Abstract：
Cryptosporidium spp. are important diarrhea-associated pathogens in humans and livestock. Among the known species, Cryptosporidium xiaoi, which causes cryptosporidiosis in sheep and goats, was previously recognized as a genotype of the bovine-specific Cryptosporidium bovis based on their high sequence identity in the ssrRNA gene. However, the lack of genomic data has limited characterization of the genetic differences between the two closely related species. In this study, we sequenced the genomes of two C. xiaoi isolates and performed comparative genomic analysis to identify the sequence uniqueness of this ovine-adapted species compared with other Cryptosporidium spp. Our results showed that C. xiaoi is genetically related to C. bovis as shown by their 95.8% genomic identity and similar gene content. Consistent with this, both C. xiaoi and C. bovis appear to have fewer genes encoding mitochondrial metabolic enzymes and invasion-related protein families. However, they appear to possess several species-specific genes. Further analysis indicates that the sequence differences between these two Cryptosporidium spp. are mainly in 24 highly polymorphic genes, half of which are located in the subtelomeric regions. Some of these subtelomeric genes encode secretory proteins that have undergone positive selection. In addition, the genomes of two C. xiaoi isolates, identified as subtypes XXIIIf and XXIIIh, share 99.9% nucleotide sequence identity, with six highly divergent genes encoding putative secretory proteins. Therefore, these species-specific genes and sequence polymorphism in subtelomeric genes probably contribute to the different host preference of C. xiaoi and C. bovis.
摘要：
隐孢子虫。是人类和家畜中重要的腹泻相关病原体。在已知的物种中，隐孢子虫,导致绵羊和山羊隐孢子虫病，基于它们在ssrRNA基因中的高度序列同一性，先前被认为是牛特异性隐孢子虫的基因型。然而,缺乏基因组数据限制了两个密切相关物种之间遗传差异的表征。在这项研究中,我们对两种C.xiaoi分离株的基因组进行了测序，并进行了比较基因组分析，以确定与其他隐孢子虫属物种相比，这种适应绵羊的物种的序列独特性。我们的结果表明，C.xiaoi与C.bovis具有95.8％的基因组同一性和相似的基因含量。与此一致，C.xiaoi和C.bovis似乎都具有较少的编码线粒体代谢酶和入侵相关蛋白家族的基因。然而,它们似乎拥有几个物种特异性基因。进一步分析表明，这两个隐孢子虫之间的序列差异。主要在24个高度多态性的基因中，其中一半位于亚端粒区。这些亚端粒基因中的一些编码已经历正选择的分泌蛋白。此外,两个C.Xiaoi分离株的基因组，鉴定为亚型XXIIIf和XXIIIh，共享99.9%的核苷酸序列同一性，有六个高度不同的基因编码推定的分泌蛋白。因此,这些物种特异性基因和亚端粒基因中的序列多态性可能导致C.xiaoi和C.bovis的不同宿主偏好。
