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Zhou L, Höfte M, Hennessy RC. Does regulation hold the key to optimizing lipopeptide production in Pseudomonas for biotechnology? Front Bioeng Biotechnol 2024; 12:1363183. [PMID: 38476965 PMCID: PMC10928948 DOI: 10.3389/fbioe.2024.1363183] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/29/2023] [Accepted: 02/12/2024] [Indexed: 03/14/2024] Open
Abstract
Lipopeptides (LPs) produced by Pseudomonas spp. are specialized metabolites with diverse structures and functions, including powerful biosurfactant and antimicrobial properties. Despite their enormous potential in environmental and industrial biotechnology, low yield and high production cost limit their practical use. While genome mining and functional genomics have identified a multitude of LP biosynthetic gene clusters, the regulatory mechanisms underlying their biosynthesis remain poorly understood. We propose that regulation holds the key to unlocking LP production in Pseudomonas for biotechnology. In this review, we summarize the structure and function of Pseudomonas-derived LPs and describe the molecular basis for their biosynthesis and regulation. We examine the global and specific regulator-driven mechanisms controlling LP synthesis including the influence of environmental signals. Understanding LP regulation is key to modulating production of these valuable compounds, both quantitatively and qualitatively, for industrial and environmental biotechnology.
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Affiliation(s)
- Lu Zhou
- Laboratory of Phytopathology, Department of Plants and Crops, Faculty of Bioscience Engineering, Ghent University, Ghent, Belgium
| | - Monica Höfte
- Laboratory of Phytopathology, Department of Plants and Crops, Faculty of Bioscience Engineering, Ghent University, Ghent, Belgium
| | - Rosanna C. Hennessy
- Department of Plant and Environmental Sciences, University of Copenhagen, Copenhagen, Denmark
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Cai Y, Zhang X. The atypical organization of the luxI/R family genes in AHL-driven quorum-sensing circuits. J Bacteriol 2024; 206:e0043023. [PMID: 38240569 PMCID: PMC10882985 DOI: 10.1128/jb.00430-23] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/23/2024] Open
Abstract
Quorum sensing (QS) is an elaborate regulatory mechanism associated with virulence and bacterial adaptation to the changing environment. QS is widespread in Proteobacteria and acts primarily through N-acylhomoserine lactone (AHL) signals. At the core of the AHL-driven QS systems are the AHL synthase gene (luxI family) and its cognate transcriptional regulator gene (luxR family). Several QS systems display one or more genes intervening between the luxI and luxR, in which gene arrangements are notably different due to the relative position and the transcriptional orientation between the essential luxI/R and the genes of location correlation. These adjacent genes may exert a regulatory impact on the primary QS genes or contribute toward an extension of QS regulatory control. In this review, we describe the organization of AHL-driven QS genes based on previous research and specific genome databases and provide new insights into these atypical QS gene arrangements.
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Affiliation(s)
- Yuyuan Cai
- State Key Laboratory of Microbial Metabolism, School of Life Sciences and Biotechnology, Shanghai Jiao Tong University, Shanghai, China
| | - Xuehong Zhang
- State Key Laboratory of Microbial Metabolism, School of Life Sciences and Biotechnology, Shanghai Jiao Tong University, Shanghai, China
- National Experimental Teaching Center for Life Sciences and Biotechnology, Shanghai Jiao Tong University, Shanghai, China
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Girard L, Höfte M, De Mot R. Lipopeptide families at the interface between pathogenic and beneficial Pseudomonas-plant interactions. Crit Rev Microbiol 2020; 46:397-419. [PMID: 32885723 DOI: 10.1080/1040841x.2020.1794790] [Citation(s) in RCA: 30] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
Lipopeptides (LPs) are a prominent class of molecules among the steadily growing spectrum of specialized metabolites retrieved from Pseudomonas, in particular soil-dwelling and plant-associated isolates. Among the multiple LP families, pioneering research focussed on phytotoxic and antimicrobial cyclic lipopeptides (CLPs) of the ubiquitous plant pathogen Pseudomonas syringae (syringomycin and syringopeptin). Their non-ribosomal peptide synthetases (NRPSs) are embedded in biosynthetic gene clusters (BGCs) that are tightly co-clustered on a pathogenicity island. Other members of the P. syringae group (Pseudomonas cichorii) and some species of the Pseudomonas asplenii group and Pseudomonas fluorescens complex have adopted these biosynthetic strategies to co-produce their own mycin and peptin variants, in some strains supplemented with an analogue of the P. syringae linear LP (LLP), syringafactin. This capacity is not confined to phytopathogens but also occurs in some biocontrol strains, which indicates that these LP families not solely function as general virulence factors. We address this issue by scrutinizing the structural diversity and bioactivities of LPs from the mycin, peptin, and factin families in a phylogenetic and evolutionary perspective. BGC functional organization (including associated regulatory and transport genes) and NRPS modular architectures in known and candidate LP producers were assessed by genome mining.
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Affiliation(s)
- Léa Girard
- Centre of Microbial and Plant Genetics, Faculty of Bioscience Engineering, KU Leuven, Heverlee-Leuven, Belgium
| | - Monica Höfte
- Department of Plants and Crops, Laboratory of Phytopathology, Faculty of Bioscience Engineering, Ghent University, Ghent, Belgium
| | - René De Mot
- Centre of Microbial and Plant Genetics, Faculty of Bioscience Engineering, KU Leuven, Heverlee-Leuven, Belgium
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Licciardello G, Caruso A, Bella P, Gheleri R, Strano CP, Anzalone A, Trantas EA, Sarris PF, Almeida NF, Catara V. The LuxR Regulators PcoR and RfiA Co-regulate Antimicrobial Peptide and Alginate Production in Pseudomonas corrugata. Front Microbiol 2018; 9:521. [PMID: 29662475 PMCID: PMC5890197 DOI: 10.3389/fmicb.2018.00521] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/17/2017] [Accepted: 03/08/2018] [Indexed: 02/02/2023] Open
Abstract
Cyclic lipopeptides (CLPs) are considered as some of the most important secondary metabolites in different plant-associated bacteria, thanks to their antimicrobial, cytotoxic, and surfactant properties. In this study, our aim was to investigate the role of the Quorum Sensing (QS) system, PcoI/PcoR, and the LuxR-type transcriptional regulator RfiA in CLP production in the phytopatogenic bacterium, Pseudomonas corrugata based on our previous work where we reported that the pcoR and rfiA mutants were devoid of the CLPs cormycin and corpeptin production. Due to the close genetic link between the QS system and the RfiA (rfiA is co-transcribed with pcoI), it was difficult to ascertain the specific regulatory role in the expression of target genes. A transcriptional approach was undertaken to identify the specific role of the PcoR and RfiA transcriptional regulators for the expression of genes involved in CLP production. The RNA-seq-based transcriptional analysis of the wild-type (WT) strain CFBP 5454 in comparison with GL2 (pcoR mutant) and GLRFIA (rfiA mutant) was performed in cultural conditions favoring CLP production. Differential gene expression revealed that 152 and 130 genes have significantly different levels of expression in the pcoR and rfiA mutants, respectively. Of these, the genes linked to the biosynthesis of CLPs and alginate were positively controlled by both PcoR and RfiA. Blast homology analysis showed that 19 genes in a large CLP biosynthetic cluster involved in the production of three antimicrobial peptides, which span approximately 3.5% of the genome, are strongly over-expressed in the WT strain. Thus, PcoR and RfiA function mainly as activators in the production of bioactive CLPs, in agreement with phenotype analysis of mutants. RNA-seq also revealed that almost all the genes in the structural/biosynthetic cluster of alginate exopolysaccharide (EPS) are under the control of the PcoR-RfiA regulon, as supported by the 10-fold reduction in total EPS yield isolated in both mutants in comparison to the parent strain. A total of 68 and 38 gene expressions was independently regulated by PcoR or RfiA proteins, respectively, but at low level. qPCR experiments suggest that growth medium and plant environment influence the expression of CLP and alginate genes.
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Affiliation(s)
- Grazia Licciardello
- Parco Scientifico e Tecnologico della Sicilia, Catania, Italy
- Dipartimento di Agricoltura, Alimentazione e Ambiente, Università degli Studi di Catania, Catania, Italy
| | - Andrea Caruso
- Dipartimento di Agricoltura, Alimentazione e Ambiente, Università degli Studi di Catania, Catania, Italy
| | - Patrizia Bella
- Dipartimento di Scienze Agrarie, Alimentari e Forestali, Università degli Studi di Palermo, Palermo, Italy
| | - Rodolpho Gheleri
- School of Computing, Federal University of Mato Grosso do Sul, Campo Grande, Brazil
| | - Cinzia P. Strano
- Dipartimento di Agraria, Università degli Studi “Mediterranea” di Reggio Calabria, Reggio Calabria, Italy
| | - Alice Anzalone
- Dipartimento di Agricoltura, Alimentazione e Ambiente, Università degli Studi di Catania, Catania, Italy
| | - Emmanouil A. Trantas
- Department of Agriculture, School of Agriculture, Food and Nutrition, Technological Educational Institute of Crete, Heraklion, Greece
| | - Panagiotis F. Sarris
- Department of Biosciences, College of Life and Environmental Sciences, University of Exeter, Exeter, United Kingdom
- Institute of Molecular Biology and Biotechnology, Foundation for Research and Technology – Hellas, Heraklion, Greece
| | - Nalvo F. Almeida
- School of Computing, Federal University of Mato Grosso do Sul, Campo Grande, Brazil
| | - Vittoria Catara
- Dipartimento di Agricoltura, Alimentazione e Ambiente, Università degli Studi di Catania, Catania, Italy
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Huang CJ, Pauwelyn E, Ongena M, Debois D, Leclère V, Jacques P, Bleyaert P, Höfte M. Characterization of Cichopeptins, New Phytotoxic Cyclic Lipodepsipeptides Produced by Pseudomonas cichorii SF1-54 and Their Role in Bacterial Midrib Rot Disease of Lettuce. MOLECULAR PLANT-MICROBE INTERACTIONS : MPMI 2015; 28:1009-22. [PMID: 25961750 DOI: 10.1094/mpmi-03-15-0061-r] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
The lettuce midrib rot pathogen Pseudomonas cichorii SF1-54 produces seven bioactive compounds with biosurfactant properties. Two compounds exhibited necrosis-inducing activity on chicory leaves. The structure of the two phytotoxic compounds, named cichopeptin A and B, was tentatively characterized. They are related cyclic lipopeptides composed of an unsaturated C12-fatty acid chain linked to the N-terminus of a 22-amino acid peptide moiety. Cichopeptin B differs from cichopeptin A only in the last C-terminal amino acid residue, which is probably Val instead of Leu/Ile. Based on peptide sequence similarity, cichopeptins are new cyclic lipopeptides related to corpeptin, produced by the tomato pathogen Pseudomonas corrugata. Production of cichopeptin is stimulated by glycine betaine but not by choline, an upstream precursor of glycine betaine. Furthermore, a gene cluster encoding cichopeptin synthethases, cipABCDEF, is responsible for cichopeptin biosynthesis. A cipA-deletion mutant exhibited significantly less virulence and rotten midribs than the parental strain upon spray inoculation on lettuce. However, the parental and mutant strains multiplied in lettuce leaves at a similar rate. These results demonstrate that cichopeptins contribute to virulence of P. cichorii SF1-54 on lettuce.
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Affiliation(s)
- Chien-Jui Huang
- 1 Department of Crop Protection, Laboratory of Phytopathology, Ghent University, Coupure Links 653, 9000 Ghent, Belgium
- 2 Department of Plant Medicine, National Chiayi University, No. 300, Syuefu Rd., Chiayi City, 60004, Taiwan (R.O.C.)
| | - Ellen Pauwelyn
- 1 Department of Crop Protection, Laboratory of Phytopathology, Ghent University, Coupure Links 653, 9000 Ghent, Belgium
- 3 Inagro vzw, Ieperseweg 87, 8800 Rumbeke, Belgium
| | - Marc Ongena
- 4 Walloon Centre for Industrial Biology, University of Liège-Gembloux Agro-Bio Tech, Passage des Déportés 2, 5030 Gembloux, Belgium
| | - Delphine Debois
- 5 Mass Spectrometry Laboratory (LSM/GIGA-R), Chemistry Department, University of Liege, 4000 Liege, Belgium
| | - Valerie Leclère
- 6 Laboratoire de Procédés Biologiques, Génie Enzymatique et Microbien (ProBioGEM), Université de Lille Sciences et Technologies, 59655 Villeneuve d'Ascq Cedex, France
| | - Philippe Jacques
- 6 Laboratoire de Procédés Biologiques, Génie Enzymatique et Microbien (ProBioGEM), Université de Lille Sciences et Technologies, 59655 Villeneuve d'Ascq Cedex, France
| | | | - Monica Höfte
- 1 Department of Crop Protection, Laboratory of Phytopathology, Ghent University, Coupure Links 653, 9000 Ghent, Belgium
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Trantas EA, Licciardello G, Almeida NF, Witek K, Strano CP, Duxbury Z, Ververidis F, Goumas DE, Jones JDG, Guttman DS, Catara V, Sarris PF. Comparative genomic analysis of multiple strains of two unusual plant pathogens: Pseudomonas corrugata and Pseudomonas mediterranea. Front Microbiol 2015; 6:811. [PMID: 26300874 PMCID: PMC4528175 DOI: 10.3389/fmicb.2015.00811] [Citation(s) in RCA: 29] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/23/2015] [Accepted: 07/22/2015] [Indexed: 11/13/2022] Open
Abstract
The non-fluorescent pseudomonads, Pseudomonas corrugata (Pcor) and P. mediterranea (Pmed), are closely related species that cause pith necrosis, a disease of tomato that causes severe crop losses. However, they also show strong antagonistic effects against economically important pathogens, demonstrating their potential for utilization as biological control agents. In addition, their metabolic versatility makes them attractive for the production of commercial biomolecules and bioremediation. An extensive comparative genomics study is required to dissect the mechanisms that Pcor and Pmed employ to cause disease, prevent disease caused by other pathogens, and to mine their genomes for genes that encode proteins involved in commercially important chemical pathways. Here, we present the draft genomes of nine Pcor and Pmed strains from different geographical locations. This analysis covered significant genetic heterogeneity and allowed in-depth genomic comparison. All examined strains were able to trigger symptoms in tomato plants but not all induced a hypersensitive-like response in Nicotiana benthamiana. Genome-mining revealed the absence of type III secretion system and known type III effector-encoding genes from all examined Pcor and Pmed strains. The lack of a type III secretion system appears to be unique among the plant pathogenic pseudomonads. Several gene clusters coding for type VI secretion system were detected in all genomes. Genome-mining also revealed the presence of gene clusters for biosynthesis of siderophores, polyketides, non-ribosomal peptides, and hydrogen cyanide. A highly conserved quorum sensing system was detected in all strains, although species specific differences were observed. Our study provides the basis for in-depth investigations regarding the molecular mechanisms underlying virulence strategies in the battle between plants and microbes.
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Affiliation(s)
- Emmanouil A Trantas
- Plant Biochemistry and Biotechnology Laboratory, Department of Agriculture, School of Agriculture and Food Technology, Technological Educational Institute of Crete Heraklion, Greece
| | | | - Nalvo F Almeida
- School of Computing, Federal University of Mato Grosso do Sul Campo Grande, Brazil
| | - Kamil Witek
- The Sainsbury Laboratory, John Innes Centre Norwich, UK
| | - Cinzia P Strano
- Department of Agriculture, Food and Environment, University of Catania Catania, Italy
| | - Zane Duxbury
- The Sainsbury Laboratory, John Innes Centre Norwich, UK
| | - Filippos Ververidis
- Plant Biochemistry and Biotechnology Laboratory, Department of Agriculture, School of Agriculture and Food Technology, Technological Educational Institute of Crete Heraklion, Greece
| | - Dimitrios E Goumas
- Plant Biochemistry and Biotechnology Laboratory, Department of Agriculture, School of Agriculture and Food Technology, Technological Educational Institute of Crete Heraklion, Greece ; Plant Pathology and Bacteriology Laboratory, Department of Agriculture, School of Agriculture and Food Technology, Technological Educational Institute of Crete Heraklion, Greece
| | | | - David S Guttman
- Centre for the Analysis of Genome Evolution & Function, University of Toronto Toronto, ON, Canada
| | - Vittoria Catara
- Department of Agriculture, Food and Environment, University of Catania Catania, Italy
| | - Panagiotis F Sarris
- Plant Biochemistry and Biotechnology Laboratory, Department of Agriculture, School of Agriculture and Food Technology, Technological Educational Institute of Crete Heraklion, Greece ; The Sainsbury Laboratory, John Innes Centre Norwich, UK
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Strano CP, Bella P, Licciardello G, Fiore A, Lo Piero AR, Fogliano V, Venturi V, Catara V. Pseudomonas corrugata crpCDE is part of the cyclic lipopeptide corpeptin biosynthetic gene cluster and is involved in bacterial virulence in tomato and in hypersensitive response in Nicotiana benthamiana. MOLECULAR PLANT PATHOLOGY 2015; 16:495-506. [PMID: 25231335 PMCID: PMC6638327 DOI: 10.1111/mpp.12207] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/16/2023]
Abstract
Pseudomonas corrugata CFBP 5454 produces two kinds of cyclic lipopeptides (CLPs), cormycin A and corpeptins, both of which possess surfactant, antimicrobial and phytotoxic activities. In this study, we identified genes coding for a putative non-ribosomal peptide synthetase and an ABC-type transport system involved in corpeptin production. These genes belong to the same transcriptional unit, designated crpCDE. The genetic organization of this locus is highly similar to other Pseudomonas CLP biosynthetic clusters. Matrix-assisted laser desorption ionization-time of flight-mass spectrometry (MALDI-TOF-MS) analysis revealed that transporter and synthetase genomic knock-out mutants were unable to produce corpeptins, but continued to produce cormycin A. This suggests that CrpCDE is the only system involved in corpeptin production in P. corrugata CFBP 5454. In addition, phylogenetic analysis revealed that the CrpE ABC transporter clustered with the transporters of CLPs with a long peptide chain. Strains depleted in corpeptin production were significantly less virulent than the wild-type strain when inoculated in tomato plants and induced only chlorosis when infiltrated into Nicotiana benthamiana leaves. Thus, corpeptins are important effectors of P. corrugata interaction with plants. Expression analysis revealed that crpC transcription occurs at high cell density. Two LuxR transcriptional regulators, PcoR and RfiA, have a pivotal role in crpC expression and thus in corpeptin production.
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Affiliation(s)
- Cinzia Patricia Strano
- Dipartimento di Scienze delle Produzioni Agrarie e Alimentari (DISPA), Università degli Studi di Catania, Via Santa Sofia 100, 95131, Catania, Italy
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Licciardello G, Jackson R, Bella P, Strano C, Catara A, Arnold D, Venturi V, Silby M, Catara V. Draft genome sequence of Pseudomonas corrugata, a phytopathogenic bacterium with potential industrial applications. J Biotechnol 2014; 175:65-6. [DOI: 10.1016/j.jbiotec.2014.02.003] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/16/2014] [Accepted: 02/06/2014] [Indexed: 10/25/2022]
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Kerényi Á, Bihary D, Venturi V, Pongor S. Stability of multispecies bacterial communities: signaling networks may stabilize microbiomes. PLoS One 2013; 8:e57947. [PMID: 23483950 PMCID: PMC3587416 DOI: 10.1371/journal.pone.0057947] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2012] [Accepted: 01/27/2013] [Indexed: 11/19/2022] Open
Abstract
Multispecies bacterial communities can be remarkably stable and resilient even though they consist of cells and species that compete for environmental resources. In silico models suggest that common signals released into the environment may help selected bacterial species cluster at common locations and that sharing of public goods (i.e. molecules produced and released for mutual benefit) can stabilize this coexistence. In contrast, unilateral eavesdropping on signals produced by a potentially invading species may protect a community by keeping invaders away from limited resources. Shared bacterial signals, such as those found in quorum sensing systems, may thus play a key role in fine tuning competition and cooperation within multi-bacterial communities. We suggest that in addition to metabolic complementarity, signaling dynamics may be important in further understanding complex bacterial communities such as the human, animal as well as plant microbiomes.
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Affiliation(s)
- Ádám Kerényi
- Institute of Biophysics, Biological Research Centre of the Hungarian Academy of Sciences, Szeged, Hungary
| | - Dóra Bihary
- Faculty of Information Technology, Pázmány Péter Catholic University, Budapest, Hungary
| | - Vittorio Venturi
- Group of Bacteriology and Plant Bacteriology, International Centre for Genetic Engineering and Biotechnology, Trieste, Italy
- * E-mail: (SP); (VV)
| | - Sándor Pongor
- Faculty of Information Technology, Pázmány Péter Catholic University, Budapest, Hungary
- Group of Protein Structure and Bioinformatics, International Centre for Genetic Engineering and Biotechnology, Trieste, Italy
- * E-mail: (SP); (VV)
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Licciardello G, Strano CP, Bertani I, Bella P, Fiore A, Fogliano V, Venturi V, Catara V. N-acyl-homoserine-lactone quorum sensing in tomato phytopathogenic Pseudomonas spp. is involved in the regulation of lipodepsipeptide production. J Biotechnol 2012; 159:274-82. [DOI: 10.1016/j.jbiotec.2011.07.036] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2011] [Revised: 07/17/2011] [Accepted: 07/27/2011] [Indexed: 11/25/2022]
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Functional characterization of the quorum sensing regulator RsaL in the plant-beneficial strain Pseudomonas putida WCS358. Appl Environ Microbiol 2011; 78:726-34. [PMID: 22113916 DOI: 10.1128/aem.06442-11] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
In many bacteria, quorum sensing (QS) systems rely on a signal receptor and a synthase producing N-acyl-homoserine lactone(s) as the signal molecule(s). In some species, the rsaL gene, located between the signal receptor and synthase genes, encodes a repressor limiting signal synthase expression and hence signal molecule production. Here we investigate the molecular mechanism of action of the RsaL protein in the plant growth-promoting rhizobacterium Pseudomonas putida WCS358 (RsaL(WCS)). In P. putida WCS358, RsaL(WCS) displayed a strong repressive effect on the promoter of the QS signal synthase gene, ppuI, while it did not repress the same promoter in Pseudomonas aeruginosa. DNase I protection assays showed that purified RsaL(WCS) specifically binds to ppuI on a DNA region overlapping the predicted σ(70)-binding site, but such protection was observed only at high protein concentrations. Accordingly, electrophoretic mobility shift assays showed that the RsaL(WCS) protein was not able to form stable complexes efficiently with a probe encompassing the ppuI promoter, while it formed stable complexes with the promoter of lasI, the gene orthologous to ppuI in P. aeruginosa. This difference seems to be dictated by the lower dyad symmetry of the RsaL(WCS)-binding sequence on the ppuI promoter relative to that on the lasI promoter. Comparison of the results obtained in vivo and in vitro suggests that RsaL(WCS) needs a molecular interactor/cofactor specific for P. putida WCS358 to repress ppuI transcription. We also demonstrate that RsaL(WCS) regulates siderophore-mediated growth limitation of plant pathogens and biofilm formation, two processes relevant for plant growth-promoting activity.
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