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Title: Understanding the genomics and specialised metabolites of the biopesticidal bacterium Burkholderia ambifaria
Author: Mullins, Alex
ISNI:       0000 0004 8500 6304
Awarding Body: Cardiff University
Current Institution: Cardiff University
Date of Award: 2019
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Burkholderia ambifaria is a versatile bacterium frequently isolated from the environment in association with the rhizosphere of important crops species, and occasionally found as an opportunistic pathogen of cystic fibrosis patients. B. ambifaria strains were exploited successfully as biological pesticides during the 1990s, but declined in popularity following concerns over the pathogenicity of associated species in the Burkhlderia cepacia complex. A collection of environmentally and clinically sourced B. ambifaria strains were sequenced with the purpose of developing a deeper understanding of the biopesticide. Comparative genomics were combined with in vitro metabolite analyses, antagonism assays, and agriculturally relevant biological control assays to determine the contribution of antimicrobial metabolites to biocontrol. Genome mining for biosynthetic gene clusters (BGCs) revealed a considerable specialised metabolite potential, and multiple BGCs associated with characterised antimicrobials. Regulatory gene mining of quorum sensing associated luxR genes revealed an uncharacterised LuxRI system linked to an unknown BGC. Insertional mutagenesis and mass spectrometry confirmed the BGC as the biosynthetic origin of the historical Burkholderia polyyne metabolite cepacin. Comparison of the B. ambifaria BCC0191 wild-type with the cepacin-deficient mutant highlighted the importance of cepacin in the biological control of Pythium ultimum with a Pisum sativum crop model. The biocontrol phenotype was maintained following the deletion of the third replicon, and subsequent virulence testing in a murine respiratory inhalation model demonstrated a reduced persistence compared to the wild-type. This study systematically defined the specialised metabolite biosynthetic potential of B. ambifaria, and demonstrated the importance of the polyyne cepacin in biological control. Maintenance of biocontrol and loss of virulence following third-replicon deletion presents an opportunity to attenuate B. ambifaria and address the pathogenicity concerns that led to the decline of B. ambifaria as a biopesticide.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available