Pseudoscorpion Wolbachia symbionts: Diversity and Evidence for a New Supergroup S

Abstract Background Wolbachia are the most widely spread endosymbiotic bacteria, present in a wide variety of insects and two families of nematodes, but as of now, relatively little genomic data has been available. The Wolbachia symbiont can be parasitic, as described for many arthropod systems, an obligate mutualist, as in filarial nematodes or a combination of both in some organisms. They are currently classified into 16 monophyletic lineage groups ("supergroups"). Although the nature of these symbioses remains largely unknown, expanded Wolbachia genomic data will contribute to understanding their diverse symbiotic mechanisms and evolution. Results This report focuses on Wolbachia infections in three pseudoscorpion species infected by two distinct groups of Wolbachia strains , based upon multi-locus phylogenies. Geogarypus minor harbours w Gmin and Chthonius ischnocheles harbours w Cisc, both closely related to supergroup H, while Atemnus politus harbours w Apol, a member of a novel supergroup S along with Wolbachia from the pseudoscorpion Cordylochernes scorpioides ( w Csco), most closely related to Wolbachia supergroups C and F. Using target enrichment by hybridization with Wolbachia -specific biotinylated probes to capture large fragments of Wolbachia DNA, we produced two draft genomes of w Apol. Annotation of w Apol highlights presence of a biotin operon, which is incomplete in many sequenced Wolbachia genomes. Conclusions The present study highlights at least two symbiont acquisition events among pseudoscorpion species. Phylogenomic analysis indicates that the Wolbachia from Atemnus politus ( w Apol), forms a separate supergroup ("S") with the Wolbachia from Cordylochernes scorpioides (w Csco). Interestingly, the biotin operon, present in w Apol, appears to have been horizontally transferred multiple times along Wolbachia evolutionary history.