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Symbiosis is usually a matter of degrees, not absolutes!

By Batbileg Bor, Assistant Member of the Staff

Darwin gave us the concept of “tree of life.” Woese resolved life into three branches (Archaea, Bacteria, and Eukaryota). But could the microscopic world hide life so foreign that it does not fit into any of these branches? Closest yet to this idea is the newly added major lineage (>73 Phyla) of the domain Bacteria termed the Candidate Phyla Radiation (CPR) [1]. Curiously, many of these bacteria may be symbiotic to other microorganisms, inferred from their ultrasmall cell sizes, highly reduced genomes and the environment in which they are from [2]. This generalization was partially validated by the cultivation of Nanosynbacter lyticus strain TM7x, a member of the Saccharibacteria phylum within the CPR, revealing that Saccharibacteria live as obligate symbionts attached to suitable host bacteria [3, 4]. As the only cultivated member of the vast CPR, combined with its occurrence in the human microbiome, studies of Saccharibacteria physiology have been filled with serendipitous discoveries along the way.

We began our study with a simple question: Can TM7x grow on other Actinomyces sp. besides the original bacterial host on which it was isolated?

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