Palaeosymbiosis Revealed by Genomic Fossils of Wolbachia in a Strongyloidean Nematode

Wolbachia are common endosymbionts of terrestrial arthropods,and are also found in nematodes: the animal-parasitic filaria,and the plant-parasite radopholus similis. lateral transfer of wolbachia dna to the host genome is common. we generated a draft genome sequence for the strongyloidean nematode parasite dictyocaulus viviparus,the cattle lungworm. in the assembly,we identified nearly 1 mb of sequence with similarity to wolbachia. the fragments were unlikely to derive from a live wolbachia infection: most were short,and the genes were disabled through inactivating mutations. many fragments were co-assembled with definitively nematode-derived sequence. we found limited evidence of expression of the wolbachia-derived genes. the d. viviparus wolbachia genes were most similar to filarial strains and strains from the host-promiscuous clade f. we conclude that d. viviparus was infected by wolbachia in the past,and that clade f-like symbionts may have been the source of filarial wolbachia infections. © 2014 koutsovoulos et al.