Quorum sensing inhibitors: a bargain of effects

Many opportunistic pathogenic bacteria rely on quorum sensing (QS) circuits as central regulators of virulence expression. In Pseudomonas aeruginosa, QS-regulated gene expression contributes to the formation and maintenance of biofilms and their tolerance to conventional antimicrobials and the host innate immune system. Therefore, QS is an obvious target for a novel class of antimicrobial drugs which would function to efficiently block reception of the cognate QS signals in vivo, and thereby be capable of inducing chemical attenuation of pathogens. As QS is not directly involved in processes essential for growth of the bacteria, inhibition of QS does not impose harsh selective pressure for development of resistance as with antibiotics. Numerous chemical libraries of both natural and synthetic origin have been screened and several QS-inhibitory compounds have been identified. In animal pulmonary infection models, such inhibitors have proven able to significantly improve clearing of the infecting bacteria and reduce mortality. In addition, several enzymes that are able to inactivate the bacterial QS signal molecules have been identified. This inactivation leads to blockage of QS-mediated virulence of plant pathogens in several models.

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Kin selection, quorum sensing and virulence in pathogenic bacteria

Proceedings of The Royal Society B Biological Sciences ◽

10.1098/rspb.2012.0843 ◽

2012 ◽

Vol 279 (1742) ◽

pp. 3584-3588 ◽

Cited By ~ 56

Author(s):

Kendra P. Rumbaugh ◽

Urvish Trivedi ◽

Chase Watters ◽

Maxwell N. Burton-Chellew ◽

Stephen P. Diggle ◽

...

Keyword(s):

Quorum Sensing ◽

Bacterial Growth ◽

Kin Selection ◽

Pathogenic Bacteria ◽

Signal Molecules ◽

Selection Experiment ◽

Wild Type ◽

Bacterial Strains ◽

Strain Diversity

Bacterial growth and virulence often depends upon the cooperative release of extracellular factors excreted in response to quorum sensing (QS). We carried out an in vivo selection experiment in mice to examine how QS evolves in response to variation in relatedness (strain diversity), and the consequences for virulence. We started our experiment with two bacterial strains: a wild-type that both produces and responds to QS signal molecules, and a lasR (signal-blind) mutant that does not release extracellular factors in response to signal. We found that: (i) QS leads to greater growth within hosts; (ii) high relatedness favours the QS wild-type; and (iii) low relatedness favours the lasR mutant. Relatedness matters in our experiment because, at relatively low relatedness, the lasR mutant is able to exploit the extracellular factors produced by the cells that respond to QS, and hence increase in frequency. Furthermore, our results suggest that because a higher relatedness favours cooperative QS, and hence leads to higher growth, this will also lead to a higher virulence, giving a relationship between relatedness and virulence that is in the opposite direction to that usually predicted by virulence theory.

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Signal Integration in Quorum Sensing Enables Cross-Species Induction of Virulence in Pectobacterium wasabiae

mBio ◽

10.1128/mbio.00398-17 ◽

2017 ◽

Vol 8 (3) ◽

Cited By ~ 13

Author(s):

Rita S. Valente ◽

Pol Nadal-Jimenez ◽

André F. P. Carvalho ◽

Filipe J. D. Vieira ◽

Karina B. Xavier

Keyword(s):

Signal Transduction ◽

Quorum Sensing ◽

Plant Pathogen ◽

Bacterial Species ◽

Homoserine Lactone ◽

Signal Molecules ◽

Acyl Homoserine Lactone ◽

Interspecies Interactions ◽

Major Factors

ABSTRACT Bacterial communities can sense their neighbors, regulating group behaviors in response to cell density and environmental changes. The diversity of signaling networks in a single species has been postulated to allow custom responses to different stimuli; however, little is known about how multiple signals are integrated and the implications of this integration in different ecological contexts. In the plant pathogen Pectobacterium wasabiae (formerly Erwinia carotovora), two signaling networks—the N-acyl homoserine lactone (AHL) quorum-sensing system and the Gac/Rsm signal transduction pathway—control the expression of secreted plant cell wall-degrading enzymes, its major virulence determinants. We show that the AHL system controls the Gac/Rsm system by affecting the expression of the regulatory RNA RsmB. This regulation is mediated by ExpR2, the quorum-sensing receptor that responds to the P. wasabiae cognate AHL but also to AHLs produced by other bacterial species. As a consequence, this level of regulation allows P. wasabiae to bypass the Gac-dependent regulation of RsmB in the presence of exogenous AHLs or AHL-producing bacteria. We provide in vivo evidence that this pivotal role of RsmB in signal transduction is important for the ability of P. wasabiae to induce virulence in response to other AHL-producing bacteria in multispecies plant lesions. Our results suggest that the signaling architecture in P. wasabiae was coopted to prime the bacteria to eavesdrop on other bacteria and quickly join the efforts of other species, which are already exploiting host resources. IMPORTANCE Quorum-sensing mechanisms enable bacteria to communicate through small signal molecules and coordinate group behaviors. Often, bacteria have various quorum-sensing receptors and integrate information with other signal transduction pathways, presumably allowing them to respond to different ecological contexts. The plant pathogen Pectobacterium wasabiae has two N-acyl homoserine lactone receptors with apparently the same regulatory functions. Our work revealed that the receptor with the broadest signal specificity is also responsible for establishing the link between the main signaling pathways regulating virulence in P. wasabiae. This link is essential to provide P. wasabiae with the ability to induce virulence earlier in response to higher densities of other bacterial species. We further present in vivo evidence that this novel regulatory link enables P. wasabiae to join related bacteria in the effort to degrade host tissue in multispecies plant lesions. Our work provides support for the hypothesis that interspecies interactions are among the major factors influencing the network architectures observed in bacterial quorum-sensing pathways. IMPORTANCE Quorum-sensing mechanisms enable bacteria to communicate through small signal molecules and coordinate group behaviors. Often, bacteria have various quorum-sensing receptors and integrate information with other signal transduction pathways, presumably allowing them to respond to different ecological contexts. The plant pathogen Pectobacterium wasabiae has two N-acyl homoserine lactone receptors with apparently the same regulatory functions. Our work revealed that the receptor with the broadest signal specificity is also responsible for establishing the link between the main signaling pathways regulating virulence in P. wasabiae. This link is essential to provide P. wasabiae with the ability to induce virulence earlier in response to higher densities of other bacterial species. We further present in vivo evidence that this novel regulatory link enables P. wasabiae to join related bacteria in the effort to degrade host tissue in multispecies plant lesions. Our work provides support for the hypothesis that interspecies interactions are among the major factors influencing the network architectures observed in bacterial quorum-sensing pathways.

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Quorum-Sensing System and Stationary-Phase Sigma Factor (rpoS) of the Onion Pathogen Burkholderia cepacia Genomovar I Type Strain, ATCC 25416

Applied and Environmental Microbiology ◽

10.1128/aem.69.3.1739-1747.2003 ◽

2003 ◽

Vol 69 (3) ◽

pp. 1739-1747 ◽

Cited By ~ 56

Author(s):

Claudio Aguilar ◽

Iris Bertani ◽

Vittorio Venturi

Keyword(s):

Quorum Sensing ◽

Stationary Phase ◽

Sigma Factor ◽

Burkholderia Cepacia ◽

Type Strain ◽

Plant Pathogens ◽

Signal Molecules ◽

Strain Atcc ◽

Sensing System ◽

Quorum Sensing System

ABSTRACT Bacterial strains belonging to Burkholderia cepacia can be human opportunistic pathogens, plant pathogens, and plant growth promoting and have remarkable catabolic activity. B. cepacia consists of several genomovars comprising what is now known as the B. cepacia complex. Here we report the quorum-sensing system of a genomovar I onion rot type strain ATCC 25416. Quorum sensing is a cell-density-dependent regulatory response which involves the production of N-acyl homoserine lactone (HSL) signal molecules. The cep locus has been inactivated in the chromosome, and it has been shown that CepI is responsible for the biosynthesis of an N-hexanoyl HSL (C6-HSL) and an N-octanoyl HSL (C8-HSL) and that the cep locus regulates protease production as well as onion pathogenicity via the expression of a secreted polygalacturonase. A cep-lacZ-based sensor plasmid has been constructed and used to demonstrate that CepR responded to C6-HSL with only 15% of the molar efficiency of C8-HSL, that a cepR knockout mutant synthesized 70% less HSLs, and that CepR responded best towards long-chain HSLs. In addition, we also report the cloning and characterization of the stationary-phase sigma factor gene rpoS of B. cepacia ATCC 25416. It was established that quorum sensing in B. cepacia has a negative effect on rpoS expression as determined by using an rpoS-lacZ transcriptional fusion; on the other hand, rpoS-null mutants displayed no difference in the accumulation of HSL signal molecules.

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Novel bacteria degrading N-acylhomoserine lactones and their use as quenchers of quorum-sensing-regulated functions of plant-pathogenic bacteria

Microbiology ◽

10.1099/mic.0.26375-0 ◽

2003 ◽

Vol 149 (8) ◽

pp. 1981-1989 ◽

Cited By ~ 164

Author(s):

Stéphane Uroz ◽

Cathy D'Angelo-Picard ◽

Aurélien Carlier ◽

Miena Elasri ◽

Carine Sicot ◽

...

Keyword(s):

Quorum Sensing ◽

Pathogenic Bacteria ◽

Rhodococcus Erythropolis ◽

Homoserine Lactone ◽

Signal Molecules ◽

In Planta ◽

Signal Molecule ◽

Violacein Production ◽

Regulated Functions

Bacteria degrading the quorum-sensing (QS) signal molecule N-hexanoylhomoserine lactone were isolated from a tobacco rhizosphere. Twenty-five isolates degrading this homoserine lactone fell into six groups according to their genomic REP-PCR and rrs PCR-RFLP profiles. Representative strains from each group were identified as members of the genera Pseudomonas, Comamonas, Variovorax and Rhodococcus. All these isolates degraded N-acylhomoserine lactones other than the hexanoic acid derivative, albeit with different specificity and kinetics. One of these isolates, Rhodococcus erythropolis strain W2, was used to quench QS-regulated functions of other microbes. In vitro, W2 strongly interfered with violacein production by Chromobacterium violaceum, and transfer of pathogenicity in Agrobacterium tumefaciens. In planta, R. erythropolis W2 markedly reduced the pathogenicity of Pectobacterium carotovorum subsp. carotovorum in potato tubers. These series of results reveal the diversity of the QS-interfering bacteria in the rhizosphere and demonstrate the validity of targeting QS signal molecules to control pathogens with natural bacterial isolates.

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Evaluation of the Probiotic Profile of the Lactobacillus Acidophilus Used in Pharmaceutical and Food Applications

Acta Scientiarum Health Sciences ◽

10.4025/actascihealthsci.v40i1.36664 ◽

2018 ◽

Vol 40 (1) ◽

pp. 36664

Author(s):

Jucelaine Deon Schmitt ◽

Luciana Oliveira de Fariña ◽

Márcia Regina Simões ◽

Luciana Bill Mikito Kottwitz

Keyword(s):

Gastrointestinal Tract ◽

Lactobacillus Acidophilus ◽

Bile Salts ◽

Pathogenic Bacteria ◽

Growth Conditions ◽

Commercial Use ◽

Inhibitory Compounds ◽

Food Applications ◽

Fermented Dairy

Lactobacillus acidophilus used in three different applications, compounding pharmacies (LA1), fermented dairy (LA2), and allopathic compoundings (LA3) were tested to evaluate the existence of significant differences between them and in different growth conditions. In the evaluation of resistance to different commercial use antibiotics, all strains were sensitive to the antibiotics ampicillin, chloramphenicol, doxycycline, and tetracycline. LA1 was considered moderately sensitive (MS) to erythromycin and LA3 was MS to clindamycin and erythromycin. LA3 was classified between MS to resistant to erythromycin. All three strains were resistant to gentamicin. When evaluating acid pH resistance, the three origins presented similar behavior, with a decrease in cell viability at pH 2, maintaining constant viability at pH 3 and 4. In the test of resistance to the gastrointestinal tract conditions and hydrophobicity, LA2 presented better results. The three strains showed production of inhibitory compounds against pathogenic bacteria and deconjugated tauroconjugated bile salts (TDCA). It was concluded that, depending on the origin, Lactobacillus acidophilus may present different behaviors that will determine its growth and, consequently, its action in vivo. Due to the practicality of access, economy, and the satisfactory results in the tests performed, LA2 can be considered the strain of choice among those studied.

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Structural determinants driving homoserine lactone ligand selection in thePseudomonas aeruginosaLasR quorum-sensing receptor

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1817239116 ◽

2018 ◽

Vol 116 (1) ◽

pp. 245-254 ◽

Cited By ~ 16

Author(s):

Amelia R. McCready ◽

Jon E. Paczkowski ◽

Brad R. Henke ◽

Bonnie L. Bassler

Keyword(s):

Quorum Sensing ◽

Ligand Binding ◽

Homoserine Lactone ◽

Communication Process ◽

Signal Molecules ◽

Structural Determinants ◽

Homoserine Lactones ◽

Ligand Selectivity ◽

Ligand Promiscuity

Quorum sensing is a cell–cell communication process that bacteria use to orchestrate group behaviors. Quorum sensing is mediated by signal molecules called autoinducers. Autoinducers are often structurally similar, raising questions concerning how bacteria distinguish among them. Here, we use thePseudomonas aeruginosaLasR quorum-sensing receptor to explore signal discrimination. The cognate autoinducer, 3OC12homoserine lactone (3OC12HSL), is a more potent activator of LasR than other homoserine lactones. However, other homoserine lactones can elicit LasR-dependent quorum-sensing responses, showing that LasR displays ligand promiscuity. We identify mutants that alter which homoserine lactones LasR detects. Substitution at residue S129 decreases the LasR response to 3OC12HSL, while enhancing discrimination against noncognate autoinducers. Conversely, the LasR L130F mutation increases the potency of 3OC12HSL and other homoserine lactones. We solve crystal structures of LasR ligand-binding domains complexed with noncognate autoinducers. Comparison with existing structures reveals that ligand selectivity/sensitivity is mediated by a flexible loop near the ligand-binding site. We show that LasR variants with modified ligand preferences exhibit altered quorum-sensing responses to autoinducers in vivo. We suggest that possessing some ligand promiscuity endows LasR with the ability to optimally regulate quorum-sensing traits.

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Strategies for inhibiting quorum sensing

Emerging Topics in Life Sciences ◽

10.1042/etls20160021 ◽

2017 ◽

Vol 1 (1) ◽

pp. 23-30 ◽

Cited By ~ 5

Author(s):

Paul Williams

Keyword(s):

Quorum Sensing ◽

Regulatory Networks ◽

Pathogenic Bacteria ◽

Bacterial Cells ◽

Therapy Outcomes ◽

Signal Molecule ◽

Bacterial Populations ◽

Conventional Antibiotics ◽

Micro Organisms

The ability of bacterial cells to synchronize their behaviour through quorum sensing (QS) regulatory networks enables bacterial populations to mount co-operative responses against competing micro-organisms and host immune defences and to adapt to environmental challenges. Since QS controls the ability of many pathogenic bacteria to cause disease, it is an attractive target for novel antibacterial agents that control infection through inhibition of virulence and by rendering biofilms more susceptible to conventional antibiotics and host clearance pathways. QS systems provide multiple druggable molecular targets for inhibitors (QSIs) that include the enzymes involved in QS signal molecule biosynthesis and the receptors involved in signal transduction. Considerable advances in our understanding of the chemical biology of QS systems and their inhibition have been made, some promising QS targets structurally characterized, QSI screens devised and inhibitors identified. However, much more work is required before any QSI ‘hits’ with the appropriate pharmacological and pharmacokinetic properties can enter human clinical trials. Indeed, the relative efficacy of QSIs alone or as prophylactics or therapeutics or as adjuvants in combination with conventional antibiotics still needs to be extensively evaluated in vivo. Particular attention must be given to the measurement of successful QSI therapy outcomes with respect to bacterial clearance, immune response and pathophysiology. Currently, our understanding of the potential of QS as a promising antibacterial target suggests that it is likely to be of value with respect to a limited number of major pathogens.

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l-Canavanine Made by Medicago sativa Interferes with Quorum Sensing in Sinorhizobium meliloti

Journal of Bacteriology ◽

10.1128/jb.187.24.8427-8436.2005 ◽

2005 ◽

Vol 187 (24) ◽

pp. 8427-8436 ◽

Cited By ~ 90

Author(s):

Neela D. Keshavan ◽

Puneet K. Chowdhary ◽

Donovan C. Haines ◽

Juan E. González

Keyword(s):

Quorum Sensing ◽

Medicago Sativa ◽

Sinorhizobium Meliloti ◽

Signal Molecules ◽

Bacterial Strains ◽

Signal Molecule ◽

Gram Negative ◽

Bacterial Quorum Sensing ◽

Bacterial Quorum ◽

Regulated Gene Expression

ABSTRACT Sinorhizobium meliloti is a gram-negative soil bacterium, capable of establishing a nitrogen-fixing symbiosis with its legume host, alfalfa (Medicago sativa). Quorum sensing plays a crucial role in this symbiosis, where it influences the nodulation process and the synthesis of the symbiotically important exopolysaccharide II (EPS II). S. meliloti has three quorum-sensing systems (Sin, Tra, and Mel) that use N-acyl homoserine lactones as their quorum-sensing signal molecule. Increasing evidence indicates that certain eukaryotic hosts involved in symbiotic or pathogenic relationships with gram-negative bacteria produce quorum-sensing-interfering (QSI) compounds that can cross-communicate with the bacterial quorum-sensing system. Our studies of alfalfa seed exudates suggested the presence of multiple signal molecules capable of interfering with quorum-sensing-regulated gene expression in different bacterial strains. In this work, we choose one of these QSI molecules (SWI) for further characterization. SWI inhibited violacein production, a phenotype that is regulated by quorum sensing in Chromobacterium violaceum. In addition, this signal molecule also inhibits the expression of the S. meliloti exp genes, responsible for the production of EPS II, a quorum-sensing-regulated phenotype. We identified this molecule as l-canavanine, an arginine analog, produced in large quantities by alfalfa and other legumes.

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Clearance of Pseudomonas aeruginosa Foreign-Body Biofilm Infections through Reduction of the Cyclic Di-GMP Level in the Bacteria

Infection and Immunity ◽

10.1128/iai.00332-13 ◽

2013 ◽

Vol 81 (8) ◽

pp. 2705-2713 ◽

Cited By ~ 51

Author(s):

Louise D. Christensen ◽

Maria van Gennip ◽

Morten T. Rybtke ◽

Hong Wu ◽

Wen-Chi Chiang ◽

...

Keyword(s):

Pseudomonas Aeruginosa ◽

Pathogenic Bacteria ◽

Silicone Implants ◽

Content Type ◽

Biofilm Control ◽

Secondary Messenger ◽

Diguanosine Monophosphate ◽

Opportunistic Pathogenic

ABSTRACTOpportunistic pathogenic bacteria can engage in biofilm-based infections that evade immune responses and develop into chronic conditions. Because conventional antimicrobials cannot efficiently eradicate biofilms, there is an urgent need to develop alternative measures to combat biofilm infections. It has recently been established that the secondary messenger cyclic diguanosine monophosphate (c-di-GMP) functions as a positive regulator of biofilm formation in several different bacteria. In the present study we investigated whether manipulation of the c-di-GMP level in bacteria potentially can be used for biofilm controlin vivo. We constructed aPseudomonas aeruginosastrain in which a reduction in the c-di-GMP level can be achieved via induction of theEscherichia coliYhjH c-di-GMP phosphodiesterase. Initial experiments showed that induction ofyhjHexpression led to dispersal of the majority of the bacteria inin vitro-grownP. aeruginosabiofilms. Subsequently, we demonstrated thatP. aeruginosabiofilms growing on silicone implants, located in the peritoneal cavity of mice, dispersed after induction of the YhjH protein. Bacteria accumulated temporarily in the spleen after induction of biofilm dispersal, but the mice tolerated the dispersed bacteria well. The present work provides proof of the concept that modulation of the c-di-GMP level in bacteria is a viable strategy for biofilm control.

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Co-existence of Quorum Sensing and Quorum Sensing Inhibitory Compounds in Marine Sponge Sarcotragus spinosulus

10.20944/preprints201912.0184.v1 ◽

2019 ◽

Author(s):

Kumar Saurav ◽

Nicola Borbone ◽

Ilia Burgsdorf ◽

Roberta Teta ◽

Alessia Caso ◽

...

Keyword(s):

Quorum Sensing ◽

Acyl Chain ◽

Genetic Regulation ◽

Marine Sponges ◽

Signal Molecules ◽

E Coli ◽

Inhibitory Compounds ◽

Dependent Inhibition ◽

Eukaryotic Organisms ◽

And Function

Marine sponges, a well documented prolific source of natural products, harbors numerous microbial communities believed to possess N-acyl homoserine lactones (AHLs) mediated Quorum sensing (QS) as one of the mechanisms of interaction. Bacteria and eukaryotic organisms are known to produce molecules that can interfere with QS signaling, thus affecting microbial genetic regulation and function. In the present study, we established the potential for production of both QS signal molecules as well as QS interfering molecules (QSI) in the same sponge species Sarcotragus spinosulus. A total of eighteen saturated acyl chain AHLs were identified along with six putative unsaturated acyl chain AHLs. Bioassay guided purification led to the isolation of two brominated metabolites with QS-interfering activity. The structures of these compounds were elucidated by comparative spectral analysis of 1HNMR and HR-MS data and was identified as 3-Br-N-methyltyramine (1) and 5,6-dibromo-N,N-dimethyltryptamine (2). The QSI activity of compounds 1 and 2 were evaluated using reporter gene assays for long- and short-chain signals (E. coli pSB1075 and E. coli pSB401) and was confirmed by measuring dose dependent inhibition of proteolytic activity and pyocyanin production in P. aeruginosa PAO1. The obtained results showed the co-existence of QS and QSI in S. spinosulus, a complex network which may mediate the orchestrated function of the microbiome within the sponge holobiont.

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