The Pseudomonas chlororaphis PCL1391 Sigma Regulator psrA Represses the Production of the Antifungal Metabolite Phenazine-1-Carboxamide

The rhizobacterium Pseudomonas chlororaphis PCL1391 produces the antifungal metabolite phenazine-1-carboxamide (PCN), which is a crucial trait in its competition with the phytopathogenic fungus Fusarium oxysporum f. sp. radicis-lycopersici in the rhizosphere. The expression of the PCN biosynthetic gene cluster in PCL1391 is population density-dependent and is regulated by the quorum-sensing genes phzI and phzR via synthesis of the autoinducer Nhexanoyl-L-homoserine lactone (C6-HSL). Here, we describe the identification of an additional regulatory gene of PCN biosynthesis in PCL1391. A mutation in the psrA gene (Pseudomonas sigma regulator), the gene product of which is a member of the TetR/AcrR family of transcriptional regulators, resulted in increased production of autoinducer molecules and PCN. Expression studies showed that inactivation of psrA resulted in increased expression of the phzI and phzR genes and the phz biosynthetic operon and that introduction of functional copies of psrA represses the expression of these genes, resulting in reduced production of autoinducer signal and PCN. Surprisingly, inactivation of psrA in the phzI or phzR quorum-sensing mutants, which do not produce detectable amounts of PCN and autoinducers by themselves, restored PCN biosynthesis. This phenomenon was accompanied by the appearance of compounds with autoinducer activities migrating at the positions of C4-HSL and C6-HSL on C18 reverse phase-thin-layer chromatography. These observations indicate that PsrA also represses at least one silent, yet unidentified, quorum-sensing system or autoinducer biosynthetic pathway in PCL1391. The expression of psrA declines at the onset of the stationary phase at the same moment at which quorum-sensing (-regulated) genes are activated. In addition, expression studies in a psrA- and a multicopy psrA background showed that psrA is autoregulated. Multiple copies of psrA repress its own expression. Mutation of gacS, encoding the sensor kinase member of a two-component global regulatory system significantly reduced production of autoinducers and PCN. We show a novel link between global regulation and quorum sensing via the PsrA regulator.

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Influence of fusaric acid on phenazine-1-carboxamide synthesis and gene expression of Pseudomonas chlororaphis strain PCL1391

Microbiology ◽

10.1099/mic.0.28063-0 ◽

2005 ◽

Vol 151 (8) ◽

pp. 2805-2814 ◽

Cited By ~ 60

Author(s):

E. Tjeerd van Rij ◽

Geneviève Girard ◽

Ben J. J. Lugtenberg ◽

Guido V. Bloemberg

Keyword(s):

Quorum Sensing ◽

Root Rot ◽

Ferric Iron ◽

Fusaric Acid ◽

Constitutive Expression ◽

Homoserine Lactone ◽

Pseudomonas Chlororaphis ◽

Iron Starvation ◽

Antifungal Metabolite ◽

Microarray Analyses

Production of the antifungal metabolite phenazine-1-carboxamide (PCN) by Pseudomonas chlororaphis strain PCL1391 is essential for the suppression of tomato foot and root rot caused by the soil-borne fungus F. oxysporum f. sp. radicis-lycopersici. The authors have shown previously that fusaric acid (FA), a phytotoxin produced by Fusarium oxysporum, represses the production of PCN and of the quorum-sensing signal N-hexanoyl-l-homoserine lactone (C6-HSL). Here they report that PCN repression by FA is maintained even during PCN-stimulating environmental conditions such as additional phenylalanine, additional ferric iron and a low Mg2+ concentration. Constitutive expression of phzI or phzR increases the production of C6-HSL and abolishes the repression of PCN production by FA. Transcriptome analysis using P. chlororaphis PCL1391 microarrays showed that FA represses expression of the phenazine biosynthetic operon (phzABCDEFGH) and of the quorum-sensing regulatory genes phzI and phzR. FA does not alter expression of the PCN regulators gacS, rpoS and psrA. In conclusion, reduction of PCN levels by FA is due to direct or indirect repression of phzR and phzI. Microarray analyses identified genes of which the expression is strongly influenced by FA. Genes highly upregulated by FA are also upregulated by iron starvation in Pseudomonas aeruginosa. This remarkable overlap in the expression profile suggests an overlapping stress response to FA and iron starvation.

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Quorum-Sensing System Affects Gall Development Incited by Pantoea agglomerans pv. gypsophilae

Molecular Plant-Microbe Interactions ◽

10.1094/mpmi-21-8-1094 ◽

2008 ◽

Vol 21 (8) ◽

pp. 1094-1105 ◽

Cited By ~ 15

Author(s):

Laura Chalupowicz ◽

Shulamit Manulis-Sasson ◽

Maxim Itkin ◽

Ayelet Sacher ◽

Guido Sessa ◽

...

Keyword(s):

Quorum Sensing ◽

Regulatory Gene ◽

Regulatory System ◽

Homoserine Lactone ◽

Culture Collection ◽

Pantoea Agglomerans ◽

Type Iii Effectors ◽

Mass Spectral ◽

Type Iii ◽

A Minor

The quorum-sensing (QS) regulatory system of the gall-forming Pantoea agglomerans pv. gypsophilae was identified. Mass spectral analysis, together with signal-specific biosensors, demonstrated that P. agglomerans pv. gypsophilae produced N-butanoyl-l-homoserine lactone (C4-HSL) as a major and N-hexanoyl-l-homoserine lactone (C6-HSL) as a minor QS signal. Homologs of luxI and luxR regulatory genes, pagI and pagR, were characterized in strain P. agglomerans pv. gypsophilae Pag824-1 and shown to be convergently transcribed and separated by 14 bp. The deduced PagI (23.8 kDa) and PagR (26.9 kDa) show high similarity with SmaI (41% identity) and SmaR (43% identity), respectively, of Serratia sp. American Type Culture Collection 39006. PagR possesses characteristic autoinducer binding and a helix-turn-helix DNA-binding domain. Gall formation by P. agglomerans pv. gypsophilae depends on a plasmid-borne hrp/hrc gene cluster, type III effectors, and phytohormones. Disruption of pagI, pagR, or both genes simultaneously in Pag824-1 reduced gall size in gypsophila cuttings by 50 to 55% when plants were inoculated with 106 CFU/ml. Higher reductions in gall size (70 to 90%) were achieved by overexpression of pagI or addition of exogenous C4-HSL. Expression of the hrp/hrc regulatory gene hrpL and the type III effector pthG in the pagI mutant, as measured with quantitative reverse-transcriptase polymerase chain reaction, was reduced by 5.8 and 6.6, respectively, compared with the wild type, suggesting an effect of the QS system on the Hrp regulon.

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N-Acylhomoserine lactone quorum-sensing signalling in antagonistic phenazine-producing Pseudomonas isolates from the red cocoyam rhizosphere

Microbiology ◽

10.1099/mic.0.043125-0 ◽

2011 ◽

Vol 157 (2) ◽

pp. 459-472 ◽

Cited By ~ 22

Author(s):

K. De Maeyer ◽

J. D'aes ◽

G. K. H. Hua ◽

M. Perneel ◽

L. Vanhaecke ◽

...

Keyword(s):

Quorum Sensing ◽

Regulatory System ◽

Homoserine Lactone ◽

Antagonistic Activity ◽

Signal Molecules ◽

Pseudomonas Chlororaphis ◽

Homoserine Lactones ◽

Acylhomoserine Lactone ◽

Phenazine Production ◽

Phenazine Antibiotics

Forty fluorescent Pseudomonas strains isolated from white and red cocoyam roots were tested for their ability to synthesize N-acyl-l-homoserine lactones (acyl-HSLs). Remarkably, only isolates from the red cocoyam rhizosphere that were antagonistic against the cocoyam root rot pathogen Pythium myriotylum and synthesized phenazine antibiotics produced acyl-HSLs. This supports the assumption that acyl-HSL production is related to the antagonistic activity of the strains. After detection, the signal molecules were identified through TLC-overlay and liquid chromatography-multiple MS (LC-MS/MS) analysis. In our representative strain, Pseudomonas CMR12a, production of the signal molecules could be assigned to two quorum-sensing (QS) systems. The first one is the QS system for phenazine production, PhzI/PhzR, which seemed to be well conserved, since it was genetically organized in the same way as in the well-described phenazine-producing Pseudomonas strains Pseudomonas fluorescens 2-79, Pseudomonas chlororaphis PCL1391 and Pseudomonas aureofaciens 30-84. The newly characterized genes cmrI and cmrR make up the second QS system of CMR12a, under the control of the uncommon N-3-hydroxy-dodecanoyl-homoserine lactone (3-OH-C12-HSL) and with low similarity to other Pseudomonas QS systems. No clear function could yet be assigned to the CmrI/CmrR system, although it contributes to the biocontrol capability of CMR12a. Both the PhzI/PhzR and CmrI/CmrR systems are controlled by the GacS/GacA two-component regulatory system.

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Phenazine-1-Carboxamide Production in the Biocontrol Strain Pseudomonas chlororaphis PCL1391 Is Regulated by Multiple Factors Secreted into the Growth Medium

Molecular Plant-Microbe Interactions ◽

10.1094/mpmi.2001.14.8.969 ◽

2001 ◽

Vol 14 (8) ◽

pp. 969-979 ◽

Cited By ~ 109

Author(s):

Thomas F. C. Chin-A-Woeng ◽

Daan van den Broek ◽

Gert de Voer ◽

Koen M. G. M. van der Drift ◽

Sietske Tuinman ◽

...

Keyword(s):

Growth Medium ◽

Homoserine Lactone ◽

Dependent Manner ◽

Pseudomonas Chlororaphis ◽

In Vitro Production ◽

Expression Studies ◽

Multiple Copies ◽

Cell Densities ◽

Vitro Production

Pseudomonas chlororaphis PCL1391 controls tomato foot and root rot caused by Fusarium oxysporum f. sp. radicislycopersici. The production of phenazine-1-carboxamide (PCN) is crucial for this biocontrol activity. In vitro production of PCN is observed only at high-population densities, suggesting that production is under the regulation of quorum sensing. The main autoinducer molecule produced by PCL1391 was identified structurally as N-hexanoyl-l-homoserine lactone (C6-HSL). The two other autoinducers that were produced comigrate with N-butanoyl-l-homoserine lactone (C4-HSL) and N-octanoyl-l-homoserine lactone (C8-HSL). Two PCL1391 mutants lacking production of PCN were defective in the genes phzI and phzR, respectively, the nucleotide sequences of which were determined completely. Production of PCN by the phzI mutant could be complemented by the addition of exogenous synthetic C6-HSL, but not by C4-HSL, C8-HSL, or any other HSL tested. Expression analyses of Tn5luxAB reporter strains of phzI, phzR, and the phz biosynthetic operon clearly showed that phzI expression and PCN production is regulated by C6-HSL in a population density-dependent manner. The introduction of multiple copies of the regulatory genes phzI and phzR on various plasmids resulted in an increase of the production of HSLs, expression of the PCN biosynthetic operon, and consequently, PCN production, up to a sixfold increase in a copy-dependent manner. Surprisingly, our expression studies show that an additional, yet unidentified factor(s), which are neither PCN nor C4-HSL or C8-HSL, secreted into the growth medium of the overnight cultures, is involved in the positive regulation of phzI, and is able to induce PCN biosynthesis at low cell densities in a growing culture, resulting in an increase of PCN production.

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Quorum Sensing: a Transcriptional Regulatory System Involved in the Pathogenicity of Burkholderia mallei

Infection and Immunity ◽

10.1128/iai.72.11.6589-6596.2004 ◽

2004 ◽

Vol 72 (11) ◽

pp. 6589-6596 ◽

Cited By ~ 57

Author(s):

Ricky L. Ulrich ◽

David DeShazer ◽

Harry B. Hines ◽

Jeffrey A. Jeddeloh

Keyword(s):

Quorum Sensing ◽

Virulence Factor ◽

Regulatory System ◽

In Silico Analysis ◽

Homoserine Lactone ◽

Burkholderia Mallei ◽

Wild Type ◽

Transcriptional Regulatory ◽

A Cell

ABSTRACT Numerous gram-negative bacterial pathogens regulate virulence factor expression by using a cell density mechanism termed quorum sensing (QS). An in silico analysis of the Burkholderia mallei ATCC 23344 genome revealed that it encodes at least two luxI and four luxR homologues. Using mass spectrometry, we showed that wild-type B. mallei produces the signaling molecules N-octanoyl-homoserine lactone and N-decanoyl-homoserine lactone. To determine if QS is involved in the virulence of B. mallei, we generated mutations in each putative luxIR homologue and tested the pathogenicities of the derivative strains in aerosol BALB/c mouse and intraperitoneal hamster models. Disruption of the B. mallei QS alleles, especially in RJ16 (bmaII) and RJ17 (bmaI3), which are luxI mutants, significantly reduced virulence, as indicated by the survival of mice who were aerosolized with 104 CFU (10 50% lethal doses [LD50s]). For the B. mallei transcriptional regulator mutants (luxR homologues), mutation of the bmaR5 allele resulted in the most pronounced decrease in virulence, with 100% of the challenged animals surviving a dose of 10 LD50s. Using a Syrian hamster intraperitoneal model of infection, we determined the LD50s for wild-type B. mallei and each QS mutant. An increase in the relative LD50 was found for RJ16 (bmaI1) (>967 CFU), RJ17 (bmaI3) (115 CFU), and RJ20 (bmaR5) (151 CFU) compared to wild-type B. mallei (<13 CFU). These findings demonstrate that B. mallei carries multiple luxIR homologues that either directly or indirectly regulate the biosynthesis of an essential virulence factor(s) that contributes to the pathogenicity of B. mallei in vivo.

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Inhibition of Quorum Sensing in Serratia marcescens AS-1 by Synthetic Analogs of N-Acylhomoserine Lactone

Applied and Environmental Microbiology ◽

10.1128/aem.00593-07 ◽

2007 ◽

Vol 73 (20) ◽

pp. 6339-6344 ◽

Cited By ~ 80

Author(s):

Tomohiro Morohoshi ◽

Toshitaka Shiono ◽

Kiyomi Takidouchi ◽

Masashi Kato ◽

Norihiro Kato ◽

...

Keyword(s):

Quorum Sensing ◽

Serratia Marcescens ◽

Biofilm Formation ◽

Acyl Chain ◽

Regulatory System ◽

Homoserine Lactone ◽

Signal Molecule ◽

Swarming Motility ◽

Gram Negative ◽

Acylhomoserine Lactone

ABSTRACT Quorum sensing is a regulatory system for controlling gene expression in response to increasing cell density. N-Acylhomoserine lactone (AHL) is produced by gram-negative bacteria, which use it as a quorum-sensing signal molecule. Serratia marcescens is a gram-negative opportunistic pathogen which is responsible for an increasing number of serious nosocomial infections. S. marcescens AS-1 produces N-hexanoyl homoserine lactone (C6-HSL) and N-(3-oxohexanoyl) homoserine lactone and regulates prodigiosin production, swarming motility, and biofilm formation by AHL-mediated quorum sensing. We synthesized a series of N-acyl cyclopentylamides with acyl chain lengths ranging from 4 to 12 and estimated their inhibitory effects on prodigiosin production in AS-1. One of these molecules, N-nonanoyl-cyclopentylamide (C9-CPA), had a strong inhibitory effect on prodigiosin production. C9-CPA also inhibited the swarming motility and biofilm formation of AS-1. A competition assay revealed that C9-CPA was able to inhibit quorum sensing at four times the concentration of exogenous C6-HSL and was more effective than the previously reported halogenated furanone. Our results demonstrated that C9-CPA was an effective quorum-sensing inhibitor for S. marcescens AS-1.

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Two Opines Control Conjugal Transfer of an Agrobacterium Plasmid by Regulating Expression of Separate Copies of the Quorum-Sensing Activator Gene traR

Journal of Bacteriology ◽

10.1128/jb.184.4.1121-1131.2002 ◽

2002 ◽

Vol 184 (4) ◽

pp. 1121-1131 ◽

Cited By ~ 29

Author(s):

Philippe Oger ◽

Stephen K. Farrand

Keyword(s):

Quorum Sensing ◽

Regulatory System ◽

Homoserine Lactone ◽

Conjugal Transfer ◽

Environmental Cues ◽

Upstream Gene ◽

Catabolic Plasmid ◽

Ti Plasmids ◽

Control Transfer ◽

Crown Gall Tumors

ABSTRACT Conjugal transfer of Ti plasmids from Agrobacterium spp. is controlled by a hierarchical regulatory system designed to sense two environmental cues. One signal, a subset of the opines produced by crown gall tumors initiated on plants by the pathogen, serves to induce production of the second, an acyl-homoserine lactone quorum-sensing signal, the quormone, produced by the bacterium itself. This second signal activates TraR, and this transcriptional activator induces expression of the tra regulon. Opines control transfer because the traR gene is a member of an operon the expression of which is regulated by the conjugal opine. Among the Ti plasmid systems studied to date, only one of the two or more opine families produced by the associated tumor induces transfer. However, two chemically dissimilar opines, nopaline and agrocinopines A and B, induce transfer of the opine catabolic plasmid pAtK84b found in the nonpathogenic Agrobacterium radiobacter isolate K84. In this study we showed that this plasmid contains two copies of traR, and each is associated with a different opine-regulated operon. One copy, traR noc, is the last gene of the nox operon and was induced by nopaline but not by agrocinopines A and B. Mutating traR noc abolished induction of transfer by nopaline but not by the agrocinopines. A mutation in ocd, an upstream gene of the nox operon, abolished utilization of nopaline and also induction of transfer by this opine. The second copy, traR acc, is located in an operon of four genes and was induced by agrocinopines A and B but not by nopaline. Genetic analysis indicated that this gene is required for induction of transfer by agrocinopines A and B but not by nopaline. pAtK84b with mutations in both traR genes was not induced for transfer by either opine. However, expression of a traR gene in trans to this plasmid resulted in opine-independent transfer. The association of traR noc with nox is unique, but the operon containing traR acc is related to the arc operons of pTiC58 and pTiChry5, two Ti plasmids inducible for transfer by agrocinopines A-B and C-D, respectively. We conclude that pAtK84b codes for two independently functioning copies of traR, each regulated by a different opine, thus accounting for the activation of the transfer system of this plasmid by the two opine types.

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RsmA and the Quorum-Sensing Signal, N-[3-Oxohexanoyl]- l-Homoserine Lactone, Control the Levels of rsmB RNA in Erwinia carotovora subsp. carotovora by Affecting Its Stability

Journal of Bacteriology ◽

10.1128/jb.184.15.4089-4095.2002 ◽

2002 ◽

Vol 184 (15) ◽

pp. 4089-4095 ◽

Cited By ~ 40

Author(s):

Asita Chatterjee ◽

Yaya Cui ◽

Arun K. Chatterjee

Keyword(s):

Quorum Sensing ◽

Rna Binding ◽

Critical Role ◽

Regulatory System ◽

Erwinia Carotovora ◽

Homoserine Lactone ◽

Negative Regulator ◽

System Control ◽

Transcriptional Fusion ◽

Extracellular Protein Production

ABSTRACT RsmA (for regulator of secondary metabolism), RsmC, and rsmB RNA, the components of a posttranscriptional regulatory system, control extracellular protein production and pathogenicity in Erwinia carotovora subsp. carotovora. RsmA, an RNA binding protein, acts as a negative regulator by promoting message decay. rsmB RNA, on the other hand, acts as a positive regulator by neutralizing the effect of RsmA. RsmC modulates the levels of RsmA and rsmB RNA by positively regulating rsmA and negatively controlling rsmB. The level of rsmB RNA is substantially higher in RsmA+ bacteria than in RsmA− mutants. We show that rsmB RNA is more stable in the presence of RsmA than in its absence. RsmA does not stimulate the expression of an rsmB-lacZ transcriptional fusion; in fact, the β-galactosidase level is somewhat higher in RsmA− bacteria than in RsmA+ bacteria. We also investigated the basis for increased levels of rsmA and rsmB RNAs in the absence of the quorum-sensing signal, N-[3-oxohexanoyl]-l-homoserine lactone (OHL). The absence of OHL activates transcription of rsmA but not of rsmB. Instead, increased stability of rsmB RNA in the presence of RsmA accounts for the elevated levels of the rsmB RNA in OHL− bacteria. Mutant studies disclosed that while RsmA, OHL, and RsmC control the levels of rsmB RNA, high levels of rsmB RNA occur in the absence of RsmC or OHL only in RsmA+ bacteria, indicating a critical role for RsmA in modulating the levels of rsmB RNA. The findings reported here firmly establish that the quorum-sensing signal is channeled in E. carotovora subsp. carotovora via the rsmA-rsmB posttranscriptional regulatory system.

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Regulation of the N-Acyl Homoserine Lactone-Dependent Quorum-Sensing System in Rhizosphere Pseudomonas putida WCS358 and Cross-Talk with the Stationary-Phase RpoS Sigma Factor and the Global Regulator GacA

Applied and Environmental Microbiology ◽

10.1128/aem.70.9.5493-5502.2004 ◽

2004 ◽

Vol 70 (9) ◽

pp. 5493-5502 ◽

Cited By ~ 59

Author(s):

Iris Bertani ◽

Vittorio Venturi

Keyword(s):

Quorum Sensing ◽

Stationary Phase ◽

Pseudomonas Putida ◽

Family Member ◽

Growth Phase ◽

Sigma Factor ◽

Response Regulator ◽

Expression Profiles ◽

Regulatory System ◽

Homoserine Lactone

ABSTRACT Quorum sensing is a cell population-density dependent regulatory system which in gram-negative bacteria often involves the production and detection of N-acyl homoserine lactones (AHLs). Some Pseudomonas putida strains have been reported to produce AHLs, and one quorum-sensing locus has been identified. However, it appears that the majority of strains do not produce AHLs. In this study we report the identification and regulation of the AHL-dependent system of rhizosphere P. putida WCS358. This system is identical to the recently identified system of P. putida strain IsoF and very similar to the las system of Pseudomonas aeruginosa. It is composed of three genes, the luxI family member ppuI, the putative repressor rsaL, and the luxR family member ppuR. A genomic ppuR::Tn5 mutant of strain WCS358 was identified by its inability to produce AHLs when it was cross-streaked in close proximity to an AHL biosensor, whereas an rsaL::Tn5 genomic mutant was identified by its ability to overproduce AHL molecules. Using transcriptional promoter fusions, we studied expression profiles of the rsaL, ppuI, and ppuR promoters in various genetic backgrounds. At the onset of the stationary phase, the autoinducer synthase ppuI gene expression is under positive regulation by PpuR-AHL and under negative regulation by RsaL, indicating that the molecules could be in competition for binding at the ppuI promoter. In genomic rsaL::Tn5 mutants ppuI expression and production of AHL levels increased dramatically; however, both processes were still under growth phase regulation, indicating that RsaL is not involved in repressing AHL production at low cell densities. The roles of the global response regulator GacA and the stationary-phase sigma factor RpoS in the regulation of the AHL system at the onset of the stationary phase were also investigated. The P. putida WCS358 gacA gene was cloned and inactivated in the genome. It was determined that the three global regulatory systems are closely linked, with quorum sensing and RpoS regulating each other and GacA positively regulating ppuI expression. Studies of the regulation of AHL quorum-sensing systems have lagged behind other studies and are important for understanding how these systems are integrated into the overall growth phase and metabolic status of the cells.

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Quorum Sensing in a Methane-Oxidizing Bacterium

Journal of Bacteriology ◽

10.1128/jb.00773-16 ◽

2016 ◽

Vol 199 (5) ◽

Cited By ~ 14

Author(s):

Aaron W. Puri ◽

Amy L. Schaefer ◽

Yanfen Fu ◽

David A. C. Beck ◽

E. Peter Greenberg ◽

...

Keyword(s):

Quorum Sensing ◽

Greenhouse Gas ◽

Bacterial Species ◽

Homoserine Lactone ◽

Sole Source ◽

Biosynthetic Gene Cluster ◽

Freshwater Ecosystems ◽

Dependent Manner ◽

Content Type ◽

Methane Oxidizer

ABSTRACT Aerobic methanotrophic bacteria use methane as their sole source of carbon and energy and serve as a major sink for the potent greenhouse gas methane in freshwater ecosystems. Dissecting the molecular details of how these organisms interact in the environment may increase our understanding of how they perform this important ecological role. Many bacterial species use quorum sensing (QS) systems to regulate gene expression in a cell density-dependent manner. We have identified a QS system in the genome of Methylobacter tundripaludum, a dominant methane oxidizer in methane enrichments of sediment from Lake Washington (Seattle, WA). We determined that M. tundripaludum produces primarily N-3-hydroxydecanoyl-l-homoserine lactone (3-OH-C10-HSL) and that its production is governed by a positive feedback loop. We then further characterized this system by determining which genes are regulated by QS in this methane oxidizer using transcriptome sequencing (RNA-seq) and discovered that this system regulates the expression of a putative nonribosomal peptide synthetase biosynthetic gene cluster. Finally, we detected an extracellular factor that is produced by M. tundripaludum in a QS-dependent manner. These results identify and characterize a mode of cellular communication in an aerobic methane-oxidizing bacterium. IMPORTANCE Aerobic methanotrophs are critical for sequestering carbon from the potent greenhouse gas methane in the environment, yet the mechanistic details of chemical interactions in methane-oxidizing bacterial communities are not well understood. Understanding these interactions is important in order to maintain, and potentially optimize, the functional potential of the bacteria that perform this vital ecosystem function. In this work, we identify a quorum sensing system in the aerobic methanotroph Methylobacter tundripaludum and use both chemical and genetic methods to characterize this system at the molecular level.

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