Comparative genomics provides a timeframe for Wolbachia evolution and exposes a recent biotin synthesis operon transfer.

The genus Wolbachia (Alphaproteobacteria) comprises the most abundant inherited intracellular bacteria1. Despite their relevance as manipulators of human pathogen transmission2 and arthropod reproduction3, many aspects of their evolutionary history are not well understood4. In arthropods, Wolbachia infections are typically transient on evolutionary timescales5,6 and co-divergence between hosts and Wolbachia is supposedly rare. Consequently, much of our knowledge of Wolbachia genome evolution derives from very recently diverged strains, and a timescale for Wolbachia is lacking. Here, we investigated the genomes of four Wolbachia strains that have persisted within and co-diverged with their host lineage for ∼2 million years. Although the genomes showed very little evolutionary change on a nucleotide level, we found evidence for a recent lateral transfer of a complete biotin synthesis operon that has the potential to transform Wolbachia-host relationships7. Furthermore, this evolutionary snapshot enabled us to calibrate the divergence times of the supergroup A and B Wolbachia lineages using genome-wide data sets and relaxed molecular clock models. We estimated the origin of Wolbachia supergroups A and B to be ∼200 million years ago (Ma), which is considerably older than previously appreciated. This age coincides with the diversification of many insect lineages8 that represent most of Wolbachia's host spectrum.