title: Antimicrobial and Insecticidal: Cyclic Lipopeptides and Hydrogen Cyanide Produced by Plant-BeneficialPseudomonasStrains CHA0, CMR12a, and PCL1391 Contribute to Insect Killing.
abstract: Particular groups of plant-beneficial fluorescent pseudomonads are not only root colonizers that provide plant disease suppression, but in addition are able to infect and kill insect larvae. The mechanisms by which the bacteria manage to infest this alternative host, to overcome its immune system, and to ultimately kill the insect are still largely unknown. However, the investigation of the few virulence factors discovered so far, points to a highly multifactorial nature of insecticidal activity. Antimicrobial compounds produced by fluorescent pseudomonads are effective weapons against a vast diversity of organisms such as fungi, oomycetes, nematodes, and protozoa. Here, we investigated whether these compounds also contribute to insecticidal activity. We tested mutants of the highly insecticidal strainsPseudomonas protegensCHA0,Pseudomonas chlororaphisPCL1391, andPseudomonassp. CMR12a, defective for individual or multiple antimicrobial compounds, for injectable and oral activity against lepidopteran insect larvae. Moreover, we studied expression of biosynthesis genes for these antimicrobial compounds for the first time in insects. Our survey revealed that hydrogen cyanide and different types of cyclic lipopeptides contribute to insecticidal activity. Hydrogen cyanide was essential to full virulence of CHA0 and PCL1391 directly injected into the hemolymph. The cyclic lipopeptide orfamide produced by CHA0 and CMR12a was mainly important in oral infections. Mutants of CMR12a and PCL1391 impaired in the production of the cyclic lipopeptides sessilin and clp1391, respectively, showed reduced virulence in injection and feeding experiments. Although virulence of mutants lacking one or several of the other antimicrobial compounds, i.e., 2,4-diacetylphloroglucinol, phenazines, pyrrolnitrin, or pyoluteorin, was not reduced, these metabolites might still play a role in an insect background since all investigated biosynthetic genes for antimicrobial compounds of strain CHA0 were expressed at some point during insect infection. In summary, our study identified new factors contributing to insecticidal activity and extends the diverse functions of antimicrobial compounds produced by fluorescent pseudomonads from the plant environment to the insect host.
authors.affiliation: Plant Pathology, Institute of Integrative Biology, ETH Zürich Zürich, Switzerland.
authors.forename: Pascale
authors.initials: P
authors.lastname: Flury
authors.affiliation: Plant Pathology, Institute of Integrative Biology, ETH Zürich Zürich, Switzerland.
authors.forename: Pilar
authors.initials: P
authors.lastname: Vesga
authors.affiliation: Department of Fundamental Microbiology, University of Lausanne Lausanne, Switzerland.
authors.forename: Maria
authors.initials: M
authors.lastname: Péchy-Tarr
authors.affiliation: Plant Pathology, Institute of Integrative Biology, ETH Zürich Zürich, Switzerland.
authors.forename: Nora
authors.initials: N
authors.lastname: Aellen
authors.affiliation: Plant Pathology, Institute of Integrative Biology, ETH Zürich Zürich, Switzerland.
authors.forename: Francesca
authors.initials: F
authors.lastname: Dennert
authors.affiliation: Plant Pathology, Institute of Integrative Biology, ETH Zürich Zürich, Switzerland.
authors.forename: Nicolas
authors.initials: N
authors.lastname: Hofer
authors.affiliation: Department of Fundamental Microbiology, University of Lausanne Lausanne, Switzerland.
authors.forename: Karent P
authors.initials: KP
authors.lastname: Kupferschmied
authors.affiliation: Department of Fundamental Microbiology, University of Lausanne Lausanne, Switzerland.
authors.forename: Peter
authors.initials: P
authors.lastname: Kupferschmied
authors.affiliation: Plant Pathology, Institute of Integrative Biology, ETH ZürichZürich, Switzerland; Laboratory of Experimental Entomology, Institute of Biology, University of LatviaRiga, Latvia.
authors.forename: Zane
authors.initials: Z
authors.lastname: Metla
authors.affiliation: Laboratory of Phytopathology, Faculty of Bioscience Engineering, Ghent University Ghent, Belgium.
authors.forename: Zongwang
authors.initials: Z
authors.lastname: Ma
authors.affiliation: Plant Pathology, Institute of Integrative Biology, ETH Zürich Zürich, Switzerland.
authors.forename: Sandra
authors.initials: S
authors.lastname: Siegfried
authors.affiliation: Microbial Biotechnology and Health, Institute of Biology Leiden, Leiden University Leiden, Netherlands.
authors.forename: Sandra
authors.initials: S
authors.lastname: de Weert
authors.affiliation: Microbial Biotechnology and Health, Institute of Biology Leiden, Leiden University Leiden, Netherlands.
authors.forename: Guido
authors.initials: G
authors.lastname: Bloemberg
authors.affiliation: Laboratory of Phytopathology, Faculty of Bioscience Engineering, Ghent University Ghent, Belgium.
authors.forename: Monica
authors.initials: M
authors.lastname: Höfte
authors.affiliation: Department of Fundamental Microbiology, University of Lausanne Lausanne, Switzerland.
authors.forename: Christoph J
authors.initials: CJ
authors.lastname: Keel
authors.affiliation: Plant Pathology, Institute of Integrative Biology, ETH Zürich Zürich, Switzerland.
authors.forename: Monika
authors.initials: M
authors.lastname: Maurhofer
keywords: Gac regulatory system; Pseudomonas chlororaphis; Pseudomonas fluorescens; Pseudomonas protegens; insecticidal activity; orfamide; secondary metabolites; sessilin