Ultrasmall Archaea

Enigmatic, ultrasmall, uncultivated Archaea in PNAS.

Metagenomics has provided access to genomes of as yet uncultivated microorganisms in natural environments, yet there are gaps in our knowledge—particularly for Archaea—that occur at relatively low abundance and in extreme environments. Ultrasmall cells (< 500 nm in diameter) from lineages without cultivated representatives that branch near the crenarchaeal>/euryarchaeal divide have been detected in a variety of acidic ecosystems.