Metagenomic studies reveal the critical and wide-ranging ecological importance of uncultivated Archaea: the role of ammonia oxidizers.

Microbial genome sequencing has entered a new phase, where DNA sequence information is gathered from entire microbial communities (metagenomics or environmental genomics) rather than from individual microorganisms. By providing access to the genetic material of vast numbers of organisms, most of which are organisms that have never been isolated or cultivated, a new level of insight is being gained into the diversity and extent of the microbial processes that are presently occuring in environmental communities. By extending metagenomic-based approaches to the study of very complex and methodologically recalcitrant soil environments, a recent study has found that ammonia-oxidizing archaea are more abundant in many soils than bacteria.1 These findings not only highlight the undoubtedly critical yet unknown roles that archaea play in global nutrient cycles but illustrate the importance of genomic studies for informing us about the functional capacity of life on Earth.