1 An uncultured human-associated bacterium model Authors

An uncultured human-associated bacterium model The Bacteria Domain experienced an explosion of novel lineages identified within the last decade, especially of lineages made entirely of uncultured members1. Since numerous cultivable bacteria have been shown to be instrumental in human development2, health3 and diseases4,5, it is reasonable to speculate that strains from uncultured groups, which comprise nearly 80 % of the human gut6 and 68 % of human oral7 microbial consortia, participate in similar functions. The study of human-associated uncultured bacteria, however, has many practical limitations, such as access to patient samples, unpredictable microbial composition, and low relative abundance, all of which challenge experimental promptness and reproducibility. We propose that uncultured bacteria from environmental sources can serve as a model to better understand the roles their counterparts play in humans. In this study, we illustrate this concept using an environmental TM7 bacterium with ≥98.5 % 16S rDNA gene homology to a group of TM7 bacteria found in both the human oral cavity and skin. Our TM7 model was readily detectable with molecular techniques as viable cells in sludge and in quantities greater than its human-associated relatives. Our approach circumvents difficulties imposed by sampling human