Plasmids from Euryarchaeota
Résumé
Archaea were confused with bacteria, under the term prokaryotes, until their originality was recognized in 1977 by Carl Woese and his collaborators of the “Urbana school” ( 1 , 2 ). The classification of all cellular organisms into three domains based on rRNA was later confirmed by comparative genomic analyses that have shown that most universal proteins exist in three versions (sensu Woese), one in each domain: Archaea, Bacteria, and Eukarya ( 3 ). At the phenotypic level, archaea strikingly resemble bacteria in terms of size and shape, chromosome structure, and compact gene organization. However, when inspected at the molecular or biochemical level, archaea are either unique, for instance in terms of their lipids ( 4 ), or rather similar to eukaryotes ( 5 , 6 ). Archaea resemble eukarya with respect to both their informational systems (DNA replication, transcription, translation) and their operational systems (ATP production, protein secretion, vesicle formation, cytoskeleton, protein modification machinery) ( 7 ). However, we will see in this chapter that archaeal plasmids (and mobilome in general) have a strong bacterial flavor, a paradox that remains to be explained ( 7 ).