The Cooccurrence of Archaea and Bacteria Among Diverse Globally Distributed Ecosystems

Archaeal microorganisms have traditionally been considered ecological extremophiles and have been generally considered to only exist in the harshest environments. While Archaea are especially dominant in some of the most extreme environments known, the use of cultivation-independent methods to survey microbial diversity has elucidated a widespread diversity of Archaea in both mesic and extreme environments. Indeed, while Archaea were traditionally thought to inhabit distinct, more extreme environments compared to the better-studied bacterial domain, they are now known to coexist and comprise a significant community fraction in a variety of ecosystems that were once thought to be predominantly bacterial. Here, I outline some of the major advances that have led to our current understanding of the coexistence between Archaea and Bacteria, and how our understanding of archaeal ecology has changed over the previous several decades. In particular, I emphasize how the two domains overlap in various ecosystems at the level of biogeochemical interactions.