Background: Ixodes ricinus ticks act as vectors for numerous pathogens that present substantial health threats. Additionally, they harbor vertically transmitted symbionts, some of which have been linked to diseases. The difficulty of isolating and cultivating these symbionts has has hampered our understanding of their biological role, their potential to cause disease, and their modes of transmission. To expand our understanding on the tick symbiont Midichloria mitochondrii and on Rickettsia helvetica, which has been linked to disease in humans, we utilized deep sequencing on sixteen individual adult female ticks. Among these, eight were collected from a coastal sand dune environment, while another eight were obtained from forested areas in the Netherlands. Results: By employing a combination of next-generation and third-generation sequencing techniques, we successfully reconstructed the complete genomes of M. mitochondrii from eleven individuals, R. helvetica from eight individuals and the mitochondrial genome from all ticks. Additionally, we visualised the location of R. helvetica in tick organs and constructed genome-scale metabolic models (GEMs) of both symbionts to study their growth related environmental dependencies. Our analysis revealed a strong cophylogeny between M. mitochondrii and mitochondrial genomes, suggesting frequent maternal transmission. In contrast, the absence of cophylogeny between R. helvetica and the mitochondrial genomes, coupled with its presence in the receptaculum seminis of I. ricinus females, raises the possibility of paternal transmission of R. helvetica. Notably, the genetic diversity of R. helvetica was found to be very low, except for the rickA virulence gene, where the presence of up to thirteen insertions of a 33nt-long repeat led to significant variability. However, this variation could not account for the differences in infection prevalence observed across eight distinct locations in the Netherlands. Conclusions: By employing deep sequencing, it becomes feasible to extract complete genomes and genetic data of symbionts directly from their host organisms. This methodology serves as a robust means to gain fresh insights into their interactions. Our observations, which suggest paternal transmission of R. helvetica, a relatively unexplored mode of transmission in ticks, require validation through experimental investigations. The genetic variations identified in the rickA virulence gene of R. helvetica have the potential to influence the infectivity and transmission dynamics of R. helvetica.

中文翻译：

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对 16 种蓖麻硬蜱的深度测序揭示了它们与内共生体相互作用的见解。

背景：蓖麻硬蜱是多种病原体的载体，对健康构成重大威胁。此外，它们还含有垂直传播的共生体，其中一些与疾病有关。分离和培养这些共生体的困难阻碍了我们对它们的生物学作用、它们引起疾病的潜力以及它们的传播方式的理解。为了扩大我们对蜱虫共生体线粒体线粒体和与人类疾病有关的瑞士立克次体的了解，我们对 16 只成年雌性蜱虫进行了深度测序。其中，八个是从沿海沙丘环境中收集的，另外八个是从荷兰森林地区收集的。结果：通过结合下一代和第三代测序技术，我们成功重建了 11 个个体的 M. mitochondrii、8 个个体的 R. helvetica 的完整基因组以及所有蜱的线粒体基因组。此外，我们可视化了 R. helvetica 在蜱器官中的位置，并构建了两种共生体的基因组规模代谢模型 (GEM)，以研究它们与生长相关的环境依赖性。我们的分析揭示了线粒体分枝杆菌和线粒体基因组之间存在很强的共系统发育，表明母体传播频繁。相比之下，R. helvetica 和线粒体基因组之间不存在共系统发育，再加上其存在于雌性蓖麻的精囊中，增加了 R. helvetica 父系遗传的可能性。值得注意的是，除了 rickA 毒力基因外，R. helvetica 的遗传多样性非常低，其中多达 13 个 33nt 长重复序列的插入导致了显着的变异。然而，这种差异无法解释荷兰八个不同地点观察到的感染流行率的差异。结论：通过采用深度测序，直接从宿主生物中提取共生体的完整基因组和遗传数据变得可行。这种方法是获得对他们的相互作用的新见解的强大手段。我们的观察结果表明，R. helvetica 存在父系传播，这是一种相对未被探索的蜱传播模式，需要通过实验研究进行验证。在 R. helvetica 的 rickA 毒力基因中鉴定出的遗传变异有可能影响 R. helvetica 的感染性和传播动力学。