The Mitochondrial Genome Of Toxascaris Leonina From South China Tiger: Sequence Analysis And Phylogenetic Implications

Toxascaris leonina is a kind of gastrointestinal roundworms parasitized in the gastrointestinal tract of carnivorous animals, mainly including canine and feline, which can cause gastrointestinal disorders of the host, such as symptoms of diarrhea, malnutrition,edema and gastroenteritis. Meanwhile it has a worldwide distribution and prevalence,causing economic losses and posing potential serious public health problems. In the zoo of our country, most of the felines have been infected by T. leonina, such as African lions,Siberian tiger, South China tigers, lynx and so on, and it is more serious than the infection of companion animals. Currently the use of modern molecular biology technique on species identification, genetic diversity and phylogeny of T. leonina isolated from dogs have been already reported and become more and more common. However, the research of T. leonina isolated from South China tiger are limited to the morphology, the studies of life cycle, the desease prevention and control. The studies about sequence analysis and evolution of the T.leonina isolated from South China tiger haven’t been reported yet.In this study, we isolated worms from feces of the South China tiger naturally infected with T. leonina in the Guangzhou Zoo, then we amplified the mitochondrial genes by using general PCR technology and analyzed their sequence. Results show that the full-length of the mitochondrial genome was 14277 bp, which contained 12 protein-coding genes, 22 t RNA genes and 2 r RNA genes, plus 2 non-coding region, which is the same as the classifications and numbers of general Phasmidia nematodes. And its base content of mitochondria was A=21.64 %, G=20.77 %, T=49.39 %, C=8.19 %, which were biased toward A and T.In order to explore the genetic evolution of T. leonina from South China tiger, this study taked 12 mitochondrial protein-coding genes as genetic markers and used MP method,ML method, BI method to construct phylogenetic tree for Toxascaris from south china tiger and other twelve different nematodes. The result shows that T. leonina was upon the branch of Bayilsascazis, Toxascaris and Ascaris. It had the most close phylogenetic relationships with canine T. leonina, and more phylogenetic relationships with Ascaris suum.This study enriches the database of mitochondrial gene of Toxascaris, and provides the basis for the parasites’ genetic diversity among different hosts. Furthermore, based on the nucleotides sequences of mitochondrial genes, this study constructs the phylogenetic tree and discusses the classifying status, phylogeny and phylogenetic implication of the T.leonina from South China tigers at the molecular level.