Isolation of a hyperthermophilic archaeum predicted by in situ RNA analysis.

A variety of hyperthermophilic bacteria and archaea have been isolated from high-temperature environments by plating and serial dilutions. However, these techniques allow only the small percentage of organisms able to form colonies, or those that are predominant within environmental samples, to be obtained in pure culture. Recently, in situ 16S ribosomal RNA analyses of samples from the Obsidian hot pool at Yellowstone National Park, Wyoming, revealed a variety of archaeal sequences, which were all different from those of previously isolated species. This suggests substantial diversity of archaea with so far unknown morphological, physiological and biochemical features, which may play an important part within high-temperature ecosystems. Here we describe a procedure to obtain pure cultures of unknown organisms harbouring specific 16S rRNA sequences identified previously within the environment. It combines visual recognition of single cells by phylogenetic staining and cloning by 'optical tweezers'. Our result validates polymerase chain reaction data on the existence of large archael communities.