Background: Spirometra erinaceieuropaei, the causative agent of food/water-borne sparganosis, has been widely reported worldwide. However, the taxonomy of the genus Spirometra has always been complicated. The main objectives of this study were to assemble 7 complete mitochondrial genomes of Spirometra erinaceieuropaei, collected from different hosts in the Hunan province of China, and to analyze the phylogenetic relationship and genetic diversity of cestode species.
Methods: In this study, seven Spirometra erinaceieuropaei (three spargana and 4 adults) were collected from different hosts in Hunan province, China. The long-PCR was performed to amplify the four large fragments of the Spirometra mitochondria (mt) genome by using specific primers reported in a previous study. Then, the mt genome of each S. erinaceieuropaei was assembled and annotated after overlapping four large fragments. Sliding window analysis was carried out to explore the nucleotide variation of the mt genome between 7 isolates obtained in this study and 8 reported Spirometra. The genetic diversity of cestode species was also investigated by Bayesian analysis based on 12 protein-coding genes.
Results: Seven mt genomes of S. erinaceieuropaei obtained in this study were successfully assembled and annotated. The genome features of S. erinaceieuropaei are similar to other reported cestode species, containing 12 protein-coding genes (PCGs), 22 transfer RNA genes (tRNAs), and two ribosomal RNA genes (rRNA), large non-coding regions (NC), and small non-coding regions (NR). Sequencing analysis revealed 97.40%-99.90% sequence similarity among seven mt genomes identified in this study. Sliding window analysis indicated that the Korea isolate (KJ599680) might be the differential specie of genus Spirometra, and nad4L, cox3, and nad6 were the top three genes with the lowest variation rates in mt DNA. Phylogenetic analysis based on 12 PCGs further demonstrated that S. mansoni (AB374543) might be the misnamed S. erinaceieuropaei.
Conclusion: The results of the current study supports the previously reported conclusion that multiple genotypes exist within S. erinaceieuropaei, and the Korean isolate (KJ599680) be a novel genotype or even a novel species of the genus Spirometra, and we strongly suggests that S. decipines may be a misnamed of S. erinaceieuropaei like S. mansoni is. nad4L, cox3 and nad6 are more suitable molecular genetic markers than cox1 for S. erinaceieuropaei identification. However, the authentic relationships among S. erinaceieuropaei isolates from different hosts and geographical sites are still unknown. More samples must be collected in different host and geographical positions to help us understand the genus Spirometra.