Quorum quenching activity of AiiA lactonase KMMI17 from endophytic Bacillus thuringiensis KMCL07 on AHL- mediated pathogenic phenotype in Pseudomonas aeruginosa

Microbial diversity and interactions: Synergistic effects and potential applications of Pseudomonas and Bacillus consortia

Microbial diversity and interactions in the rhizosphere play a crucial role in plant health and ecosystem functioning. Among the myriads of rhizosphere microbes, Pseudomonas and Bacillus are prominent players known for their multifaceted functionalities and beneficial effects on plant growth. The molecular mechanism of interspecies interactions between natural isolates of Bacillus and Pseudomonas in medium conditions is well understood, but the interaction between the two in vivo remains unclear. This paper focuses on the possible synergies between Pseudomonas and Bacillus associated in practical applications (such as recruiting beneficial microbes, cross-feeding and niche complementarity), and looks forward to the application prospects of the consortium in agriculture, human health and bioremediation. Through in-depth understanding of the interactions between Pseudomonas and Bacillus as well as their application prospects in various fields, this study is expected to provide a new theoretical basis and practical guidance for promoting the research and application of rhizosphere microbes.

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.

Quorum quenching strategies of endophytic Bacillus thuringiensis KMCL07 against soft rot pathogen Pectobacterium carotovorum subsp. carotovorum

Phytopathogens are global threats to agriculture, causing substantial economic losses and decreased crop productivity. Developing a control strategy without emerging resistance or creating environmental and health hazards is necessary. The majority of potential pathogens of crops are gram-negative and they communicate through Acyl homoserine lactones (AHLs)-mediated quorum sensing (QS) systems to establish their pathogenicity. By synthesizing small signal molecules, they collectively respond, regulate the expression of virulence factors, biofilm development, secondary metabolite production, and interactions with the host and other microbes in a population-density-dependent manner. Targeting QS mechanisms has been put forward as an attractive approach for conventional infection control. The quorum quenching endophytic Bacillus thuringiensis strain KMCL07 cell free lysate (CFL) was used to attenuate the virulence of the soft-rot Pectobacterium carotovorum subsp. carotovorum (Pcc) by targeting its QS system. The CFL inhibition ability of Pcc on the AHL signal molecules were tested using a biosensor strain (Chromobacterium subtsugae), which showed a significant (p < 0.001) reduction in the production of AHL signalling molecules without inhibiting Pcc growth. Pcc pathogenicity is related to the expression of various virulence traits like the secretion of extracellular enzymes, motility, and biofilm. The test results showed a significant degree (p < 0.0001) of inhibition in the production of virulence-causing extracellular enzymes (Pel, Cel, and Prt) when Pcc was treated with CFL. Soft rot in-vitro assays revealed that CFL, irrespective of different families, showed a significant level (p ≤ 0.0001) of reduction in disease severity and effectively reduced tissue maceration under different temperature ranges (25°, 30°, and 40 °C). LC-MS analysis confirmed the hydrolytic degradation of QS signalling molecules (3-oxo-C6-HSL and 3-oxo-C8-HSL) by CFL indicating the presence of lactonase enzyme activity. These results suggest that CFL can degrade a wide range of AHL molecules, and control soft rot in a wide variety of hosts and temperatures without affecting the host. Applying cell free lysates (CFLs) from endophytic bacteria to control soft rot pathogens can be an environmentally friendly way to improve plant health. CFLs protect plants by preventing the establishment of pathogenic organisms.

Bacterial communication intelligently regulates their interactions in anammox consortia under decreasing temperatures

Bacterial communication could affect their interactions, but whether this regulation has "intelligence" is still unknown. Here, we operated an anammox reactor under temperature gradient from 35 °C to 15 °C. As results, expression abundance of bacterial communication genes increased by 12 % significantly after temperature declined. Division of labor among distinct signal molecules was evidenced by complementary roles of acyl-homoserine lactones (AHLs) and diffusible signal factor (DSF) in affecting bacterial interactions and niche differentiation respectively. DSF based inter-and intra-communication helped bacteria match their investments and rewards during cross-feedings. When temperature was below 25 °C, transcription regulator Clp governed by DSF inclined to promote folate and molybdenum cofactor biosynthesis, which coincidentally benefited one anammox species more than another. Meanwhile, for the anammox species with lower benefits, Clp also inclined to decrease biosynthesis of costly tryptophan and vitamin B1 rewarding others. Interestingly, bacterial communication inclined to influence the bacteria with many cooperators in the community or with high capacity to export cofactors for cross-feedings when temperature decreased. As results, these bacteria were enriched which could lead to closer interactions in whole community to adapt to low temperatures. The discovered intelligence of bacterial communication opened another window for understanding bacterial sociobiology.

Quorum quenching activity of endophytic Bacillus sp. EBS9 from Tecomella undulata and its biocontrol applications

This study investigates the quorum quenching (QQ) activity of an endophytic bacterium, Bacillus sp. EBS9, isolated from the native medicinal plant Tecomella undulata of Rajasthan, and its biocontrol potential against the soft rot pathogen Pectobacterium carotovorum subsp. carotovorum (Pcc). QQ activity was confirmed by the loss of violacein pigment in Chromobacterium violaceum (MCC 2290). Quorum quenching metabolites were extracted using ethyl acetate, and the Quorum Quenching Extract (QQE) demonstrated positive activity in assays with C. violaceum CV026 (MCC 2216). HRLC-MS analysis identified diketopiperazines, L,L-Cyclo (leucylprolyl) and Cyclo (L-Phe-L-Pro), which are N-acyl homoserine lactones (AHLs) antagonists competing for LuxR receptor binding sites. In vitro and in planta assays evaluated QQB's biocontrol potential using treatment I (Pcc), treatment II (Pcc + QQB), and a control (sterile water). In the in vitro soft rot attenuation assay showed that treatment I caused severe maceration in vegetable slices, particularly in radish, exhibiting the highest maceration diameter (25.33 ± 3.52 mm) and percentage (46.14 ± 5.70 %). However, co-inoculation with QQB significantly reduced maceration across all tested vegetables. In the plate assay, germination rates decreased to approximately 50 % in both Vigna radiata and Raphanus sativus for treatment I, but improved to 86.67 % in treatment II. The seed vigour and germination indices also improved with QQB treatment in both plant species. In the pot assay after 30 days, in contrast to a 50 % decrease in root and shoot lengths in treatment I, treatment II led to a substantial recovery, with root lengths increase by 112.07 % and 138.76 %, while shoot length by 315.65 % and 163.63 % in V. radiata and R. sativus, respectively. This study highlights the QQ and biocontrol potential of Bacillus sp. EBS9 against P. carotovorum (Pcc), suggesting its promise in effective management of phytopathogens, which is crucial for agricultural productivity while minimizing environmental impact.

Helicobacter pylori biofilm interference by N-acyl homoserine lactonases: in vitro and in silico approaches

BACKGROUND

Qurom quenching enzyme have an impact on treatment efficacy and prevent the recurrence of Helicobacter pylori biofilm-related infections, although it has not been thoroughly investigated in vitro and in silico. The current study aims to characterize the N-acyl homoserine lactonase, the quorum quenching AiiA protein of Bacillus licheniformis against H. pylori biofilm.

METHODS AND RESULTS

In this study, AiiA protein were screened for their anti-biofilm activity, was found to effectively control biofilm formation of H. pylori with concentrations ranging from 2 to 10 µg/mL. According to CLSM and COMSTAT analysis, the untreated substratum had the robust biofilm biomass of 25-18 µM and biovolume of 3-4 mm3 /mm2. The total biofilm biovolume and average biofilm thickness were considerably reduced by 40% with a single application of 10 µg/mL of AiiA protein. The biofilm treated with AiiA exhibited a lower urease and polysaccharides than to the untreated biofilm. Further, in silico analysis, exhibited a greater interaction of AiiA against the outer membrane proteins of H. pylori compared to virulence factors. The conserved domains in the binding pockets of AiiA proteins showed a highest binding affinity proving the catalytic activity of the protein.

CONCLUSION

In this study, the H. pylori biofilm architecture, exopolysaccharide and urease were significantly controlled by our purified N-acyl homoserine lactonase from B. licheniformis. Furthermore, the molecular docking showed the significant interaction between AiiA and key biofilm forming and virulence proteins proved an excellent antibiofilm activity controlling the infections of H. pylori human pathogen.

Anti-quorum sensing and anti-biofilm activities of Pasteurella multocida strains

A total of 52 Pasteurella multocida strains of capsular serogroups (A, B and D) were screened for anti-quorum sensing activity against Chromobacterium violaceum. Of which, 12 strains of serogroups A were found to possess anti-quorum sensing activity. Inhibition activity was highest for strain NIVEDIPm9 and lowest for strain NIVEDIPm30 based on zone of pigment inhibition. Further, cell free extract of NIVEDIPm9 strain showed highest anti-biofilm activity in reference E. coli strain and concentration dependent degradation activity of C6-AHL molecule. In whole genome sequence annotation of NIVEDIPm9 strain predicted the presence of four metallo-β-lactamases (MBL) fold metallo-hydrolase proteins. In docking studies, MBL1 and MBL3 proteins showed high binding affinity with autoinduce signalling molecules AHL compound of OH-C10, binding energy value were -6.3 and -6.2 kcal/mol. Interaction study of VAF and quorum sensing molecules showed that OmpA and HgbA proteins were stimulated by all the ten molecules (C4-AHLs, C6-AHLs, C10-AHLs, C14-AHLs, 3-oxo-C10-AHLs, 3OH-C10-HSL, C8-HSL, C10-HSL, C12-HSL, C14-HSL), while toxA gene was stimulated by OH-C10-AHL molecule, sodC gene was stimulated by none. In conclusion, we described the anti-quorum sensing activities of diverse P. multocida strains causing Pasteurellosis in livestock.

Metabolite from supernatant of soil and plant-associated bacteria control biofilm of fish pathogens

OBJECTIVES

This research aimed to identify and quantify the antibiofilm activity of bioactive compounds from bacteria isolated from rhizosphere and nodule butterfly pea (Clitoria ternatea), rhizosphere clove afo 3 (Syzygium aromaticum), nodule mimosa (Mimosa pudica L.), and soil from gold mining land which were recovered from Ternate, Tidore, Obi Island, and Marotai Island, Eastern part of Indonesia.

RESULTS

Eight supernatants from soil and plant-associated bacteria were found to have quorum quenching activity against Chromobacterium violaceum. All supernatants exhibited antibiofilm activity against biofilm formed by Aeromonas hydrophila and Vibrio harveyi. The supernatant of FT5 showed the highest activity in disrupting (66.59%) and inhibiting (85.63%) the biofilm of A. hydrophila. For V. harveyi, the supernatant of PTM3 showed the highest disruption activity (72.61%), whileRCA7 showed the highest inhibition activity(75.68%). The Gas Chromatography-Mass Spectrometry (GC-MS) identified fatty acids, ester, and diketopiperazine as the compounds related to the antibiofilm activity. Molecular identification revealed that the isolates belong to the genera Bacillus, Priestia, and Chryseobacterium.

Quorum Sensing Inhibitors: An Alternative Strategy to Win the Battle against Multidrug-Resistant (MDR) Bacteria

Antibiotic resistance is a major problem and a major global health concern. In total, there are 16 million deaths yearly from infectious diseases, and at least 65% of infectious diseases are caused by microbial communities that proliferate through the formation of biofilms. Antibiotic overuse has resulted in the evolution of multidrug-resistant (MDR) microbial strains. As a result, there is now much more interest in non-antibiotic therapies for bacterial infections. Among these revolutionary, non-traditional medications is quorum sensing inhibitors (QSIs). Bacterial cell-to-cell communication is known as quorum sensing (QS), and it is mediated by tiny diffusible signaling molecules known as autoinducers (AIs). QS is dependent on the density of the bacterial population. QS is used by Gram-negative and Gram-positive bacteria to control a wide range of processes; in both scenarios, QS entails the synthesis, identification, and reaction to signaling chemicals, also known as auto-inducers. Since the usual processes regulated by QS are the expression of virulence factors and the creation of biofilms, QS is being investigated as an alternative solution to antibiotic resistance. Consequently, the use of QS-inhibiting agents, such as QSIs and quorum quenching (QQ) enzymes, to interfere with QS seems like a good strategy to prevent bacterial infections. This review sheds light on QS inhibition strategy and mechanisms and discusses how using this approach can aid in winning the battle against resistant bacteria.

Quenching and quorum sensing in bacterial bio-films

Quorum sensing (QS) is the ability of bacteria to monitor their population density and adjust gene expression accordingly. QS-regulated processes include host-microbe interactions, horizontal gene transfer, and multicellular behaviours (such as the growth and development of biofilm). The creation, transfer, and perception of bacterial chemicals known as autoinducers or QS signals are necessary for QS signalling (e.g. N-acylhomoserine lactones). Quorum quenching (QQ), another name for the disruption of QS signalling, comprises a wide range of events and mechanisms that are described and analysed in this study. In order to better comprehend the targets of the QQ phenomena that organisms have naturally developed and are currently being actively researched from practical perspectives, we first surveyed the diversity of QS-signals and QS-associated responses. Next, the mechanisms, molecular players, and targets related to QS interference are discussed, with a focus on natural QQ enzymes and compounds that function as QS inhibitors. To illustrate the processes and biological functions of QS inhibition in microbe-microbe and host-microbe interactions, a few QQ paradigms are described in detail. Finally, certain QQ techniques are offered as potential instruments in a variety of industries, including agriculture, medical, aquaculture, crop production, and anti-biofouling areas.

Emerging trends in the inhibition of bacterial molecular communication: An overview

Quorum sensing (QS) is a molecular cell-cell communication utilized by several bacteria and some fungi. It involves cell density dependent gene expression that includes extra polymeric substance production, sporulation, antibiotic production, motility, competence, symbiosis and conjugation. These expressions were carried out by different signaling molecules like acyl homo-serine lactone (AHL) and auto-inducing peptides (AIPs) which was effluxed by gram negative and gram positive bacteria. Pathogenic bacteria and biofilms often exhibit high resistance to antibiotics, attributed to the presence of antibiotic efflux pumps, reduced membrane permeability, and enzymes that deactivate quorum sensing (QS) inhibitors. To counteract virulence and multi-drug resistance (MDR), novel strategies such as employing quorum sensing (QS) inhibitors and quorum quenchers are employed. It targets signaling molecules with synthesis and prevents the signal from binding to receptors. In this present review, the mechanisms of QS along with inhibitors from different sources are described. These strategies potentially interfere with QS and it can be applied in different fields, mainly in hospitals and marine environments where the pathogenic infections and biofilm formation are highly involved.

A review of chemical signaling pathways in the quorum sensing circuit of Pseudomonas aeruginosa

Pseudomonas aeruginosa, an increasingly common competitive and biofilm organism in healthcare infection with sophisticated, interlinked and hierarchic quorum systems (Las, Rhl, PQS, and IQS), creates the greatest threats to the medical industry and has rendered prevailing chemotherapy medications ineffective. The rise of multidrug resistance has evolved into a concerning and potentially fatal occurrence for human life. P. aeruginosa biofilm development is assisted by exopolysaccharides, extracellular DNA, proteins, macromolecules, cellular signaling and interaction. Quorum sensing is a communication process between cells that involves autonomous inducers and regulators. Quorum-induced infectious agent biofilms and the synthesis of virulence factors have increased disease transmission, medication resistance, infection episodes, hospitalizations and mortality. Hence, quorum sensing may be a potential therapeutical target for bacterial illness, and developing quorum inhibitors as an anti-virulent tool could be a promising treatment strategy for existing antibiotics. Quorum quenching is a prevalent technique for treating infections caused by microbes because it diminishes microbial pathogenesis and increases microbe biofilm sensitivity to antibiotics, making it a potential candidate for drug development. This paper examines P. aeruginosa quorum sensing, the hierarchy of quorum sensing mechanism, quorum sensing inhibition and quorum sensing inhibitory agents as a drug development strategy to supplement traditional antibiotic strategies.

Revealing the Bacterial Quorum-Sensing Effect on the Biofilm Formation of Diatom Cylindrotheca sp. Using Multimodal Imaging

Diatoms contribute to carbon fixation in the oceans by photosynthesis and always form biofouling organized by extracellular polymeric substances (EPS) in the marine environment. Bacteria-produced quorum-sensing signal molecules N-acyl homoserine lactones (AHLs) were found to play an important role in the development of Cylindrotheca sp. in previous studies, but the EPS composition change was unclear. This study used the technology of alcian blue staining and scanning electron microscopy (SEM), confocal laser scanning microscopy (CLSM), and time-of-flight secondary ion mass spectrometry (ToF-SIMS) to directly observe the biofilm formation process. The results showed that AHLs promote the growth rates of diatoms and the EPS secretion of biofilm components. AHLs facilitated the diatom-biofilm formation by a forming process dependent on the length of carbon chains. AHLs increased the biofilm thickness and the fluorescence intensity and then altered the three-dimensional (3D) structures of the diatom-biofilm. In addition, the enhanced EPS content in the diatom-biofilm testified that AHLs aided biofilm formation. This study provides a collection of new experimental evidence of the interaction between bacteria and microalgae in fouling biofilms.

Selection and Molecular Response of AHL-lactonase (aiiA) Producing Bacillus sp. Under Penicillin G-induced Conditions

Quorum sensing (QS) is the process by which microorganisms employ chemicals called autoinducers (AIs) to communicate with their population. The QS mechanism generally controls the expression of the virulence related genes in bacteria. N-acyl homoserine lactones (AHLs) are the most widespread QS molecules. Due to their diverse AHL-lactonase activities, Bacillus species make particularly suitable candidates for procedures such as demolition of pathogenic bacterial QS signals and bioremediation of β-lactam antibiotics from contaminated environments. In this study, seven Bacillus strains with Quorum quenching (QQ) activity were isolated using an enrichment medium supplemented with Penicillin G (PenG). The AHL-lactonase encoding gene (aiiA) was amplified by PCR and sequenced. Amino acid sequences underwent multiple sequence alignment. Docking studies were carried out with both C6HSL and PenG ligand using AutoDock tools. The aiiA amino acid sequences of the isolates were found to be well conserved. Furthermore, amino acid sequence alignment revealed that 74.9% of amino acid sequences were conserved in the genus Bacillus. Docking of the C6HSL to wild type (3DHA) and H97D variant reduced the docking score by only 0.1 kcal/mol for the mutated protein. When PenG docked with a higher (1.5 kcal/mol) score as a ligand to wild-type and mutant receptors, the docking score for the mutated protein likewise decreased by 0.1 kcal/mol. This research contributed to the diversification of organisms with QQ activity and beta-lactam antibiotic resistance. It also clarified the binding score of the PenG ligand to the Bacillus AHL lactonase molecule for the first time.

Frenemies of the soil: Bacillus and Pseudomonas interspecies interactions

Bacillus and Pseudomonas ubiquitously occur in natural environments and are two of the most intensively studied bacterial genera in the soil. They are often coisolated from environmental samples, and as a result, several studies have experimentally cocultured bacilli and pseudomonads to obtain emergent properties. Even so, the general interaction between members of these genera is virtually unknown. In the past decade, data on interspecies interactions between natural isolates of Bacillus and Pseudomonas has become more detailed, and now, molecular studies permit mapping of the mechanisms behind their pairwise ecology. This review addresses the current knowledge about microbe-microbe interactions between strains of Bacillus and Pseudomonas and discusses how we can attempt to generalize the interaction on a taxonomic and molecular level.

Nanomaterials and Coatings for Managing Antibiotic-Resistant Biofilms

Biofilms are a global health concern responsible for 65 to 80% of the total number of acute and persistent nosocomial infections, which lead to prolonged hospitalization and a huge economic burden to the healthcare systems. Biofilms are organized assemblages of surface-bound cells, which are enclosed in a self-produced extracellular polymer matrix (EPM) of polysaccharides, nucleic acids, lipids, and proteins. The EPM holds the pathogens together and provides a functional environment, enabling adhesion to living and non-living surfaces, mechanical stability, next to enhanced tolerance to host immune responses and conventional antibiotics compared to free-floating cells. Furthermore, the close proximity of cells in biofilms facilitates the horizontal transfer of genes, which is responsible for the development of antibiotic resistance. Given the growing number and impact of resistant bacteria, there is an urgent need to design novel strategies in order to outsmart bacterial evolutionary mechanisms. Antibiotic-free approaches that attenuate virulence through interruption of quorum sensing, prevent adhesion via EPM degradation, or kill pathogens by novel mechanisms that are less likely to cause resistance have gained considerable attention in the war against biofilm infections. Thereby, nanoformulation offers significant advantages due to the enhanced antibacterial efficacy and better penetration into the biofilm compared to bulk therapeutics of the same composition. This review highlights the latest developments in the field of nanoformulated quorum-quenching actives, antiadhesives, and bactericides, and their use as colloid suspensions and coatings on medical devices to reduce the incidence of biofilm-related infections.

Evidence for Complex Interplay between Quorum Sensing and Antibiotic Resistance in Pseudomonas aeruginosa

Quorum sensing (QS) is a cell-density-dependent, intercellular communication system mediated by small diffusible signaling molecules. QS regulates a range of bacterial behaviors, including biofilm formation, virulence, drug resistance mechanisms, and antibiotic tolerance. Enzymes capable of degrading signaling molecules can interfere in QS-a process termed as quorum quenching (QQ). Remarkably, previous work reported some cases where enzymatic interference in QS was synergistic to antibiotics against Pseudomonas aeruginosa. The premise of combination therapy is attractive to fight against multidrug-resistant bacteria, yet comprehensive studies are lacking. Here, we evaluate the effects of QS signal disruption on the antibiotic resistance profile of P. aeruginosa by testing 222 antibiotics and antibacterial compounds from 15 different classes. We found compelling evidence that QS signal disruption does indeed affect antibiotic resistance (40% of all tested compounds; 89/222), albeit not always synergistically (not synergistic for 19% of compounds; 43/222). For some tested antibiotics, such as sulfathiazole and trimethoprim, we were able to relate the changes in resistance caused by QS signal disruption to the modulation of the expression of key genes of the folate biosynthetic pathway. Moreover, using a P. aeruginosa-based Caenorhabditis elegans killing model, we confirmed that enzymatic QQ modulates the effects of antibiotics on P. aeruginosa's pathogenicity in vivo. Altogether, these results show that signal disruption has profound and complex effects on the antibiotic resistance profile of P. aeruginosa. This work suggests that combination therapy including QQ and antibiotics should be discussed not globally but, rather, in case-by-case studies. IMPORTANCE Quorum sensing (QS) is a cell-density-dependent communication system used by a wide range of bacteria to coordinate behaviors. Strategies pertaining to the interference in QS are appealing approaches to control microbial behaviors that depend on QS, including virulence and biofilms. Interference in QS was previously reported to be synergistic with antibiotics, yet no systematic assessment exists. Here, we evaluate the potential of combination treatments using the model opportunistic human pathogen Pseudomonas aeruginosa PA14. In this model, collected data demonstrate that QS largely modulates the antibiotic resistance profile of PA14 (for more than 40% of the tested drugs). However, the outcome of combination treatments is synergistic for only 19% of them. This research demonstrates the complex relationship between QS and antibiotic resistance and suggests that combination therapy including QS inhibitors and antibiotics should be discussed not globally but, rather, in case-by-case studies.

Quorum sensing mediates gut bacterial communication and host-microbiota interaction

Gut bacteria employ quorum sensing (QS) to coordinate their activities and communicate with one another, this process relies on the production, detection, and response to autoinducers, which are extracellular signaling molecules. In addition to synchronizing behavioral activities within the species, QS plays a crucial role in the gut host-microbiota interaction. In this review, an overview of classical QS systems is presented as well as the interspecies communication mediated by QS, and recent advances in the host-microbiota interaction mediated by QS. A greater knowledge of the communication network of gut microbiota is not only an opportunity and a challenge for developing nutritional and therapeutic strategies against bacterial illnesses, but also a means for improving gut health.

Quorum Quenching: A Drug Discovery Approach Against Pseudomonas aeruginosa

Pseudomonas aeruginosa, a ubiquitous opportunistic and nosocomial biofilm-forming pathogen with complex, interconnected and hierarchical nature of QS systems (Las, Rhl, PQS, and IQS), is posing the biggest challenge to the healthcare sector and have made current chemotherapies incapable. Conventional antibiotics designed to intercept the biochemical or physiological processes precisely of planktonic microorganisms exert extreme selective pressure and develop resistance against them thereby emphasizing the development of alternative therapeutic approaches. Additionally, quorum sensing induced pathogenic microbial biofilms and production of virulence factors have intensified the pathogenicity, drug resistance, recurrence of infections, hospital visits, morbidity, and mortality many-folds. In this regard, QS could be a potential druggable target and the discovery of QS inhibiting agents as an anti-virulent measure could serve as an alternative therapeutic approach to conventional antibiotics. Quorum quenching (QQ) is a preferred strategy to combat microbial infections since it attenuates the pathogenicity of microbes and enhances the microbial biofilm susceptibility to antibiotics, thus qualifying as a suitable target for drug discovery. This review discusses the QS-induced pathogenicity of P. aeruginosa, the hierarchical QS systems, and QS inhibition as a drug discovery approach to complement classical antibiotic strategy.

Quorum-Sensing Inhibition by Gram-Positive Bacteria

The modern paradigm assumes that interspecies communication of microorganisms occurs through precise regulatory mechanisms. In particular, antagonism between bacteria or bacteria and fungi can be achieved by direct destruction of the targeted cells through the regulated production of antimicrobial metabolites or by controlling their adaptive mechanisms, such as the formation of biofilms. The quorum-quenching phenomenon provides such a countermeasure strategy. This review discusses quorum-sensing suppression by Gram-positive microorganisms, the underlying mechanisms of this process, and its molecular intermediates. The main focus will be on Gram-positive bacteria that have practical applications, such as starter cultures for food fermentation, probiotics, and other microorganisms of biotechnological importance. The possible evolutionary role of quorum-quenching mechanisms during the development of interspecies interactions of bacteria is also considered. In addition, the review provides possible practical applications for these mechanisms, such as the control of pathogens, improving the efficiency of probiotics, and plant protection.

Quorum quenching and anti-biofilm activities of halotolerant Bacillus strains isolated in different environments in Algeria

AIMS

The current study aimed to screen Bacillus strains with wide-spectrum quorum quenching (QQ) activity against N-acyl-l-homoserine lactones (AHLs), helpful in controlling virulence traits in Gram-negatives, including biofilm formation and also with anti-biofilm activity against Gram-positives.

METHODS AND RESULTS

A total of 94 halotolerant strains of Bacillus isolated from soil and salt-lake sediment samples in Algeria were examined for the presence of QQ activity against AHLs, the presence of the aiiA gene, encoding an AHL lactonase enzyme typical of Bacillus spp., antimicrobial and anti-biofilm activities against Pseudomonas aeruginosa and Streptococcus mutans. Of all strains of Bacillus spp. isolated, 48.9% showed antibacterial activity. In addition, 40% of these isolates showed a positive QQ activity against long-chain AHLs, of which seven strains presented the aiiA gene. Among the species with broad-spectrum QQ activity, the cell extract of Bacillus thuringiensis DZ16 showed antibiofilm activity against P. aeruginosa PAO1, reducing 60% using the Amsterdam active attachment (AAA) biofilm cultivation model. In addition, the cell extract of B. subtilis DZ17, also presenting a broad-spectrum QQ activity, significantly reduced Strep. mutans ATCC 25175 biofilm formations by 63% and 53% in the xCELLigence and the AAA model, respectively, without affecting growth. Strain DZ17 is of particular interest due to its explicit halophilic nature because it can thrive at salinities in the range of 6%-30%.

CONCLUSIONS

B. thuringiensis DZ16 and B. subtilis DZ17 strains have interesting antibacterial, QQ, and anti-biofilm activities. The high range of salinities accepted by these strains increases their biotechnological potential. This may open up their use as probiotics, the treatment and prevention of conventional and emerging infectious diseases.

SIGNIFICANCE AND IMPACT OF STUDY

The use of safe, economical and effective probiotics is limited to control the infections related to multi-resistant bacteria. In our study, we provide two promising agents with QQ, anti-biofilm and antibacterial activities.

Cyclobutanone Inhibitor of Cobalt-Functionalized Metallo-γ-Lactonase AiiA with Cyclobutanone Ring Opening in the Active Site

An α-amido cyclobutanone possessing a C10 hydrocarbon tail was designed as a potential transition-state mimetic for the quorum-quenching metallo-γ-lactonase autoinducer inactivator A (AiiA) with the support of in-house modeling techniques and found to be a competitive inhibitor of dicobalt(II) AiiA with an inhibition constant of K _i = 0.007 ± 0.002 mM. The catalytic mechanism of AiiA was further explored using our product-based transition-state modeling (PBTSM) computational approach, providing substrate-intermediate models arising during enzyme turnover and further insight into substrate-enzyme interactions governing native substrate catalysis. These interactions were targeted in the docking of cyclobutanone hydrates into the active site of AiiA. The X-ray crystal structure of dicobalt(II) AiiA cocrystallized with this cyclobutanone inhibitor unexpectedly revealed an N-(2-oxocyclobutyl)decanamide ring-opened acyclic product bound to the enzyme active site (PDB 7L5F). The C10 alkyl chain and its interaction with the hydrophobic phenylalanine clamp region of AiiA adjacent to the active site enabled atomic placement of the ligand atoms, including the C10 alkyl chain. A mechanistic hypothesis for the ring opening is proposed involving a radical-mediated process.

Marine-Source Quorum Quenching Enzyme YtnP to Improve Hygiene Quality in Dental Units

Biofilm in dental unit water lines may pose a health risk to patients and dental practitioners. An AdiC-like quorum quenching enzyme, YtnP, was cloned from a deep-sea probiotic Bacillus velezensis, and heterologously expressed in E. coli to examine the application on the improvement of hygiene problems caused by biofilm infection of Pseudomonas aeruginosa in dental units. Pseudomonas bacteria were isolated from dental chair units and used to grow static biofilms in the laboratory. A water filter system was designed to test the antifouling activity of YtnP in Laboratory, to simulate the biofilm contamination on water filter in dental unit water lines. The results demonstrated that the enzyme of YtnP was able to degrade the N-acyl homoserine lactones, significantly inhibited the EPS generation, biofilm formation, and virulence factors production (pyocyanin and rhamnolipid) of P. aeruginosa, and was efficient on the antifouling against P. aeruginosa. The findings in this study indicated the possibility of YtnP as novel disinfectant reagent for hygiene treatment in dental units.

Regulatory Mechanisms and Promising Applications of Quorum Sensing-Inhibiting Agents in Control of Bacterial Biofilm Formation

A biofilm is an assemblage of microbial cells attached to a surface and encapsulated in an extracellular polymeric substance (EPS) matrix. The formation of a biofilm is one of the important mechanisms of bacterial resistance, which not only leads to hard-to-control bacterial infections in humans and animals but also enables bacteria to be a major problem in various fields, such as food processing, wastewater treatment and metalworking. Quorum sensing (QS) is a bacterial cell-to-cell communication process that depends on the bacterial population density and is mediated by small diffusible signaling molecules called autoinducers (AIs). Bacteria use QS to regulate diverse arrays of functions, including virulence and biofilm formation. Therefore, the interference with QS by using QS inhibiting agents, including QS inhibitors (QSIs) and quorum quenching (QQ) enzymes, to reduce or even completely repress the biofilm formation of pathogenic bacteria appears to be a promising approach to control bacterial infections. In this review, we summarize the mechanisms of QS-regulating biofilm formation and QS-inhibiting agents that control bacterial biofilm formation, strategies for the discovery of new QS inhibiting agents, and the current applications of QS-inhibiting agents in several fields to provide insight into the development of effective drugs to control pathogenic bacteria.

Quorum quenching enzymes and their effects on virulence, biofilm, and microbiomes: a review of recent advances

INTRODUCTION

Numerous bacterial behaviors are regulated by a cell-density dependent mechanism known as Quorum Sensing (QS). QS relies on communication between bacterial cells using diffusible signaling molecules known as autoinducers. QS regulates physiological processes such as metabolism, virulence, and biofilm formation. Quorum Quenching (QQ) is the inhibition of QS using chemical or enzymatic means to counteract behaviors regulated by QS.

AREAS COVERED

We examine the main, diverse QS mechanisms present in bacterial species, with a special emphasis on AHL-mediated QS. We also discuss key in vitro and in vivo systems in which interference in QS was investigated. Additionally, we highlight promising developments, such as the substrate preference of the used enzymatic quencher, in the application of interference in QS to counter bacterial virulence.

EXPERT OPINION

Enabled via the recent isolation of highly stable quorum quenching enzymes and/or molecular engineering efforts, the effects of the interference in QS were recently evaluated outside of the traditional model of single species culture. Signal disruption in complex microbial communities was shown to result in the disruption of complex microbial behaviors, and changes in population structures. These new findings, and future studies, may result in significant changes in the traditional views about QS.