Archaeal Cells

AbstractAt a first glance, Archaea are structurally seen quite similar to Bacteria, and for a long time they were named ‘Archaebacteria’. They can form cocci, rods, spirals or irregular shaped cells and are equally sized as Bacteria. Together they are referred to as ‘Prokaryotes’ because neither Archaea nor Bacteria have a nucleus. Although this term indeed might be helpful in habitual language use, it does not refer to a phylogenetic group. In fact, transcription and translation machineries of Archaea have much more in common with eukaryotic cells than with Bacteria. In addition, there are many features that remain characteristic for Archaea, given by the fact that many representatives live and thrive under extreme environmental conditions. In the review, the authors give a comprehensive overview about the stunning diversity of structural features in archaeal cell envelopes, membranes and cell appendages.Key Concepts:By application of recently developed PCR techniques, Archaea can be found in almost every habitat and sometimes are even more abundant than bacteria.Archaea show special adaptations to their sometimes extreme environments, like caldarchaeols, which are more stable at high temperatures.Like Bacteria, Archaea are also surrounded by a lipid bilayer, but in the latter case the lipid moiety consists of C5‐isoprenoid units that are coupled to glycerol via ether bonds at (sn)‐2,3 positions of the glycerol.Cell walls can be as simple as a proteinaceous surface layer or as complicated as in some methanogens with multiple layers, additional sheats enclosing several cells and even more complex cell wall compounds.Archaea exhibit a broad variety in cell appendages that are different to bacterial ones in fine structure, composition, biosynthesis and anchorage in the cell.