The bacterial symbiont Wolbachia can protect insects against viral pathogens, and the varying levels of antiviral protection are correlated with the endosymbiont load within the insects. To understand why Wolbachia strains differ in their antiviral effects, we investigated the factors controlling Wolbachia density in five closely related strains in their natural Drosophila hosts. We found that Wolbachia density varied greatly across different tissues and between flies of different ages, and these effects depended on the host–symbiont association. Some endosymbionts maintained largely stable densities as flies aged while others increased, and these effects in turn depended on the tissue being examined. Measuring Wolbachia rRNA levels in response to viral infection, we found that viral infection itself also altered Wolbachia levels, with Flock House virus causing substantial reductions in symbiont loads late in the infection. This effect, however, was virus‐specific as Drosophila C virus had little impact on Wolbachia in all of the five host systems. Because viruses have strong tissue tropisms and antiviral protection is thought to be cell‐autonomous, these effects are likely to affect the virus‐blocking phenomenon. However, we were unable to find any evidence of a correlation between Wolbachia and viral titres within the same tissues. We conclude that Wolbachia levels within flies are regulated in a complex host–symbiont–virus‐dependent manner and this trinity is likely to influence the antiviral effects of Wolbachia .

中文翻译：

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年龄，组织，基因型和病毒感染调节果蝇中的沃尔巴氏菌水平。

细菌共生沃尔巴克氏菌可以保护昆虫免受病毒病原体的侵害，而不同水平的抗病毒保护作用与昆虫内共生菌的负荷有关。要了解为什么Wolbachia菌株在抗病毒效果上有所不同，我们调查了在其天然果蝇宿主中的五个紧密相关菌株中控制Wolbachia密度的因素。我们发现沃尔巴克氏菌不同组织之间以及不同年龄的苍蝇之间的密度差异很大，这些影响取决于宿主-共生体的关联。随着苍蝇的衰老，一些共生共生体在很大程度上保持了稳定的密度，而另一些则增加了，而这些影响又取决于所检查的组织。通过测量针对病毒感染的Wolbachia rRNA水平，我们发现病毒感染本身也改变了Wolbachia水平，而羊群之家病毒会导致感染后期共生体负荷显着降低。但是，这种作用是病毒特异性的，因为果蝇C病毒对沃尔巴克氏菌几乎没有影响在所有五个主机系统中。由于病毒具有强烈的组织嗜性，并且抗病毒保护被认为具有细胞自主性，因此这些作用可能会影响病毒阻断现象。但是，我们找不到在同一组织内沃尔巴赫氏菌与病毒滴度之间相关性的任何证据。我们得出的结论是，果蝇中的Wolbachia水平以复杂的宿主-共生体-病毒依赖性方式进行调节，这种三位一体可能影响Wolbachia的抗病毒作用。