Carroll, Daire (2021) A quantitative framework for studying bacterial colonisation of the rhizoplane. PhD thesis, University of Warwick.

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Abstract

Colonisation of the root surface, or rhizoplane, is one of the first steps for microorganisms within soil to become established in the plant microbiome. However, the timing and relative contributions of processes, such as microbial movement, attachment, and proliferation to colonisation are not well characterized. This limits our ability to comprehend the complex dynamics of microbial communities in soil. The aim of this thesis was to develop a set of experimental and theoretical frameworks that can be used to isolate and quantify key microbial processes involved in rhizoplane colonisation. A model plant and bacterial system, consisting of Pseudomonas fluorescens isolate SBW25, transformed with a fluorescent marker plasmid, and Lettuce (Lactuca sativa) was selected for characterisation. A liquid microcosm system was developed which enabled inoculation of plants with bacterial suspensions and manipulation of the plant following treatment. Using this system, a framework for the independent quantification of bacterial attachment and proliferation on the root surface was developed. This allowed previously indistinguishable components of the colonisation process to be independently quantified. The timing and spatial distribution of colonisation in a granular environment was further analysed through the live imaging of plants grown in transparent soil. A chemotaxis assay was developed for the measurement of bacterial movement in transparent soil in response to plant root exudate. Data from chemotaxis assays was used to construct a model of bacterial diffusion and convection in soil. These novel characterisations of bacterial movement, attachment to the root surface, and proliferation offers new insight into the timing of rhizoplane colonisation by Pseudomonas fluorescens SBW25. The techniques and analyses developed in this thesis could be applied to many different combinations of plants and microorganisms. Potential applications include the selection of microbial traits which improve maintenance of targeted isolates in agricultural systems, and the development of biological fertilizers.

Item Type:	Thesis (PhD)
Subjects:	Q Science > QK Botany Q Science > QR Microbiology S Agriculture > S Agriculture (General) S Agriculture > SB Plant culture
Library of Congress Subject Headings (LCSH):	Rhizosphere, Colonization (Ecology), Roots (Botany), Pseudomonas fluorescens, Lettuce, Soil ecology
Official Date:	August 2021
Dates:	Date Event August 2021 UNSPECIFIED
Institution:	University of Warwick
Theses Department:	School of Life Sciences
Thesis Type:	PhD
Publication Status:	Unpublished
Supervisor(s)/Advisor:	Gifford, Miriam L. ; Dupuy, Lionel ; Holden, Nicola ; Holmes, Ashleigh
Format of File:	pdf
Extent:	283 leaves : illustrations
Language:	eng

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