonas aeruginosa is a Gram-negative bacterium that is notorious for airway infections in cystic fibrosis (CF) subjects. Bacterial quorum sensing (QS) coordinates virulence factor expression and biofilm formation at population level. Better understanding of QS in the bacterium-host interaction is required. Here, we set up a new P. aeruginosa infection model, using 2D upper airway nasal organoids that were derived from 3D organoids. Using dual RNA-sequencing, we dissected the interaction between organoid epithelial cells and WT or QS-mutant P. aeruginosa strains. Since only a single healthy individual and a single CF subject were used as donors for the organoids, conclusions about CF-specific effects could not be deduced. However, P. aeruginosa induced epithelial inflammation, whereas QS signaling did not affect the epithelial airway cells. Conversely, the epithelium influenced infection-related processes of P. aeruginosa, including QS-mediated regulation. Comparison of our model with samples from the airways of CF subjects indicated that our model recapitulates important aspects of infection in vivo. Hence, the 2D airway organoid infection model is relevant and may help to reduce the future burden of P. aeruginosa infections in CF.

Insight into the environmental cues modulating the expression of bacterial toxin-antitoxin systems

Bacteria require sophisticated sensing mechanisms to adjust their metabolism in response to stressful conditions and survive in hostile environments. Among them, toxin-antitoxin (TA) systems play a crucial role in bacterial adaptation to environmental challenges. TA systems are considered as stress-responsive elements, consisting of both toxin and antitoxin genes, typically organized in operons or encoded on complementary DNA strands. A decrease in the antitoxin-toxin ratio, often triggered by specific stress conditions, leads to toxin excess, disrupting essential cellular processes and inhibiting bacterial growth. These systems are categorized into eight types based on the nature of the antitoxin (RNA or protein) and the mode of action of toxin inhibition. While the well-established biological roles of TA systems include phage inhibition and the maintenance of genetic elements, the environmental cues regulating their expression remain insufficiently documented. In this review, we highlight the diversity and complexity of the environmental cues influencing TA systems expression. A comprehensive understanding of how these genetic modules are regulated could provide deeper insights into their functions and support the development of innovative antimicrobial strategies.

Acyl-Homoserine Lactone Enhances the Resistance of Anammox Consortia under Heavy Metal Stress: Quorum Sensing Regulatory Mechanism

Anaerobic ammonium oxidation (anammox) represents an energy-efficient process for the removal of biological nitrogen from ammonium-rich wastewater. However, the susceptibility of anammox bacteria to coexisting heavy metals considerably restricts their use in engineering practices. Here, we report that acyl-homoserine lactone (AHL), a signaling molecule that mediates quorum sensing (QS), significantly enhances the nitrogen removal rate by 24% under Cu2+ stress. A suite of macro-/microanalytical and bioinformatic analyses was exploited to unravel the underlying mechanisms of AHL-induced Cu2+ resistance. Macro-/microanalytical evidence indicated that AHL regulations on the production, spatial distribution, and functional groups of extracellular polymeric substances were not significant, ruling out extracellular partitioning and complexation as a principal mechanism. Meanwhile, molecular biological evidence showed that AHL upregulated the transcriptional levels of resistance genes (sod, kat, cysQ, and czcC responsible for antioxidation defense, Cu2+ sequestration, and transport) to appreciable extents, indicating intracellular resistance as the primary mechanism. This study yielded a mechanistic understanding of the regulatory roles of AHL in extracellular and intracellular resistance of anammox consortia, providing a fundamental basis for utilizing QS regulation for efficient nitrogen removal in wastewaters with heavy metal stress.