Genetic diversity of African isolates of Toxoplasma gondii

Alruhaili, MHB

Abstract

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.

Citation

Alruhaili, M. (in press). Genetic diversity of African isolates of Toxoplasma gondii. (Thesis). University of Salford

• Thesis Type: Thesis
• Acceptance Date: Jan 11, 2016
• Deposit Date: Jun 16, 2016
• Publicly Available Date: Jun 16, 2016
• Additional Information: Funders : Saudi Embassy in London