Modelling rhizosphere interactions of Burkholderia species

Research output: ThesisDoctoral Thesis

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Abstract

[Truncated abstract] Genus Burkholderia encompasses a diverse collection of bacteria that inhabit rhizospheres throughout the world. Species can provide beneficial returns for eukaryotes, such as nitrogen fixation and nodule formation in plants and biocontrol of cropping systems. Burkholderia members can also cause disease in various animals, fungi and plants. These seemingly conflicting characteristics point to the capacity of Burkholderia spp. to interact with diverse eukaryotes. Within terrestrial ecosystems, Burkholderia spp. must negotiate favourable outcomes with both the primary producers and the primary decomposers, namely plants and fungi. It is these ongoing negotiations which govern many rhizosphere processes and lead to niche differentiation for Burkholderia spp. This research set out to design an in vitro model for investigating Burkholderiaeukaryote interactions. Surface and cellular interactions between Burkholderia spp. and both plants and fungi were then investigated. Specifically, mechanisms of adherence and invasion of plant and fungal cells were studied. The Burkholderia spp. B. vietnamiensis and B. pseudomallei were applied to mycorrhizal fungus spores as well as to several plant species. Bacterial inoculation had varying effects on germination of plant and fungal dormant forms. B. vietnamiensis-inoculation consistently increased Gigaspora decipiens spore germination, while B. pseudomallei produced no significant change. The effect of B. vietnamiensis on Acacia colei seed germination was density dependant, resulting in either increases or decreases in seed germination rates. ... Detection of B. pseudomallei in surface waters and soils was improved by the use of a rapid on-site molecular method. The related species B. thailandensis and B. ubonensis were also cultured from northern Western Australia. Mycorrhizal spores were isolated from soils of melioidosis-endemic regions. Burkholderia spp., including B. pseudomallei and B. vietnamiensis were detected in extracts of these mycorrhizal spores. Therefore, associations of Burkholderia spp. with mycorrhizal spores extend beyond the in vitro setting. These studies have increased our understanding of several specific interactions between Burkholderia spp. and eukaryotes of the rhizosphere. Common themes in adherence and invasion have emerged. Burkholderia spp. are able to closely associate with eukaryotes and to gain access to protected niches. Such access helps to explain the persistence of these bacteria in the environment during periods of desiccation and nutrient limitation.
Original languageEnglish
QualificationDoctor of Philosophy
Publication statusUnpublished - 2007

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