The complete mitochondrial genome of the gullet worm Gongylonema pulchrum: gene content, arrangement, composition and phylogenetic implications

Background: Gongylonema pulchrum (Nematoda: Gongylonematidae), a thread-like spirurid gullet worm, infects a range of mammalian definitive hosts, including cattle, pigs, equines, goats, primates and humans, and can cause gongylonemiasis. Methods: In the present study, the complete mitochondrial (mt) genome of Gongylonema pulchrum was obtained using Long-range PCR and subsequent primer walking. The phylogenetic position of Gongylonema pulchrum within the Spiruromorpha was established using Bayesian analyses of the protein-coding genes at the amino acid level. Results: The length of this AT-rich (75.94%) mt genome is 13,798 bp. It contains 12 protein-coding genes, two ribosomal RNA genes, 22 transfer RNA genes and one non-coding region. The gene arrangement is the same as those of Thelazia callipaeda (Thelaziidae) and Setaria digitata (Onchocercidae), but distinct from that of Heliconema longissimum (Physalopteridae). Phylogenetic analyses, based on the concatenated amino acid sequence data for all 12 protein-coding genes using Bayesian inference (BI) method, showed that Gongylonema pulchrum (Gongylonematidae) was more closely related to Spirocerca lupi (Spiruroidea) than other members of the infraorder Spiruromorpha. Conclusions: The present study represents the first mt genome sequence for the family Gongylonematidae, which provides the opportunity to develop novel genetic markers for studies of epidemiology, population genetics and systematics of this nematode of human and animal health significance.