The diversity and evolutionary relationships of ticks and tick-borne bacteria in China

Phylogenetic tree of tick and tick-associated bacteria in this study. We collected more than 20,000 contemporary and historical (up to 60 years of preservation) tick samples representing a wide range of tick biodiversity across diverse geographic regions in China. Metagenomic sequencing was performed on individual ticks to obtain the complete or near-complete mitochondrial (mt) genome sequences from 46 tick species, among which mitochondrial genomes were revealed for the first time for 23 species. These new mt genomes data greatly expanded the diversity of many tick groups and revealed five cryptic species. Utilizing the same metagenomic sequence data we identified divergent and abundant bacteria in <i>Haemaphysalis</i>, <i>Ixodes</i>, <i>Dermacentor</i> and <i>Carios </i>ticks, including nine species of pathogenetic bacteria and potentially new species within the genus <i>Borrelia</i>. We also used these data to explore the evolutionary relationship between ticks and their associated bacteria, revealing a pattern of long-term co-divergence relationship between ticks and <i>Rickettsia</i> and <i>Coxiella </i>bacteria.

本研究涉及的蜱虫及其携带细菌的系统发育树。本研究采集了超过20000份现代样本与保存时长可达60年的历史蜱虫样本，涵盖中国不同地理区域内丰富的蜱类生物多样性。研究对单只蜱虫开展宏基因组测序（metagenomic sequencing），获得了46种蜱虫的完整或近完整的线粒体基因组（mitochondrial genome，以下简称mt基因组）序列，其中23个物种的线粒体基因组为首次报道。这些新增的mt基因组数据极大拓展了多个蜱类类群的多样性，并揭示了5个隐存物种（cryptic species）。利用同一套宏基因组测序数据，研究团队在血蜱属（Haemaphysalis）、硬蜱属（Ixodes）、革蜱属（Dermacentor）以及卡里奥蜱属（Carios）的蜱虫体内鉴定出了遗传分化显著且丰度较高的细菌，其中包括9种致病细菌（pathogenetic bacteria），以及疏螺旋体属（Borrelia）内的潜在新物种。研究团队还利用该数据集探究了蜱虫与其携带细菌的进化关系，揭示了蜱虫与立克次体属（Rickettsia）、柯克斯体属（Coxiella）细菌之间存在长期共分化的进化模式。