Cylicocyclus spp. are common parasites in the intestine of equine animals. Hosts infected by these strongylid nematodes might face emaciation, anemia, and even death, all of which lead to significant economic losses. In the present study, the complete mitochondrial genome (mitogenome) of Cylicocyclus radiatus, the type species of the genus Cylicocyclus, was sequenced and characterized for the first time using next-generation sequencing technology. Results show that the mitogenome of C. radiatus is a double-stranded 13,836 bp circular molecule, containing 12 protein-coding genes, 22 tRNA genes, two rRNA genes, and two non-coding regions. Moreover, it has a clear bias in nucleotide composition and codon preference towards protein-coding genes with elevated AT content. All protein-coding genes are initiated by ATT and TTG codons, and almost all of them end with complete TAA and TAG termination codons; only the COШ gene harbors the incomplete T termination codon. All tRNA genes fold into an atypical clover-leaf secondary structure. The tRNA-Ser genes possess a TΨC arm and variable loop, but lack the dihydrouridine arm and loop. Twenty tRNAs contain the dihydrouridine arm and loop, in which the variable TΨC arm and loop are replaced by a "TV-replacement loop". Most tRNA gene secondary structures contain G-U, U-U, and A-G mismatches. Phylogenetic analysis based on nucleotide sequences of the 12 protein-coding genes using maximum likelihood and Bayesian inference indicated that C. radiatus is related more closely to Cylicocyclus nassatus than to Cylicocyclus insigne. In summary, this study provides the first annotated sequence of the mitogenome of C. radiatus, paving the way for further research on species classification and the molecular evolution of strongylid nematodes.

中文翻译：

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辐射圆环的第一个完整的线粒体基因组的表征和系统发育分析。

圆环菌属 是马类动物肠道中常见的寄生虫。被这些强线虫感染的宿主可能面临消瘦，贫血甚至死亡，所有这些都会导致重大的经济损失。在本研究中，使用下一代测序技术首次对放射状的圆环线虫（Cylicocyclus属的种）的完整线粒体基因组（有丝分裂基因组）进行了测序和鉴定。结果表明，放射线虫的有丝分裂基因组是一个双链的13836 bp的环状分子，包含12个蛋白质编码基因，22个tRNA基因，两个rRNA基因和两个非编码区。此外，它在核苷酸组成和密码子偏爱方面对AT含量升高的蛋白质编码基因具有明显的偏见。所有蛋白质编码基因均由ATT和TTG密码子启动，它们几乎都以完整的TAA和TAG终止密码子结尾；只有CO 3基因带有不完整的T终止密码子。所有的tRNA基因都折叠成非典型的三叶草叶二级结构。tRNA-Ser基因具有TΨC臂和可变环，但缺少二氢尿苷臂和环。二十个tRNA包含二氢尿苷臂和环，其中可变的TΨC臂和环被“电视替换环”代替。大多数tRNA基因二级结构包含GU，UU和AG错配。系统进化分析基于12种蛋白质编码基因的核苷酸序列，采用最大似然法和贝叶斯推论表明，放射状梭状芽胞杆菌与nyluscyclus nassatus的相关性比与Cylicocyclus insigne密切相关。总而言之，这项研究提供了C.radiatus有丝分裂基因组的第一个注释序列，