The quorum sensing SinI/R system contributes to cadmium immobilization in Ensifer adhaerens NER9 in the cadmium-contaminated solution.

In this study, the cadmium (Cd)-tolerant Ensifer adhaerens strain NER9 with quorum sensing (QS) systems (responsible for N-acyl homoserine lactone (AHL) production) was characterized for QS system-mediated Cd immobilization and the underlying mechanisms involved. Whole-genome sequence analysis revealed that strain NER9 contains the QS SinI/R and TraI/R systems. Strains NER9 and the NER9∆sinI/R, NER9∆traI/R, and NER9∆sinI/R-traI/R mutants were constructed and compared for QS SinI/R and TraI/R system-mediated Cd immobilization in the solution and the mechanisms involved. After 24 h of incubation, strain NER9 significantly decreased the Cd concentration in the Cd-contaminated solution compared with the NER9∆sinI/R, NER9∆traI/R, and NER9∆sinI/R-traI/R mutants. The NER9∆sinI/R mutant had a greater impact on Cd immobilization and a lower impact on the activities of AHLs than did the NER9∆traI/R mutant. The NER9∆sinI/R mutant had significantly greater Cd concentrations and lower cell wall- and exopolysaccharide (EPS)-adsorbed Cd contents than did strain NER9. Furthermore, the NER9∆sinI/R mutant presented a decrease in the number of functional groups interacting with Cd, compared with strain NER9. These results suggested that the SinI/R system in strain NER9 contributed to Cd immobilization by mediating cell wall- and EPS-adsorption in Cd-containing solution.

Cultivation of phosphate-accumulating biofilm: Study of the effects of acyl-homoserine lactones (AHLs) and cyclic dimeric guanosine monophosphate (c-di-GMP) on the formation of biofilm and the enhancement of phosphate metabolism capacity.

This study investigated the mechanisms of microbial growth and metabolism during biofilm cultivation in the biofilm sequencing batch reactor (BSBR) process for phosphate (P) enrichment. The results showed that the sludge discharge was key to biofilm growth, as it terminated the competition for carbon (C) source between the nascent biofilm and the activated sludge. For the tested reactor, after the sludge discharge on 18 d, P metabolism and C source utilization improved significantly, and the biofilm grew rapidly. The P concentration of the recovery liquid reached up to 157.08 mg/L, which was sufficient for further P recovery via mineralization. Meta-omics methods were used to analyze metabolic pathways and functional genes in microbial growth during biofilm cultivation. It appeared that the sludge discharge activated the key genes of P metabolism and inhibited the key genes of C metabolism, which strengthened the polyphosphate-accumulating metabolism (PAM) as a result. The sludge discharge not only changed the types of polyphosphate-accumulating organisms (PAOs) but also promoted the growth of dominant PAOs. Before the sludge discharge, the necessary metabolic abilities that were spread among different microorganisms gradually concentrated into a small number of PAOs, and after the sludge discharge, they further concentrated into Candidatus_Contendobacter (P3) and Candidatus_Accumulibacter (P17). The messenger molecule C-di-GMP, produced mostly by P3 and P17, facilitated P enrichment by regulating cellular P and C metabolism. The glycogen-accumulating organism (GAO) Candidatus_Competibacter secreted N-Acyl homoserine lactones (AHLs), which stimulated the secretion of protein in extracellular polymeric substances (EPS), thus promoting the adhesion of microorganisms to biofilm and improving P metabolism via EPS-based P adsorption. Under the combined action of the dominant GAOs and PAOs, AHLs and C-di-GMP mediated QS to promote biofilm development and P enrichment. The research provides theoretical support for the cultivation of biofilm and its wider application.

Pseudomonas fuscovaginae quorum sensing studies: 5% dominates cell-to-cell conversations.

A common feature of N-acyl-l-homoserine lactone (AHL) quorum-sensing (QS) systems is that the AHL signal is autoinducing. Once induced, a cell will further amplify the signal via a positive feedback loop. Pseudomonas fuscovaginae UPB0736 has two fully functional AHL QS systems, called PfsI/R and PfvI/R, which are inactive in a standard laboratory setting. In this work, we induce the QS systems with exogenous AHL signals and characterize the AHL signal amplification effect and QS activation dynamics at community and single-cell level. While the cognate signal is in both cases significantly further amplified to physiologically relevant levels, we observe only a limited response in terms of AHL synthase gene promoter activity. Additionally, the PfsI/R QS system exhibits a unique dramatic phenotypic heterogeneity, where only up to 5% of all cells amplify the signal further and are, thus, considered to be QS active. IMPORTANCE: Bacteria use N-acyl-l-homoserine lactone (AHL) quorum-sensing (QS) systems for population-wide phenotypic coordination. The QS configuration in Pseudomonas fuscovaginae is dramatically different from other model examples of AHL QS signaling and, thus, represents an important exception to the norm, which usually states that QS triggers population-wide phenotypic transitions in relation to cell density. We argue that the differences in QS dynamics of P. fuscovaginae highlight its different evolutionary purpose, which is ultimately dictated by the selective pressures of its natural habitat. We hope that this example will further expand our understanding of the complex and yet unknown QS-enabled sociomicrobiology. Furthermore, we argue that exemptions to the QS norm will be found in other plant-pathogenic bacterial strains that grow in similar environments and that molecularly similar QS systems do not necessarily share a similar evolutionary purpose; therefore, generalizations about bacterial cell-to-cell signaling systems function should be avoided.

Improvement of violacein production using abiotic stresses and microbial adaptation.

The aim of the current research was to improve violacein production with Janthinobacterium lividum using abiotic stresses and bacterial adaptation against stress. Initially, the effect of carbon sources and the medium volume: air ratio on violacein production was assessed. Then, the production of violacein under hydrogen peroxide (H2O2) and ampicillin (Amp) stresses and acyl homoserine lactone (AHL) was evaluated. In the next step, J. lividum was adapted against increased concentrations of Amp. Finally, the production of violacein was analyzed in adapted bacterium cultivated in the presence of optimal amounts of H2O2, Amp, and AHL. The alterations in the expression of some of genes involved in violacein production was evaluated using Real-time PCR (RT-PCR). The highest amount of violacein was achieved using medium volume: air ratio of 10% v/v (in 100 ml flasks) and glycerol as carbon source. Also, H2O2 (103 mg/l) and Amp (130 mg/l) stresses increased the production of violacein significantly compared to normal conditions (57 mg/l) and violacein production in the presence of crude AHL increased from 56 mg/l to 210 mg/l. The production of violacein with adapted bacterium under the above-mentioned stresses and AHL was about 1.3 g/l. RT-PCR results showed that the expression of the AHL encoding gene (luxI) was repressed in the presence of stresses and glycerol. Also, the expression of vioA increased in the presence of Amp but H2O2 had no significant effect on vioA expression. Totally, we showed that microbial adaptation and abiotic stresses are cost-effective methods to generate significant improvement in violacein production.

Potential of the quorum-quenching and plant-growth promoting halotolerant Bacillus toyonensis AA1EC1 as biocontrol agent.

The use of fertilizers and pesticides to control plant diseases is widespread in intensive farming causing adverse effects together with the development of antimicrobial resistance pathogens. As the virulence of many Gram-negative phytopathogens is controlled by N-acyl-homoserine lactones (AHLs), the enzymatic disruption of this type of quorum-sensing (QS) signal molecules, mechanism known as quorum quenching (QQ), has been proposed as a promising alternative antivirulence therapy. In this study, a novel strain of Bacillus toyonensis isolated from the halophyte plant Arthrocaulon sp. exhibited numerous traits associated with plant growth promotion (PGP) and degraded a broad range of AHLs. Three lactonases and an acylase enzymes were identified in the bacterial genome and verified in vitro. The AHL-degrading activity of strain AA1EC1 significantly attenuated the virulence of relevant phytopathogens causing reduction of soft rot symptoms on potato and carrots. In vivo assays showed that strain AA1EC1 significantly increased plant length, stem width, root and aerial dry weights and total weight of tomato and protected plants against Pseudomonas syringae pv. tomato. To our knowledge, this is the first report to demonstrate PGP and QQ activities in the species B. toyonensis that make this strain as a promising phytostimulant and biocontrol agent.

Decoding Microcystis aeruginosa quorum sensing through AHL-mediated transcriptomic molecular regulation mechanisms.

Acyl-homoserine lactone (AHL) serves as a key signaling molecule for quorum sensing (QS) in bacteria. QS-related genes and physiological processes in Microcystis aeruginosa remain elusive. In this study, we elucidated the regulatory role of AHL-mediated QS in M. aeruginosa. Using AHL activity extract and transcriptomic analysis, we revealed significant effects of the AHL on growth and photosynthesis. AHL significantly increased chlorophyll a (Chl-a) content and accelerated photosynthetic rate thereby promoting growth. Transcriptome analysis revealed that AHL stimulated the up-regulation of photosynthesis-related genes (apcABF, petE, psaBFK, psbUV, etc.) as well as nitrogen metabolism and ribosomal metabolism. In addition, AHL-regulated pathways are associated with lipopolysaccharide and phenazine synthesis. Our findings deepen the understanding of the QS system in M. aeruginosa and are important for gaining insights into the role of QS in Microcystis bloom formation. It also provides new insights into the prevalence of M. aeruginosa in water blooms.

Engineering quorum quenching acylases with improved kinetic and biochemical properties.

Many Gram-negative bacteria use N-acyl-L-homoserine lactone (AHL) signals to coordinate phenotypes such as biofilm formation and virulence factor production. Quorum-quenching enzymes, such as AHL acylases, chemically degrade these molecules which prevents signal reception by bacteria and inhibits undesirable biofilm-related traits. These capabilities make acylases appealing candidates for controlling microbes, yet candidates with high activity levels and substrate specificity and that are capable of being formulated into materials are needed. In this work, we undertook engineering efforts against two AHL acylases, PvdQ and MacQ, to generate these improved properties using the Protein One-Stop Shop Server. The engineering of acylases is complicated by low-throughput enzymatic assays. Alleviating this challenge, we report a time-course kinetic assay for AHL acylases that monitors the real-time production of homoserine lactone. Using the assay, we identified variants of PvdQ that were significantly stabilized, with melting point increases of up to 13.2°C, which translated into high resistance against organic solvents and increased compatibility with material coatings. While the MacQ mutants were unexpectedly destabilized, they had considerably improved kinetic properties, with >10-fold increases against N-butyryl-L-homoserine lactone and N-hexanoyl-L-homoserine lactone. Accordingly, these changes resulted in increased quenching abilities using a biosensor model and greater inhibition of virulence factor production of Pseudomonas aeruginosa PA14. While the crystal structure of one of the MacQ variants, M1, did not reveal obvious structural determinants explaining the observed changes in kinetics, it allowed for the capture of an acyl-enzyme intermediate that confirms a previously hypothesized catalytic mechanism of AHL acylases.

AHL-Based Quorum Sensing Regulates the Biosynthesis of a Variety of Bioactive Molecules in Bacteria.

Bacteria are social microorganisms that use communication systems known as quorum sensing (QS) to regulate diverse cellular behaviors including the production of various secreted molecules. Bacterial secondary metabolites are widely studied for their bioactivities including antibiotic, antifungal, antiparasitic, and cytotoxic compounds. Besides playing a crucial role in natural bacterial niches and intermicrobial competition by targeting neighboring organisms and conferring survival advantages to the producer, these bioactive molecules may be of prime interest to develop new antimicrobials or anticancer therapies. This review focuses on bioactive compounds produced under acyl homoserine lactone-based QS regulation by Gram-negative bacteria that are pathogenic to humans and animals, including the Burkholderia, Serratia, Pseudomonas, Chromobacterium, and Pseudoalteromonas genera. The synthesis, regulation, chemical nature, biocidal effects, and potential applications of these identified toxic molecules are presented and discussed in light of their role in microbial interactions.

The second messenger (cyclic diguanylate and autoinducer-2) promotes N-acylated-homoserine lactones-based quorum sensing for enhanced recovery of stored aerobic granular sludge.

Efficient quorum sensing (QS) response is the premise for recovering the activities of stored aerobic granular sludge (AGS). This study aims to explore the crosstalk between the secondary messenger and the N-acylated-homoserine lactones (AHLs) to yield protein-rich granules efficiently from stored AGS by enhancing its QS efficiency selectively. 80 nmol/L cyclic diguanylate (c-di-GMP) with 20 nmol/L AHLs could increase the activity of isocitrate lyase activity (ICD) by 89 % and isocitrate dehydrogenase activity (ICDHc) by 113.5 %, to accelerate the tricarboxylic acid (TCA) cycle for yielding excess proteins by 166.4 %. In contrast, 80 nmol/L autoinducer-2 (AI-2) with 20 nmol/L AHLs could increase the activities of ICD and ICDHc by 485 % and 54.5 %, respectively, accelerating the glyoxylate (GCA) cycle to activate fat acid synthesis for stimulating polysaccharides (PS) secretion by 137.9 %. The strategy with c-di-GMP successfully recovers the refrigerated-stored and dried-stored AGS into proteins-rich AGS, with enriched functional strains for the PN secretion.

Quorum sensing regulation in Microcystis aeruginosa: Insights into AHL-mediated physiological processes and MC-LR production.

Quorum sensing (QS) is a widespread regulatory mechanism in Gram-negative bacteria, primarily involving the secretion of N-acyl homoserine lactone (AHL) to facilitate population density sensing. However, the existence of QS in blue-green algae, a subset of photoautotrophic Gram-negative bacteria forming high-density communities in water blooms, remains elusive. This study delves into the unexplored realm of QS in Microcystis aeruginosa (M. aeruginosa) by investigating AHL-related regulatory mechanisms and their impact on various physiological processes. Utilizing high-performance liquid chromatography coupled with mass spectrometry (HPLC-MS) and biosensors, a hitherto unknown long-chain AHL exhibiting a mass-to-charge ratio of 318 was identified in sterile M. aeruginosa cultures. Our investigation focused on discerning correlations between AHL activity fluctuations and key parameters such as microcystin (MC-LR) production, algal density, photosynthesis, buoyancy, and aggregation. Furthermore, the AHL extract was introduced during the logarithmic stage of M. aeruginosa cultures to observe the response in physiological processes. The results revealed that AHL, functioning as an autoinducer (AI), positively influenced algal growth and photosynthesis, as evidenced by the upregulated photosynthetic conversion efficiency of PSI and chlorophyll synthesis gene (psbA). AI also played a crucial role in altering surface characteristics through the synthesis of polysaccharides and proteins in EPS, subsequently promoting cell aggregation. Concomitantly, AI upregulated mcyD, enhancing the synthesis of MC-LR. Notably, our investigation pinpointed the initiation of QS in Microcystis at a density of approximately 1.22 × 10^7 cells/mL. This groundbreaking evidence underscores the regulatory role of AI in governing the physiological processes of growth, aggregation, buoyancy, and MC-LR production by activating pertinent gene expressions. This study significantly expands the understanding of QS in AHL, providing crucial insights into the regulatory networks operating in blue-green algae.

Deciphering the potential role of quorum quenching in efficient aerobic denitrification driven by a synthetic microbial community.

Low efficiency is one of the main challenges for the application of aerobic denitrification technology in wastewater treatment. To improve denitrification efficiency, a synthetic microbial community (SMC) composed of denitrifiers Acinetobacter baumannii N1 (AC), Pseudomonas aeruginosa N2 (PA) and Aeromonas hydrophila (AH) were constructed. The nitrate (NO3--N) reduction efficiency of the SMC reached 97 % with little nitrite (NO2--N) accumulation, compared to the single-culture systems and co-culture systems. In the SMC, AH proved to mainly contribute to NO3--N reduction with the assistance of AC, while PA exerted NO2--N reduction. AC and AH secreted N-hexanoyl-DL-homoserine lactone (C6-HSL) to promote the electron transfer from the quinone pool to nitrate reductase. The declined N-(3-oxododecanoyl)-L-homoserine lactone (3OC12-HSL), resulting from quorum quenching (QQ) by AH, stimulated the excretion of pyocyanin, which could improve the electron transfer from complex III to downstream denitrifying enzymes for NO2--N reduction. In addition, C6-HSL mainly secreted by PA led to the up-regulation of TCA cycle-related genes and provided sufficient energy (such as NADH and ATP) for aerobic denitrification. In conclusion, members of the SMC achieved efficient denitrification through the interactions between QQ, electron transfer, and energy metabolism induced by N-acyl-homoserine lactones (AHLs). This study provided a theoretical basis for the engineering application of synthetic microbiome to remove nitrate wastewater.

Metagenomic analysis reveals impact of acyl homoserine endolipid-like signaling molecules on the aqueous sediment resistome under florfenicol stress.

Quorum sensing potentially helps microorganisms adapt to antibiotic stress encountered in the environment. This experiment investigated the effect of acyl homoserine endolipid-like signaling molecules on microbial antibiotic resistance gene structures in aqueous sediments under florfenicol stress. Additional acyl homoserine endolipid-like signaling molecules (AHLs) alter the structure of multidrug resistance genes in florfenicol-stressed sediments, particularly the multidrug resistance efflux pump gene family. Prophages and integrative and conjugative elements (ICEs) determined the resistance genes structure, and pathways related to mobile genetic elements (MGEs) transfer may play an essential role in this process. The practical application of AHLs to regulate quorum sensing systems may alter bacterial stress responses to environmental florfenicol residues, thereby reducing the development of antibiotic resistance in the environment.

Comprehensive analysis of effects of magnetic nanoparticles on aerobic granulation and microbial community composition: From the perspective of acyl-homoserine lactones mediated communication.

As dosing additives benefit for aerobic granular sludge (AGS) cultivation, effects of different concentrations (0, 10, 50 and 100 mg/L) of magnetic nanoparticles (Fe3O4 NPs) on aerobic granulation, contaminant removal and potential microbial community evolution related to acyl-homoserine lactones (AHLs) mediated bacterial communication were investigated with municipal wastewater. Results showed that the required time to achieve granulation ratio > 70 % was reduced by 60, 90 and 30 days in phase II with addition of 10, 50, 100 mg/L Fe3O4 NPs, respectively. 50 mg/L Fe3O4 NPs can improve contaminant removal efficiency. The promotion of relative abundance of AHLs-producing and AHLs-producing/quenching populations and AHLs-related functional genes accompanied with faster granulation. Iron-cycling-related bacteria were closely related with AHLs-related bacteria during AGS formation. Co-occurrence network analyses showed that AHLs-mediated communication may play an important role in coordinating microbial community composition and functional bacteria participating in nitrogen and polyphosphate metabolisms during aerobic granulation process.

Heterologous production of rhamnolipids in Pseudomonas chlororaphis subsp chlororaphis ATCC 9446 based on the endogenous production of N-acyl-homoserine lactones.

Rhamnolipids (RL) are biosurfactants naturally produced by the opportunistic pathogen Pseudomonas aeruginosa. Currently, RL are commercialized for various applications and produced by Pseudomonas putida due to the health risks associated with their large-scale production by P. aeruginosa. In this work, we show that RL containing one or two rhamnose moieties (mono-RL or di-RL, respectively) can be produced by the innocuous soil-bacterium Pseudomonas chlororaphis subsp chlororaphis ATCC 9446 at titres up to 66 mg/L (about 86% of the production of P. aeruginosa PAO1 in the same culture conditions). The production of RL depends on the expression of P. aeruginosa PAO1 genes encoding the enzymes RhlA, RhlB and RhlC. These genes were introduced in a plasmid, together with a transcriptional regulator (rhlR) forming part of the same operon, with and without RhlC. We show that the activation of rhlAB by RhlR depends on its interaction with P. chlororaphis endogenous acyl-homoserine lactones, which are synthetized by either PhzI or CsaI autoinducer synthases (producing 3-hydroxy-hexanoyl homoserine lactone, 3OH-C6-HSL, or 3-oxo-hexanoyl homoserine lactone, 3O-C6-HSL, respectively). P. chlororaphis transcriptional regulator couple with 3OH-C6-HSL is the primary activator of gene expression for phenazine-1-carboxylic acid (PCA) and phenazine-1-carboxamide (PCN) production in this soil bacterium. We show that RhlR coupled with 3OH-C6-HSL or 3O-C6-HSL promotes RL production and increases the production of PCA in P. chlororaphis. However, PhzR/3OH-C6-HSL or CsaR/3O-C6-HSL cannot activate the expression of the rhlAB operon to produce mono-RL. These results reveal a complex regulatory interaction between RhlR and P. chlororaphis quorum-sensing signals and highlight the biotechnology potential of P. chlororaphis ATCC 9446 expressing P. aeruginosa rhlAB-R or rhlAB-R-C for the industrial production of RL.

RsaM: a unique dominant regulator of AHL quorum sensing in bacteria.

Quorum sensing (QS) in proteobacteria is a mechanism to control gene expression orchestrated by the LuxI/LuxR protein family pair, which produces and responds to N-acyl homoserine lactone (AHL) diffusible signal molecules. QS is often regarded as a cell density response via the sensing of/response to the concentrations of AHLs, which are constantly basally produced by bacterial cells. The luxI/R systems, however, undergo supra-regulation in response to external stimuli and many regulators have been implicated in controlling QS in bacteria, although it remains unclear how most of these regulators and cues contribute to the QS response. One regulator, called RsaM, has been reported in a few proteobacterial species to have a stringent role in the control of AHL QS. RsaMs are small, in the range of 140-170 aa long, and are found in several genera, principally in Burkholderia and Acinetobacter. The gene encoding RsaM is always located as an independent transcriptional unit, situated adjacent to QS luxI and/or luxR loci. One of the most remarkable aspects of RsaM is its uniqueness; it does not fall into any of the known bacterial regulatory families and it possesses a distinct and novel fold that does not exhibit binding affinity for nucleic acids or AHLs. RsaM stands out as a distinctive regulator in bacteria, as it is likely to have an important ecological role, as well as unravelling a novel way of gene regulation in bacteria.

Biocontrol of biofilm forming Burkholderia cepacia using a quorum quenching crude lactonase enzyme extract from a marine Chromohalobacter sp. strain D23.

Biofilm plays advantageous role in Burkholderia cepacia by exerting multi-drug resistance. As quorum sensing (QS) system regulates biofilm formation and pathogenicity in B. cepacia strains, quorum quenching (QQ) may be a novel strategy to control persistent B. cepacia infections. In these regards, 120 halophilic bacteria were isolated from marine sample and tested using Chromobacterium violaceum and C. violaceum CV026-based bioassays initially, showing reduced violacein synthesis by QQ enzyme by 6 isolates. Among them, Chromohalobacter sp. D23 significantly degraded both C6-homoserine lactone (C6-HSL) and C8-HSL due to potent lactonase activity, which was detected by C. violaceum CV026 biosensor. Further high-performance liquid chromatography (HPLC) study confirmed degradation of N-acyl homoserine lactones (N-AHLs) particularly C6-HSL and C8-HSL by crude lactonase enzyme. Chromohalobacter sp. D23 reduced biofilm formation in terms of decreased total biomass and viability in biofilm-embedded cells in B. cepacia significantly which was also evidenced by fluorescence microscopic images. An increase in antibiotic susceptibility of B. cepacia biofilm was achieved when crude lactonase enzyme of Chromohalobacter sp. strain D23 was combined with chloramphenicol (1-5 × MIC). Chromohalobacter sp. D23 also showed prominent decrease in QS-mediated synthesis of virulence factors such as extracellular polymeric substances (EPS), extracellular protease, and hemolysin in B. cepacia. Again crude lactonase enzyme of Chromohalobacter sp. strain D23 inhibited B. cepacia biofilm formation inside nasal oxygen catheters in vitro. Finally, antibiotic susceptibility test and virulence tests revealed sensitivity of Chromohalobacter sp. strain D23 against a wide range of conventional antibiotics as well as absence of gelatinolytic, hemolytic, and serum coagulating activities. Therefore, the current study shows potential quorum quenching as well as anti-biofilm activity of Chromohalobacter sp. D23 against B. cepacia.

Joining the bacterial conversation: increasing the cultivation efficiency of soil bacteria with acyl-homoserine lactones and cAMP.

IMPORTANCE: Microorganisms are a repository of interesting metabolites and functions. Therefore, accessing them is an important exercise for advancing not only basic questions about their physiology but also to advance technological applications. In this sense, increasing the culturability of environmental microorganisms remains an important endeavor for modern microbiology. Because microorganisms do not live in isolation in their environments, molecules can be added to the cultivation strategies to "inform them" that they are present in growth-permissive environmental conditions. Signaling molecules such as acyl-homoserine lactones and 3',5'-cyclic adenosine monophosphate belong to the plethora of molecules used by bacteria to communicate with each other in a phenomenon called quorum sensing. Therefore, including quorum sensing molecules can be an incentive for microorganisms, specifically soil bacteria, to increase their numbers on solid media.

N -acylhomoserine lactone-degrading activity of Trichoderma species and its application in the inhibition of bacterial quorum sensing.

Many gram-negative pathogens can activate virulence factors under the control of N-acylhomoserine lactone (AHL）-mediated quorum sensing. AHL-degrading enzymes have been investigated for their application in disease control. Trichoderma is a genus of fungi inhabiting various types of soil and are widely used as biocontrol agents for plant pathogens. When the AHL-degrading activity of 33 strains belonging to Trichoderma species was investigated, most strains can degrade AHL. AHL lactonase catalyzes AHL ring opening by hydrolyzing lactone. Two model strains, Trichoderma atroviride MAFF 242473 and MAFF 242475, degrade AHL using their AHL lactonase activity and rapidly metabolize ring-opening AHL. Moreover, co-inoculation with MAFF 242473 and MAFF 242475 effectively inhibited AHL production by the plant pathogens, Pantoea ananatis and Pectobacterium carotovorum subsp. carotovorum. Our study suggested that Trichoderma might be an effective biocontrol agent to inhibit the expression of virulence factors via AHL-mediated quorum sensing.

Membrane-enclosed Pseudomonas quinolone signal attenuates bacterial virulence by interfering with quorum sensing.

Outer membrane vesicle (OMV)-delivered Pseudomonas quinolone signal (PQS) plays a critical role in cell-cell communication in Pseudomonas aeruginosa. However, the functions and mechanisms of membrane-enclosed PQS in interspecies communication in microbial communities are not clear. Here, we demonstrate that PQS delivered by both OMVs from P. aeruginosa and liposome reduces the competitiveness of Burkholderia cenocepacia, which usually shares the same niche in the lungs of cystic fibrosis patients, by interfering with quorum sensing (QS) in B. cenocepacia through the LysR-type regulator ShvR. Intriguingly, we found that ShvR regulates the production of the QS signals cis-2-dodecenoic acid (BDSF) and N-acyl homoserine lactone (AHL) by directly binding to the promoters of signal synthase-encoding genes. Perception of PQS influences the regulatory activity of ShvR and thus ultimately reduces QS signal production and virulence in B. cenocepacia. Our findings provide insights into the interspecies communication mediated by the membrane-enclosed QS signal among bacterial species residing in the same microbial community.IMPORTANCEQuorum sensing (QS) is a ubiquitous cell-to-cell communication mechanism. Previous studies showed that Burkholderia cenocepacia mainly employs cis-2-dodecenoic acid (BDSF) and N-acyl homoserine lactone (AHL) QS systems to regulate biological functions and virulence. Here, we demonstrate that Pseudomonas quinolone signal (PQS) delivered by outer membrane vesicles from Pseudomonas aeruginosa or liposome attenuates B. cenocepacia virulence by targeting the LysR-type regulator ShvR, which regulates the production of the QS signals BDSF and AHL in B. cenocepacia. Our results not only suggest the important roles of membrane-enclosed PQS in interspecies and interkingdom communications but also provide a new perspective on the use of functional nanocarriers loaded with QS inhibitors for treating pathogen infections.

Backbone 1H, 13C and 15N assignments of the apo-acyl carrier protein (ACP1) of Pseudomonas aeruginosa.

The N-acyl-L-homoserine lactone (AHL) quorum sensing regulates virulence in the opportunistic pathogen, Pseudomonas aeruginosa. The LasI and RhlI AHL synthases use acyl carrier protein substrates to synthesize, respectively, the 3-oxododecanoyl-L-homoserine lactone (3-oxoC12-HSL) and butyryl-L-homoserine lactone (C4-HSL) QS signals for this bacterium. Although P. aeruginosa genome contains three open reading frames to encode three acyl carrier proteins, namely the ACP1, ACP2 and ACP3, microarray and gene replacement studies show that only the ACP1 carrier protein is under quorum sensing regulation. In this study, we isotopically enriched one of the acyl carrier proteins, ACP1 from P. aeruginosa and describe the backbone resonance assignments for this protein to delineate the structural and molecular basis of ACP1 recognition in P. aeruginosa AHL quorum sensing signal synthesis.