BIOPHARM, Research Institute of Biopharmacy and Veterinary Drugs, a.s., Pohori-Chotoun, Jilove u Prahy 254 49, Czech Republic.
Vet Parasitol. 2011 Dec 29;183(1-2):47-53. doi: 10.1016/j.vetpar.2011.06.020. Epub 2011 Jun 30.
Although the validity of the coccidian species, Eimeria mivati, has been questioned by many researchers for a long time there has not been any molecular analysis that would help resolve this issue. Here we report on the discovery of the two types of small ribosomal subunit (18S) gene within the Eimeria mitis genome that correspond to the known 18S sequences of E. mitis and E. mivati, and this is in conflict with the existence of E. mivati as an independent species. We have carried out five single oocyst isolations to obtain five single-oocyst-derived strains of E. mitis and these were analyzed by the sequencing of 18S and mitochondrial cytochrome c oxidase subunit I genes. The two types of 18S gene were found to be present in each strain in roughly equal ratios. This indicates that if the strains carrying only one or the other 18S type exist, they will likely cross-breed and still represent a single species. However, the more probable explanation is that all strains of E. mitis contain two types of 18S gene and that the occasional detection of only one or the other type by sequencing might be caused by insufficient sampling. This is also the first report of the two types of 18S gene in Eimeria, which has already been described in some other apicomplexan species, most notably Plasmodium. We also found that these two types of ribosomal RNA differ significantly in their secondary structure. The biological significance of the two 18S gene variants in E. mitis is not known, however, we hypothesize that these variants might be used in different stages of the parasite's life-cycle as it is in other apicomplexan species investigated so far.
虽然球虫种，Eimeria mivati 的有效性长期以来一直受到许多研究人员的质疑，但目前还没有任何分子分析可以帮助解决这个问题。在这里，我们报告了在 Eimeria mitis 基因组中发现两种类型的小核糖体亚基（18S）基因，它们与已知的 E. mitis 和 E. mivati 的 18S 序列相对应，这与 E. mivati 作为一个独立物种的存在相矛盾。我们进行了五次单卵囊分离，获得了五种单卵囊衍生的 E. mitis 株，并通过 18S 和线粒体细胞色素 c 氧化酶亚基 I 基因测序进行了分析。发现两种类型的 18S 基因在每个菌株中大致以相等的比例存在。这表明，如果只携带一种或另一种 18S 类型的菌株存在，它们很可能会杂交，仍然代表一个单一的物种。然而，更有可能的解释是，所有 E. mitis 菌株都含有两种类型的 18S 基因，而测序时偶尔只检测到一种或另一种类型可能是由于采样不足所致。这也是首次在 Eimeria 中发现两种类型的 18S 基因，这种情况已经在其他一些顶复门物种中得到描述，尤其是疟原虫。我们还发现，这两种类型的核糖体 RNA 在二级结构上有很大的差异。然而，E. mitis 中这两种 18S 基因变体的生物学意义尚不清楚，我们假设这些变体可能在寄生虫生命周期的不同阶段使用，就像迄今为止在其他顶复门物种中研究的那样。
