The Orientia tsutsugamushi genome reveals massive proliferation of conjugative type IV secretion system and host-cell interaction genes
The Orientia tsutsugamushi genome reveals massive proliferation of conjugative type IV secretion system and host-cell interaction genes
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DOI：
10.1073/pnas.0611553104
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发表时间：
2007-05-08
影响因子：
11.1
通讯作者：
Kim, Ik-Sang
中科院分区：
文献类型：
--
作者：
Cho, Nam-Hyuk;Kim, Hang-Rae;Kim, Ik-Sang
恙虫病是由专性细胞内恙虫病东方立克次体（以前称为恙虫病立克次体）引起的。这种细菌在恙螨中是母系遗传的，并通过喂养幼虫传播给人类。我们在这里报告了Boryong菌株的2，127，051-bp基因组，这代表了迄今为止测序的最高度重复的细菌基因组。恙虫病病原体的重复密度是其近亲普氏立克次体（流行性斑疹伤寒的病原体）的200倍。共359个tra基因的接合IV型分泌系统的组件被确定在基因组中的79个位点。与这些相关的是> 200个用于信号传导和宿主细胞相互作用蛋白的基因，例如组氨酸激酶、锚定重复蛋白和四肽重复蛋白。此外，O.恙虫病基因组含有> 400个转座酶、60个噬菌体整合酶和70个逆转录酶。缺失和重排产生了独特的基因组合，以及频繁的假基因化的tra集群。基因组内和跨菌株的tra簇的比较分析表明通过基因转换的序列均质化，而通过复制、缺失和转座子整合到扩增片段中获得复杂性、多样性和假基因化。结果表明，一个大规模增殖接合转移系统的基因组内重复或多个整合。对宿主-细胞相互作用基因的多样化选择沿着重复的群体瓶颈可能会驱使罕见的基因组变体固定，从而使细菌基因组中的低复杂性选择短路。
Scrub typhus is caused by the obligate intracellular rickettsia Orientia tsutsugamushi (previously called Rickettsia tsutsugamushi). The bacterium is maternally inherited in trombicuid mites and transmitted to humans by feeding larvae. We report here the 2,127,051-bp genome of the Boryong strain, which represents the most highly repeated bacterial genome sequenced to date. The repeat density of the scrub typhus pathogen is 200-fold higher than that of its close relative Rickettsia prowazekii, the agent of epidemic typhus. A total of 359 tra genes for components of conjugative type IV secretion systems were identified at 79 sites in the genome. Associated with these are > 200 genes for signaling and host-cell interaction proteins, such as histidine kinases, ankyrin-repeat proteins, and tetratrico peptide-repeat proteins. Additionally, the O. tsutsugamushi genome contains > 400 transposases, 60 phage integrases, and 70 reverse transcriptases. Deletions and rearrangements have yielded unique gene combinations as well as frequent pseudogenization in the tra clusters. A comparative analysis of the tra clusters within the genome and across strains indicates sequence homogenization by gene conversion, whereas complexity, diversity, and pseudogenization are acquired by duplications, deletions, and transposon integrations into the amplified segments. The results suggest intragenomic duplications or multiple integrations of a massively proliferating conjugative transfer system. Diversifying selection on host-cell interaction genes along with repeated population bottlenecks may drive rare genome variants to fixation, thereby short-circuiting selection for low complexity in bacterial genomes.