Passage of Wolbachia pipientis through mutant drosophila melanogaster induces phenotypic and genomic changes.

Wolbachia pipientis is a nearly ubiquitous, maternally transmitted bacterium that infects the germ line of insect hosts. Estimates are that Wolbachia infects 40 to 60% of insect species on the planet, making it one of the most prevalent infections on Earth. However, we know surprisingly little about the molecular mechanisms used by Wolbachia to infect its hosts. We passaged Wolbachia through normally restrictive Drosophila melanogaster hosts, bottlenecking Wolbachia through stochastic segregation while simultaneously selecting for mutants that could recolonize these previously restrictive hosts. Here, we show that Wolbachia alters its behavior when passaged through heterozygous mutant flies. After only three generations, Wolbachia was able to colonize the previously restrictive hosts at control titers. Additionally, the Wolbachia organisms passaged through heterozygous mutant D. melanogaster alter their pattern of tissue-specific Wsp protein production, suggesting a behavioral response to the host genotype. Using whole-genome resequencing, we identified the mutations accumulated by these lineages of Wolbachia and confirmed the existence and persistence of the mutations through clone library Sanger sequencing. Our results suggest that Wolbachia can quickly adapt to new host contexts, with genomic mutants arising after only two generations.