Caenorhabditis elegans is a natural predator of the mushroom pathogen Pseudomonas fluorescens NZI7. The bacterial mechanisms for reducing predation by the nematode through the secretion of secondary metabolites have been described, but not yet fully explored. The behaviour of nematodes is influenced by the different factors produced by the pseudomonads. In this thesis we develop a range of assays to link the behaviour of C. elegans to these factors to identify their role in bacteria-nematode interactions. We show that these factors play two distinct roles: they may either repel nematodes, or harm them. This permits the classification of mutants of P. fl. NZI7 lacking these factors as either attractive, edible or both. Many studies of C. elegans behaviour have demonstrated that the nematode can distinguish between different food sources. Our results show two distinct types of response: chemotaxis drives the response to attractive or repellent stimuli, and nematodes also show a choice behaviour that is independent of chemotaxis. This choice behaviour is determined by bacterial edibility and requires nematodes to come into contact with the bacteria. This contact is the foundation of the bacterial dispersal by nematodes. By making use of the luminescence property of the available bacterial mutants, we demonstrate an intimate link between the behaviour of C. elegans and the success with which bacteria are disseminated: if nematodes are induced to regularly leave a bacterial colony, whether through their genotype or the low edibility of the food, then they will spread bacteria effectively. Throughout this thesis, we use computational simulations based on a hybrid cellular automaton model to represent the nematode-bacteria interactions. These simulations recreate the observed behaviour of the system, thus they help to confirm our hypotheses and establish the fundamental aspects of the interactions between the two species.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:730028 |
| Date | January 2016 |
| Creators | Wilkins, Annekathrin |
| Contributors | Yates, Christian ; Hodgkin, Jonathan ; Preston, Gail |
| Publisher | University of Oxford |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | https://ora.ox.ac.uk/objects/uuid:6bf58183-f197-490d-86d4-633ae8d46c06 |
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