No detectable effect of Wolbachia w Mel on the prevalence and abundance of the RNA virome of Drosophila melanogaster

Wolbachia is an endosymbiotic bacterium that can block viral infections in arthropods, generating interest in its potential to control the spread of mosquito-borne disease.Drosophila melanogaster is model organism forWolbachia infection, and thew Mel strain ofWolbachia can improve host survival following viral infection. However, it is unclear whetherw Mel induces anti-viral blocking against the broader native virome ofD. melanogaster , or whether the major effect ofWolbachia is a reduction in viral abundance rather than viral clearance. We examined the effect ofWolbachia on viral abundance by comparing the total transcriptome ofw Mel-positive andw Mel-negativeD. melanogaster populations sampled from six locations in Australia. In addition, we examined the impact ofw Mel on individual flies by obtaining transcriptome data from 20w Mel-positive and 20w Mel-negativeD. melanogaster from the location (Melbourne) with highest density ofw Mel. These data revealed high viral abundance in bothWolbachia -positive and -negative populations and individuals. Notably, none of the viral species identified, representing RNA viruses from at least nine families/floating genera, showed evidence of protection byw Mel. Although the viral loads of picorna-like viruses are reduced byw Mel under experimental conditions, we observed no such effect here. These data show thatD. melanogaster can harbour abundant RNA viruses regardless of itsWolbachia status and imply that the interaction betweenWolbachia and viruses in nature is more complex than simple blocking.