While there has been increasing awareness of candidate phyla within domain Bacteria, the Archaea are even more poorly characterized. Our paper led by Cindy Castelle (UC Berkeley) has just been published in Current Biology, describing research that used shotgun metagenomics to reconstruct archaeal genomes from groundwater samples recovered at Rifle, CO. The results have illuminated previously unknown members of domain Archaea, and allowed inferences to be made about functional roles for these microorganisms.
Paper is available here