Quorum Quenching Activity Research Articles

Diversity of Bacteria with Quorum Sensing and Quenching Activities from Hydrothermal Vents in the Okinawa Trough

Quorum sensing (QS) is a chemical communication system by which bacteria coordinate gene expression and social behaviors. Quorum quenching (QQ) refers to processes of inhibiting the QS pathway. Deep-sea hydrothermal vents are extreme marine environments, where abundant and diverse microbial communities live. However, the nature of chemical communication in bacteria inhabiting the hydrothermal vent is poorly understood. In this study, the QS and QQ activities with N-acyl homoserine lactones (AHLs) as the autoinducer were detected in bacteria isolated from hydrothermal vents in the Okinawa Trough. A total of 18 and 108 isolates possessed AHL-producing and AHL-degrading abilities, respectively. Bacteria mainly affiliated with Rhodobacterales, Hyphomicrobiales, Enterobacterales and Sphingomonadales showed QS activities; QQ was mainly associated with Bacillales, Rhodospirillales and Sphingomonadales. The results showed that the bacterial QS and QQ processes are prevalent in hydrothermal environments in the Okinawa Trough. Furthermore, QS significantly affected the activities of extracellular enzymes represented by β-glucosidase, aminopeptidase and phosphatase in the four isolates with higher QS activities. Our results increase the current knowledge of the diversity of QS and QQ bacteria in extreme marine environments and shed light on the interspecific relationships to better investigate their dynamics and ecological roles in biogeochemical cycling.

Enhancing quorum quenching media with 3D robust electrospinning coating: A novel biofouling control strategy for membrane bioreactors

Bacterial quorum quenching (QQ) is an effective strategy for controlling biofouling in membrane bioreactor (MBR) by interfering the releasing and degradation of signal molecules during quorum sensing (QS) process. However, due to the framework feature of QQ media, the maintenance of QQ activity and the restriction of mass transfer threshold, it has been difficult to design a more stable and better performing structure in a long period of time. In this research, electrospun fiber coated hydrogel QQ beads (QQ-ECHB) were fabricated by using electrospun nanofiber coated hydrogel to strengthen layers of QQ carriers for the first time. The robust porous PVDF 3D nanofiber membrane was coated on the surface of millimeter-scale QQ hydrogel beads. Biocompatible hydrogel entrapping quorum quenching bacteria (sp.BH4) was employed as the core of the QQ-ECHB. In MBR with the addition of QQ-ECHB, the time to reach transmembrane pressure (TMP) of 40 kPa was 4 times longer than conventional MBR. The robust coating and porous microstructure of QQ-ECHB contributed to keeping a lasting QQ activity and stable physical washing effect at a very low dosage (10g beads/5L MBR). Physical stability and environmental-tolerance tests also verified that the carrier can maintain the structural strength and keep the core bacteria stable when suffering long-term cyclic compression and great fluctuations in sewage quality.

Quorum-quenching potential of recombinant PvdQ-engineered bacteria for biofilm formation.

Quorum sensing (QS) is a core mechanism for bacteria to regulate biofilm formation, and therefore, QS inhibition or quorum quenching (QQ) is used as an effective and economically feasible strategy against biofilms. In this study, the PvdQ gene encoding AHL acylase was introduced into Escherichia coli (DE3), and a PvdQ-engineered bacterium with highly efficient QQ activity was obtained and used to inhibit biofilm formation. Gene sequencing and western blot analysis showed that the recombinant pET-PvdQ strain was successfully constructed. The color reaction of Agrobacterium tumefaciens A136 indicated that PvdQ engineering bacteria had shown strong AHL signal molecule quenching activity and significantly inhibited the adhesion (motility) of Pseudomonas aeruginosa and biofilm formation of activated sludge bacteria in Membrane Bio-Reactor (MBR; inhibition rate 51-85%, p < 0.05). In addition, qRT-PCR testing revealed that recombinant PvdQ acylase significantly reduced the transcription level of QS biofilm formation-related genes (cdrA, pqsA, and lasR; p < 0.05). In this study, QQ genetically engineered bacteria enhanced by genetic engineering could effectively inhibit the QS signal transduction mechanism and have the potential to control biofilm formation of pathogenic bacteria in the aquaculture environment, providing an environmentally friendly and alternative antibiotic strategy to suppress biofilm contamination.

Silica reinforced core-shell quorum quenching beads to control biofouling in an MBR

Quorum quenching (QQ) is a strategy to alleviate membrane biofouling in membrane bioreactors (MBRs). As a stable inorganic material with a large specific surface area, silica is often used to prepare of microbial immobilization composites. This study selected two different sizes of silica materials (silica beads and Nano-silica) to make the core encapsulate a QQ bacterial strain (Rhodococcus sp. BH4). The compressive strength and stability under extreme environments were characterized, and the positive effect of silica on QQ beads was verified. The results showed that both QQ beads could resist the impact of high pressure, acid, alkali, salt and EDTA buffer. It was proved that they have the potential to quench effectively continuously. Both beads were still more than 70 % QQ activity after five months of use. In the lab-scale continuous MBR experiment, the time of transmembrane pressure (TMP) reaching 50 kPa in both experimental groups was more than 3 times that in the blank group. The TMP contamination time was extended from 5 to 6 days in the blank group to 18–19 days. Among them, silica beads greatly improve the compressive strength of the beads, and also have a better performance in QQ.

Identification of Quorum Quenching N-Acyl Homoserine Lactonases from Priestia aryabhattai J1D and Bacillus cereus G Isolated from the Rhizosphere

Several pathogenic bacteria communicate using N-acyl homoserine lactone (AHL) as a quorum sensing (QS) molecule. The process of interfering with the QS system is known as quorum quenching (QQ), it is an effective tool to control QS-dependent virulence in pathogens. In the present study, rhizosphere bacterial isolates were screened for their ability to produce AHL lactonase enzyme as QQ molecules, which hydrolyses AHL signalling molecules and consequently blocks the QS system. Potent N-hexanoyl-l-homoserine lactone (C6HSL) hydrolytic QQ activity was detected in rhizosphere isolates namely Bacillus cereus G and Priestia aryabhattai J1D. The cell-free supernatant of the bacterial isolates indicated a reduction in biofilm formation in the human pathogens Vibrio cholerae, Pseudomonas aeruginosa, and Staphylococcus aureus without inhibiting cells, signifying their biocontrol property. Furthermore, liquid chromatography high resolution mass spectrometry analysis confirmed C6HSL hydrolytic activity by AHL lactonase produced by these rhizosphere isolates. Also, the aiiA homologous gene from the bacterial isolates showed similarity with the aiiA lactonase gene from Bacillus species, which was further confirmed by homology modelling. In silico structure analysis by comparing with the structure of Bacillus revealed the similarity in the active site, indicating the same degradation pattern. Based on available reported data, the present study indicates the first report of the presence of the aiiA lactonase gene in P. aryabhattai.

α-Terpineol synergizes with gentamicin to rescue Caenorhabditis elegans from Pseudomonas aeruginosa infection by attenuating quorum sensing-regulated virulence

AimsThis study scrutinized α-Terpineol (α-T) for its anti-virulence and anti-fouling potential against P. aeruginosa PAO1 in conjunction with gentamicin (GeN) using in-vitro, in-silico, and in-vivo approaches. Main methodsThe quorum quenching (QQ) potential of the drug combination was studied using a quorum sensing (QS) biosensor strain and tested for synergy using chequerboard and time-kill kinetics assays. The effect of α-T and GeN on bacterial motility, QS-regulated virulence factor production, and biofilm formation was assessed in P. aeruginosa PAO1 along with molecular docking analysis. The protective effects of α-T-GeN combination were also examined in a Caenorhabditis elegans infection model through slow-killing (SK) assays. Key findingsThe drug combination displayed synergy, enhanced QQ activity, and suppressed AHL production in PAO1. At sub-inhibitory concentrations, the drug combination suppressed the expression of genes regulating QS and pseudomonal virulence, thereby inhibiting the production of virulence factors in PAO1. The drug combination compromised all forms of pseudomonal motility, strongly inhibited biofilm formation, and successfully eradicated preformed biofilms. Based on these findings, it is concluded that GeN (alone) does not harbor any QQ properties, but enhances the QQ potential of α-T. Moreover, combinational treatment protected C. elegans from pseudomonal infection and improved survival rates by 73 % at 96 h. SignificanceFor the first time, the molecular mechanism responsible for the anti-QS activity of α-T was unraveled through a comprehensive investigation, thereby asserting its potential as an anti-virulent drug against P. aeruginosa.

Exploiting Conserved Quorum Sensing Signals in Streptococcus mutans and Streptococcus pneumoniae

Bacterial species of the Streptococcus genera are considered either commensal bacteria or potential pathogens, according to their metabolic evolution and production of quorum sensing (QS)-controlled virulence factors. S. mutans, in particular, has become one of the best-studied examples of bacteria that are able to get along or cheat commensal species, even of the same genera. S. mutans and S. pneumoniae share homolog QS pathways and a competence stimulating peptide (CSP) for regulating bacteriocin production. Intriguingly, the abundance of S. pneumoniae and S. mutans alternates in complex microbial communities, thus opening the role for the fratricide communication of homolog QS systems. Since the inhibition of the QS has been proposed in treating bacterial infections, in this study, we designed and synthesized analogs of S. pneumoniae CSP with precise residual modifications. We reported that S. pneumoniae CSP analogs reduced the expression of genes involved in the QS of S. mutans and biofilm formation without affecting bacterial growth. The CSP analogs inhibited bacteriocin production in S. mutans, as reported by co-cultures with commensal bacteria of the oral cavity. The peptide CSP1AA, bearing substitutions in the residues involved in QS receptor recognition and activation, reported the most significant quorum-quenching activities. Our findings provide new insights into specific chemical drivers in the CSP sequences controlling the interconnection between S. mutans and S. pneumoniae. We think that the results reported in this study open the way for new therapeutic interventions in controlling the virulence factors in complex microbial communities such as the oral microbiota.

Isolation and identification of a novel aerobic denitrifying bacterium with quorum quenching activity and the effect of environmental factors on its performance

A novel aerobic denitrifying bacterium capable of quorum quenching (QQ), Acinetobacter strain WZL728, was first isolated. WZL728 showed excellent aerobic denitrification performance and QQ activity. Besides, its optimal aerobic denitrification condition was pH 7.1, temperature 32.0 °C, C/N ratio 7.4 and shaking speed 108.0 rpm. However, its optimal QQ condition was pH 7.2, temperature 32.4 °C, C/N ratio 7.1 and shaking speed 96.1 rpm. The QQ activity of WZL728 was more tolerant to environmental changes than its aerobic denitrification performance because of the different response of its denitrification and QQ function genes expression. Moreover, it was revealed that the strain degraded N-acyl-homoserine lactones (AHLs) with long acyl chains by secreting extracellular QQ acylase. Due to the high QQ activity of the aerobic denitrifying bacterium, it may have great potential for controlling membrane biofouling in the field of wastewater treatment. • A novel aerobic denitrifier with QQ activity (WZL728) was isolated and identified. • WZL728 efficiently removed nitrate and degraded AHLs under aerobic conditions. • The QQ of WZL728 was more tolerant to environmental changes than denitrification. • WZL728 hydrolyzed AHLs with long acyl chains by secreting exogenous acylase.

Polyelectrolyte-silica composite quorum quenching biomedia as new antifouling agents for anaerobic membrane bioreactor treatment

Anaerobic membrane bioreactors (AnMBRs) have received increasing attention because of their low energy requirements; however, membrane fouling is the major deterrent to their widespread application. Here, we report a novel composite biomedium composed of quorum quenching (QQ) bacteria (Rhodococcus sp. BH4), porous silica, and polyelectrolytes for biofouling control in AnMBRs. The facultative character of BH4 is described for the first time, showing its QQ activity (the pseudo-first-order rate constant of degradation of N-octanoyl-l-homoserine lactone, 15.3–16.3 h−1) and biofilm inhibition (33–44 % reduction compared to the control) under anaerobic conditions. The results showed that the composite QQ media caused a significant delay in AnMBR membrane fouling (>2.5 and 1.9 times, respectively) compared to the cases with no or vacant media. The QQ media maintained >90 % of its original tensile strength after 40 days of use in the AnMBR, exhibiting more excellent durability than hydrogel-based media. QQ media contributed to the reduced production of biopolymers (e.g., proteins) and signal molecules (e.g., short- and medium-chain acyl-homoserine lactones) in the AnMBR. Finally, the QQ media did not impact anaerobic treatment performance, such as organic removal or methane production. The findings of this study demonstrate the QQ efficacy and sustainability of the BH4 strain and its composite media in AnMBRs.

Extracellular lactonase-mediated quorum quenching by a novel Bacillus velezensis.

Many Gram-negative bacteria coordinate their gene expression via quorum sensing (QS) mediated by small diffusible autoinducer molecules such as Acyl Homoserine Lactones (AHL). The degradation of AHLs or quorum quenching (QQ) imparts less selection pressure on the target organisms leading to a possible alternative to antimicrobial agents and traditional biofilm control methods. Here, a novel strain of Bacillus velezensis, strain PM7, exhibiting extracellular QQ activity against Gram-negative bacteria has been isolated. Analytical studies of the AHL degradation using LC-MS as well as bioreporters revealed the mechanism of QQ as homoserine lactone ring hydrolysis. Using molecular techniques, the presence of an aiiA homologues gene, specific for acyl homoserine lactonase enzyme, was confirmed in the bacterium. A biofilm inhibitory activity in the range of 36.9%-77.4% was achieved by the PM7 against three different Gram-negative bacteria. Moreover, a significant reduction (P<.05) in the QS-controlled traits such as violacein production in Chromobacterium violaceum (73%), swarming motility and prodigiosin production (67.2%) in Serratia marcescens, and exopolysaccharide production (97.9%) in Pseudomonas aeruginosa, was also observed. The extracellular and broad-spectrum lactonase of this novel strain can be beneficial for its use in QQ applications.

Multidrug-Resistant Biofilm, Quorum Sensing, Quorum Quenching, and Antibacterial Activities of Indole Derivatives as Potential Eradication Approaches.

Challenges encountered in relapse of illness caused by resistance of microorganisms to antimicrobial agents (drugs) are due to factors of severe stress initiated by random use of antibiotics and insufficient beneficial approaches. These challenges have resulted to multiple drug resistance (MDR) and, subsequently, biofilm formation. A type of intercellular communication signal called quorum sensing (QS) has been studied to cause the spread of resistance, thereby enabling a formation of stable community for microorganisms. The QS could be inhibited using QS inhibitors (QSIs) called quorum-quenching (QQ). The QQ is an antibiofilm agent. Indole derivatives from plant sources can serve as quorum-quenching eradication approach for biofilm, as well as a promising nontoxic antibiofilm agent. In other words, phytochemicals in plants help to control and prevent biofilm formation. It could be recommended that combination strategies of these indoles' derivatives with antibiotics would yield enhanced results.

Quorum Sensing Orchestrates Antibiotic Drug Resistance, Biofilm Formation, and Motility in Escherichia coli and Quorum Quenching Activities of Plant-derived Natural Products: A Review

Quorum sensing (QS) is a type of cell-to-cell communication that is influenced by an increase in signaling molecules known as autoinducers, which is correlated to the increase in the density of microbial communities. In this review, we aim to discuss and provide updates on the different signaling molecules used by Escherichia coli, such as acyl-homoserine lactone (AHL), autoinducer-2 (AI-2), and indole to influence key phenotypes such as antibiotic drug resistance, biofilm formation, and motility during quorum sensing. Based on the literature, E. coli signaling molecules have different functions during cell-to-cell communication such that the increase in AHL and indole was found to cause the modulation of antibiotic resistance and inhibition of biofilm formation and motility. Meanwhile, AI-2 is known to modulate biofilm formation, antibiotic resistance, and motility. On the other hand, in the existing literature, we found that various plants possess phytochemicals that can be used to alter QS and its downstream key phenotypes such as biofilm formation, swimming and swarming motility, and genes related to motility, curli and AI-2 production. However, the exact physiological and molecular mechanisms of these natural compounds are still understudied. Understanding the mechanisms of those phytochemicals during QS are therefore highly recommended to conduct as a necessary step for future scholars to develop drugs that target the actions of QS-signaling molecules and receptors linked to antibiotic resistance, biofilm formation, and motility without putting bacteria under stress, thereby preventing the development of drug resistance.

Synthesis and Evaluation of Quorum Quenching activity of Ag, TiO2 and ZnO metal nanoparticles against wild type and mutant strains of Chromobacterium violaceum

The conventional strategies to combat pathogenic microbes seem to be inefficient to curb the menace of pathogens. The bacterial biofilm is a product of the quorum sensing (QS) process mediated by acylhomoserine lactones (AHL) in many pathogens. The QS inhibitors or quorum quenching (QQ) molecules that disrupt bacterial communication offer an alternative promising strategy to lower antibiotic resistance in pathogens. The nanoparticles can exhibit QQ potential that interrupts cell-to-cell communication. In the present study, laboratory synthesized metal-based nanoparticles such as silver (Ag), titanium oxide(TiO2) and zinc oxide (ZnO) were characterized using powder X-Ray diffractometer, UV-Visible spectroscopy, EDS, Cyclic voltammetry and TEM imaging technique. Ag and TiO2 nanoparticles were synthesized by the green synthesis method in the form of quantum dots, which was evidenced from TEM images on a less than 7nm scale. Silver quantum dots with size variation from 2.4nm to 4.2nm and TiO2 with size ranging from 4.9nm to 8.5nm were detected. The synthesized nanoparticles were elucidated for their potential as QQ by employing both wild and mutant strains of Chromobacterium violaceum. Nanoparticles affected violacein pigment production in both the strains of C. violaceum. Lower concentrations of NPs did not show any considerable effect on the AHLdependent Quorum sensing system, however, at moderate to higher concentrations, metal NPs exhibit Quorum Q activity. Higher concentrations of AgNPs and ZnONPs (i.e. 250 ppm and above) show cell inhibitory activity. In the percent pigment(violacein) inhibition assay, maximum pigment inhibition was detected at a concentration range of 100-125ppm in both the strains of C. violaceum without inhibiting cell growth. In the case of TiO2NPs, maximum pigment inhibition was detected at 500ppm without affecting cell growth in both the strains of C. violaceum. The percent pigment inhibition observed in all nanoparticles was nearly similar in both strains of C. violaceum indicating that the mechanism of action of pigment inhibition is due to interference at the reception of the AHL signaling molecule.

New quorum quenching bacteria for controlling biofilm thickness in the membrane aerated biofilm reactor

The uncontrolled increase of biofilm thickness on the membrane surface directly affects substrate diffusion rate, pollutant removal efficiency, and microbial ecology of the membrane aerated biofilm reactor (MABR). This study aimed to control the biofilm growth using a promising antifouling strategy called quorum quenching (QQ). For this purpose, new QQ bacteria (Bacillus methylotrophicus BT1, Klebsiella pneumoniae BT2, Lysinibacillus fusiformis BT3, and Achromobacter xylosoxidans BT4) were isolated and immobilized to control the biofilm thickness on the membrane fibers in MABR. The Bacillus methylotrophicus BT1 with the highest QQ activity disrupted bacterial communication among microorganisms, provided a relatively thin and dense biofilm thickness (250 µm), and exhibited the best MABR performance. The amount of EPS secreted by the microorganisms significantly decreased due to the increase in the QQ activities of the QQ bacteria. A significant COD removal performance improvement of 74.5% compared to the control-MABR was achieved by MABR containing BT1. Microbial analysis revealed a change in the microbial community structure of biofilms in the MABRs containing different QQ bacteria. In conclusion, the newly isolated QQ bacteria effectively could be controlled biofilm formation on the membrane fibers in MABR systems, and the results obtained can form the basis for larger-scale studies.

Gentamicin Augments the Quorum Quenching Potential of Cinnamaldehyde In Vitro and Protects Caenorhabditis elegans From Pseudomonas aeruginosa Infection.

The quorum sensing (QS) circuitry of Pseudomonas aeruginosa represents an attractive target to attenuate bacterial virulence and antibiotic resistance. In this context, phytochemicals harboring anti-virulent properties have emerged as an alternative medicine to combat pseudomonal infections. Hence, this study was undertaken to investigate the synergistic effects and quorum quenching (QQ) potential of cinnamaldehyde (CiNN) in combination with gentamicin (GeN) against P. aeruginosa. The QQ activity of this novel combination was evaluated using a QS reporter strain and synergism was studied using chequerboard assays. Further, the genotypic and phenotypic expression of pseudomonal virulence factors was examined alongside biofilm formation. The combination of CiNN and GeN exhibited synergy and promising anti-QS activity. This drug combination was shown to suppress AHL production and downregulate the expression of critical QS genes in P. aeruginosa PAO1. Molecular docking revealed strong interactions between the QS receptors and CiNN, asserting its QQ potential. Bacterial motility was compromised along with a significant reduction in pyocyanin (72.3%), alginate (58.7%), rhamnolipid (33.6%), hemolysin (82.6%), protease (70.9%), and elastase (63.9%) production. The drug combination successfully eradicated preformed biofilms and inhibited biofilm formation by abrogating EPS production. Our findings suggest that although GeN alone could not attenuate QS, but was able to augment the anti-QS potential of CiNN. To validate our results using an infection model, we quantified the survival rates of Caenorhabditis elegans following PAO1 challenge. The combination significantly rescued C. elegans from PAO1 infection and improved its survival rate by 54% at 96 h. In summary, this study is the first to elucidate the mechanism behind the QQ prospects of CiNN (augmented in presence of GeN) by abrogating AHL production and increasing the survival rate of C. elegans, thereby highlighting its anti-virulent properties.

Exploring communication signals inside the microbial community of a Listeria monocytogenes-carrying biofilm contamination site

In nature, bacterial pathogens like L. monocytogenes, live in nature associated with other microbial species in spatially-structured communities called biofilms. In the food industry, biofilms contribute to the survival and persistence of L. monocytogenes within processing facilities, thereby enhancing its risk of cross-contaminating food products. The challenge of combating biofilms has triggered the search for new antibiofilm strategies including devising ways to interfere with cell communication mechanisms (quorum-sensing) that are known to be involved with biofilm development regulation. The aim of this study was to explore cell communication signals in a L. monocytogenes-carrying microbial community isolated from a meat processing plant (location No. 96) in order to elucidate the ecological interactions that could serve as a starting point for the development of new antibiofilm strategies. Quorum quenching (QQ) and quorum sensing (QS) activities were screened among 31 bacterial strains isolated from location No. 96. Whereas no QQ activity was detected against short-chain lactone N-hexanoyl-DL-homoserine lactone (C6-HSL), it was detected against N-dodecanoyl-DL-homoserine lactone (C12-HSL) in 7 isolates (23%), particularly in Pseudomonas monteilli, Rhodococcus sp. and Rhodococcus erythropolis. QS activity assays detected HC4, C4, C6, OC6, HC10 and C16 in all the extracts, being C4, C6 and OC6 with predominantly produced by Pseudomonas monteilli, Pseudomonas gesardii, Psychrobacter maritimus and Paracoccus sp. High production levels of C16-HSL by Paracoccus sp. and the role of this long-chain lactone as a self-inhibitor of cell aggregation led us to carry out further studies focused on the effects of a Paracoccus lactone extract (PLE) against the biofilm formation by L. monocytogenes. A quantitative microscopic analysis demonstrated a significant decrease (p < 0.05) in the area occupied by biofilms formed on stainless steel (SS) coupons by different strains of L. monocytogenes in the presence of PLEs. Conversely, no significant differences were observed in the total number of viable adhered cells on SS coupons with or without PLE. The observed effect was partially reproduced by the addition of pure C16-HSL to 24 h-biofilms of L. monocytogenes L1.96. These results demonstrate that the observed effects can be attributed, at least partially, to the HSLs contained in the PLE. Overall, the present results highlight how interspecies communication within a biofilm can open up new insights for the development of new ways to combat biofilm.

Isolation of Bacteria Capable of Degrading Various AHLs for Biofouling Control in Membrane Bioreactors

Membrane bioreactors (MBRs) are widely used to treat wastewater, mainly due to the production of high-quality effluent. However, biofilm forming on the surface of membranes can cause many problems, which remains one of the major limitations of this technique. Bacterial quorum quenching (QQ) has been proven to be a successful strategy to control biofouling in MBRs. However, for many QQ bacterial isolates, the detailed degradation rates of acyl homoserine lactones (AHLs) have rarely been reported. Therefore, this study aimed to isolate potential QQ bacteria and investigate their degradation rates against eight different AHLs. Results showed that four isolates (A9, A12, B11, and D3) exhibited consistent C8-HSL–(N-octanoyl-L-homoserine lactone) removal capabilities. These four isolates removed at least 70% of all AHLs tested within 180 min. They might have different QQ enzymes, based on our observation that the locations of enzyme activities differed. The bacteria most closely related to A9, A12, and B11 were Brucella anthropic, Bacillus cereus, and Bacillus toyonensis, respectively. Bacillus species have shown QQ activity in many studies, but AHL-reducing Brucella species have not been previously reported. Overall, this study extends our current knowledge of QQ bacteria that could be used to mitigate biofilm formation on MBR membranes.

Quorum Quenching Bacteria Bacillus velezensis DH82 on Biological Control of Vibrio parahaemolyticus for Sustainable Aquaculture of Litopenaeus vannamei

Aquatic pathogens such as Vibrio parahaemolyticus cause a bacterial infection that reduces the economic benefits of aquaculture and affects the food quality and safety of human beings. Quorum quenching (QQ) is considered a novel strategy of microbial antagonism that inhibits pathogens and reduces the abuse of antibiotics. This study investigates a QQ bacterial strain, Bacillus velezensis DH82 from the deep sea Yap trench, in vitro to examine the effects of DH82 and its functional products against V. parahaemolyticus, focusing on the Quorum sensing (QS) regulation and the inhibition of pathogenicity and bacterial growth. The study also conducted in vivo investigation in the aquaculture of Litopenaeus vannamei challenged with V. parahaemolyticus by immersion and injection challenge. The results of the QS regulator transcription level demonstrated the multiple QQ enzymes in DH82 regulated the pathogenicity but could not fully control the biofilm formation; the effective antibacterial activity of extracellular peptides on microbial antagonism verified the inhibition on bacterial growth of V. parahaemolyticus. The in vivo experiment in aquaria demonstrated the effective enrichment of DH82 and inhibition of Vibrio in both the aquatic system and the shrimp intestine. The dietary DH82 relieved the negative effect of Vibrio on the activity of enzyme acid phosphatase (ACP), alkaline phosphatase (AKP), superoxide dismutase (SOD) under challenge of Vibrio pathogens, and was not harmful to host according to lysozyme (LZM) activity. DH82 also ameliorated the damage to the intestine and muscles induced by V. parahaemolyticus infection according to tissue imaging. Though DH82 did present some dose-dependent adverse effects to the host, the findings revealed the effective QQ and antibacterial activity of DH82 on emerging biocontrol against V. parahaemolyticus, therefore indicating the potential application of DH82 as a biological control reagent in the sustainable and green production of aquaculture.

Bacillus subtilis BR4 derived stigmatellin Y interferes Pqs-PqsR mediated quorum sensing system of Pseudomonas aeruginosa.

Cell-to-cell communication is essentially required in bacteria for the production of multiple virulence factors and successful colonization in the host. Targeting the virulence factors production without hampering the growth of the pathogens is a potential strategy to control pathogenesis. To accomplish this, a total of 43 mangrove isolates were screened for quorum quenching (QQ) activity against Pseudomonas aeruginosa (PA), in which eight bacteria have shown antibiofilm activity without hampering the growth of the PA. Prominent QQ activity was observed in Bacillus subtilis BR4. Previously, we found that BR4 produces stigmatellin Y, a structural analogue of PQS signal of PA, which could competitively bind with PqsR receptor and inhibits the quorum sensing (QS) system of PA. Further, stigmatellin Y containing ethyl acetate extract (S-EAE) (100 µg ml-1 ) of BR4 significantly inhibits (p < 0.001) the biofilm formation of PA. Confocal laser scanning microscope (CLSM) and scanning electron microscope (SEM) analysis also fortified the QQ activity of BR4. Furthermore, S-EAE of BR4 (500 µg ml-1 ) has significantly reduced the production of virulence factors, including protease, elastase, pyocyanin and extracellular polysaccharides substances. Furthermore, liquid chromatography-mass spectrometry (LC-MS)/MS analysis affirms that BR4 intercepts the PQS-mediated QS system by reducing the synthesis of as many PQS signals, including precursor molecule (243.162313 Da) of PQS signal. Thus, S-EAE of B. subtilis BR4 could be used as a promising therapeutic agent to combat QS system-mediated pathogenesis of PA. Further therapeutic potentials of stigmatellin Y to be evaluated in clinical studies for the treatment of multidrug resistant PA.

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

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. A total of 94halotolerant 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 DZ16showed 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%. B. thuringiensis DZ16 and B. subtilis DZ17strains 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. 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.