Multiple Acquisitions of Pathogen-Derived Francisella Endosymbionts in Soft Ticks
Multiple Acquisitions of Pathogen-Derived Francisella Endosymbionts in Soft Ticks
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DOI：
10.1093/gbe/evy021
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发表时间：
2018-02-01
影响因子：
3.3
通讯作者：
Raghavan, Rahul
中科院分区：
文献类型：
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作者：
Gerhart, Jonathan G.;Dutcher, H. Auguste;Raghavan, Rahul
蜱的细菌内共生体由于其与蜱媒介病原体的密切进化关系而引起了人们的兴趣。例如，虽然许多蜱虫含有类似弗朗西斯菌的内共生体，但其他蜱虫则传播哺乳动物病原体土拉弗朗西斯菌。我们最近对存在于硬蜱斑状钝瘤（fl - am）中的一种FLE的基因组进行了测序，并表明它可能是从致病祖先进化而来的。为了扩大我们对线虫的了解，在本研究中，我们对moubata鸟蜱（Ornithodoros moubata）的一种线虫的FLE基因组进行了测序，并将其与软蜱Argus (Persicargas) arboreus的fl - am、Francisella sp. ma067296（导致机会性人类感染的临床分离株）和土拉菌F. tularensis（已确定的人类病原体）的FLE基因组进行了比较。研究人员确定，乳突菌和乳突菌MA067296属于哺乳动物病原体的姐妹分类群，并且含有土拉菌中存在的毒力基因的灭活版本，这表明乳突菌和乳突菌最近的共同祖先是一种潜在的哺乳动物病原体。我们的分析还显示，两种软蜱（moubata和arboboreus）可能分别获得了它们的le，这表明在le中观察到的毒力衰减不是单一获得事件之后物种形成的结果，而可能是由于致病性francisellae在不同蜱系中独立过渡到非致病性le。此外，我们还发现，le编码了几种B族维生素和辅助因子生产的完整途径，这表明它们可以在蜱虫中作为营养供应的内共生体发挥作用。
Bacterial endosymbionts of ticks are of interest due to their close evolutionary relationships with tick-vectored pathogens. For instance, whereas many ticks contain Francisella-like endosymbionts (FLEs), others transmit the mammalian pathogen Francisella tularensis. We recently sequenced the genome of an FLE present in the hard tick Amblyomma maculatum (FLE-Am) and showed that it likely evolved from a pathogenic ancestor. In order to expand our understanding of FLEs, in the current study we sequenced the genome of an FLE in the soft tick Ornithodoros moubata and compared it to the genomes of FLE-Am, Francisella persica-an FLE in the soft tick Argus (Persicargas) arboreus, Francisella sp. MA067296-a clinical isolate responsible for an opportunistic human infection, and F. tularensis, the established human pathogen. We determined that FLEs and MA067296 belonged to a sister taxon of mammalian pathogens, and contained inactivated versions of virulence genes present in F. tularensis, indicating that the most recent common ancestor shared by FLEs and F. tularensis was a potential mammalian pathogen. Our analyses also revealed that the two soft ticks (O. moubata and A. arboreus) probably acquired their FLEs separately, suggesting that the virulence attenuation observed in FLEs are not the consequence of a single acquisition event followed by speciation, but probably due to independent transitions of pathogenic francisellae into nonpathogenic FLEs within separate tick lineages. Additionally, we show that FLEs encode intact pathways for the production of several B vitamins and cofactors, denoting that they could function as nutrient-provisioning endosymbionts in ticks.