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

The Bacteria Domain experienced an explosion of novel lineages identified within the last decade, especially of lineages made entirely of uncultured members. Since molecular approaches were applied to identify uncultured microbes, the number of Bacteria phyla increased from 12 (none uncultured) in 1987 to about 52 in 2003, half of which were termed candidate division since all of its members were yet uncultured. The proportion of candidate divisions is expected to increase as more prokaryotic DNA sequences are generated and today the NCBI Taxonomy Database (not peer-reviewed) lists 24 Bacteria phyla (those with at least some cultured species), 70 candidate divisions, and many unclassified entries. For this paper, we will capitalize Bacteria to refer to the domain and use bacteria to refer to members within the domain Bacteria.

Since numerous cultivable bacteria have been shown to be instrumental in human development, health and diseases, it is reasonable to speculate that strains from uncultured groups, which comprise nearly 80% of the human gut and 68% of human oral microbial consortia, participate in similar functions. The study of human-associated uncultured prokaryotes, 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.

The Bacteria Candidate Division TM7 was first reported in 2001 in diverse environmental sources including soil, freshwater, seawater, hot springs, mouse feces, and termite guts. Recently, TM7 has been detected in various human body sites and associated with the diseases periodontitis, vaginosis, and inflammatory bowel disease. Yet, nothing is known about the direct role TM7 bacteria play in human health.

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