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Open Access Research

Genetic diversity among Toxoplasma gondii strains from different hosts and geographical regions revealed by sequence analysis of GRA5 gene

Jia Chen12, Zhong-Yuan Li12, Dong-Hui Zhou1, Guo-Hua Liu13 and Xing-Quan Zhu13*

Author Affiliations

1 State Key Laboratory of Veterinary Etiological Biology, Key Laboratory of Veterinary Parasitology of Gansu Province, Lanzhou Veterinary Research Institute, Chinese Academy of Agricultural Sciences, Lanzhou, Gansu Province 730046, China

2 College of Veterinary Medicine, South China Agricultural University, Guangzhou, Guangdong Province, 510642, China

3 College of Veterinary Medicine, Hunan Agricultural University, Changsha, Hunan Province 410128, China

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Parasites & Vectors 2012, 5:279  doi:10.1186/1756-3305-5-279

Published: 3 December 2012

Abstract

Background

Toxoplasma 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.

Methods

The 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.

Results

The 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.

Conclusions

This 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.

Keywords:
Toxoplasma gondii; Toxoplasmosis; GRA5 gene; Genetic diversity; Genotyping