Evidence for mitochondrial pseudogenes (numts) as a source of contamination in the phylogeny of human whipworms.

Abstract

Trichuris trichiura and T. suis are whipworms of humans and pigs, respectively, but it has recently been suggested that humans may be infected with multiple genotypes or species of Trichuris and cross-infection with Trichuris of pig origin has also been reported. In addition, the species status of Trichuris in non-human primates is unsettled and it is unknown how many whipworm species we share with other primates. Herein, we inferred the phylogeny of Trichuris collected from human, baboon and pig based on nuclear (18S and beta-tubulin) and mitochondrial (cox1) genes and evaluated the use of three PCR linked restriction fragment length polymorphism (PCR-RFLP) to identify worms. We found that all baboon worms clustered with human worms and that all these primate worms are different from T. suis. In general, there was an agreement between the phylogeny established based on the nuclear and mtDNA genes. However, we found evidence for non-targeted cox1 gene amplification for a subset of the human worms and suggest the presence of mitochondrial pseudogenes (numts) of pig cox1 gene in the human Trichuris genome. In conclusion, phylogenetic characterization of human whipworm based on the cox1 gene alone may be problematic without suitable preceded measures to avoid the numts amplification.