Archaea are nowadays known as the third domain of life. Before 1970 archaea were thought to belong to the domain bacteria, since archaeal cells have similar sizes as bacterial cells and like bacteria possess neither a nucleus nor cell organelles.
In the 1970s Carl Woese sequenced ribosomal RNAs of prokaryotic organisms and discovered two different types of rRNA sequences. Because of this discovery Woese proposed that the prokaryotic domain has to be subdivided into two separate domains, namely "Bacteria" and "Archaea". Since then more and more data accumulated which show that Archaea indeed belong to a separate domain.
Initially people thought that archaea are "freaks" living only at sites with extreme living conditions like f.i. hot geysers in Yellowstone National Park and Black Smokers at the bottom of the ocean. But nowadays it is known that archaea also constitute a big part of the biomass in "normal" environments.
Asgard archaea: Close relatives to the first eukaryotic cell?
Recent investigations of metagenomes from samples isolated from aquatic sediments revealed new archaeal genomic sequences that contain many genes with eukaryotic features. These archaea were grouped into the new archaeal superphylum Asgard archaea. This phylum contains Thor-, Odin-, Helmdall- and Lokiarchaeota. Currently these archaea could not be cultivated in the laboratory, only the genomes of these organisms could be assembled from the metagenomic sequences.
We are working with halophilic archaea (Haloferax volcanii, Halorubrum lacusprofundi and Natrialba magadii), which require a lot of salt to grow. For example Haloferax volcanii needs 2.1 M NaCl to grow and to be able to live in such high salt concentrations it accumulates similar amounts of salt inside the cell. Halophilic archaea are generally easy to grow in the lab. Haloferax can also be genetically manipulated and we can use CRISPRi for gene repression.