The Antiviral Effects of the Symbiont Bacteria Wolbachia in Insects

Abstract

Wolbachia is a maternally transmitted bacterium that lives inside arthropod cells. Historically, it was viewed primarily as a parasite that manipulates host reproduction, but more recently it was discovered that Wolbachia can also protect Drosophila species against infection by RNA viruses. Combined with Wolbachia's ability to invade insect populations due to reproductive manipulations, this provides a way to modify mosquito populations to prevent them transmitting viruses like dengue. In this review, we discuss the main advances in the field since Wolbachia's antiviral effect was discovered 12 years ago, identifying current research gaps and potential future developments. We discuss that the antiviral effect works against a broad range of RNA viruses and depends on the Wolbachia lineage. We describe what is known about the mechanisms behind viral protection, and that recent studies suggest two possible mechanisms: activation of host immunity or competition with virus for cellular resources. We also discuss how association with Wolbachia may influence the evolution of virus defense on the insect host genome. Finally, we investigate whether the antiviral effect occurs in wild insect populations and its ecological relevance as a major antiviral component in insects.

Keywords: Wolbachia; antiviral; arboviruses; endosymbiont; evolution; insects; review; wild populations.

Figure 1

Wolbachia antiviral effect in insects. (A) Wolbachia protects insects against RNA viruses. The protection is dependent on Wolbachia density, which varies between strains. Strains can be experimentally transferred to new hosts, such as mosquitoes. (B) Wolbachia can activate host immune system in some cases, but the mechanism of defense can also be related to competition with virus for cellular resources. The specific mechanism is not yet known. (C) Host immune response fight against virus, but its action and evolution are slowed down in the presence of Wolbachia. Colored arrows and their width represent genome and its participation in antiviral effect, respectively. (D) Environmental conditions, as temperature, determine Wolbachia antiviral response. In hot climate, Wolbachia may have a more important role protecting the host, and this can lead to higher Wolbachia prevalence on hot climate regions. But it is not yet known if Wolbachia reduces the virome in wild insect populations. This figure is made in conjunction with icons provided by thenounproject.com. The icons are: “Bacteria” by farra nugraha; “Virus” by KonKapp; “Immune System” by Bartama Graphic; “Immunity” by Timofey Rostilov; “Forest” by ProSymbols; “Sun” by Alice Design; and, “Cold” by Landan Lloyd.