Lima Luciana, Espinosa-Álvarez Oneida, Ortiz Paola A, Trejo-Varón Javier A, Carranza Julio C, Pinto C Miguel, Serrano Myrna G, Buck Gregory A, Camargo Erney P, Teixeira Marta M G
Departamento de Parasitologia, Instituto de Ciências Biomédicas, Universidade de São Paulo, São Paulo, SP 05508-900, Brazil.
Laboratorio de Investigaciones en Parasitología Tropical, Facultad de Ciencias, Universidad del Tolima, Ibagué, Colombia.
Acta Trop. 2015 Nov;151:166-77. doi: 10.1016/j.actatropica.2015.07.015. Epub 2015 Jul 19.
Trypanosoma cruzi is a complex of phenotypically and genetically diverse isolates distributed in six discrete typing units (DTUs) designated as TcI-TcVI. Five years ago, T. cruzi isolates from Brazilian bats showing unique patterns of traditional ribosomal and spliced leader PCRs not clustering into any of the six DTUs were designated as the Tcbat genotype. In the present study, phylogenies inferred using SSU rRNA (small subunit of ribosomal rRNA), gGAPDH (glycosomal glyceraldehyde 3-phosphate dehydrogenase) and Cytb (cytochrome b) genes strongly supported Tcbat as a monophyletic lineage prevalent in Brazil, Panama and Colombia. Providing strong support for Tcbat, sequences from 37 of 47 nuclear and 12 mitochondrial genes (retrieved from a draft genome of Tcbat) and reference strains of all DTUs available in databanks corroborated Tcbat as an independent DTU. Consistent with previous studies, multilocus analysis of most nuclear genes corroborated the evolution of T. cruzi from bat trypanosomes its divergence into two main phylogenetic lineages: the basal TcII; and the lineage clustering TcIV, the clade comprising TcIII and the sister groups TcI-Tcbat. Most likely, the common ancestor of Tcbat and TcI was a bat trypanosome. However, the results of the present analysis did not support Tcbat as the ancestor of all DTUs. Despite the insights provided by reports of TcIII, TcIV and TcII in bats, including Amazonian bats harbouring TcII, further studies are necessary to understand the roles played by bats in the diversification of all DTUs. We also demonstrated that in addition to value as molecular markers for DTU assignment, Cytb, ITS rDNA and the spliced leader (SL) polymorphic sequences suggest spatially structured populations of Tcbat. Phylogenetic and phylogeographical analyses, multiple molecular markers specific to Tcbat, and the degrees of sequence divergence between Tcbat and the accepted DTUs strongly support the definitive classification of Tcbat as a new DTU.
克氏锥虫是一个表型和基因多样的分离株复合体，分布在六个离散分型单元（DTUs）中，分别命名为TcI - TcVI。五年前，从巴西蝙蝠中分离出的克氏锥虫，其传统核糖体和剪接引导PCR呈现独特模式，未聚类到六个DTUs中的任何一个，被指定为Tcbat基因型。在本研究中，使用小亚基核糖体RNA（SSU rRNA）、糖体甘油醛-3-磷酸脱氢酶（gGAPDH）和细胞色素b（Cytb）基因推断的系统发育强烈支持Tcbat作为在巴西、巴拿马和哥伦比亚普遍存在的单系谱系。从47个核基因中的37个和12个线粒体基因（从Tcbat的基因组草图中获取）以及数据库中所有DTUs的参考菌株的序列，为Tcbat作为一个独立的DTU提供了有力支持。与先前的研究一致，对大多数核基因的多位点分析证实了克氏锥虫从蝙蝠锥虫进化而来，并分化为两个主要的系统发育谱系：基部的TcII；以及聚类TcIV的谱系、包含TcIII的分支和姐妹群TcI - Tcbat。很可能，Tcbat和TcI的共同祖先是一种蝙蝠锥虫。然而，本分析结果不支持Tcbat是所有DTUs的祖先。尽管关于蝙蝠中TcIII、TcIV和TcII的报道提供了一些见解，包括亚马逊蝙蝠中携带TcII，但仍需要进一步研究以了解蝙蝠在所有DTUs多样化过程中所起的作用。我们还证明，除了作为DTU分类的分子标记具有价值外，Cytb、ITS rDNA和剪接引导（SL）多态序列表明Tcbat存在空间结构的种群。系统发育和系统地理学分析、特定于Tcbat的多个分子标记以及Tcbat与公认DTUs之间的序列分歧程度，强烈支持将Tcbat明确分类为一个新的DTU。
