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dc.contributor.author
Vesga Aguado, Maria del Pilar
dc.contributor.supervisor
Maurhofer, Monika
dc.contributor.supervisor
Keel, Christoph
dc.contributor.supervisor
Jackson, Robert
dc.contributor.supervisor
McDonald, Bruce
dc.date.accessioned
2020-10-15T09:25:40Z
dc.date.available
2020-10-14T17:35:56Z
dc.date.available
2020-10-15T09:25:40Z
dc.date.issued
2020
dc.identifier.uri
http://hdl.handle.net/20.500.11850/445991
dc.identifier.doi
10.3929/ethz-b-000445991
dc.description.abstract
This thesis focuses on a special group of plant-beneficial pseudomonads with insecticidal activity. Bacteria belonging to the Pseudomonas fluorescens group are excellent root-colonizers with many plant beneficial effects. These bacteria can promote plant growth through the production of hormones and increase the availability of certain soil nutrients. Fluorescent Pseudomonas are also able to control the emergence of soilborne diseases mainly by the production of antimicrobial secondary metabolites and to induce systemic resistance in the plant host rendering it ready for the attack of pathogens or predators. Intriguingly, two species within the fluorescent pseudomonads, P. chlororaphis and P. protegens, possess the ability to colonize and kill Lepidopteran insects in addition to all these plant beneficial activities. In the last decade, several factors contributing to the insecticidal activity of these fascinating bacteria were identified, and insecticidal pseudomonads have emerged as promising candidates for the biological control of soil-derived insect pests for which no satisfactory control methods exist. The major aims of this thesis were to study the nature of Pseudomonas-insect interactions and its ecological significance, and to investigate, in a susceptible insect species, the pathogenicity process and the factors required at different phases during insect colonization and killing. In the first part of the thesis, we investigated whether the inability, of model strain P. protegens CHA0, to kill certain insect species, is due to its failure to persist in the animals. Based on feeding assays in combination with bacterial monitoring we showed that P. protegens CHA0 is highly lethal to larvae of Plutella xylostella (Lepidoptera) and Pieris brassicae (Lepidoptera) while being pathogenic, but less effective against larvae of Delia radicum (Diptera). P. protegens CHA0 had no effect on larvae of Otiorhynchus sulcatus (Coleoptera). However, P. protegens CHA0 persisted from larval to adult stage in all these species and was transmitted to a new plant host by D. radicum flies. These findings indicate that insecticidal pseudomonads can establish different relationships with insects ranging from exploiting insects as food source to using them as vectors for dispersal. A central part of the thesis concentrated on identifying the specific sets of genes a pseudomonad needs when colonizing a plant or an insect hosts, and to identify the specific role of individual factors during insect colonization and throughout disease progression. To this end, a large-scale transcriptomics dataset of P. protegens strain CHA0 was generated which includes data from the colonization of wheat roots, the gut of P. xylostella after oral uptake and the Galleria mellonella hemolymph after injection. The transcriptomic profiles strongly varied depending on the environment. Furthermore, we could associate specific factors to different hosts or different stages of insect infection. In addition, new traits contributing to insecticidal activity were identified, such as effector proteins (toxins) released by two-partner secretion systems (TPS). Their role during infection of P. xylostella was verified using a mutational approach. Altogether, this data allowed us to propose a comprehensive insect colonization and pathogenesis model for P. protegens CHA0. The ecological relevance of non-pathogenic interactions with insects described in the first part of the thesis, and the natural association of P. protegens and P. chlororaphis to insects, still remains unknown. To address these questions, we searched for insecticidal Pseudomonas in arthropods collected from a wheat field, a potato field and neighbouring grassland. We found that P. protegens and P. chlororaphis are naturally present in healthy insects and myriapods and isolated a set of new strains from arthropods, soil and roots. Although all strains, independently of their host of origin or their phylogenetic position, had oral activity against P. xylostella, the insecticidal capacities of different P. chlororaphis isolates were not as homogeneous as observed for P. protegens. Phylogenetically closely related P. chlororaphis strains differed in insect killing speed and efficiency. We hypothesize that the lower insecticidal activity observed for two Coleoptera isolates could be related to mutations in key insecticidal factors, such as the Fit toxin and TPSA proteins, that we discovered using a single nucleotide polymorphism analysis based on the whole genomes. These findings point towards an order-specificity or adaptation to certain insect hosts and show the ubiquitous nature of these special pseudomonads. This thesis substantially improves our knowledge about the pathogenesis of insect infecting Pseudomonas and the ecology of arthropod-Pseudomonas relationships. The novel information we gained is of great scientific, but also agricultural and environmental value, since it is highly important for the development of new biocontrol tools within the frame of a sustainable agriculture relying on environmentally friendly pest control methods.
en_US
dc.format
application/pdf
en_US
dc.language.iso
en
en_US
dc.publisher
ETH Zurich
en_US
dc.subject
Pseudomonas protegens
en_US
dc.subject
PSEUDOMONAS (MICROBIOLOGY)
en_US
dc.subject
Pseudomonas chlororaphis
en_US
dc.subject
biocontrol
en_US
dc.subject
Pest insect
en_US
dc.subject
Host pathogen interactions
en_US
dc.title
Plant-Beneficial Fluorescent Pseudomonads with Insecticidal Activity: Molecular Traits and Ecology of Insect-Associated Lifestyles
en_US
dc.type
Doctoral Thesis
dc.date.published
2020-10-15
ethz.size
279 p.
en_US
ethz.code.ddc
DDC - DDC::5 - Science::570 - Life sciences
en_US
ethz.grant
Molecular determinats contributing to insect and plant associated lifestyles of beneficial pseudomonads
en_US
ethz.grant
Insecticidal activity in root-colonizing plant-beneficial pseudomonads: Molecular mechanisms and exploitation for pest control
en_US
ethz.identifier.diss
26822
en_US
ethz.publication.place
Zurich
en_US
ethz.publication.status
published
en_US
ethz.leitzahl
ETH Zürich::00002 - ETH Zürich::00012 - Lehre und Forschung::00007 - Departemente::02350 - Dep. Umweltsystemwissenschaften / Dep. of Environmental Systems Science::02222 - Zurich-Basel Plant Science Center / Zurich-Basel Plant Science Center
en_US
ethz.leitzahl
ETH Zürich::00002 - ETH Zürich::00012 - Lehre und Forschung::00007 - Departemente::02350 - Dep. Umweltsystemwissenschaften / Dep. of Environmental Systems Science::02720 - Institut für Integrative Biologie / Institute of Integrative Biology::03516 - McDonald, Bruce / McDonald, Bruce
en_US
ethz.leitzahl.certified
ETH Zürich::00002 - ETH Zürich::00012 - Lehre und Forschung::00007 - Departemente::02350 - Dep. Umweltsystemwissenschaften / Dep. of Environmental Systems Science::02720 - Institut für Integrative Biologie / Institute of Integrative Biology::03516 - McDonald, Bruce / McDonald, Bruce
en_US
ethz.tag
transcriptomics
en_US
ethz.tag
genomics
en_US
ethz.tag
microbiology
en_US
ethz.grant.agreementno
159520
ethz.grant.agreementno
138248
ethz.grant.fundername
SNF
ethz.grant.fundername
SNF
ethz.grant.funderDoi
10.13039/501100001711
ethz.grant.funderDoi
10.13039/501100001711
ethz.grant.program
Projektförderung in Biologie und Medizin (Abteilung III)
ethz.relation.isCitedBy
https://doi.org/10.1038/s41396-018-0317-4
ethz.relation.isCitedBy
https://doi.org/10.1038/s41396-020-0729-9
ethz.date.deposited
2020-10-14T17:36:06Z
ethz.source
FORM
ethz.eth
yes
en_US
ethz.availability
Embargoed
en_US
ethz.date.embargoend
2022-10-15
ethz.rosetta.installDate
2020-10-15T09:26:27Z
ethz.rosetta.lastUpdated
2020-10-15T09:26:27Z
ethz.rosetta.exportRequired
true
ethz.rosetta.versionExported
true
ethz.COinS
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