Antiviral Protection and the Importance of Wolbachia Density and Tissue Tropism in Drosophila simulans

<jats:title>ABSTRACT</jats:title> <jats:p> <jats:named-content xmlns:xlink="http://www.w3.org/1999/xlink" content-type="genus-species" xlink:type="simple">Wolbachia</jats:named-content> , a maternally transmitted endosymbiont of insects, is increasingly being seen as an effective biological control agent that can interfere with transmission of pathogens, including dengue virus. However, the mechanism of antiviral protection is not well understood. The density and distribution of <jats:named-content xmlns:xlink="http://www.w3.org/1999/xlink" content-type="genus-species" xlink:type="simple">Wolbachia</jats:named-content> in host tissues have been implicated as contributing factors by previous studies with both mosquitoes and flies. <jats:named-content xmlns:xlink="http://www.w3.org/1999/xlink" content-type="genus-species" xlink:type="simple">Drosophila</jats:named-content> flies infected with five diverse strains of <jats:named-content xmlns:xlink="http://www.w3.org/1999/xlink" content-type="genus-species" xlink:type="simple">Wolbachia</jats:named-content> were screened for the ability to mediate antiviral protection. The three protective <jats:named-content xmlns:xlink="http://www.w3.org/1999/xlink" content-type="genus-species" xlink:type="simple">Wolbachia</jats:named-content> strains were more closely related and occurred at a higher density within whole flies than the two nonprotective <jats:named-content xmlns:xlink="http://www.w3.org/1999/xlink" content-type="genus-species" xlink:type="simple">Wolbachia</jats:named-content> strains. In this study, to further investigate the relationship between whole-fly <jats:named-content xmlns:xlink="http://www.w3.org/1999/xlink" content-type="genus-species" xlink:type="simple">Wolbachia</jats:named-content> density and the ability to mediate antiviral protection, tetracycline was used to decrease the abundance of the high-density, protective <jats:named-content xmlns:xlink="http://www.w3.org/1999/xlink" content-type="genus-species" xlink:type="simple">Wolbachia</jats:named-content> strain <jats:italic>w</jats:italic> Au prior to viral challenge. Antiviral protection was lost when the density of the protective <jats:named-content xmlns:xlink="http://www.w3.org/1999/xlink" content-type="genus-species" xlink:type="simple">Wolbachia</jats:named-content> strain was decreased to an abundance similar to that of nonprotective <jats:named-content xmlns:xlink="http://www.w3.org/1999/xlink" content-type="genus-species" xlink:type="simple">Wolbachia</jats:named-content> strains. We determined the <jats:named-content xmlns:xlink="http://www.w3.org/1999/xlink" content-type="genus-species" xlink:type="simple">Wolbachia</jats:named-content> density and distribution in tissues of the same five fly- <jats:named-content xmlns:xlink="http://www.w3.org/1999/xlink" content-type="genus-species" xlink:type="simple">Wolbachia</jats:named-content> combinations as used previously. The <jats:named-content xmlns:xlink="http://www.w3.org/1999/xlink" content-type="genus-species" xlink:type="simple">Wolbachia</jats:named-content> density within the head, gut, and Malpighian tubules correlated with the ability to mediate antiviral protection. These findings may facilitate the development of <jats:named-content xmlns:xlink="http://www.w3.org/1999/xlink" content-type="genus-species" xlink:type="simple">Wolbachia</jats:named-content> biological control strategies and help to predict host- <jats:named-content xmlns:xlink="http://www.w3.org/1999/xlink" content-type="genus-species" xlink:type="simple">Wolbachia</jats:named-content> pairings that may interfere with virus-induced pathology. </jats:p>