Genes of archaea encoding homologues of ammonia monooxygenases have been found on a widespread basis and in large amounts in almost all terrestrial and marine environments, indicating that ammonia oxidizing archaea (AOA) might play a major role in nitrification on Earth. However, only one pure isolate of this group from a marine environment has so far been obtained, demonstrating archaeal ammonia oxidation coupled with autotrophic growth similar to the bacterial counterparts. Here we describe the cultivation and isolation of an AOA from soil. It grows on ammonia or urea as an energy source and is capable of using higher ammonia concentrations than the marine isolate, Nitrosopumilus maritimus. Surprisingly, although it is able to grow chemolithoautotrophically, considerable growth rates of this strain are obtained only upon addition of low amounts of pyruvate or when grown in coculture with bacteria. Our findings expand the recognized metabolic spectrum of AOA and help explain controversial results obtained in the past on the activity and carbon assimilation of these globally distributed organisms.