Noda Satoko, Shimizu Daichi, Yuki Masahiro, Kitade Osamu, Ohkuma Moriya
Graduate School of Life and Environmental Sciences, University of Yamanashi.
Biomass Research Platform Team, RIKEN Biomass Engineering Program Cooperation Division, RIKEN Center for Sustainable Resource Science.
Microbes Environ. 2018 Mar 29;33(1):26-33. doi: 10.1264/jsme2.ME17096. Epub 2018 Jan 24.
Cellulolytic flagellated protists inhabit the hindgut of termites. They are unique and essential to termites and related wood-feeding cockroaches, enabling host feeding on cellulosic matter. Protists of two genera in the family Teranymphidae (phylum Parabasalia), Eucomonympha and Teranympha, are phylogenetically closely related and harbor intracellular endosymbiotic bacteria from the genus Treponema. In order to obtain a clearer understanding of the evolutionary history of this triplex symbiotic relationship, the molecular phylogenies of the three symbiotic partners, the Teranymphidae protists, their Treponema endosymbionts, and their host termites, were inferred and compared. Strong congruence was observed in the tree topologies of all interacting partners, implying their cospeciating relationships. In contrast, the coevolutionary relationship between the Eucomonympha protists and their endosymbionts was more complex, and evidence of incongruence against cospeciating relationships suggested frequent host switches of the endosymbionts, possibly because multiple Eucomonympha species are present in the same gut community. Similarities in the 16S rRNA and gyrB gene sequences of the endosymbionts were higher among Teranympha spp. (>99.25% and >97.2%, respectively), whereas those between Teranympha and Eucomonympha were lower (<97.1% and <91.9%, respectively). In addition, the endosymbionts of Teranympha spp. formed a phylogenetic clade distinct from those of Eucomonympha spp. Therefore, the endosymbiont species of Teranympha spp., designated here as "Candidatus Treponema teratonymphae", needs to be classified as a species distinct from the endosymbiont species of Eucomonympha spp.
纤维素分解鞭毛虫原生生物栖息于白蚁的后肠。它们对于白蚁及相关食木蟑螂而言独特且至关重要，使宿主能够以纤维素物质为食。Teranymphidae科（副基体门）两个属的原生生物，即真共生隐滴虫属和特氏隐滴虫属，在系统发育上密切相关，并含有来自密螺旋体属的细胞内共生细菌。为了更清楚地了解这种三重共生关系的进化历史，对三个共生伙伴（Teranymphidae原生生物、它们的密螺旋体共生菌以及它们的宿主白蚁）的分子系统发育进行了推断和比较。在所有相互作用伙伴的树形拓扑结构中观察到了强烈的一致性，这意味着它们的共 speciating 关系。相比之下，真共生隐滴虫属原生生物与其共生菌之间的协同进化关系更为复杂，与共 speciating 关系不一致的证据表明共生菌频繁发生宿主转换，这可能是因为同一肠道群落中存在多种真共生隐滴虫属物种。特氏隐滴虫属物种的共生菌在16S rRNA和gyrB基因序列上的相似性更高（分别>99.25%和>97.2%），而特氏隐滴虫属和真共生隐滴虫属之间的相似性则较低（分别<97.1%和<91.9%）。此外，特氏隐滴虫属物种的共生菌形成了一个与真共生隐滴虫属物种不同的系统发育分支。因此，特氏隐滴虫属物种的共生菌物种，在此指定为“候选密螺旋体特氏隐滴虫”，需要被分类为与真共生隐滴虫属物种的共生菌物种不同的物种。
