1 The Forsyth Institute, Cambridge, MA, USA.
2 Department of Oral Medicine, Infection and Immunity, Harvard School of Dental Medicine, Boston, MA, USA.
J Dent Res. 2019 May;98(5):500-509. doi: 10.1177/0022034519831671. Epub 2019 Mar 20.
Bacteria from the Saccharibacteria phylum (formerly known as TM7) are ubiquitous members of the human oral microbiome and are part of the Candidate Phyla Radiation. Recent studies have revealed remarkable 16S rRNA diversity in environmental and mammalian host-associated members across this phylum, and their association with oral mucosal infectious diseases has been reported. However, due to their recalcitrance to conventional cultivation, TM7's physiology, lifestyle, and role in health and diseases remain elusive. The recent cultivation and characterization of Nanosynbacter lyticus type strain TM7x (HMT_952)-the first Saccharibacteria strain coisolated as an ultrasmall obligate parasite with its bacterial host from the human oral cavity-provide a rare glimpse into the novel symbiotic lifestyle of these enigmatic human-associated bacteria. TM7x is unique among all bacteria: it has an ultrasmall size and lives on the surface of its host bacterium. With a highly reduced genome, it lacks the ability to synthesize any of its own amino acids, vitamins, or cell wall precursors and must parasitize other oral bacteria. TM7x displays a highly dynamic interaction with its bacterial hosts, as reflected by the reciprocal morphologic and physiologic changes in both partners. Furthermore, depending on environmental conditions, TM7x can exhibit virulent killing of its host bacterium. Thus, Saccharibacteria potentially affect oral microbial ecology by modulating the oral microbiome structure hierarchy and functionality through affecting the bacterial host's physiology, inhibiting the host's growth dynamics, or affecting the relative abundance of the host via direct killing. At this time, several other uncharacterized members of this phylum have been detected in various human body sites at high prevalence. In the oral cavity alone, at least 6 distinct groups vary widely in relative abundance across anatomic sites. Here, we review the current knowledge on the diversity and unique biology of this recently uncovered group of ultrasmall bacteria.
栖居于人体口腔微生物组的泉古菌门（原 TM7 门）细菌是普遍存在的成员，也是候选门辐射的一部分。最近的研究揭示了该门环境和哺乳动物宿主相关成员中令人瞩目的 16S rRNA 多样性，并且已经报道了它们与口腔黏膜传染病的关联。然而，由于它们难以进行常规培养，TM7 的生理学、生活方式以及在健康和疾病中的作用仍然难以捉摸。最近对共生体 Nanosynbacter lyticus 模式菌株 TM7x（HMT_952）——第一个从人体口腔中与其细菌宿主一起被共分离出来的微小严格需氧寄生菌——的培养和特性研究为这些神秘的人类相关细菌的新型共生生活方式提供了难得的一瞥。TM7x 在所有细菌中是独一无二的：它具有极小的尺寸，并且生活在其宿主细菌的表面。由于基因组高度简化，它无法合成自身的任何氨基酸、维生素或细胞壁前体，必须寄生在其他口腔细菌上。TM7x 与其细菌宿主之间存在高度动态的相互作用，这反映在两个伙伴的形态和生理变化上。此外，根据环境条件的不同，TM7x 可以表现出对宿主细菌的致命杀伤。因此，泉古菌通过影响细菌宿主的生理学、抑制宿主的生长动态、或通过直接杀伤来影响宿主的相对丰度，从而可能通过调节口腔微生物组结构层次和功能来影响口腔微生物生态。此时，在各种人体部位中已经检测到该门的其他几个未被描述的成员，其存在的普遍性很高。仅在口腔中，至少有 6 个不同的组在解剖部位之间的相对丰度上差异很大。在这里，我们综述了关于这个最近被发现的微小细菌群多样性和独特生物学的现有知识。
