Molecular Typing of Acanthamoeba Using Mitochondrial rDNA Spacers

Acanthamoeba is a widespread free-living amoeba known as an opportunistic parasite of humans and other animals. It comprises several species, whose characterisation relies currently on the analysis of 18S rDNA sequences, recognising more than twenty genotypes; however, the distinction between closely related lineages remains unclear. In this study, the spacer region between the mitochondrial large and small subunits of rRNA genes was analysed for its usefulness as a marker for molecular typing. Previous studies have shown that the mitochondrial spacer contains a group of five transfer RNA (tRNA) genes, and that its length and sequence vary considerably between strains. A total of forty-two mitochondrial spacers were examined here, including twenty-five newly recovered sequences, from ten genotypes covering the three morphological groups of Acanthamoeba. The results showed that lineage-specific profiles can be defined for morphological groups 2 and 3 species (MG2 and MG3), with phylogenetic analysis consistent with that of rDNA, allowing for strain identification at the subtype level. In addition, morphological group 1 (MG1) species have a different tRNA gene arrangement distinguishing them from the others. Mitochondrial spacers therefore appear to be promising phylogenetic markers for the molecular typing of Acanthamoeba.