Akter Arzuba, Ooka Tadasuke, Gotoh Yasuhiro, Yamamoto Seigo, Fujita Hiromi, Terasoma Fumio, Kida Kouji, Taira Masakatsu, Nakadouzono Fumiko, Gokuden Mutsuyo, Hirano Manabu, Miyashiro Mamoru, Inari Kouichi, Shimazu Yukie, Tabara Kenji, Toyoda Atsushi, Yoshimura Dai, Itoh Takehiko, Kitano Tomokazu, Sato Mitsuhiko P, Katsura Keisuke, Mondal Shakhinur Islam, Ogura Yoshitoshi, Ando Shuji, Hayashi Tetsuya
Division of Microbiology, Department of Infectious Diseases, Faculty of Medicine, University of Miyazaki, Miyazaki, Japan.
Department of Microbiology, Graduate School of Medical and Dental Sciences, Kagoshima University, Kagoshima, Japan.
Genome Biol Evol. 2017 Jan 1;9(1):124-133. doi: 10.1093/gbe/evw304.
Rickettsiae are obligate intracellular bacteria that have small genomes as a result of reductive evolution. Many Rickettsia species of the spotted fever group (SFG) cause tick-borne diseases known as "spotted fevers". The life cycle of SFG rickettsiae is closely associated with that of the tick, which is generally thought to act as a bacterial vector and reservoir that maintains the bacterium through transstadial and transovarial transmission. Each SFG member is thought to have adapted to a specific tick species, thus restricting the bacterial distribution to a relatively limited geographic region. These unique features of SFG rickettsiae allow investigation of how the genomes of such biologically and ecologically specialized bacteria evolve after genome reduction and the types of population structures that are generated. Here, we performed a nationwide, high-resolution phylogenetic analysis of Rickettsia japonica, an etiological agent of Japanese spotted fever that is distributed in Japan and Korea. The comparison of complete or nearly complete sequences obtained from 31 R. japonica strains isolated from various sources in Japan over the past 30 years demonstrated an extremely low level of genomic diversity. In particular, only 34 single nucleotide polymorphisms were identified among the 27 strains of the major lineage containing all clinical isolates and tick isolates from the three tick species. Our data provide novel insights into the biology and genome evolution of R. japonica, including the possibilities of recent clonal expansion and a long generation time in nature due to the long dormant phase associated with tick life cycles.
立克次氏体是专性细胞内细菌，由于进化简化而拥有较小的基因组。斑点热群（SFG）中的许多立克次氏体物种会引发被称为“斑点热”的蜱传疾病。SFG立克次氏体的生命周期与蜱的生命周期密切相关，蜱通常被认为是细菌的载体和储存宿主，通过经变态和经卵传递来维持细菌。一般认为，SFG的每个成员都已适应特定的蜱种，从而将细菌的分布限制在相对有限的地理区域。SFG立克次氏体的这些独特特征使得我们能够研究这类在生物学和生态学上具有特殊性的细菌在基因组简化后其基因组如何进化以及会产生何种类型的种群结构。在此，我们对日本斑点热的病原体日本立克次氏体进行了一项全国范围的高分辨率系统发育分析，该病原体分布于日本和韩国。对过去30年从日本不同来源分离出的31株日本立克次氏体菌株所获得的完整或近乎完整序列进行比较，结果显示基因组多样性水平极低。特别是，在包含所有临床分离株以及来自三种蜱种的蜱分离株的主要谱系的27株菌株中，仅鉴定出34个单核苷酸多态性。我们的数据为日本立克次氏体的生物学和基因组进化提供了新的见解，包括近期克隆扩张的可能性以及由于与蜱生命周期相关的长时间休眠期而在自然环境中具有较长世代时间的可能性。
