The discovery of ammonia-oxidizing archaea - Cultivation and characterization of a novel, globally abundant archaeal group of chemolithoautrophs synthesizing unique membrane lipids

The discovery of ammonia-oxidizing archaea - Cultivation and characterization of a novel, globally abundant archaeal group of chemolithoautrophs synthesizing unique membrane lipids

PD Dr. Martin Könneke

MARUM – Center for Marine Environmental Sciences

University of Bremen, Germany

More than 20 years ago, planktonic archaea were recognized to represent one of the most abundant microorganism groups in the World’s oceans by accounting for about 20 % of the total microbial community in the pelagic realm. Despite the high abundance of the so-called Marine Group I Crenarchaeota their ecophysiology and contribution to biogeochemical cycles have remained unknown for a long time because of the lack of cultured representatives.

The presentation summarizes the discovery of the first cultured member of this group, its description as an ammonia-oxidizing archaeon, and its implications on the global nitrogen cycle and on the phylogenetic and physiological diversity of the domain Archaea. The first isolate, Nitrosopumilus maritimus was obtained from an aquarium and provided for the first time direct evidence for archaeal nitrification. Following the principle of cultivation, we succeeded to grow the first thermophilic ammonia-oxidizing archaeon (AOA) from a Yellowstone hot spring and the first AOA isolated from soil.

In addition this contribution presents the unique membrane lipids of AOA which form the basis of the geochemical paleotemperature proxy TEX86. Cultivation experiments in combination with state- of-the–art analytical methods showed that the lipidome of AOA is more complex than initially thought and demonstrated that the composition is strongly affected by physiological parameters rather than by temperature. Additionally we identified novel lipid compounds that may represent useful biomarkers to detect active and fossil AOA in natural samples.

In conclusion, the discovery of AOA has changed the traditional view of the microbial nitrogen cycle and expanded the habitat range of nitrification. In particular, marine AOA were shown to be perfectly adapted to extremely low nutrient conditions and to represent the primary ammonia oxidizers in oligotrophic environments, such as the open ocean.