In Search of an Uncultured Human-Associated TM7 Bacterium in the Environment

We have identified an environmental bacterium in the Candidate Division TM7 with ≥98.5% 16S rDNA gene homology to a group of TM7 bacteria associated with the human oral cavity and skin. The environmental TM7 bacterium (referred to as TM7a-like) was readily detectable in wastewater with molecular techniques over two years of sampling. We present the first images of TM7a-like cells through FISH technique and the first images of any TM7 as viable cells through the STARFISH technique. In situ quantification showed TM7 concentration in wastewater up to five times greater than in human oral sites. We speculate that upon further characterization of the physiology and genetics of the TM7a-like bacterium from environmental sources and confirmation of its genomic identity to human-associated counterparts it will serve as model organisms to better understand its role in human health. The approach proposed circumvents difficulties imposed by sampling humans, provides an alternative strategy to characterizing some diseases of unknown etiology, and renders a much needed understanding of the ecophysiological role hundreds of unique Bacteria and Archaea strains play in mixed microbial communities.

本研究在候选门TM7 (Candidate Division TM7)中鉴定出一株环境细菌，其与一类定殖于人类口腔与皮肤的TM7菌群的16S核糖体DNA (16S rDNA)基因同源性≥98.5%。该环境TM7细菌（被称为类TM7a菌株）在为期两年的采样周期内，可通过分子技术在废水样本中稳定检出。本研究首次通过荧光原位杂交 (Fluorescence In Situ Hybridization，FISH) 技术获取了类TM7a菌体的显微图像，并通过STARFISH技术获得了首组TM7门活菌的显微成像结果。原位定量分析显示，废水中TM7的浓度最高可达人类口腔位点的五倍。我们推测，若能进一步完成环境来源类TM7a菌株的生理学与遗传学特征解析，并确认其与人类相关同源菌株的基因组同一性，该菌株将可作为模式生物，助力我们更深入地理解其在人类健康中发挥的作用。本研究提出的研究策略规避了人类样本采集所面临的诸多现实难题，为解析部分病因不明的疾病提供了全新的研究思路，同时填补了学界亟需的、关于数百株独特细菌域 (Bacteria)与古菌域 (Archaea)菌株在混合微生物群落中所发挥的生态生理角色的认知空白。