Name: Dr. Karl Stetter
Institution: Universitat Regensburg
Location: Regensburg, Germany
Tell me a bit about how you came to be interested in Archaea and what your work entails.
Already in January 1977 after meeting Carl Woese at Urbana, my mentor Otto Kandler informed me about Woese`s revolutionary discovery of the archaea and his concept to represent a so far unknown third domain of life. His findings had been based only on ss rRNA partial sequences. At that time, as a postdoc in Wolfram Zillig`s lab, I had studied the transcription in Lactobacilli. Similar to all other bacterial DNA-dependent RNA Polymerases (RNAP) known and in contrast to eukaryotic RNAP, these RNAP were sensitive to the antibiotic Rifampicin and exhibited the same pretty simple subunit pattern. In order to test Woese`s concept, Wolfram Zillig and I purified the RNAP from the few archaea first recognized by Carl Woese (Methanobacterium, Halobacterium, Sulfolobus and Thermoplasma). Very excitingly, they all turned out to be resistant against Rifampicin and their highly complex subunit patterns exhibited no structural analogy to the composition of bacterial RNAP, strongly supporting Woese`s idea of a separate phylogenetic history. They even appeared more like eukaryotic RNAP including in their Rifampicin resistance. This evidence made me very excited about the archaea and completely changed my scientific interests. As a microbiologist, I urgently wanted to find further archaea and Carl Woese and Otto Kandler stimulated me to do so. In the following decade, my group and I successfully began to hunt for novel archaea mainly in hot anaerobic terrestrial and submarine environments all over the world. For the first time, we found hyperthermophilic anaerobic archaea, some of which even grow optimally at above 100 °C, the regular boiling point of water. In a very exciting collaboration, Carl Woese investigated the phylogenetic position of our new isolates within the tree of life. In order to grow enough cell masses for molecular and biochemical studies, I built up the Archaea Center at the University of Regensburg and provided cell masses to researchers all over the world. A few of my isolates (e. g. Pyrococcus furiosus, Methanopyrus kandleri and Nanoarchaeum equitans) became model organisms. They are world-wide investigated in great detail, which makes me very happy, of course.
Karl Stetter's group in Pisciarelli Solfatara, Naples, Italy (1982).
EM micrograph of the hyperthermophilic isolate Pyrococcus furiosus, which grows optimally at 100 °C (isolated by Karl Stetter).
Looking back at the last 40 years, what would you describe as the most exciting areas of research linked to the study of the Archaea? And where do you see the field headed in the next decade?
Due to Carl Woese`s discovery, E. coli was not anymore the general model for a “prokaryote”! A completely unexpected novel continent of life had been found by him and began to be explored by enthusiastic scientists all over the world. Many important discoveries opened our mind for a deeper understanding of life, its origins, evolution and strategies. For example, novel types of metabolism, a variety of so far unknown cell walls, cell membranes consisting of ether lipids, extremely heat stable proteins up to 140 °C and a simple version of the eukaryotic transcription apparatus had been found for the first time. Last but not least, an incredible variety of very different archaeal viruses had been detected.
Recent environmental studies by metagenomics reveal that archaea are not limited to extreme environments, but exist almost everywhere. Novel phylogenetic lineages have been detected recently which even harbor most genes that had been taken to be specific for eukaryotes. Therefore, now the three- domain concept is going to be challenged by a two domain tree, consisting of archaea and bacteria, in which eukaryotes are forming just an additional archaeal lineage. Cultivation and investigation of their closest relatives in the future should lead to a deeper understanding of the evolution of eukaryotes and, therefore of our ancestry.
What would you like the public (and general microbiological audience) to appreciate about Archaea?
The discovery and studies of archaea have changed our view about life on Earth and its incredible ability to cope with all kinds of environments possibly even on other planets. Most likely as our direct ancestors, archaea may tell us more about ourselves than bacteria ever could. In addition, archaea are key players in biotechnology, for example in bio-mining, hydrogen and biogas production and waste recycling. Their unique cell components permit novel technical applications, like heat-stable enzymes in oil recovery and as technical catalysts in chemistry.
Are there any particular papers that you feel are absolute must reads for those that aren’t necessarily familiar with the field (and briefly, why)?
Stetter, K., Hyperthermophiles in the history of life. Philos Trans R Soc Lond B Biol Sci. 361(1474):1837-42 (2006).
Friend, T., The third domain: the untold story of archaea and the future of biotechnology. Joseph Henry Press (2007).
Tim Friend was a USA-Today journalist who wrote about the third domain in a very understandable and excitig way.
Sapp, J., The new foundations of evolution: on the tree of life. Oxford University Press (2009).
Jan Sapp`s book as a historian is very detailed and specialized.