Characterisation of large and small subunit rRNA and mini-exon genes further supports the distinction of six Trypanosoma cruzi lineages

Abstract

It has been proposed that isolates of Trypanosoma cruzi, the agent of American trypanosomiasis, can be ordered into two primary phylogenetic lineages, first based on multilocus enzyme electrophoresis and random amplified polymorphic DNA, and subsequently based on the 24Sα rRNA and mini-exon genes. Recent multilocus enzyme electrophoresis and random amplified polymorphic DNA data have additionally shown that the major multilocus enzyme electrophoresis/random amplified polymorphic DNA lineage II is further subdivided into five smaller lineages, designated IIa–IIe. In this study, the precise correspondence between the multilocus enzyme electrophoresis/random amplified polymorphic DNA and rRNA/mini-exon lineages was investigated. Using the 24Sα rRNA and mini-exon markers in combination, five sets of strains were distinguished, corresponding to the multilocus enzyme electrophoresis/random amplified polymorphic DNA lineages I, IIa, IIc, IId and to lineages IIb/IIe together, respectively. The previous categorisation into only two primary lineages based on 24Sα rRNA and mini-exon characterisation is explained, in part, by the lack of representativeness of the breadth of T. cruzi diversity in earlier study samples. Additionally, a PCR assay based on a length-variable region of the 18S rRNA gene distinguished lineage IIe from lineage IIb. Thus, the six multilocus enzyme electrophoresis/random amplified polymorphic DNA lineages could be readily identified by combining data from the 24Sα rRNA, mini-exon and 18S rRNA characterisation assays, further supporting the relevance of these genetic units for T. cruzi strain classification and subspecific nomenclature. The recently proposed groups T. cruzi I and T. cruzi II correspond to multilocus enzyme electrophoresis/random amplified polymorphic DNA lineages I and IIb, respectively. Our findings show that T. cruzi lineage characterisation based on a single marker (either mini-exon or 24Sα rRNA) has insufficient resolution, and leads to important reinterpretations of recent epidemiological and evolutionary studies based on the oversimplified rRNA/mini-exon dichotomic classification of T. cruzi isolates.