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Title: Functional genomics of the insect-vector symbiont, Sodalis glossinidius
Author: Gordon, Lauren
ISNI:       0000 0004 9352 0549
Awarding Body: University of Liverpool
Current Institution: University of Liverpool
Date of Award: 2020
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Animal- (AAT) and human African trypanosomiasis (HAT) is endemic within sub-Saharan Africa and is caused by Trypanosoma spp. parasites vectored by biting tsetse flies. The facultative secondary symbiont, Sodalis glossinidius, has been controversially implemented in increased parasite establishment in tsetse. As the role of S. glossinidius in tsetse is not fully understood within the literature, the research presented here aimed to utilise a functional genomics approach to elucidate S. glossinidius functionality from a genetic context. Initial phenotypic-level in vitro media screening experiments confirmed S. glossinidius heterotrophy and revealed higher growth levels in the presence of glucose: S. glossinidius was unable to grow in a minimal salts medium (M9) devoid of a sufficient organic carbon source, and showed higher growth values in glucose-positive M9 variations compared to equivalent glucose-negative counterparts. This glucose utilisation was also observed with better growth between a complex medium rich in glucose (Mitsuhashi and Maramorosch Insect Medium) versus one with lower concentrations (Schneider’s Insect Medium). Subsequent genotypic-level transposon-directed insertion site sequencing (TraDIS) library selection experiments supported S. glossinidius glucose utilisation with essential gene candidacy in glycolysis, gluconeogenesis and the pentose phosphate pathway. These results, in combination within essentiality in the citric acid cycle, a wide range of carbon source metabolism pathways, and virulence-associated genes (Omp porins, flagellar components and type III secretion system constituents), experimentally confirm the sequence-inferred literature consensus that S. glossinidius has retained a functional repertoire more aligned with free-living organisms. Many of the essential gene candidates were pseudogenes, which when considered with the literature evidence that S. glossinidius is actively maintaining a core pseudogene set across lineages, experimentally supports the theory that symbionts in early stages of genome degradation associated with the free-living to symbiont lifestyle switch preference pseudogene retention. The novel TraDIS library presented here provides the currently missing tool for subsequent targeted functionality in vivo experiments, aimed at fully understanding the S. glossinidius role in the tsetse system.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral