Wolbachia reduces virus infection in a natural population of Drosophila

Abstract

Wolbachia is a maternally transmitted bacterial symbiont that is estimated to infect approximately half of arthropod species. In the laboratory it can increase the resistance of insects to viral infection, but its effect on viruses in nature is unknown. Here we report that in a natural population of Drosophila melanogaster, individuals that are infected with Wolbachia are less likely to be infected by viruses. By characterising the virome by metagenomic sequencing and then testing individual flies for infection, we found the protective effect of Wolbachia was virus-specific, with the prevalence of infection being up to 15% greater in Wolbachia-free flies. The antiviral effects of Wolbachia may contribute to its extraordinary ecological success, and in nature the symbiont may be an important component of the antiviral defences of insects.

Fig. 1. Viruses associated with wild D. melanogaster.

The total number of RNAseq reads that map to each virus (left). The prevalence of selected viruses estimated using quantitative PCR to test single flies for infection (right). Error bars are 95% confidence intervals.

Fig. 2. Viral prevalence and load in Wolbachia-free and Wolbachia-infected flies.

A The prevalence of viruses in male D. melanogaster. The bars are the posterior means of the random effect estimates of a glm. The p values are posterior probabilities that the prevalence differs in Wolbachia-free and Wolbachia-infected flies, estimated from the glm. B The risk of viral infection in Wolbachia-free flies relative to Wolbachia-infected flies. Values above 1 indicate that Wolbachia-free flies are more likely to be infected. The points are posterior means and the error bars are 95% credible intervals estimated from a glm. C Viral load of Galbut virus in flies with and without Wolbachia. Viral load is measured by quantitative PCR relative to the Rpl32 mRNA. The P-value is the result of a one-way ANOVA.