Oceans of Archaea

E arth’s microbiota is remarkably pervasive, thriving at extremely high temperature, low and high pH, high salinity, and low water availability. One lineage of microbial life in particular, the Archaea, is especially adept at exploiting environmental extremes. Despite their success in these challenging habitats, the Archaea may now also be viewed as a cosmopolitan lot. These microbes exist in a wide variety of terrestrial, freshwater, and marine habitats, sometimes in very high abundance. The oceanic Marine Group I Crenarchaeota, for example, rival total bacterial biomass in waters below 100 m. These widespread Archaea appear to derive from thermophilic ancestors that invaded diverse low-temperature environments. Novel cultivation strategies, in situ biochemical and geochemical methods, and environmental genomics promise to further our understanding of these and other ubiquitous and abundant Archaea.