A Wolbachia deubiquitylating enzyme induces cytoplasmic incompatibility

Wolbachia are obligate intracellular bacteria(1) that infect arthropods, including approximately two-thirds of insect species(2). Wolbachia manipulate insect reproduction by enhancing their inheritance through the female germline. The most common alteration is cytoplasmic incompatibility (CI)(3-5), where eggs from uninfected females fail to develop when fertilized by sperm from Wolbachia-infected males. By contrast, if female and male partners are both infected, embryos are viable. CI is a gene-drive mechanism impacting population structure(6) and causing reproductive isolation(7), but its molecular mechanism has remained unknown. We show that a Wolbachia deubiquitylating enzyme (DUB) induces CI. The CI-inducing DUB, CidB, cleaves ubiquitin from substrates and is encoded in a two-gene operon, and the other protein, CidA, binds CidB. Binding is strongest between cognate partners in cidA-cidB homologues. In transgenic Drosophila, the cidA-cidB operon mimics CI when sperm introduce it into eggs, and a catalytically inactive DUB does not induce sterility. Toxicity is recapitulated in yeast by CidB alone; this requires DUB activity but is rescued by coexpressed CidA. A paralogous operon involves a putative nuclease (CinB) rather than a DUB. Analogous binding, toxicity and rescue in yeast were observed. These results identify a CI mechanism involving interacting proteins that are secreted into germline cells by Wolbachia, and suggest new methods for insect control.