Original research

Imperiali N, Chiriboga X, Schlaeppi K, Fesselet M, Villacrés D, Jaffuel G, Bender SF, Dennert F, Blanco-Pérez R, van der Heijden M, Maurhofer M, Mascher F, Turlings T, Keel C , Campos-Herrera R. Combined field inoculations of Pseudomonas bacteria, arbuscular mycorrhizal fungi and entomopathogenic nematodes and their effects on wheat performance. Frontiers in Plant Science – Plant Microbe Interactions 8:1809. DOI: 10.3389/fpls.2017.01809.

Imperiali N, Dennert F, Schneider J, Laessle T, Velatta C, Fesselet M, Wyler M, Mascher F, Mavrodi O, Mavrodi D, Maurhofer M and Keel C. 2017. Relationships between root pathogen resistance, abundance and expression of Pseudomonas antimicrobial genes, and soil properties in representative Swiss agricultural soils. Frontiers in Plant Science – Plant Microbe Interactions 8:427. DOI: 10.3389/fpls.2017.00427.

Flury P, Vesga P, Péchy-Tarr M, Aellen N, Dennert F, Hofer N, Kupferschmied KP, Kupferschmied P, Metla Z, Ma Z, Siegfried S, de Weert S, Bloemberg G, Höfte M, Keel C, Maurhofer M. 2017. Antimicrobial and insecticidal: cyclic lipopeptides and hydrogen cyanide produced by plant-beneficial Pseudomonas strains CHA0, CMR12a and PCL1391 contribute to insect killing. Frontiers in Microbiology – Plant Microbe Interactions 8:100. DOI: 10.3389/fmicb.2017.00100.

Kupferschmied P, Chai T, Flury P, Blom J, Smits THM, Maurhofer M, Keel C. 2016. Specific surface glycan decorations enable antimicrobial peptide resistance in plant-beneficial pseudomonads with insect-pathogenic properties. Environmental Microbiology 18: 4265–4281.

Pagnussat LA, Salcedo F, Maroniche G, Keel C, Valverde C, Creus CM. 2016. Interspecific cooperation: enhanced growth, attachment and strain-specific distribution in biofilms through Azospirillum brasilensePseudomonas protegens co-cultivation. FEMS Microbiology Letters 363: fnw238.

Bensidhoum L, Elhafid N, Tabli N, Kupferschmied P, Weiss A, Rothballer M, Schmid M, Keel C, Hartmann A. 2016. Heavy metal tolerant Pseudomonas protegens isolates from agricultural well water in northeastern Algeria with plant growth promoting, insecticidal and antifungal activities. European Journal of Soil Biology 75:38-46.

Flury P, Aellen N, Ruffner B, Péchy-Tarr M, Fataar S, Metla Z, Dominguez-Ferreras A, Bloemberg G, Frey J, Goesmann A, Raaijmakers JM, Duffy B, Höfte M, Blom J, Smits THM, Keel C, Maurhofer M. 2016. Insect pathogenicity in plant-beneficial pseudomonads: phylogenetic distribution and comparative genomics. The ISME Journal 10:2527–2542.

Ruffner B, Péchy-Tarr M, Höfte M, Bloemberg G, Grunder J, Keel C, Maurhofer M. 2015. Evolutionary patchwork of an insecticidal toxin shared between plant-associated pseudomonads and the insect pathogens Photorhabdus and Xenorhabdus. BMC Genomics 16:609. doi: 10.1186/s12864-015-1763-2.

Kupferschmied P, Péchy-Tarr M, Imperiali N, Maurhofer M, Keel C. 2014. Domain shuffling in a sensor protein contributed to the evolution of insect pathogenicity in plant-beneficial Pseudomonas protegens. PLoS Pathogens 10:e1003964. doi: 10.1371/journal.ppat.1003964.

Jousset A, Schuldes J, Keel C, Maurhofer M, Daniel R, Scheu S, Thuermer A. 2014. Full-genome sequence of the plant growth-promoting bacterium Pseudomonas protegens CHA0. Genome Announcements 2:e00322-14. doi: 10.1128/genomeA.00322-14.

Péchy-Tarr M, Borel N, Kupferschmied P, Turner V, Binggeli O, Radovanovic D, Maurhofer M, Keel C. 2013. Control and host-dependent activation of insect toxin expression in a root-associated biocontrol pseudomonad. Environmental Microbiology 15:736-50.

Ruffner B, Péchy-Tarr M, Ryffel F, Hoegger P, Obrist C, Rindlisbacher A, Keel C, Maurhofer M. 2013. Oral insecticidal activity of plant-associated pseudomonads. Environmental Microbiology 15:751-63.

Meyer JB, Song-Wilson Y, Foetzki A, Luginbühl C, Winzeler M, Kneubühler Y, Matasci C, Mascher-Frutschi F, Kalinina O, Boller T, Keel C, Maurhofer M. 2013. Does wheat genetically modified for disease resistance affect root-colonizing pseudomonads and arbuscular mycorrhizal fungi? PLoS One 8:e53825. doi: 10.1371/journal.pone.0053825.

Troxler J, Svercel M, Natsch A, Zala M, Keel C, Moënne-Loccoz Y, Défago G. 2012. Persistence of a biocontrol Pseudomonas inoculant as high populations of culturable and non-culturable cells in 200-cm-deep soil profiles. Soil Biology and Biochemistry 44:122-9.

Meyer JB, Frapolli M, Keel C, Maurhofer M. 2011. Pyrroloquinoline quinone biosynthesis gene pqqC, a novel molecular marker for studying the phylogeny and diversity of phosphate-solubilizing pseudomonads. Applied and Environmental Microbiology 77:7345-54.

Foetzki A, Winzeler M, Boller T, Felber F, Gruissem G, Keel C, Keller B, Mascher F, Maurhofer M, Nentwig W, Romeis J, Sautter C, Schmid B, Bigler F. 2011. Freilandversuche mit gentechnisch verändertem Weizen mit Mehltauresistenz. Agrarforschorschung Schweiz 2:446-53.

Subramoni S, Gonzalez JF, Johnson A, Péchy-Tarr M, Rochat L, Paulsen I, Loper JE, Keel C, Venturi V. 2011. Bacterial subfamily of LuxR regulators that respond to plant compounds. Applied and Environmental Microbiology 77:4579-88.

de Werra P, Huser A, Tabacchi R, Keel C, Maurhofer M. 2011. Plant- and microbe-derived compounds affect the expression of genes encoding antifungal compounds in a pseudomonad with biocontrol activity. Applied and Environmental Microbiology 77:2807-12.

Jousset A, Rochat L, Lanoue A, Bonkowski M, Keel C, Scheu S. 2011. Plants respond to pathogen infection by enhancing the antifungal gene expression of root-associated bacteria. Molecular Plant-Microbe Interactions 24:352-8.

Meyer JB, Lutz MP, Frapolli M, Péchy-Tarr M, Rochat L, Keel C, Défago G, Maurhofer M. 2010. Interplay between wheat cultivars, biocontrol pseudomonads, and soil. Applied and Environmental Microbiology 76:6196-204.

Jousset A, Rochat L, Scheu S, Bonkowski M, Keel C. 2010. Predator-prey chemical warfare determines the expression of biocontrol genes by rhizosphere-associated Pseudomonas fluorescens. Applied and Environmental Microbiology 76:5263-8. (Must read by Faculty of 1000 Biology, FF9).

Rochat L, Péchy-Tarr M, Baehler E, Maurhofer M, Keel C. 2010. Combination of fluorescent reporters for simultaneous monitoring of root colonization and antifungal gene expression by a biocontrol pseudomonad on cereals with flow cytometry. Molecular Plant-Microbe Interactions 23:949-61. (Article featured on the cover page).

Scheublin TR, Sanders IR, Keel C, van der Meer JR. 2010. Characterisation of microbial communities colonising the hyphal surfaces of arbuscular mycorrhizal fungi. ISME Jounal 4:752-63.

Vallet-Gely I, Novikov A, Augusto L, Liehl P, Bolbach G, Péchy-Tarr M, Cosson P, Keel C, Caroff M, Lemaitre B. 2010. Association of hemolytic activity of Pseudomonas entomophila, a versatile soil bacterium, with cyclic lipopeptide production. Applied and Environmental Microbiology 76:910-21.

Bjørnlund L, Rønn R, Péchy-Tarr M, Maurhofer M, Keel C, Nybroe O. 2009. Functional GacS in Pseudomonas DSS73 prevents digestion by Caenorhabditis elegans and protects the nematode from killer flagellates. ISME Journal 3:770-9.

de Werra P, Péchy-Tarr M, Keel C, Maurhofer M. 2009. Role of gluconic acid production in the regulation of biocontrol traits of Pseudomonas fluorescens CHA0. Applied and Environmental Microbiology 75:4162-74.

Jousset A, Rochat L, Péchy-Tarr M, Keel C, Scheu S, Bonkowski M. 2009. Predators promote defence of rhizosphere bacterial populations by selective feeding on non-toxic cheaters. ISME Journal 3:666-74. (Research highlight in Nature Reviews Microbiology 7, 2009)

Takeuchi K, Kiefer P, Reimmann C, Keel C, Dubuis C, Rolli J, Vorholt JA, Haas D. 2009. Small RNA-dependent expression of secondary metabolism is controlled by Krebs cycle function in Pseudomonas fluorescens. Journal of Biological Chemistry 284:34976-8.

Pechy-Tarr M, Bruck DJ, Maurhofer M, Fischer E, Vogne C, Henkels MD, Donahue KM, Grunder J, Loper JE, Keel C. 2008. Molecular analysis of a novel gene cluster encoding an insect toxin in plant-associated strains of Pseudomonas fluorescens. Environmental Microbiology 10:2368-6. (Recommended by Faculty of 1000 Biology, FF6).

de Werra P, Baehler E, Huser A, Keel C, Maurhofer M. 2008. Detection of plant-modulated alterations in antifungal gene expression in Pseudomonas fluorescens CHA0 on roots by flow cytometry. Applied and Environmental Microbiology 74:1339-49. (Recommended by Faculty of 1000 Biology, FF6).

Rezzonico F, Zala M, Keel C, Duffy B, Moënne-Loccoz Y, Défago G. 2007. Is the ability of biocontrol fluorescent pseudomonads to produce the antifungal metabolite 2,4-diacetylphloroglucinol really synonymous with higher plant protection? New Phytologist 173:861-72.

Bottiglieri M, Keel C. 2006. Characterization of PhlG, a hydrolase that specifically degrades the antifungal compound 2,4-diacetylphloroglucinol in the biocontrol agent Pseudomonas fluorescens CHA0. Applied and Environmental Microbiology 72:418-27.

Baehler E, de Werra P, Wick LY, Péchy-Tarr M, Mathys S, Maurhofer M, Keel C. 2006. Two novel MvaT-like global regulators control exoproduct formation and biocontrol activity in root-associated Pseudomonas fluorescens CHA0. Molecular Plant-Microbe Interactions 19:313-29.

Péchy-Tarr M, Bottiglieri M, Mathys S, Lejbølle KB, Schnider-Keel U, Maurhofer M, Keel C. 2005. RpoN (sigma54) controls production of antifungal compounds and biocontrol activity in Pseudomonas fluorescens CHA0. Molecular Plant-Microbe Interactions 18:260-72. (Recommended by Faculty of 1000 Biology, FF8).

Kohlmeier S, Smits TH, Ford RM, Keel C, Harms H, Wick LY. 2005. Taking the fungal highway: mobilization of pollutant-degrading bacteria by fungi. Environmental Science and Technology 39:4640-6.

Baehler E, Bottiglieri M, Péchy-Tarr M, Maurhofer M, Keel C. 2005. Use of green fluorescent protein-based reporters to monitor balanced production of antifungal compounds in the biocontrol agent Pseudomonas fluorescens CHA0. Journal of Applied Microbiology 99:24-38.

Maurhofer M, Baehler E, Notz R, Martinez V, Keel C, 2004. Cross talk between 2,4-diacetylphloroglucinol-producing biocontrol pseudomonads on wheat roots. Applied and Environmental Microbiology 70:1990-8.

Duffy B, Keel C, Défago G. 2004. Potential role of pathogen signaling in multitrophic plant-microbe interactions involved in disease protection. Applied and Environmental Microbiology 70:1836-42.

Zuber S, Carruthers F, Keel C, Mattart A, Blumer C, Pessi G, Gigot-Bonnefoy C, Schnider-Keel U, Heeb S, Reimmann C, Haas D. 2003. GacS sensor domains pertinent to the regulation of exoproduct formation and to the biocontrol potential of Pseudomonas fluorescens CHA0. Molecular Plant-Microbe Interactions 16:634-44

Smits TH, Wick LY, Harms H, Keel C. 2003. Characterization of the surface hydrophobicity of filamentous fungi. Environmental Microbiology 5:85-91.

Valverde C, Heeb S, Keel C, Haas D, 2003. RsmY, a small regulatory RNA, is required in concert with RsmZ for GacA-dependent expression of biocontrol traits in Pseudomonas fluorescens CHA0. Molecular Microbiology 50:1361-79.

Reimmann C, Ginet N, Michel L, Keel C, Michaux P, Krishnapillai V, Zala M, Heurlier K, Triandafillu K, Harms H, Défago G, Haas D. 2002. Genetically programmed autoinducer destruction reduces virulence gene expression and swarming motility in Pseudomonas aeruginosa PAO1. Microbiology 148:923-32.

Mascher F, Moënne-Loccoz Y, Schnider-Keel U, Keel C, Haas D, Défago G. 2002. Inactivation of the regulatory gene algU or gacA can affect the ability of biocontrol Pseudomonas fluorescens CHA0 to persist as culturable cells in nonsterile soil. Applied and Environmental Microbiology 68:2085-8.

Keel C, Ucurum Z, Michaux P, Adrian M, Haas D. 2002. Deleterious impact of a virulent bacteriophage on survival and biocontrol activity of Pseudomonas fluorescens strain CHAO in natural soil. Molecular Plant-Microbe Interactions 15:567-76.

Johansen JE, Binnerup SJ, Lejbølle KB, Mascher F, Sørensen J, Keel C. 2002. Impact of biocontrol strain Pseudomonas fluorescens CHA0 on rhizosphere bacteria isolated from barley (Hordeum vulgare L.) with special reference to Cytophaga-like bacteria. Journal of Applied Microbiology 93:1065-74.

Schnider-Keel U, Lejbølle KB, Baehler E, Haas D, Keel C. 2001. The sigma factor AlgU (AlgT) controls exopolysaccharide production and tolerance towards desiccation and osmotic stress in the biocontrol agent Pseudomonas fluorescens CHA0. Applied and Environmental Microbiology 67:5683-93.

Bull CT, Duffy B, Voisard C, Défago G, Keel C, Haas D. 2001. Characterization of spontaneous gacS and gacA regulatory mutants of Pseudomonas fluorescens biocontrol strain CHAO. Antonie Van Leeuwenhoek 79:327-36.

Schnider-Keel U, Seematter A, Maurhofer M, Blumer C, Duffy B, Gigot-Bonnefoy C, Reimmann C, Notz R, Défago G, Haas D, Keel C. 2000. Autoinduction of 2,4-diacetylphloroglucinol biosynthesis in the biocontrol agent Pseudomonas fluorescens CHA0 and repression by the bacterial metabolites salicylate and pyoluteorin. Journal of Bacteriology 182:1215-25.

Heeb S, Itoh Y, Nishijyo T, Schnider U, Keel C, Wade J, Walsh U, O’Gara F, Haas D. 2000. Small, stable shuttle vectors based on the minimal pVS1 replicon for use in gram-negative, plant-associated bacteria. Molecular Plant-Microbe Interactions 13:232-7.

Troxler J, Zala M, Natsch A, Nievergelt J, Keel C, Défago G. 1998. Transport of a biocontrol Pseudomonas fluorescens through 2.5-m deep outdoor lysimeters and survival in the effluent water. Soil Biology and Biochemistry 30:621-31.

Laville J, Blumer C, Von Schroetter C, Gaia V, Défago G, Keel C, Haas D. 1998. Characterization of the hcnABC gene cluster encoding hydrogen cyanide synthase and anaerobic regulation by ANR in the strictly aerobic biocontrol agent Pseudomonas fluorescens CHA0. Journal of Bacteriology 180:3187-96.

Beyeler M, Keel C, Michaux P, Haas D. 1998. Enhanced production of indole-3-acetic acid by a genetically modified strain of Pseudomonas fluorescens CHA0 affects root growth of cucumber but does not improve protection of the plant against Pythium root rot. FEMS Microbiology Ecology 28:225-33.

Chin-A-Woeng TFC, Bloemberg GV, van der Bij AJ, van der Drift KMGF, Schripsema J, Kroon B, Scheffer RJ, Keel C, Bakker PAHM, Tichy H-V, de Bruijn FJ, Thomas-Otes JE, Lugtenberg B JJ. 1998. Biocontrol by phenazine-1-carboxamide-producing Pseudomonas chlororaphis PCL1391of tomato root rot caused by Fusarium oxysporum f. sp. radicis-lycopersici. Molecular Plant-Microbe Interactions 11:1069-77.

Natsch A, Keel C, Hebecker N, Laasik E, Défago G. 1998. Impact of Pseudomonas fluorescens strain CHA0 and a derivative with improved biocontrol activity on the culturable resident bacterial community on cucumber roots. FEMS Microbiology Ecology 27:365-80.

Troxler J, Zala M, Moënne-Loccoz Y, Keel C, Defago G. 1997. Predominance of nonculturable cells of the biocontrol strain Pseudomonas fluorescens CHA0 in the surface horizon of large outdoor lysimeters. Applied and Environmental Microbiology 63:3776-82.

Troxler J, Berling C-H, Moënne-Loccoz Y, Keel C, Défago G. 1997. Interactions between the biocontrol agent Pseudomonas fluorescens CHA0 and Thielaviopsis basicola in tobacco roots observed by immunofluorescence microscopy. Plant Pathology 46:62-71.

Schmidli-Sacherer P, Keel C, Défago G. 1997. The global regulator GacA of Pseudomonas fluorescens CHA0 is required for the suppression of root diseases in dicotyledons but not in Gramineae. Plant Pathology 46:80-90.

Niemann S, Keel C, Pühler A, Selbitschka W. 1997. Biocontrol strain Pseudomonas fluorescens CHA0 and its genetically modified derivative with enhanced biocontrol capability exert comparable effects on the structure of a Sinorhizobium meliloti population in a gnotobiotic system. Biology and Fertility of Soils 25:240-4.

Natsch A, Keel C, Hebecker N, Laasik E, Défago G. 1997. Influence of biocontrol strain Pseudomonas fluorescens CHA0 and its antibiotic overproducing derivative on the diversity of root colonizing pseudomonads. FEMS Microbiology Ecology 23:341-52.

Natsch A, Keel C, Troxler J, Zala M, von Albertini N, Défago G. 1996. Importance of preferential flow and soil management in vertical transport of a biocontrol strain of Pseudomonas fluorescens instructured field soil. Applied and Environmental Microbiology 62:33-40.

Keel C, Weller DM, Natsch A, Défago G, Cook RJ, Thomashow LS. 1996. Conservation of the 2,4-diacetylphloroglucinol biosynthesis locus among fluorescent Pseudomonas strains from diverse geographic locations. Applied and Environmental Microbiology 62:552-63.

Schnider U, Keel C, Voisard C, Défago G, Haas D. 1995. Tn5-directed cloning of pqq genes from Pseudomonas fluorescens CHA0: mutational inactivation of the genes results in overproduction of the antibiotic pyoluteorin. Applied and Environmental Microbiology 61:3856-64

Schnider U, Keel C, Blumer C, Troxler J, Défago G, Haas D. 1995. Amplification of the housekeeping sigma factor in Pseudomonas fluorescens CHA0 enhances antibiotic production and improves biocontrol abilities. Journal of Bacteriology 177:5387-92.

Maurhofer M, Keel C, Haas D, Défago G. 1995. Influence of plant species on disease suppression by Pseudomonas fluorescens strain CHA0 with enhanced antibiotic production. Plant Patholology 44:40-50.

Görlach J, Raesecke HR, Rentsch D, Regenass M, Roy P, Zala M, Keel C, Boller T, Amrhein N, Schmid J. 1995. Temporally distinct accumulation of transcripts encoding enzymes of the prechorismate pathway in elicitor-treated, cultured tomato cells. Proceedings of the National Academy of Sciences of the United States of America 92:3166-70.

Natsch A, Keel C, Pfirter HA, Haas D, Défago G. 1994. Contribution of the global regulator gene gacA to persistence and dissemination of Pseudomonas fluorescens biocontrol strain CHA0 introduced into soil microcosms. Applied and Environmental Microbiology 60:2553-60

Maurhofer M, Keel C, Haas D, Défago G. 1994. Pyoluteorin production by Pseudomonas fluorescens strain CHA0 is involved in the suppression of Pythium damping-off of cress but not of cucumber. European Journal of Plant Pathology 100:221-32.

Maurhofer M, Keel C, Schnider U, Voisard C, Haas D, Défago G. 1992. Influence of enhanced antibiotic production in Pseudomonas fluorescens strain CHA0 on its disease suppressive capacity. Phytopathology 82:190-5.

Keel C, Schnider U, Maurhofer M, Voisard C, Laville J, Burger U, Wirthner P, Haas D, Défago G. 1992. Suppression of root diseases by Pseudomonas fluorescens CHA0: Importance of the bacterial secondary metabolite 2,4-diacetylphloroglucinol. Molecular Plant-Microbe Interactions 5:4-13.

Laville J, Voisard C, Keel C, Maurhofer M, Défago G, Haas D. 1992. Global control in Pseudomonas fluorescens mediating antibiotic synthesis and suppression of black root rot of tobacco. Proceedings of the National Academy of Sciences of the United States of America 89:1562-6.

Keel C, Wirthner P, Oberhänsli T, Voisard C, Burger U, Haas D, Défago G. 1990. Pseudomonads as antagonists of plant pathogens in the rhizosphere: role of the antibiotic 2,4-diacetylphloroglucinol in the suppression of black root rot of tobacco. Symbiosis 9:327-41.

Voisard C, Keel C, Haas D, Dèfago G. 1989. Cyanide production by Pseudomonas fluorescens helps suppress black root rot of tobacco under gnotobiotic conditions. EMBO Journal 8:351-8.

Keel C, Voisard C, Berling C-H, Kahr G, Défago G. 1989. Iron sufficiency, a prerequisite for suppression of tobacco black root rot by Pseudomonas fluorescens strain CHA0 under gnotobiotic conditions. Phytopathology 79:584-9.