Genetic diversity of African isolates of Toxoplasma gondii

Alruhaili, MHB 2016, Genetic diversity of African isolates of Toxoplasma gondii , PhD thesis, University of Salford.

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Toxoplasma gondii is an intracellular protozoan parasite and has the ability to infect all warm-blooded animals, including humans. While the three clonal lineages of T. gondii (I, II and III) predominate in North America and Europe, strains from other regions in the world appear to have more diverse genotypes. The aim of the current research is to analyse the level of genetic variation among local African T. gondii isolates in relation to their phenotype (genotype phenotype relationships). In this study, multi-locus nested PCR sequence analysis of seven Ugandan T. gondii isolates was applied using nine different genetic markers distributed across seven chromosomes and the apicoplast genome of T. gondii, which improved the discrimination power to detect variation among the local Ugandan strains. Although these markers were sufficient to separate global variation between T.gondii strains, they were not adequate to totally resolve within closely related local isolates. To understand the impact of local variation on strain diversity, whole genome sequence was generated for two Ugandan strains type II using Illumina MiSeq paired-end sequencing, revealing variations between these strains and the type II reference strain of T. gondii (TgME49). In this study, we have perhaps the first example of the deeper sequencing of isolates from the same geographical region at the same time point, which showed that they are non-identical. Novel polymorphisms were identified in a virulence associated gene in both Ugandan strains resulting in modification of the protein structure of this gene which could be associated with phenotype variation in the in vitro growth rate of these strains. Comparing the in vitro growth rates of the sympatric Ugandan strains, a cluster of 3 strains had higher growth. These were genotypically identical by using PCR sequencing technique, while the non-identical sympatric strains had lower growth rates, providing evidence that genotype may influence phenotype. An important finding was evidence of recombination between type II and III within three Ugandan strains, revealed through multi-locus PCR sequencing, and in an additional Ugandan strain through deeper whole genome sequencing. Six polymorphic markers were identified via analysis of three biologically relevant genes families (SRS, ROPs and GRA), enhancing the resolution power to identify variations among local type II strains of T. gondii. It is recommended that further study of these polymorphic markers is carried out and that they are added into the MLST analysis of T. gondii, especially between closely related local isolates.

Item Type: Thesis (PhD)
Schools: Schools > School of Environment and Life Sciences > Biomedical Research Centre
Funders: Saudi Embassy in London
Depositing User: MHB Alruhaili
Date Deposited: 16 Jun 2016 11:12
Last Modified: 27 Aug 2021 23:25

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