Variation in Antiviral Protection Mediated by Different Wolbachia Strains in Drosophila simulans

Abstract

Drosophila C virus (DCV) is a natural pathogen of Drosophila and a useful model for studying antiviral defences. The Drosophila host is also commonly infected with the widespread endosymbiotic bacteria Wolbachia pipientis. When DCV coinfects Wolbachia-infected D. melanogaster, virus particles accumulate more slowly and virus induced mortality is substantially delayed. Considering that Wolbachia is estimated to infect up to two-thirds of all insect species, the observed protective effects of Wolbachia may extend to a range of both beneficial and pest insects, including insects that vector important viral diseases of humans, animals and plants. Currently, Wolbachia-mediated antiviral protection has only been described from a limited number of very closely related strains that infect D. melanogaster. We used D. simulans and its naturally occurring Wolbachia infections to test the generality of the Wolbachia-mediated antiviral protection. We generated paired D. simulans lines either uninfected or infected with five different Wolbachia strains. Each paired fly line was challenged with DCV and Flock House virus. Significant antiviral protection was seen for some but not all of the Wolbachia strain-fly line combinations tested. In some cases, protection from virus-induced mortality was associated with a delay in virus accumulation, but some Wolbachia-infected flies were tolerant to high titres of DCV. The Wolbachia strains that did protect occurred at comparatively high density within the flies and were most closely related to the D. melanogaster Wolbachia strain wMel. These results indicate that Wolbachia-mediated antiviral protection is not ubiquitous, a finding that is important for understanding the distribution of Wolbachia and virus in natural insect populations.

Author Summary

Many human, animal and plant viruses are transmitted between hosts by insect vectors. Understanding the processes that control virus infection in insects may facilitate strategies that aim to control the spread of important viral pathogens. Infection of the model insect Drosophila with the endosymbiotic bacteria Wolbachia can significantly affect the outcome of infection with pathogenic viruses. Wolbachia is widespread in insects, so here we tested the generality of antiviral protection across diverse strains of the bacteria. We show that some, but not all, strains of Wolbachia protect flies from pathogenic viruses. These results have implications for proposed strategies utilising Wolbachia to control the spread of insect-transmitted viral diseases, such as dengue.