He Lan, Zhang Ying, Zhang Qing-Li, Zhang Wen-Jie, Feng Hui-Hui, Khan Muhammad Kasib, Hu Min, Zhou Yan-Qin, Zhao Jun-Long
State Key Laboratory of Agricultural Microbiology, College of Veterinary Medicine, Huazhong Agricultural University, Wuhan, Hubei, 430070, China.
Parasit Vectors. 2014 Feb 28;7:82. doi: 10.1186/1756-3305-7-82.
Apicomplexan parasites of the genus Babesia, Theileria and Plasmodium are very closely related organisms. Interestingly, their mitochondrial (mt) genomes are highly divergent. Among Babesia, Babesia orientalis is a new species recently identified and specifically epidemic to the southern part of China, causing severe disease to water buffalo. However, no information on the mt genome of B. orientalis was available.
Four pairs of primers were designed based on the full genome sequence of B. orientalis (unpublished data) and by aligning reported mt genomes of B. bovis, B. bigemina, and T. parva. The entire mt genome was amplified by four sets of PCR. The obtained mt genome was annotated by aligning with published apicomplexan mt genomes and Artemis software v11. Phylogenetic analysis was performed by using cox1 and cob amino acid sequences.
The complete mt genome of B. orientalis (Wuhan strain) was sequenced and characterized. The entire mt genome is 5996 bp in length with a linear form, containing three protein-coding genes including cytochrome c oxidase I (cox1), cytochrome b (cob) and cytochrome c oxidase III (cox3) and six rRNA large subunit gene fragments. The gene arrangement in B. orientalis mt genome is similar to those of B. bovis, B. gibsoni and Theileria parva, but different from those of T. orientalis, T. equi and Plasmodium falciparum. Comparative analysis indicated that cox1 and cob genes were more conserved than cox3. Phylogenetic analysis based on amino acid sequences of cox1, cob and cox1 + cob, respectively, revealed that B. orientalis fell into Babesia clade with the closest relationship to B. bovis.
The availability of the entire mt genome sequences of B. orientalis provides valuable information for future phylogenetic, population genetics and molecular epidemiological studies of apicomplexan parasites.
巴贝斯虫属、泰勒虫属和疟原虫属的顶复门寄生虫是亲缘关系非常密切的生物。有趣的是，它们的线粒体（mt）基因组差异很大。在巴贝斯虫中，东方巴贝斯虫是最近发现的一个新物种，在中国南方地区呈地方流行性，可给水牛造成严重疾病。然而，关于东方巴贝斯虫线粒体基因组的信息尚无报道。
基于东方巴贝斯虫全基因组序列（未发表数据），并通过比对已报道的牛巴贝斯虫、双芽巴贝斯虫和微小泰勒虫的线粒体基因组，设计了4对引物。通过4组聚合酶链式反应（PCR）扩增整个线粒体基因组。将获得的线粒体基因组与已发表的顶复门线粒体基因组及Artemis软件v11进行比对注释。利用细胞色素c氧化酶I（cox1）和细胞色素b（cob）氨基酸序列进行系统发育分析。
对东方巴贝斯虫（武汉株）的完整线粒体基因组进行了测序和特征分析。整个线粒体基因组长度为5996 bp，呈线性形式，包含3个蛋白质编码基因，即细胞色素c氧化酶I（cox1）、细胞色素b（cob）和细胞色素c氧化酶III（cox3）以及6个核糖体RNA大亚基基因片段。东方巴贝斯虫线粒体基因组中的基因排列与牛巴贝斯虫、吉氏巴贝斯虫和微小泰勒虫的相似，但与东方泰勒虫、马泰勒虫和恶性疟原虫的不同。比较分析表明，cox1和cob基因比cox3更保守。分别基于cox1、cob和cox1 + cob氨基酸序列的系统发育分析显示，东方巴贝斯虫属于巴贝斯虫进化枝，与牛巴贝斯虫的亲缘关系最近。
东方巴贝斯虫完整线粒体基因组序列的获得，为未来顶复门寄生虫的系统发育、群体遗传学和分子流行病学研究提供了有价值的信息。
