Archaea
- PDF / 302,302 Bytes
- 6 Pages / 595.276 x 790.866 pts Page_size
- 79 Downloads / 193 Views
ARCHAEA
Yochelson, E. L., and Kisselev, G. N., 2003. Early Cambrian Salterella and Volborthella (Phylum Agmata) re-evaluated. Lethaia, 36, 8–20. Zhuravlev, A. Yu., and Wood, R. A., 2008. Eve of biomineralization: Controls on skeletal mineralogy. Geology, 36, 923–926.
Cross-references Animal Biocalcification, Evolution Breakup of Rodinia Ediacaran Biota Gondwanaland, Formation Origins of the Metazoa Trace Fossils: Neoproterozoic
ARCHAEA Volker Thiel University of Göttingen, Göttingen, Germany
Synonyms Archaebacteria (term abandoned) Definition The Archaea are single-celled or filamentous prokaryotes that constitute the third phylogenetic domain of life, besides the Bacteria and the Eukarya. The word “Archaea” (singular archaeum, archaeon) is derived from the Greek word for “the old ones”.
History The discovery of the Archaea dates back to 1976 when Carl Woese, at his laboratory at Illinois University, compared prokaryotic small subunit ribosomal RNA sequences using oligonucleotide catalogs (Woese, 2007). Woese recognized Methanobacterium thermoautotrophicum as the first member of a fundamentally distinct group of prokaryotes that clustered away from all other bacteria. Consequently, Woese and Fox (1977) established the concept of two separate prokaryotic “urkingdoms,” Eubacteria and Archaebacteria. Later, the term “Archaebacteria” was changed to “Archaea” to emphasize the fundamental differences between both groups. Based on these discoveries, Woese and his coworkers proposed the now-accepted division of life into the three domains of Archaea, Bacteria, and Eukarya (Figure 1; Woese et al., 1990). Specific traits Like the Bacteria, most Archaea show a cell size between 0.5 and 2 µm and lack a cell nucleus, internal membranes, and organelles. However, a number of traits distinguish the Archaea from members of the other domains of life: 1. The genetic machinery of Archaea is different from Bacteria and Eukarya. The distinctive archaeal “signature” contains more than 1,000 archaeal proteinencoding genes. These signature genes account for a significant portion (9–15%) of archaeal genomic DNA (Graham et al., 2000). The archaeal RNA polymerase, an enzyme producing RNA chains from DNA gene templates, consists of eight (methanogens
Prokaryotes
Eukaryotes
Bacteria
Archaea
Eukarya
Green non-sulfurbacteria Mitochondrium Gram positive Proteobacteria bacteria Chloroplast Cyanobacteria Flavobacteria
Thermatoga Thermodesulfobacterium Aquifex
Entamoebae
Methanosarcina Methanobacterium Thermoproteus 3 Pyrodictium 2 Marine crenarchaeota
Korarchaeota
1
Slime molds
Animals
Extreme halophiles
Fungi Ciliates
Thermoplasma Flagellates
Methanopyrus
Trichomonads
Nanoarchaeota Microsporidia 1 = Pyrolobus 2 = Thermococcus 3 = Methanococcus
Archaea, Figure 1 The phylogenetic tree of life. (Redrawn after Madigan and Martinko, 2006.)
Diplomonads
ARCHAEA
and halophiles) or ten (hyperthermophiles) individual polypeptides. These polymerases are quite different from those of the Bacteria (four polypeptides), but somewhat s
Data Loading...
