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Title: Functional analysis of a pleiotropic transcription regulator in Staphylococcus aureus - Rsp
Author: Krishna, Aishwarya
ISNI:       0000 0004 6347 2849
Awarding Body: Imperial College London
Current Institution: Imperial College London
Date of Award: 2017
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The Gram-positive commensal Staphylococcus aureus is also an opportunistic pathogen, causing both superficial and lethal infections in humans. The pathogenic versatility of S. aureus has been attributed to its ability to modulate its virulence profile via regulation of the accessory gene regulator (agr) operon. Thus, adaptation by S. aureus is primarily achieved by regulation of transcription, the first step in the gene expression pathway. The major objective of the work described in this thesis was to identify and characterise novel DNA-binding transcription factors (TFs) that regulate agr-operon expression. Using a high-throughput screen for transposon mutants displaying altered virulence factor production, the highly conserved AraC-family DNA-binding TF repressor of surface proteins (Rsp) was identified. Rsp was found to activate agr operon expression by binding directly to the agr-intergenic region. Mutational analysis identified residues in Rsp required for agr-operon activation, and provided further mechanistic insight into the Rsp-agr interaction. Although expression of the agr-operon has been shown to be important for S. aureus virulence in several animal models of infection, here we have shown that a reduction in agr expression via loss of Rsp function enhances S. aureus tolerance to 2 cell wall acting antibiotics. Thus, the results of this study confirm that Rsp is a pleiotropic transcription regulator in S. aureus and highlight the complex relationship between agr expression and virulence in S. aureus. A secondary objective of the work described in this thesis was to consider the clinical implications of mutations in S. aureus RNA polymerase (RNAP), the driver of transcription. To this end, the incidence, prevalence and distribution of RNAP mutations were analysed in 2 collections of S. aureus bacteraemia isolates. The effect of several novel mutations on RNAP stability and transcriptional activity have been predicted with the view that such mutations have the potential to induce global transcriptional changes and ultimately alter the pathogenic properties of S. aureus.
Supervisor: Wigneshweraraj, Sivaramesh ; Edwards, Andrew Sponsor: Imperial College London
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral