Comparative analyses of the complete mitochondrial genomes of the two ruminant hookworms Bunostomum trigonocephalum and Bunostomum phlebotomum

Bunostomum trigonocephalum and Bunostomum phlebotomum are blood-feeding hookworms of sheep and cattle, causing considerable economic losses to the live stock industries. Studying genetic variability within and among hookworm populations is critical to addressing epidemiological and ecological questions. Mitochondrial (mt) DNA is known to provide useful markers for investigations of population genetics of hookworms, but mt genome sequence data are scant. In the present study, the complete mitochondrial DNA (mtDNA) sequences of the sheep and goat hookworm B. trigonocephalum were determined for the first time, and the mt genome of B. phlebotomum from yak in China was also sequenced for comparative analyses of their gene contents and genome organizations. The lengths of mt DNA sequences of B. trigonocephalum sheep isolate, B.trigonocephalum goat isolate and B. phlebotomum China yak isolate were 13,764 bp, 13,771 bp and 13,803 bp in size, respectively. The identity of the mt genomes was 99.7% between B. trigonocephalum sheep isolate and B. trigonocephalum goat isolate. The identity of B. phlebotomum China yak isolate mt genomes was 85.3% with B. trigonocephalum sheep isolate, and 85.2% with B. trigonocephalum goat isolate. All the mt genes of the two hookworms were transcribed in the same direction and gene arrangements were consistent with those of the GA3 type, including 12 protein-coding genes, 2 rRNA genes and 22 tRNA genes, but lacking ATP synthetase subunit 8 gene. The mt genomes of B. trigonocephalum and B. phlebotomum were similar to prefer bases A and T, the contents of A + T are 76.5% (sheep isolate), 76.4% (goat isolate) and 76.9% (China yak isolate), respectively. Phylogenetic relationships reconstructed using concatenated amino acid sequences of 12 protein-coding genes with three methods (maximum likelihood, Bayesian inference and neighbor joining) revealed that the B. trigonocephalum and B. phlebotomum represent distinct but closely-related species. These data provide novel and useful genetic markers for studying the systematics, and population genetics of the two ruminant hookworms.