The Comparative And Phylogenetic Analyses Of Complete Mt Genomes Of Five Cyathostominae Nematodes Of Equine

Cyathostominae nematodes of equine were the most important parasites in the large intestine which belonged to Strongylidae.It can cause anemia,poor hair coat,weight loss and intermittent diarrhea,or even present a life-threatening when a large number of Strongylid nematodes infected the host,which lead serious losses to horse breeding.This kinds of nematodes are characterized by high quantities and species abundance,but classification of this group of parasitic nematodes is debated.Now information on these nematodes is limited to the morphology,prevalence and disease control,however the complete mt DNA,genetic evolution,phylogenetic relationship of these nematodes are relatively rare.Thus,the aims of this study were to: determine the species of the five nematodes(Cyathostomum pateratum,Cyathostomum catinatum,Cylicocyclus nassatus,Cylicostephanus minutus,Poteriostomum imparidentatum)based on their morphological and molecular biological characteristics;obtain complete mt genome sequences of the five nematodes;analyze and compare the five mt genomes and reconstruct the phylogenetic relationship of Cyathostominae nematodes with other nematodes based on mt DNA data.The morphological features of Cc.nassatus,Cy.catinatum,Cy.pateratum,P.imparidentatum,Cs.minutus were identical with the description in document literature,the ITS sequences of five nematodes obtained in the present study had 99.9%,99.6%,99.8%,99.7% and 99.2% identities to the corresponding available sequences in Gen Bank,which were confirmed the five species based on morphological characteristics and ITS sequences,accurately.The complete mt genomes of Cy.pateratum,Cy.catinatum,Cc.nassatus,Cs.minutus,P.imparidentatum were13822 bp,13838 bp,13846 bp,13826 bp and 13817 bp in length,respectively.All five mt genomes contained 12 protein-coding genes,22 t RNA genes,two r RNA genes,and two non-coding regions,which were all transcribed in the same direction.The overall mt genome of five nematodes prefered bases A and T,which was 75.70%(Cy.pateratum),76.12%(Cy.catinatum),74.74%(Cc.nassatus),76.77%(Cs.minutus),74.65%(P.imparidentatum),respectively.The comparison of five complete mt DNA nucleotide sequences revealed thatidentity ranged from 84.1% to 95.1%.The mt genome sequences of Cy.pateratum and Cy.catinatum had the highest identity and the lowest identity between Cy.pateratum and P.imparidentatum.The mt genome sequences of three Triodontophorus species had relatively high identity with Cyathostominae nematodes,rather than Strongylus species of the same subfamily(Strongylinae).Meanwhile,it was also found that mt genome organization for 20 Strongyloidea nematodes sequenced to date revealed that members of this superfamily possess identical gene arrangements.Phylogenetic analyses using the concatenated 12 protein-coding genes indicated that the Triodontophorus species had closer relationship with Cyathostominae species instead of Strongylus species,which provide the evidence for the hypothesis that Triodontophorus may be belonged to Cyathostominae.The complete mt genome sequences of Cy.pateratum,Cy.catinatum,Cc.nassatus,Cs.minutus,P.imparidentatum were first determined in present study.The results from the analyses indicate that the mt genome arrangements of 20 Strongyloidea nematodes sequenced to date are identical.And the findings of present study,which used comparative and phylogenetic analyses of mt DNA sequences,supported the hypothesis that Triodontophorus species belong to Cyathostominae.This study not only enrich the mt DNA database of nematodes,but also provide novel genetic markers for further studies of Strongylidae systematics,molecular taxonomy,genetic evolution,and phylogenetic relationship.