候选门级辐射类群(CPR)细菌研究进展

Progress in candidate phyla radiation (CPR) research

摘要:

候选门级辐射类群（candidate phyla radiation，CPR）是一类在自然界广泛分布的庞大细菌类群，成员众多，基于宏基因组测序结果已划分出75个门水平分支。CPR细菌是研究微生物进化与各类生境微生物协同作用的理想材料与系统，其在系统进化树中位于细菌域的最外侧，与古菌域外侧的DPANN超门毗邻，进化地位特殊。该类群具有独特的生物学特性，如细胞个体小，基因组精简，缺少三羧酸循环途径以及常见细菌电子传递链相关基因，通常需要与宿主共生、纯培养困难，目前仅在人类口腔中成功分离到一株CPR细菌（TM7菌株UB2523）。本文综述了CPR细菌的发现历程、细胞形态、代谢特征、在碳/氮/硫元素循环中的作用，以及不依赖于培养的组学技术在CPR细菌研究中的应用，可为深入探究CPR细菌的进化地位和驱动地球化学元素循环的方式，以及与宿主共生系统的互作机制提供参考。

Abstract:

The Candidate Phyla Radiation (CPR) is a proposed subdivision within the bacterial domain comprising of many candidate phyla which are widespread in multiple kinds of environments. CPR microorganisms are ideal objects to explore bacteria evolution and symbiotic lifestyle. CPR has several unique characteristics, such as small genome size, extreme small physical sizes, hard to cultivate, lacking of several metabolic enzymes including electron transport chain components and tricarboxylic acid cycle, and deep branches within the bacterial subtree of life. Most of CPR members are identified by metagenome sequencing technology and TM7 isolate UB2523 from human oral cavity was the first cultivated CPR member. In this review, we summarized the CPR discovery process, morphological and genomic characteristics, recognized roles in carbon, nitrogen and sulfur cycling, and the cultivation-independent strategies in CPR research area. As well, future expectations for CPR-driven element cycling in ecosystem and CPR-Host symbionts are indicated.