Sequence Diversity in MIC6 Gene among Toxoplasma gondii Isolates from Different Hosts and Geographical Locations

Abstract

Toxoplasma gondii is an opportunistic protozoan parasite that can infect almost all warm-blooded animals including humans with a worldwide distribution. Micronemes play an important role in invasion process of T. gondii, associated with the attachment, motility, and host cell recognition. In this research, sequence diversity in microneme protein 6 (MIC6) gene among 16 T. gondii isolates from different hosts and geographical regions and 1 reference strain was examined. The results showed that the sequence of all the examined T. gondii strains was 1,050 bp in length, and their A + T content was between 45.7% and 46.1%. Sequence analysis presented 33 nucleotide mutation positions (0-1.1%), resulting in 23 amino acid substitutions (0-2.3%) aligned with T. gondii RH strain. Moreover, T. gondii strains representing the 3 classical genotypes (Type I, II, and III) were separated into different clusters based on the locus of MIC6 using phylogenetic analyses by Bayesian inference (BI), maximum parsimony (MP), and maximum likelihood (ML), but T. gondii strains belonging to ToxoDB #9 were separated into different clusters. Our results suggested that MIC6 gene is not a suitable marker for T. gondii population genetic studies.

Keywords: MIC6; Toxoplasma gondii; sequence diversity; toxoplamosis.

Fig. 1.

Multiple alignment analyses of nucleotides (A) or amino acid sequences (B) of Toxoplasma gondii MIC6 gene. Point (.) indicates identical nucleotide or amino acid compared with that of T. gondii RH strain (upper and bottom lines), and the number indicates the variable sequence positions for nucleotide (A) or amino acid (B).

Fig. 2.

Phylogenetic analysis of 17 Toxoplasma gondii strains (including TgME49) based on MIC6 gene sequences using Bayesian inference (BI), maximum parsimony (MP), and maximum likelihood (ML) methods, with N. caninum as the out-group. Numbers nearby the branches indicate bootstrap values from different analysis in the order of BI, MP, and ML, and clusters of 3 classical genotypes were denoted by I, II, and III, respectively.