1. ¹Department of Geological and Environmental Sciences, Stanford University, Stanford, CA, USA
2. ²Department of Biological Sciences, University of Southern California, Los Angeles, CA, USA
3. ³Max Planck Institute for Marine Microbiology, Bremen, Germany

Correspondence: Professor CA Francis, Department of Geological and Environmental Sciences, Building 320 – Room 118, Stanford University, Stanford, CA 94305-2115, USA. E-mail: caf@stanford.edu

Received 16 November 2006; Revised 13 February 2007; Accepted 22 February 2007.

Abstract

Microbial activities drive the global nitrogen cycle, and in the past few years, our understanding of nitrogen cycling processes and the micro-organisms that mediate them has changed dramatically. During this time, the processes of anaerobic ammonium oxidation (anammox), and ammonia oxidation within the domain Archaea, have been recognized as two new links in the global nitrogen cycle. All available evidence indicates that these processes and organisms are critically important in the environment, and particularly in the ocean. Here we review what is currently known about the microbial ecology of anaerobic and archaeal ammonia oxidation, highlight relevant unknowns and discuss the implications of these discoveries for the global nitrogen and carbon cycles.