Chromobacterium Violaceum CV026 Research Articles

Polyketides with quorum sensing inhibitory activity from the marine-derived fungus Aspergillus sp. ZF-79

Seven compounds were isolated from a marine-derived fungus Aspergillus sp. ZF-79, including three new polyketides (1–3), named asperochrins D-F, along with four known compounds 4–7. Their structures were determined on the basis of spectroscopic methods. All the compounds were tested for quorum sensing inhibitory (QSI) activity. Compounds 1, 3, 4, 5, and 6 exhibited QSI activity against Chromobacterium violaceum CV026 with MIC values of 50, 100, 50, 50, and 6.25 μM, respectively.

Synthesis and Biological Evaluation of Novel L-Homoserine Lactone Analogs as Quorum Sensing Inhibitors of Pseudomonas aeruginosa.

In this study, we synthesized four series of novel L-homoserine lactone analogs and evaluated their in vitro quorum sensing (QS) inhibitory activity against two biomonitor strains, Chromobacterium violaceum CV026 and Pseudomonas aeruginosa PAO1. Studies of the structure-activity relationships of the set of L-homoserine lactone analogs indicated that phenylurea-containing N-dithiocarbamated homoserine lactones are more potent than (Z)-4-bromo-5-(bromomethylene)-2(5H)-furanone (C30), a positive control for biofilm formation. In particular, compared with C30, QS inhibitor 11f significantly reduced the production of virulence factors (pyocyanin, elastase and rhamnolipid), swarming motility, the formation of biofilm and the mRNA level of QS-related genes regulated by the QS system of PAO1. These results reveal 11f as a potential lead compound for developing novel antibacterial quorum sensing inhibitors.

Occurrence of diversified N‐acyl homoserine lactone mediated biofilm‐forming bacteria in rice rhizoplane

Quorum sensing (QS)-mediated biofilm-forming rhizobacteria are indispensable due to their competitiveness in the crop rhizosphere. In the present work, we have reported on the occurrence of diversified bacterial species capable of producing N-acyl homoserine lactone (AHL) as the QS signal in the roots of arice plant grown under field conditions. The AHL-producing bacteria were directly isolated from the rice root by the biosensor reporter (Chromobacterium violaceum CV026) overlay method and characterized for biofilm production by the microtiter plate method. A total of 48 QS-positive bacterial isolates were purified from different aged (7, 20, 24, 26, and 36 days) rice seedlings. The in vitro biofilm production and genetic diversity as revealed by BOX-PCR fingerprinting showed high variability among the isolates. Most of the best biofilm-forming isolates produced aN-butyryl dl-homoserine lactone (a C4-AHL type) signal in the medium. The 16S ribosomal RNA (rRNA) gene sequence of these putative elite isolates identified that they were close to Aeromonas hydrophila (QS7-4; QS36-2), A. enteropelongenes (QS20-8), A. veronii (QS36-3), Enterobacter sp. (QS20-11), Klebsiella pneumoniae (QS24-6), Kosakonia cowanii (QS24-21), Providentia rettigeri (QS24-2), Sphingomonas aquatilis (QS24-17), and Pseudomonas sihuiensis (QS24-20). These strains profusely colonized the rice root upon inoculation and formed biofilms on the surface of the root under gnotobiotic conditions. Developing inoculants from these strains would ensure competitive colonization on the rhizoplane of the crop through their biofilm and thereby improve plant growth and health.

Tyrosol from marine Fungi, a novel Quorum sensing inhibitor against Chromobacterium violaceum and Pseudomonas aeruginosa

An ethyl acetate extracts isolated from a marine fungal strain, Penicillium chrysogenum DXY-1, obtained from marine sediments surrounding the East Sea, was found to exhibit anti-quorum sensing (anti-QS) activity. Interestingly, a novel active compound was identified as tyrosol by the purification and structural characterization. At a concentration of 0.5 mg/mL, tyrosol decreased QS-regulated violacein production in Chromobacterium violaceum CV026 by 53.5% and decreased QS-regulated pyocyanin production, elastase activity and proteolytic activity in Pseudomonas aeruginosa PA01 by 63.3%, 57.8% and 9.9%, respectively. SEM images showed that tyrosol inhibited biofilm formation in P. aeruginosa PA01 without having any effect on bacterial growth. Molecular docking results revealed that the natural signal molecule C6HSL and tyrosol bound to different receptor pockets of CviR, and tyrosol inhibited the QS activity of CviR in C. violaceum by binding to the DNA-binding domain and blocking pathogenic gene expression. All the data suggest that tyrosol may act as a potential inhibitor of the QS systems to solve the looming crisis of bacterial resistance. We believe that there are other active compounds with relatively high anti-QS activity or synergistic inhibitory effects on QS in the crude extract, which warrants further research.

Lactonase SsoPox modulates CRISPR-Cas expression in gram-negative proteobacteria using AHL-based quorum sensing systems

Quorum sensing (QS) is a molecular communication system that bacteria use to harmonize the regulation of genes in a cell density-dependent manner. In proteobacteria, QS is involved, among others, in virulence, biofilm formation or CRISPR-Cas gene regulation. Here, we report for the first time the effect of a QS-interfering enzyme to alter the regulation of CRISPR-Cas systems in model and clinical strains of Pseudomonas aeruginosa, as well as in the marine bacterium Chromobacterium violaceum CV12472. The expression of CRISPR-Cas genes decreased in most cases suggesting that enzymatic disruption of QS is promising for modulating phage-bacteria interactions.

Dimeric 1,4-benzoquinone Derivatives with Cytotoxic Activities from the Marine-Derived Fungus Penicillium sp. L129.

Two new dimeric 1,4-benzoquinone derivatives, peniquinone A (1) and peniquinone B (2), a new dibenzofuran penizofuran A (3), and a new pyrazinoquinazoline derivative quinadoline D (4), together with 13 known compounds (5–17), were isolated from a marine-derived fungus Penicillium sp. L129. Their structures, including absolute configurations, were elucidated by extensive spectroscopic data and electronic circular dichroism calculations. Compound 1 exhibited cytotoxicity against the MCF-7, U87 and PC3 cell lines with IC50 values of 12.39 µM, 9.01 µM and 14.59 µM, respectively, while compound 2 displayed relatively weak cytotoxicity activities against MCF-7, U87 and PC3 cell lines with IC50 values of 25.32 µM, 13.45 µM and 19.93 µM, respectively. Furthermore, compound 2 showed weak quorum sensing inhibitory activity against Chromobacterium violaceum CV026 with an MIC value of 20 μg/well.

3-Benzyl-Hexahydro-Pyrrolo[1,2-a]Pyrazine-1,4-Dione Extracted From Exiguobacterium indicum Showed Anti-biofilm Activity Against Pseudomonas aeruginosa by Attenuating Quorum Sensing.

Bacterial cell-to-cell communication promotes biofilm formation and can potentially lead to multidrug resistance development. Quorum sensing inhibition (QSI) is an effective and widely employed strategy against biofilm formation. The extract from Exiguobacterium indicum SJ16, a gram-positive bacterium, isolated from the rhizosphere of Cyperus laevigatus showed significant anti-quorum sensing activity (about 99%) against the reference Chromobacterium violaceum CV026 strain without exerting any antibacterial effect. The potentially active QSI compound identified in the SJ16 extract was 3-Benzyl-hexahydro-pyrrolo[1, 2-a]pyrazine-1,4-dione. The SJ16 extract containing this active compound showed significant anti-quorum sensing activity against a model quorum sensing bacterium strain Pseudomonas aeruginosa PAO1 and a clinical isolate P. aeruginosa PAH by preventing biofilm formation without attenuating the cell growth within the biofilm. More specifically, the SJ16 extract changed the topography and architecture of the biofilm, thus preventing bacterial adherence and further development of the biofilm. Furthermore, it decreased virulence factors (rhamnolipid and pyocyanin), the bacterial motility, as well as the elastase, and protease activities in P. aeruginosa. Microarray analysis revealed the differential expression of quorum sensing regulatory genes. Based on these results, we herein propose a hypothetical model, characterizing the role of this QSI agent in the transcriptional regulation of quorum sensing in P. aeruginosa PAO1, demonstrating that this compound has significant drug-development potential. Further research is required to delineate its possible applications in therapeutics in the context of biofilm forming bacterial infections.

English

Many pathogenic bacteria produce virulence factors controlled by a mechanism of regulation named quorum sensing (QS). Inhibition of bacterial QS system is a more recent therapeutic approach to counterbalance the emergence of multi-drug resistant bacteria. This study aimed to assess the abilities of methanol extract from Guiera senegalensis galls and its isolated compound methyl gallate to quench the quorum sensing system. Methanol extract from galls of G. senegalensis at the concentration of 100 µg/ml demonstrated significant inhibitory effect on pyocyanin and violacein production respectively in Pseudomonas aeruginosa PAO1 and Chromobacterium violaceum CV026. Colum chromatography and recycling High Performance Liquid Chromatography (HPLC) of methanol extract from galls of G. senegalensis led to the isolation of one active quorum quenching compound. Different spectroscopic methods (MS and NMR) were used to elucidate the structure of this isolated compound as being the methyl gallate (MG). Methyl gallate at the final concentration of 12.5 µg/ml demonstrated good anti-QS activity by inhibiting violacein and pyocyanin production. Its low molecular weight and the capacity to interfere with the mechanism of QS make methyl gallate, an interesting candidate for development of drugs as an alternative to antibiotics to combat bacterial resistance. Key words: Guiera senegalensis, methyl gallate, Pseudomonas aeruginosa PAO1, quorum sensing.

Production of cross-domain signalling molecules by Halophilic archaea

Cell-cell communication through the production of autoinducer molecules has been widely studied in bacteria and found to play a pivotal role in biofilm formation and gene regulation. Quorum Sensing (QS) within the domain Archaea is understudied compared with their bacterial counterparts. The aim of this study was to determine whether archaea are capable of cross-kingdom signalling through the production of QS inducing compounds and QS inhibitory activities. A combination of culture-dependent (crude extracts from archaeal isolates) and culture-independent (genomic mining) techniques were employed to investigate the production of compounds capable of modulating bacterial QS. Crude archaeal extracts were screened for activity using the bioreporter strains Agrobacterium tumefaciens ATCC BAA-2240, Escherichia coli JM109 pSB536, pSB401 and pSB1142, Chromobacterium violaceum CV026 and Pseudomonas aeruginosa MW-1. Active strains were further characterised using initial bio-assay guided fractionation. Preliminary results revealed different strains were capable of eliciting a QS response in the bacterial bio-reporters. Initial characterisation using LC-MS, TLC-overlays, and other biochemical tests, suggests the possible production of Butyryl Homoserine Lactones or homologs of this molecule by at least one of the strains. Conversely, other halophilic archaea were capable of inhibiting the production of QS-controlled pathways, as demonstrated by the reduction in virulence factor production by P. aeruginosa. Further characterisation of these compounds will prove to be an invaluable insight into the poorly understood mechanisms behind archaeal QS and equally will reveal the role of these compounds in cross-kingdom signalling.

Anti-quorum sensing of Galla chinensis and Coptis chinensis on bacteria

This study was to develop the quorum sensing (QS) inhibitors from Traditional Chinese Medicinal Plants (TCMs). The water extracts of twenty-nine plants were screened for quorum sensing inhibitory (QSI) activity using two biomonitor strains, Chromobacterium violaceum CV026 (CV026), Agrobacterium tumefaciens A136 (A136). Two of the plants, Galla chinensis and Coptis chinensis, showed a good QS inhibition capacity far below their MIC values, and no effect on their growths. The inhibition zones were 5.16 mm and 12.50 mm for CV026 respectively, and the production of violacein were decreased by 34.5% and 50.44% at 100 μg/mL respectively. QS-mediated β-galactosidase activity in A136 was inhibited strongly of 33.20% at 100 μg/mL by Galla chinensis while Coptis chinensis showed no inhibition. The QS-regulated virulence factors, including swarming motility and biofilm on Pseudomonas aeruginosa PAO1 were inhibited significantly at 10, 50 and 100 μg/mL respectively (P < 0.05). The higher the sub-MIC concentration, the greater the inhibitory effect on the production of violacein, β-galactosidase activity, swarming motility or biofilm formation, showing a good dose-dependent manner (r = 0.9286–0.9999). These findings may be helpful to provide a new aspect regarding the treatment of bacterial infections under a lower concentration of the TCMs.

Identification and characterization of a long-chain N-acyl homoserine lactone from Rhizobium sp. isolated from Zea x mays rhizosphere

The microbiological study of maize rhizosphere (Zea x mays) cultivated in Brazil led to the isolation of a bacterium, which was identified as Rhizobium sp. based upon 16 S rRNA analysis. The chemical study of fractions obtained from bacterium extract allowed the identification of the compound N-(3-oxo-tetradec-7-enoyl)-homoserine lactone (1) using uni and bidimensional nuclear magnetic resonance spectroscopy (NMR), gas chromatography coupled to low resolution electron impact mass spectrometry (GC–MS), and ultra-high resolution Qq-time-of-flight mass spectrometry (UHR-QqTOF-MS). Biological assays with the strains Agrobacterium tumefasciens A136 and Chromobacterium violaceum CV026 were also performed and showed negative results, corroborating the hypothesis of production of only the long chain acyl homoserine lactone (AHL) 1, and the lack of presence of short or medium chain homologues, as observed by instrumental GC–MS and NMR analyses. The chemotaxonomic relevance of the presence of long chain AHL in Rhizobiaceae was discussed.

SCREENING FOR ANTI-QUORUM SENSING AND ANTI-BIOFILM ACTIVITY IN Viscum album L. EXTRACTS AND ITS BIOCHEMICAL COMPOSITION

Many opportunistic pathogenic bacteria use the Quorum Sensing (QS) system to coordinate their virulence expressions. Thus, QS can likely be a new approach to control bacterial infections. The aim of this study was to evaluate the antimicrobial, anti-biofilm, and anti-quorum sensing activities of ethanol, chloroform, and dichloromethane: methanol extracts of leaf, stem, and fruits of the European mistletoe Viscum album L. on 2 Gram-positive and 7 Gram-negative pathogenic bacteria. The extracts at concentrations ranging from 50 to 250mg/ml were tested depending on the extracts of the plant parts and the test bacteria. The extract with 50mg/ml concentration, in which no antimicrobial activity was observed, was used for anti-quorum sensing and antibiofilm studies. The dichloromethane: methanol extracts were found to show the highest biological activities. QS activities of the plant extracts were also determined using the recently established Chromobacterium violaceum CV026 reporter strain and the signaling molecule N-(ß-ketocaproyl)-L-homoserine lactone (3-oxo-C6-HSL) agar well diffusion assay. Biofilm was quantified using the microtiter plate test and the crystal violet assay. Anti-microbial, anti-biofilm, and anti-quorum sensing activity of leaf and stem extracts showed higher efficiency than fruit extracts. It was concluded that the extracts of V. album had the potential to treat microbial infections by biofilm inhibition or inhibition of QS.

Overexpressed recombinant quorum quenching lactonase reduces the virulence, motility and biofilm formation of multidrug-resistant Pseudomonas aeruginosa clinical isolates.

The increasing occurrence of resistance among Pseudomonas aeruginosa clinical isolates necessitates finding alternatives to antibiotics for controlling the infection of such pathogenic bacteria. In this study, lactonase gene ahl-1 from Bacillus weihenstephanensis isolate-P65 was successfully cloned and expressed in Escherichia coli BL21 (DE3) under the control of T7 promoter for utilizing its quorum quenching activity against three multidrug-resistant (MDR) P. aeruginosa clinical isolates. The biological activity of the overexpressed lactonase enzyme (Ahl-1), tested using a synthetic signal and Chromobacterium violaceum CV026 as a biosensor, displayed good catalytic activity using hexanoyl homoserine lactone (HHL) as a substrate and Chromobacterium violaceum (CV026) as a biosensor (77.2 and 133nmmin-1 for the crude and the purified Ahl-lactonase enzymes, respectively). Upon challenging its ability to inhibit the virulence of three MDR P. aeruginosa clinical isolates, recombinant Ahl-1 successfully prevented the accumulation of acylhomoserine lactone signals resulting in a significant reduction in the investigated virulence determinants; protease (from 40 up to 75.5%), pyocyanin (48-75.9%), and rhamnolipids (52.7-63.4%) (P value < 0.05). Ahl-1 also displayed significant inhibitory activities on the swarming motility and biofilm formation of the three tested MDR P. aeruginosa clinical isolates (P value < 0.05). Consequently, Ahl-1 lactonase enzyme in this study is considered a promising therapeutic agent to inhibit P. aeruginosa pathogenicity with no fear of emergence of resistance.

Characterization of a Novel N-Acylhomoserine Lactonase RmmL from Ruegeria mobilis YJ3.

Gram-negative bacteria utilize N-acylhomoserine lactones (AHLs) as quorum sensing (QS) signaling molecules for intercellular communication. Cell-to-cell communication depends on cell population density, and AHL-dependent QS is related to the production of multiple genes including virulence factors. Quorum quenching (QQ), signal inactivation by enzymatic degradation, is a potential strategy for attenuating QS regulated bacterial infections. Both Gram-positive and -negative bacteria have QQ enzymes that can degrade AHLs. In our previous study, strain Ruegeria mobilis YJ3, isolated from healthy shrimp, showed strong AHLs degradative activity. In the current study, an AHL lactonase (designated RmmL) was cloned and characterized from Ruegeria mobilis YJ3. Amino acid sequence analysis showed that RmmL has a conserved “HXHXDH” motif and clusters together with lactonase AidC that belongs to the metallo-β-lactamase superfamily. Recombinant RmmL could degrade either short- or long-chain AHLs in vitro. High-performance liquid chromatography analysis indicated that RmmL works as an AHL lactonase catalyzing AHL ring-opening by hydrolyzing lactones. Furthermore, RmmL can reduce the production of pyocyanin by Pseudomonas aeruginosa PAO1, while for the violacein and the extracellular protease activities by Chromobacterium violaceum CV026 and Vibrio anguillarum VIB72, no significant reduction was observed. This study suggests that RmmL might be used as a therapeutic agent in aquaculture.

The effect of the N-acyl-homoserine lactonase on the properties of Pectobacterium betavasculorum

Bacteria use quorum sensing (QS) as a mechanism of cell to cell communication that enables them to coordinate essential behaviours. To study the role of QS regulation in directing the cellular processes and virulence of Pectobacterium betavasculorum, the effect of the aiiA gene on this bacterium was investigated. In this study, plasmid pVLT33/aiiA was introduced into bacterial cells to gain Pb/pVLT33/aiiA. The pVLT33/aiiA plasmid contains a heterologous aiiA gene (encoding AiiA enzyme), which catalyzes the degradation of QS signalling molecules of the of N-acyl-homoserine lactones (AHLs). An absence or reduction of AHLs in enclosed medium was assessed with the biosensor Chromobacterium violaceum CV026 in a co-culture assay. To evaluate the effects of AHL on virulence behaviour of the mutated P. betavasculorum, motility, biofilm formation and pathogenicity assays on potato tubers were performed. The results revealed that swimming motility and biofilm formation in the Pb/pVLT33/aiiA strain were significantly influenced, while the introduction of the aiiA gene had no effect on the hypersensitive response. The enzymatic bioassay revealed that the aiiA gene completely abolished secretion of pectate lyase (Pel) and polygalacturonase (Peh) enzymes, while the breakdown of cellulose was slightly reduced. Furthermore, aiiA expression in P. betavasculorum caused reduction of tissue maceration and pathogenicity on potato tubers and cactus. It can be concluded that the main virulence behaviours of P. betavasculorum are controlled by the QS system. Hence, application of anti-QS mechanisms is a promising strategy for the prevention of diseases in which virulence is regulated by QS.

Screening of quorum quenching activity of the bacteria isolated from dairy industry waste activated sludge

Intercellular bacterial communication process via exchange of signalling molecules acyl homoserine lactone results in various group activities like bioluminescence, antibiotic production, biofilm formation, sporulation, and virulence. The signalling molecules are targeted, and the communication is interrupted by a group of bacteria termed quorum quenching bacteria. The present study aims to isolate the quorum quenching bacteria from the waste activated sludge collected from the dairy industry effluent treatment plant and explore for its quorum quenching potential. The bacteria were cultured in the KG medium containing n-hexanoyl homoserine lactone as a sole source of carbon and nitrogen. The isolates were identified by the 16S ribosomal deoxyribonucleic acid analysis and subsequently were evaluated for its quorum quenching activity through Chromobacterium violaceum CV026 biosensor assay. The n-hexanoyl homoserine lactone degradation was quantified by GC–MS analysis. The 16S ribosomal deoxyribonucleic acid analysis revealed the isolated bacteria as Klebsiella pneumoniae (JYQ1 and JYQ5), Acinetobacter baumannii JYQ2, Pseudomonas nitroreducens JYQ3, and Pseudomonas JYQ4. The biosensor strain assay and GC–MS analysis indicated that all the isolates possessed an inherent ability to degrade N-hexanoyl homoserine lactone. The strain Pseudomonas JYQ4 exhibited the highest quorum quenching activity of 84 ± 3.3% within 6 h of incubation. The strain A. baumannii JYQ2 acted both as quorum sensing and as quorum quenching bacteria as evidenced by the decrease in quorum quenching from 79 ± 3.1 to 76.8 ± 2.5%.

Detection of New Quorum Sensing N-Acyl Homoserine Lactones From Aeromonas veronii.

Sturgeon is an important fresh water-culture fish in China. A problem with sturgeon is its high susceptibility to spoilage. Food spoilage is reported to be regulated by quorum sensing (QS). To identify the QS signals acetylated homoserine lactones (AHLs) in sturgeon and test whether QS plays a role in the spoilage of sturgeon, we investigated the specific spoilage organisms (SSOs) in vacuum packaged sturgeon stored at 4°C and the production of AHLs by sturgeon SSOs. 16S rDNA sequencing and spoilage capabilities analysis revealed that Aeromonas veronii LP-11, Citrobacter freundii LPJ-2, and Raoultella ornithinolytica LPC-3 were the SSOs in sturgeon. Among the three SSOs, only A. veronii LP-11 induced the QS biosensors Agrobacterium tumefaciens KYC55 and Chromobacterium violaceum CV026, suggesting that it produced AHLs. Analysis by thin layer chromatography, high-performance liquid chromatography-triple quadrupole tandem mass spectrometry, and high-performance liquid chromatography quadrupole time-of-flight mass spectrometry (HPLC/qTOF-MS) identified that the AHLs produced by A. veronii were C6-SHL, C8-HSL, 3-oxo-C8-HSL, and 3-OH-C8-HSL. Our study revealed that QS system was probably involved in the regulation of sturgeon spoilage and for the first time reported the production of C8-HSL and 3-OH-C8-HSL by genus Aeromonas. As only HPLC/qTOF-MS effectively and accurately identified all the four AHLs produced by A. veronii LP-11, this study also showed that HPLC/qTOF-MS was the most efficient method for rapid analysis of AHLs in complex microbial sample. The study provides new insight into the microbiology of sturgeon spoilage which may be helpful for better sturgeon preservation.

Cloning and characterization of short-chain N-acyl homoserine lactone-producing Enterobacter asburiae strain L1 from lettuce leaves.

In gram‐negative bacteria, bacterial communication or quorum sensing (QS) is achieved using common signaling molecules known as N‐acyl homoserine lactones (AHL). We have previously reported the genome of AHL‐producing bacterium, Enterobacter asburiae strain L1. In silico analysis of the strain L1 genome revealed the presence of a pair of luxI/R genes responsible for AHL‐type QS, designated as easIR. In this work, the 639 bp luxI homolog, encoding 212 amino acids, have been cloned and overexpressed in Escherichia coli BL21 (DE3)pLysS. The purified protein (~25 kDa) shares high similarity to several members of the LuxI family among different E asburiae strains. Our findings showed that the heterologously expressed EasI protein has activated violacein production by AHL biosensor Chromobacterium violaceum CV026 as the wild‐type E. asburiae. The mass spectrometry analysis showed the production of N‐butanoyl homoserine lactone and N–hexanoyl homoserine lactone from induced E. coli harboring the recombinant EasI, suggesting that EasI is a functional AHL synthase. E. asburiae strain L1 was also shown to possess biofilm‐forming characteristic activity using crystal violet binding assay. This is the first report on cloning and characterization of the luxI homolog from E. asburiae.

Identification of natural product compounds as quorum sensing inhibitors in Pseudomonas fluorescens P07 through virtual screening

Pseudomonas fluorescens, a Gram-negative psychrotrophic bacteria, is the main microorganism causing spoilage of chilled raw milk and aquatic products. Quorum sensing (QS) widely exists in bacteria to monitor their population densities and regulate numerous physiological activities, such as the secretion of siderophores, swarming motility and biofilm formation. Thus, searching for quorum sensing inhibitors (QSIs) may be another promising way to control the deterioration of food caused by P. fluorescens. Here, we screened a traditional Chinese medicine (TCM) database to discover potential QSIs with lesser toxicity. The gene sequences of LuxI- and LuxR-type proteins of P. fluorescens P07 were obtained through whole-genome sequencing. In addition, the protein structures built by homology modelling were used as targets to screen for QSIs. Twenty-one compounds with a dock score greater than 6 were purchased and tested by biosensor strains (Chromobacterium violaceum CV026 and Agrobacterium tumefaciens A136). The results showed that 10 of the compounds were determined as hits (hit rate: 66.67%). Benzyl alcohol, rhodinyl formate and houttuynine were effective QSIs. The impact of the most active compound (benzyl alcohol) on the phenotypes of P. fluorescens P07, including swimming and swarming motility, production of extracellular enzymes and siderophores, N-acylhomoserine lactone (AHLs) content and biofilm formation were determined. The inhibitory mechanism of benzyl alcohol on the QS system of P. fluorescens P07 is further discussed. This study reveals the feasibility of searching for novel QSIs through virtual screening.

Anti-Quorum Sensing Potential of Antioxidant Quercetin and Resveratrol

ABSTRACT Quorum sensing system plays an active role in the regulation of pathogenicity of many microorganisms. Inhibition of pathogenicity or virulence factors will increase the success of treatment by preventing the development of antibiotic resistance. In this study, anti-quorum sensing activities of quercetin and resveratrol compounds, which have antioxidant property without damaging to host, have been determined via using biosensor bacteria: Chromobacterium violaceum ATCC 12472 and Chromobacterium violaceum CV026. As quorum sensing inhibitors, quercetin and resveratrol's cutting off the bacterial communication will prevent the treatment failures caused by the development of bacterial resistance. The development of layered drugs with antioxidant compounds such as quercetin and resveratrol will pave the way for new horizons for new therapeutic strategies.