archaea

Examples of archaea in the following topics:

• The Diversity of Life

  • The diversity of life can be classified within the three major domains (Bacteria, Eukarya and Archaea) using phylogenetic trees.
  • Woese defined Archaea as a new domain, and this resulted in a new taxonomic tree .
  • Many organisms belonging to the Archaea domain live under extreme conditions and are called extremophiles.
  • The tree shows the separation of living organisms into three domains: Bacteria, Archaea, and Eukarya.
  • Bacteria and Archaea are prokaryotes, single-celled organisms lacking intracellular organelles.

• The Origins of Archaea and Bacteria

  • Archaea are believed to have evolved from gram-positive bacteria and can occupy more extreme environments.
  • Archaea and gram-positive bacteria also share conserved indels in a number of important proteins, such as Hsp70 and glutamine synthetase.
  • It has been proposed that the archaea evolved from gram-positive bacteria in response to antibiotic selection pressure.
  • This is suggested by the observation that archaea are resistant to a wide variety of antibiotics that are primarily produced by gram-positive bacteria and that these antibiotics primarily act on the genes that distinguish archaea from bacteria.
  • A microbial mat is a multi-layered sheet of prokaryotes that includes mostly bacteria, but also archaea .

• Basic Structures of Prokaryotic Cells

  • Plasmids, which consist of extra-chromosomal DNA, are also present in many species of bacteria and archaea.
  • The chemical composition of the cell walls varies between archaea and bacteria.
  • S-layer (surface layer) proteins are also present on the outside of cell walls of both archaea and bacteria.
  • Bacteria and Archaea are both prokaryotes, but differ enough to be placed in separate domains.
  • An ancestor of modern Archaea is believed to have given rise to Eukarya, the third domain of life.

• Classification of Prokaryotes

  • The domain Bacteria comprises all organisms in the kingdom Bacteria, the domain Archaea comprises the rest of the prokaryotes, and the domain Eukarya comprises all eukaryotes, including organisms in the kingdoms Animalia, Plantae, Fungi, and Protista.
  • Two of the three domains, Bacteria and Archaea, are prokaryotic.

• Anaerobic Cellular Respiration

  • Certain prokaryotes, including some species of bacteria and archaea, use anaerobic respiration.
  • For example, the group of archaea called methanogens reduces carbon dioxide to methane to oxidize NADH.
  • Similarly, sulfate-reducing bacteria and archaea, most of which are anaerobic, reduce sulfate to hydrogen sulfide to regenerate NAD+ from NADH.

• Endosymbiotic Theory and the Evolution of Eukaryotes

  • Using DNA analysis and a new mathematical algorithm called conditioned reconstruction (CR), it has been proposed that eukaryotic cells developed from an endosymbiotic gene fusion between two species: one an Archaea and the other a Bacteria.
  • As mentioned, some eukaryotic genes resemble those of Archaea, whereas others resemble those from Bacteria.
  • More controversial is the proposal that (a) the eukaryotic nucleus resulted from the fusion of archaeal and bacterial genomes; and that (b) Gram-negative bacteria, which have two membranes, resulted from the fusion of Archaea and Gram-positive bacteria, each of which has a single membrane.

• Prokaryotic Reproduction

  • Archaea are not affected by bacteriophages, but instead have their own viruses that translocate genetic material from one individual to another.

• Evolution of Viruses

  • This phylogenetic tree of the three domains of life (Bacteria, Archaea, and Eukarya) attempts to identify when various species diverged from a common ancestor.

• Processing of tRNAs and rRNAs

  • In archaea and eukaryotes, each pre-tRNA is transcribed as a separate transcript.
  • Some bacteria and archaea pre-tRNAs already have the CCA encoded in their transcript immediately upstream of the 3' cleavage site, so they don't need to add one.

• Phylogenetic Trees

  • Notice in the rooted phylogenetic tree that the three domains (Bacteria, Archaea, and Eukarya) diverge from a single point and branch off.
  • Both of these phylogenetic trees shows the relationship of the three domains of life (Bacteria, Archaea, and Eukarya), but the (a) rooted tree attempts to identify when various species diverged from a common ancestor, while the (b) unrooted tree does not.