Mane, Lavanya; (2021) Metabolomic characterisation of the human pathogen Streptococcus pneumoniae. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Streptococcus pneumoniae metabolism is a major determinant of pathogenesis, enabling the pneumococcus to survive in diverse host microenvironments encountered during colonisation of the nasopharynx, transmission, and disease, and pointing to a distinct capacity for metabolic flexibility. However, pneumococcal metabolic pathways have mainly been inferred from genomic and transcriptomic analyses, with experimental elucidation of only the key aspects of energetic and amino acid metabolism. This thesis describes the characterisation of global carbohydrate and associated metabolism of S. pneumoniae by 13C stable isotopologue profiling using the metabolomic techniques of gas chromatography–mass spectrometry (GC-MS) and proton nuclear magnetic resonance (1H-NMR). It was determined that non-fermentative global metabolism during pneumococcal culture on two niche-specific carbohydrate sources, glucose (abundant in the blood and cerebrospinal fluid) and galactose (abundant in the nasopharynx), proceeds along identical pathways in both high and low carriage prevalence strains (23F and TIGR4, respectively). Biosynthesis of the pneumococcal polysaccharide capsule, a major virulence factor, is connected to carbohydrate metabolism. Using otherwise isogenic capsule-deficient strains TIGR4∆cps and 23F∆cps, this thesis also demonstrated differential carbohydrate-derived carbon flow dependent on capsule type – 23F is metabolically more resilient to the loss of capsule compared to TIGR4, which may contribute to their differing carriage prevalence and invasive potential. In this thesis, novel pathway activities unannotated in the pneumococcal genome corresponding to the presence of a urea cycle, and the potential de novo synthesis of glycine and proline, are also described. Finally, unexplained succinate production has led to the generation of a set of hypotheses for future investigation. Overall, the results presented here highlight the power of unbiased metabolomics analysis in uncovering novel and adaptive aspects of microbial metabolism.

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