Abstract
BackgroundToxoplasma gondii is a highly prevalent protozoan parasite infecting a wide range of animals and humans. The epidemiological and biological diversity of T. gondii has resulted in a high genetic variation and unusual population structure in this parasite. This study examined sequence diversity in dense granule 5 (GRA5) gene among T. gondii isolates from different hosts and geographical regions.MethodsThe entire genome region of the GRA5 gene was amplified and sequenced from 14 T. gondii isolates, and phylogenetic relationship among these T. gondii isolates was reconstructed using Bayesian inference (BI) and maximum parsimony (MP) based on the GRA5 sequences.ResultsThe complete sequence of the GRA5 gene was 1614 bp in length for strains TgCatBr5 and MAS, but 1617 bp for the other 12 strains. Sequence analysis identified 41 (0–1.7%) variable nucleotide positions among all isolates, with 18 variations of these being in the coding region. Variable positions in the coding region resulted in 11 amino acid substitutions, and a deletion of 3 bp in the strains TgCatBr5 and MAS leading to the deletion of one amino acid. Sequence variations resulted in the existence of polymorphic restriction sites for endonucleases AatII and MluI, allowing the differentiation of the three major clonal lineage types I, II and III by PCR-RFLP. Phylogenetic analyses using BI and MP supported the clear differentiation of the examined T. gondii strains into their respective genotypes.ConclusionsThis study demonstrated the existence of sequence variability in the GRA5 gene sequence among T. gondii isolates from different hosts and geographical regions, which allowed the differentiation of the examined T. gondii strains into their respective genotypes, suggesting that this highly polymorphic GRA5 locus may provide a new genetic marker for population genetic studies of T. gondii isolates.
Highlights
Toxoplasma gondii is a highly prevalent protozoan parasite infecting a wide range of animals and humans
In order to adapt to different environments in its hosts, T. gondii has evolved a complex life cycle involving the development of asexual forms in various warm-blooded hosts, with the occurrence of sexual replication only in the cat gut [2], as well as established different modes of transmission including the ability of transmission between intermediate hosts through carnivorous or omnivorous feeding [7]
Sequence analysis The granule 5 (GRA5) amplicons produced a single product of approximately 1600 bp in length on agarose gel for all 14 examined T. gondii strains, and the amplicons of all isolates were sequenced
Summary
Toxoplasma gondii is a highly prevalent protozoan parasite infecting a wide range of animals and humans. In order to adapt to different environments in its hosts, T. gondii has evolved a complex life cycle involving the development of asexual forms in various warm-blooded hosts, with the occurrence of sexual replication only in the cat gut [2], as well as established different modes of transmission including the ability of transmission between intermediate hosts through carnivorous or omnivorous feeding [7]. Such an adaptation to various ecological systems has given rise to a highly genetic variation and unusual population structure in the parasite [8,9]. Our thorough knowledge of genetic diversity of T. gondii is central to better understand epidemiological patterns and pathogenicity, as well as explore the new strategies for vaccination, treatment, or diagnosis of toxoplasmosis
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