Membrane-bounded nucleoid discovered in a cultivated bacterium of the candidate phylum ‘Atribacteria’

A key feature that differentiates prokaryotes from eukaryotes is the absence of an intracellular membrane surrounding the chromosomal DNA. Here, we report isolation of an anaerobic bacterium that possesses an additional intracytoplasmic membrane surrounding a nucleoid, affiliates with the yet-to-be-cultivated ubiquitous phylum Ca. Atribacteria, and possesses unique genomic features likely associated with organization of complex cellular structure. Exploration of the uncharted microorganism overturned the prevailing dogma of prokaryotic cell structure.