Phylogenetic Location of the Spirometra Sparganum Isolates from China, Based on Sequences of 28S rDNA D1

Background: The phylogenetic location of Chinese Spirometra sparganum isolates remains unclear. The aim of this study was to explore the phylogenetic location of the Spirometra sparganum isolates from China. Methods: The 28S ribosomal DNA (rDNA) D1 sequences of 14 Spirometra sparganum isolates collected from thirteen locations in China were analyzed by using Neighbor-Joining (NJ), maximum parsimony (MP) and Bayesian inference (BI), respectively. To investigate the deep variance of 28S rDNA D1 region among included species, the secondary structure of 28S rDNA D1 region was also calculated using the program RNA structure. Results: The genus Spirometra as a monophyletic group was evidenced by two inference methods (MP and BI). All sequences within the genus Spirometra had a bulge of a cytosine residue (Bulge C) in the stem 13 of the secondary structure model of 28S rRNA D1 region. Varietal sites in sequences from all thirteen Chinese isolates were appeared in loops. In loops, adenine was the most abundant base (averagely 41.9%) followed by guanine (averagely 30.0%), and cytosine (averagely 15.1%). In stems, the average percentage of G + C (58.3%) was higher than the percentage of A + T (41.7%). Conclusion: The 'Bulge C' in the stem 13 of the 28S rDNA D1 secondary structure could be as a suitable mark to identify the Spirometra species.