Biology Department, Protistology-Zoology Unit, University of Pisa, Pisa, Italy.
Microb Ecol. 2013 Feb;65(2):302-10. doi: 10.1007/s00248-012-0170-3. Epub 2013 Jan 8.
The "Midichloria clade" is a recently discovered but well-established evolutionary lineage clustering inside the order Rickettsiales (Alphaproteobacteria). Not much is known about the biology of these organisms. The best characterized ones are endocellular symbionts of very different eukaryotic hosts, ranging from arthropods to protists. "Candidatus Midichloria mitochondrii", the most studied organism of the group, is an interesting object of study because of its unique capability to infect metazoans' mitochondria and the presence of flagellar genes in its genome. With this work, we aim at increasing the knowledge on the biodiversity and phylogeny of the "Midichloria group". We characterized according to the "full cycle rRNA approach" two novel endosymbionts of ciliated protozoa, i.e. Paramecium nephridiatum and Euplotes aediculatus. According to the nomenclatural rules for uncultivated prokaryotes, we established the novel taxa "Candidatus Defluviella procrastinata" and "Candidatus Cyrtobacter zanobii" for the two bacterial symbionts. Our phylogenetic analysis based on 16S rRNA gene sequences confirms that the evolutionary histories of "Midichloria clade" representatives and of their hosts are very different. This suggests that the symbiotic processes arose many times independently, perhaps through ways of transmission still not described in Rickettsiales.
“中微体菌目”是最近发现的一个在 Rickettsiales 目（α变形菌）内部的成熟进化谱系。关于这些生物体的生物学特性，人们知之甚少。其中研究得最好的是各种真核宿主的内共生体，范围从节肢动物到原生动物。“候选中微体菌线粒体”是该群中研究最多的生物体，因为它具有独特的感染后生动物线粒体的能力以及其基因组中存在鞭毛基因而成为一个有趣的研究对象。通过这项工作，我们旨在增加对“中微体菌群”的生物多样性和系统发育的了解。我们根据“全循环 rRNA 方法”对两种新型纤毛虫内共生体，即 Paramecium nephridiatum 和 Euplotes aediculatus 进行了特征描述。根据未培养原核生物的命名规则，我们为两种细菌共生体建立了新的分类单元“候选脱氟迟缓菌”和“候选 Cyrtobacter zanobii”。我们基于 16S rRNA 基因序列的系统发育分析证实，“中微体菌目”代表及其宿主的进化历史非常不同。这表明共生过程是多次独立发生的，可能通过 Rickettsiales 中尚未描述的传播方式。
