| Strongylidae nematode is an important parasite which parasites in the large intestine of equine animals.It has the characteristics of multiple parasitic species,large numbers,fast reproduction speed and so on.The host can show anemia,diarrhea,mechanical obstruction emaciation and even death when a large number of worms parasitize in it,causing serious economic losses to equine breeding industry.The research on Strongylidae nematodes of equine mainly focuses on morphology,epidemiology and drug treatment.In recent years,some scholars have explored the genetic relationship of Strongylidae nematodes of equine by molecular method,while the results obtained are somewhat different from the traditional morphology.Due to the limitation of relevant data,the accuracy of molecular studies can not be determined.In view of this,six Strongylidae nematodes including Cylicostephanus longibursatum,Coronocyclus coronatus,Cylicocyclus leptostomus,Poteriostomum ratzii,Parapoteriostomum mettami and Strongylus edentatus obtained from horses intestines in Daqing City,Heilongjiang Province were identified by morphological and molecular in this study,and the complete mitochondrial genome sequence were amplified.Besides,the mitochondrial genomes of 29 nematodes in Strongylidae including six Strongylidae nematodes in this study were compared and analyzed.Finally,concatenated 12 protein coding gene sequences were used as markers,and the phylogenetic tree was constructed by BI,ML and MP methods to explore the genetic relationship between these six nematodes and Strongyloidea nematodes,especially with other Strongylidae nematodes of equine.The results showed that morphological and molecular biological identification were consistent,six Strongylidae nematodes of equine were identified correctly.The complete mitochondrial genome sequences of Cs.longibursatum,Co.coronatus,Cc.leptostomus,Po.ratzii,Pa.mettami and S.edentatus,were 13 803 bp,13 865 bp,13 853 bp,13804 bp,13 815 bp and 14 765 bp,respectively.They were all composed of 12 protein coding genes,22 t RNAs and 2 r RNAs,except for the three non-coding regions of S.edentatus,the other five nematodes all had two non-coding regions.All genes were in the same chain and transcription direction was the same.The contents of A and T base in mitochondrial genome of 6species of nematodes were high,which were 75.59%,75.43%,75.36%,74.65%,75.20% and78.15%,respectively.Comparative analysis in 29 species of Strongylidae nematodes of equine showed that the similarity of nucleotide sequences in mitochondrial genome was between76.20% and 98.20%,with 82.3 ～ 98.2% in the Cyathostominae nematodes and 76.6-96.2% in the subfamily Strongylinae.Notablely,the similarity of the complete mitochondrial genome sequences between the Triodontophorus and Cyathostominae nematodes was higher than that of the Strongylus nematodes of the same subfamily.The results of phylogenetic analysis showed that Cs.minutus of Cylicostephanus and Co.coronatus of Coronocyclus were not in the branches of their respective genera,and with far distance.Therefore,the Cylicostephanus and Coronocyclus should be complex genus;Pa.mettami and Po.ratzii were in the same branch,and their genetic relationship was closer than that of Poteriostomum imparidentatum of the same genus;Triodontophorus is in the branch of Cyathostominae,and its genetic relationship with Cyathostominae was closer than that of Strongylinae.This study obtained the mitochondrial genome sequences of six nematodes,Cs.longibursatum,Co.coronatus,Cc.leptostomus,Po.ratzii,Pa.mettami and S.edentatus for the first time.By comparing the mitochondrial gene sequences of Strongylidae nematodes of equine and the phylogenetic analysis,it was found that the relationship between Triodontophorus and Strongylinae was closer than that of Strongylus,supporting the hypothesis that Triodontophorus should belong to the subfamily Cyathostominae.This study provides basic data for the molecular classification,population genetics and phylogenetic analysis of Strongylidae nematodes of equine. |
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