Archaea and Bacteria
the first dawn of life, all organic beings are found to resemble each other in
descending degrees, so they can be classed in groups under groups.
Darwin, Origin of Species, Chapter 13
The figure above depicts at once many groups within
the universal tree of life with the euclidian distance in the figure representing
an evolutionary distance as determined by small subunit ribosomal RNA (ssrRNA)
of the New Domain Archaea
the 1980's with the advent of genomic sequencing techniques, bacteria were
only recognized group of single-celled organisms to have procaryotic cells
containing a nucleus. Phylogenetics (see references 1-4 below) enabled
of another group of prokaryotes that was initially and informally named "archaebacteria"
(they were renamed Archaea since their genomes are far distant from that of bacteria).
Actually, many archaeans had long been studied extensively, but with the idea
were bacteria; sequence analysis revealed that this group of prokaryotes needed
placement within the Universal Tree of Life as a distinct Domain, alongside
From Prokaryotes to Eukaryotes
cells are very tiny, 1 micron across, compared to 10 to 100 microns in most eucaryotic
cells. Prokaryotes are found everywhere eukaryotes are found, as well as
environments too extreme for eukaryotes. Instances of prokaryote and eukaryotes
symbiosis abound. Despite their diminutive size, prokaryotes are the most
and ubiquitous form of life on Earth. They comprise some 90% of the total biomass
in the seas. The organelles of eukaryotes (mitochondria in animals and chloroplasts
in plants) are thought to be evolutionary
descendents of Bacteria that invaded,
or were captured by, primitive eukaryotes as early as 3500 million years
ago in an evolutionary leap described by the theory of endosymbiosis.
Prokaryotes exhibit an amazing diversity of types
of metabolism to power themselves that is nonexistent in eukaryotes. For example,
the metabolic processes of nitrogen fixation (conversion of atmospheric nitrogen
gas to ammonia) and methanogenesis (production of methane) are unique to procaryotes
and enormously impact the nitrogen and carbon cycles in nature. Most of the earth's
atmospheric oxygen was produced by free-living bacterial cells.
- Woese, C.R.
(1987). Bacterial Evolution. Microbiol. Rev. 51:221-271.
- Woese, C.R. & R.R.
Gutell (1989). Evidence for several higher order structural
elements in ribosomal RNA. Proc. Nat. Acad. Sci. USA 86:3119-3122.
- Woese CR, Olsen
GJ. Archaebacterial phylogeny: perspectives on the urkingdoms.
Syst Appl Microbiol 1986;7:161-77
- Olsen GJ, Woese
CR. Ribosomal RNA: a key to phylogeny. FASEB J 1993 Jan;7(1):113-23
Also see: Endosymbiosis