Wolbachia promotes its own uptake by host cells

Abstract Wolbachia pipientis is an incredibly widespread bacterial symbiont of insects, present in an estimated 25-52% of species worldwide. Wolbachia is faithfully maternally transmitted both in a laboratory setting and in the wild. In an established infection, Wolbachia is primarily intracellular, residing within host-derived vacuoles that are associated with the endoplasmic reticulum. However, Wolbachia also frequently transfer between host species, requiring an extracellular stage to their life cycle. Indeed, Wolbachia has been moved between insect species for the precise goal of controlling populations. The use of Wolbachia in this application requires we better understand how it initiates and establishes new infections. Here we designed a novel method for live-tracking Wolbachia during infection using a combination of stains and microscopy. We show that live Wolbachia are taken up by host cells at a much faster rate than dead Wolbachia cells, indicating that Wolbachia play a role in their own uptake and that Wolbachia colonization is not just a passive process. We also show that the host actin cytoskeleton must be intact for this to occur, and that drugs that disrupt the actin cytoskeleton effectively abrogate Wolbachia uptake. The development of this live infection assay will assist in future efforts to characterize Wolbachia factors used during host infection.