Plant-Beneficial Fluorescent Pseudomonads with Insecticidal Activity: Molecular Traits and Ecology of Insect-Associated Lifestyles
Open access
Autor(in)
Datum
2020Typ
- Doctoral Thesis
ETH Bibliographie
yes
Altmetrics
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. Mehr anzeigen
Persistenter Link
https://doi.org/10.3929/ethz-b-000445991Publikationsstatus
publishedExterne Links
Printexemplar via ETH-Bibliothek suchen
Beteiligte
Referent: Maurhofer Bringolf, Monika
Referent: Keel, Christoph
Referent: Jackson, Robert
Referent: McDonald, Bruce
Verlag
ETH ZurichThema
Pseudomonas protegens; PSEUDOMONAS (MICROBIOLOGY); Pseudomonas chlororaphis; biocontrol; Pest insect; Host pathogen interactionsOrganisationseinheit
02222 - Zurich-Basel Plant Science Center / Zurich-Basel Plant Science Center03516 - McDonald, Bruce / McDonald, Bruce
Förderung
159520 - Molecular determinats contributing to insect and plant associated lifestyles of beneficial pseudomonads (SNF)
138248 - Insecticidal activity in root-colonizing plant-beneficial pseudomonads: Molecular mechanisms and exploitation for pest control (SNF)
Zugehörige Publikationen und Daten
Is cited by: https://doi.org/10.1038/s41396-018-0317-4
Is cited by: https://doi.org/10.1038/s41396-020-0729-9
ETH Bibliographie
yes
Altmetrics