The Bacterial Symbiont Wolbachia Induces Resistance to RNA Viral Infections in Drosophila melanogaster

Abstract

Wolbachia are vertically transmitted, obligatory intracellular bacteria that infect a great number of species of arthropods and nematodes. In insects, they are mainly known for disrupting the reproductive biology of their hosts in order to increase their transmission through the female germline. In Drosophila melanogaster, however, a strong and consistent effect of Wolbachia infection has not been found. Here we report that a bacterial infection renders D. melanogaster more resistant to Drosophila C virus, reducing the load of viruses in infected flies. We identify these resistance-inducing bacteria as Wolbachia. Furthermore, we show that Wolbachia also increases resistance of Drosophila to two other RNA virus infections (Nora virus and Flock House virus) but not to a DNA virus infection (Insect Iridescent Virus 6). These results identify a new major factor regulating D. melanogaster resistance to infection by RNA viruses and contribute to the idea that the response of a host to a particular pathogen also depends on its interactions with other microorganisms. This is also, to our knowledge, the first report of a strong beneficial effect of Wolbachia infection in D. melanogaster. The induced resistance to natural viral pathogens may explain Wolbachia prevalence in natural populations and represents a novel Wolbachia–host interaction. Many symbiotic bacteria confer fitness benefits to the organisms that they infect. Wolbachia are one of the most widespread intracellular bacteria, infecting a great number of species of insects. Here we show that in the fruit fly Drosophila melanogaster, infection with Wolbachia increases resistance to a natural pathogen of Drosophila, an RNA virus called Drosophila C virus. Furthermore, we show that Wolbachia also increases resistance of Drosophila to two other RNA viruses (Nora and Flock House virus) but not to a DNA virus (Insect Iridescent Virus 6). These results identify a significant new factor that regulates D. melanogaster resistance to infection by RNA viruses. Our results add to a growing body of literature showing that the response of an organism to a particular pathogen is modulated by prior or contemporaneous interactions with other microorganisms. That the fruit fly clearly benefits from increased resistance to viruses may provide a solution to the longstanding puzzle as to why Wolbachia is so common in natural populations of D. melanogaster.