Archaea

From Wikinfo

Jump to: navigation, search


Search for "Archaea" on Wikipedia • Wikimedia Commons • Wiktionary • Wikiquote • Wikibooks • Mediawiki • Wikia • Wikitravel • Google (excludes Wikipedia) • Yahoo (excludes Wikipedia) • Creative Commons • WorldCat Amazon • Recent NY Times • Older NY Times.

Archaea
Fossil range: Paleoarchean - Recent
Halobacteria sp. strain NRC-1, each cell about 5 μm in length.
Halobacteria sp. strain NRC-1, each cell about 5 μm in length.
Scientific classification
Domain: Archaea
Woese, Kandler & Wheelis, 1990
Phyla

Crenarchaeota
Euryarchaeota
Korarchaeota
Nanoarchaeota
Thaumarchaeota

"Archea" redirects here. For the geologic eon, see Archean. For the spider, see Archaeidae.
For criticism see Criticism of Archaea

The Archaea en-us-Archaea.ogg [ɑrˈkiə] (help·info) are a group of single-celled microorganisms. A single individual or species from this domain is called an archaeon (sometimes spelled "archeon"). Archaea, like bacteria, are prokaryotes. They have no cell nucleus or any other organelles within their cells. In the past they were viewed as an unusual group of bacteria and named archaebacteria but since the Archaea have an independent evolutionary history and show many differences in their biochemistry from other forms of life, they are now classified as a separate domain in the three-domain system. In this system, introduced by Carl Woese, the three main branches of evolutionary descent are the Archaea, Eukaryota and Bacteria. Archaea are further divided into four phyla of which two, the Crenarchaeota and the Euryarchaeota, are most intensively studied. Classifying the Archaea is still difficult, since the vast majority of these organisms have never been studied in the laboratory and have only been detected by analysis of their nucleic acids in samples from the environment.

Generally, archaea and bacteria are quite similar in size and shape, although a few archaea have very unusual shapes, such as the flat and square-shaped cells of Haloquadra walsbyi. Despite this visual similarity to bacteria, archaea possess genes and several metabolic pathways that are more closely related to those of eukaryotes: notably the enzymes involved in transcription and translation. Other aspects of archaean biochemistry are unique, such as their reliance on ether lipids in their cell membranes. The archaea exploit a much greater variety of sources of energy than eukaryotes: ranging from familiar organic compounds such as sugars, to using ammonia, metal ions or even hydrogen gas as nutrients. Salt-tolerant archaea (the Halobacteria) use sunlight as a source of energy, and other species of archaea fix carbon; however, unlike plants and cyanobacteria, no species of archaea is known to do both. Archaea reproduce asexually and divide by binary fission, fragmentation, or budding; in contrast to bacteria and eukaryotes, no species of archaea are known that form spores.

Initially, archaea were seen as extremophiles that lived in harsh environments, such as hot springs and salt lakes, but they have since been found in a broad range of habitats, such as soils, oceans, and marshlands. Archaea are particularly numerous in the oceans, and the archaea in plankton may be one of the most abundant groups of organisms on the planet. These prokaryotes are now recognized as a major part of life on Earth and may play an important role in both the carbon cycle and nitrogen cycle. No clear examples of archaeal pathogens or parasites are known, but they are often mutualists or commensals. One example are the methanogenic archaea that inhabit the gut of humans and ruminants, where they are present in vast numbers and aid in the digestion of food. Archaea have some importance in technology, with methanogens used to produce biogas and as part of sewage treatment, and enzymes from extremophile archaea that can resist high temperatures and organic solvents are exploited in biotechnology.

Contents

Classification

A new domain

Early in the 20th century, prokaryotes were regarded as a single group of organisms and classified based on their biochemistry, morphology and metabolism. For example, microbiologists tried to classify microorganisms based on the structures of their cell walls, their shapes, and the substances they consume.[1] However, a new approach was proposed in 1965,[2] using the sequences of the genes in these organisms to work out which prokaryotes are genuinely related to each other. This approach, known as phylogenetics, is the main method used today.

Archaea were first detected in extreme environments, such as volcanic hot springs.

Archaea were first classified as a separate group of prokaryotes in 1977 by Carl Woese and George E. Fox in phylogenetic trees based on the sequences of ribosomal RNA (rRNA) genes.[3] These two groups were originally named the Archaebacteria and Eubacteria and treated as kingdoms or subkingdoms, which Woese and Fox termed Urkingdoms. Woese argued that this group of prokaryotes is a fundamentally different sort of life. To emphasize this difference, these two domains were later renamed Archaea and Bacteria.[4] The word archaea comes from the Ancient Greek ἀρχαῖα, meaning "ancient things".[5]

At first, only the methanogens were placed in this new domain, and the archaea were seen as extremophiles that exist only in habitats such as hot springs and salt lakes. By the end of the 20th century, microbiologists realized that the archaea are a large and diverse group of organisms that are widely distributed in nature and are common in much less extreme habitats, such as soils and oceans.[6] This new appreciation of the importance and ubiquity of archaea came from using the polymerase chain reaction to detect prokaryotes in samples of water or soil from their nucleic acids alone. This allows the detection and identification of organisms that cannot be cultured in the laboratory, which is often difficult.[7][8]

Current classification

Further information: Biological classification and Systematics

The classification of archaea, and of prokaryotes in general, is a rapidly moving and contentious field. Current classification systems aim to organize archaea into groups of organisms that share structural features and common ancestors.[9] These classifications rely heavily on the use of the sequence of ribosomal RNA genes to reveal relationships between organisms (molecular phylogenetics).[10] Most of the culturable and well-investigated species of archaea are members of two main phyla, the Euryarchaeota and Crenarchaeota. Other groups have been tentatively created. For example, the peculiar species Nanoarchaeum equitans, which was discovered in 2003, has been given its own phylum, the Nanoarchaeota.[11] A new phylum Korarchaeota has also been proposed, it contains a small group of unusual thermophilic species that shares features of both of the main phyla, but is most closely related to the Crenarchaeota.[12][13] Other recently detected species of archaea are only distantly related to any of these groups, such as the Archaeal Richmond Mine Acidophilic Nanoorganisms (ARMAN), which were discovered in 2006.[14]

The ARMAN are a new group of archaea recently discovered in acid mine drainage.

The classification of archaea into species is also controversial. In biology, a species is a group of related organisms. A popular definition of a species in animals is a set of organisms that can breed with each other and are reproductively isolated from other groups of organisms (i.e. they cannot breed with other species).[15] However, efforts to classify prokaryotes such as archaea into species are complicated by the fact that they are asexual and show high levels of horizontal gene transfer between lineages. The area is contentious; with, for example, some data suggesting that in archaea such as the genus Ferroplasma, individual cells can be grouped into populations that have highly-similar genomes and rarely transfer genes with more divergent groups of cells.[16] These groups of cells are argued to be analogous to species. On the other hand, studies in Halorubrum found significant genetic exchange between such populations.[17] Such results have led to the argument that classifying these groups of organisms as species would have little practical meaning.[18]

Current knowledge on the diversity of archaea is fragmentary and the total number of archaean species cannot be estimated with any accuracy.[10] Even estimates of the total number of phyla in the archaea range from 18 to 23, of which only 8 phyla have representatives that have been grown in culture and studied directly. Many of these hypothetical groups are known from only a single rRNA sequence, indicating that the vast majority of the diversity among these organisms remains completely unknown.[19] The problem of how to study and classify uncultured microbes is also encountered in the Bacteria.[20]

Origin and evolution

Further information: Timeline of evolution

Although probable fossils of prokaryotic cells have been dated to almost 3.5 billion years ago, most prokaryotes do not have distinctive morphologies and the shapes of fossils cannot be used to identify them as Archaea.[21] Instead, chemical fossils, in the form of the unique lipids found in archaea, are more informative because such compounds do not occur in other groups of organisms.[22] Some publications have suggested that the remains of lipids that may be either archaean or eukaryotic were present in shales dating from 2.7 billion years ago,[23] these data have since been questioned.[24] Such lipids have also been detected in rocks dating back to the Precambrian. The oldest known traces of these isoprene lipids come from the Isua district of west Greenland, which include sediments formed 3.8 billion years old and are the oldest on Earth.[25] The origin of Archaea appears very old indeed and the archaeal lineage may be the most ancient that exists on earth.[26]

EuryarchaeotaNanoarchaeotaCrenarchaeotaProtozoaAlgaePlantaeSlime moldsAnimalFungusGram-positive bacteriaChlamydiaeChloroflexiActinobacteriaPlanctomycetesSpirochaetesFusobacteriaCyanobacteriaThermophilesAcidobacteriaProteobacteria
Phylogenetic tree showing the relationship between the archaea and other forms of life. Eukaryotes are colored red, archaea green and bacteria blue. Adapted from Ciccarelli et al.[27]

Woese argued that the bacteria, archaea, and eukaryotes each represent a separate line of descent that diverged early on from an ancestral colony of organisms.[28][29] A few biologists, however, have argued that the Archaea and Eukaryota arose from a group of bacteria.[30] It is possible that the last common ancestor of the bacteria and archaea was a thermophile, which raises the possibility that lower temperatures are "extreme environments" in archaeal terms, and organisms that live in cooler environments appeared later in the history of life on Earth.[31] Since the Archaea and Bacteria are no more related to each other than they are to eukaryotes, this has led to the argument that the term prokaryote has no real evolutionary meaning and should be discarded entirely.[32]

The relationship between archaea and eukaryotes remains an important problem. Aside from the similarities in cell structure and function that are discussed below, many genetic trees group the two together. Some early analyses even suggested that the relationship between eukaryotes and the archaeal phylum Euryarchaeota is closer than the relationship between the Euryarchaeota and the phylum Crenarchaeota.[33] However, it is now considered more likely that the ancestor of the eukaryotes diverged early from the Archaea.[34][35] The discovery of archaean-like genes in certain bacteria, such as Thermotoga maritima, makes these relationships difficult to determine, since horizontal gene transfer has occurred.[36] Some have suggested that eukaryotes arose through fusion of an archaean and eubacterium, which became the nucleus and cytoplasm; this accounts for various genetic similarities but runs into difficulties explaining cell structure.[37]

Morphology

The sizes of prokaryotic cells relative to other cells and biomolecules.

Individual archaeans range from 0.1 micrometers (μm) to over 15 μm in diameter, and occur in various shapes, commonly as spheres, rods, spirals or plates.[38] Other morphologies in the Crenarchaeota include irregularly-shaped lobed cells in Sulfolobus, thin needle-like filaments that are less than half a micrometer in diameter in Thermofilum, and almost perfectly rectangular rods in Thermoproteus and Pyrobaculum.[39] There is even a species of flat, square archaea called Haloquadra walsbyi that lives in hypersaline pools.[40] These unusual shapes are probably maintained both by their cell walls and a prokaryotic cytoskeleton. Proteins related to the cytoskeleton components of other organisms exist in the archaea,[41] and filaments are formed within their cells,[42] but in contrast to other organisms, these cellular structures are poorly understood in archaea.[43]

Some species of archaea form aggregates or filaments of cells up to 200 μm in length,[38] and these organisms can be prominent members of the communities of microbes that make up biofilms.[44] An extreme example is Thermococcus coalescens, as aggregates of these cells fuse together in culture, forming single giant cells.[45] A particularly elaborate form of multicellular colony is produced by archaea in the genus Pyrodictium. Here, the cells produce arrays of long, thin hollow tubes called cannulae that stick out from the cells' surfaces and connect them together into a dense bush-like colony.[46] The function of these cannulae is not known, but they may allow the cells to communicate or exchange nutrients with their neighbors.[47] Colonies can also be produced by an association between different species. For example, in the "string-of-pearls" community that was discovered in 2001 in a German swamp, round whitish colonies of a novel species of archaea in the phylum Euryarchaeota are spaced along thin filaments that can be up to 15 centimetres (5.9 in) long; these filaments are made of a particular species of bacteria.[48]

Cell structure

Archaea are similar to bacteria in their general cell structure, but the composition and organization of some of these structures set the archaea apart. Like bacteria, archaea lack interior membranes so their cells do not contain organelles.[32] They also resemble bacteria in that their cell membrane is usually bounded by a cell wall and they swim by the use of one or more flagella.[49] In overall structure the archaea are most similar to gram-positive bacteria, as most have a single plasma membrane and cell wall, and lack a periplasmic space; the exception to this general rule is the archaean Ignicoccus, which possess a particularly large periplasm that contains membrane-bound vesicles and is enclosed by an outer membrane.[50]

Cell membranes

Membrane structures. Top: an archaeal phospholipid, 1 isoprene sidechain, 2 ether linkage, 3 L-glycerol, 4 phosphate moieties. Middle: a bacterial and eukaryotic phospholipid: 5 fatty acid, 6 ester linkage, 7 D-glycerol, 8 phosphate moieties. Bottom: 9 lipid bilayer of bacteria and eukaryotes, 10 lipid monolayer of some archaea.

Archaeal membranes are made of molecules that differ strongly from those in other forms of life, which is evidence that archaea are related only distantly to bacteria and eukaryotes.[51] In all organisms cell membranes are made of molecules known as phospholipids. These molecules possess both a polar part that will dissolve in water (the phosphate "head"), and a "greasy" non-polar part that will not dissolve in water (the lipid tail). These dissimilar parts are connected by a glycerol group. In water, phospholipids cluster together, with the polar phosphate heads facing the water and the non-polar lipid tails facing away from the water. This causes them to assemble into layers. The major structure in cell membranes is a double layer of these phospholipids, which is called a lipid bilayer.

The phospholipids in the membranes of archaea are unusual in four ways. Firstly, bacteria and eukaryotes have membranes composed mainly of glycerol-ester lipids, whereas archaea have membranes composed of glycerol-ether lipids.[52] The difference between these two types of phospholipid is the type of bond that joins the lipids to the glycerol group; these two types of bonds are shown in yellow in the Figure at the right. In ester lipids this is an ester bond, whereas in ether lipids this is an ether bond. Ether bonds are more chemically-resistant then ester bonds, which might contribute to the ability of some archaea to survive at extremes of temperature and in very acidic or alkaline environments.[53] Bacteria and eukaryotes do contain some ether lipids, but in contrast to archaea these lipids are not a major part of their membranes.

Secondly, archaeal lipids are unique because the stereochemistry of the glycerol group is the reverse of that found in other organisms. The glycerol group can occur in two forms that are mirror images of one another, which may be called the right-handed and left-handed forms; in chemical terms these forms are called enantiomers. Just as a right hand does not fit easily into a left-handed glove, a right-handed glycerol molecule generally cannot be used or made by enzymes adapted for the left-handed form. This suggests that archaea use entirely different enzymes for synthesizing their phospholipids than do bacteria and eukaryotes; since such enzymes developed very early in life's history, this in turn suggests that the archaea split off very early from the other two domains.[51]

Thirdly, the lipid tails of the phospholipids of archaea are chemically different from those in other organisms. Archaeal lipids are based upon the isoprenoid sidechain and are long chains with multiple side-branches and sometimes even cyclopropane or cyclohexane rings.[54] This is in contrast to the fatty acids found in other organisms' membranes, which have straight chains with no branches or rings. Although isoprenoids play an important role in the biochemistry of many organisms, only the archaea use them to make phospholipids. These branched chains may help prevent archaean membranes from becoming leaky at high temperatures.[55]

Finally, in some archaea the phospholipid bilayer is replaced by a single monolayer. In effect, the archaea have fused the tails of two independent phospholipid molecules into a single molecule with two polar heads; this fusion may make their membranes more rigid and better able to resist harsh environments.[56] For example, all the lipids in Ferroplasma are of this type, which is thought to aid this organism's survival in the extraordinarily acidic environments in which it thrives.[57]

Cell wall and flagella

Further information: Cell wall

Most archaea possess a cell wall—the exceptions being Thermoplasma and Ferroplasma.[58] In most archaea the wall is assembled from surface-layer proteins, which form an S-layer.[59] An S-layer is made of a rigid array of protein molecules that cover the outside of the cell like chain mail.[60] This layer provides both chemical and physical protection, and can act as a barrier preventing macromolecules from coming into contact with the cell membrane.[61] In contrast to bacteria, most archaea lack peptidoglycan in their cell walls.[62] The exception is pseudopeptidoglycan, which is found in Methanobacteriales, but this polymer is different from the peptidoglycan of bacteria since it lacks D-amino acids and N-acetylmuramic acid.[61]

Archaea also have flagella, and these operate in a similar way to bacterial flagella - they are long stalks that are driven by rotatory motors at the base of the flagella. These motors are powered by the proton gradient across the membrane. However, archaeal flagella are notably different in their composition and development.[49] The two types of flagella evolved from different ancestors, the bacterial flagellum evolved from a type III secretion system, while archaeal flagella appear to have evolved from the bacterial type IV pili.[63] In contrast to the bacterial flagellum, which is a hollow stalk and is assembled by subunits moving up the central pore and then adding onto the tip of the flagella, archaeal flagella are synthesized by adding subunits onto their base.[64]

Continued at Archaea, part 2

See also

References

  1. ^ Staley JT (2006). "The bacterial species dilemma and the genomic-phylogenetic species concept". Philos. Trans. R. Soc. Lond., B, Biol. Sci. 361 (1475): 1899–909. DOI:10.1098/rstb.2006.1914. PMID 17062409. 
  2. ^ Zuckerkandl E, Pauling L (1965). "Molecules as documents of evolutionary history". J. Theor. Biol. 8 (2): 357–66. DOI:10.1016/0022-5193(65)90083-4. PMID 5876245. 
  3. ^ Woese C, Fox G (1977). "Phylogenetic structure of the prokaryotic domain: the primary kingdoms". Proc Natl Acad Sci USA 74 (11): 5088–90. DOI:10.1073/pnas.74.11.5088. PMID 270744. 
  4. ^ Woese CR, Kandler O, Wheelis ML (1990). "Towards a natural system of organisms: proposal for the domains Archaea, Bacteria, and Eucarya". Proc. Natl. Acad. Sci. U.S.A. 87 (12): 4576–9. DOI:10.1073/pnas.87.12.4576. PMID 2112744. 
  5. ^ archaea. (2008). In Merriam-Webster Online Dictionary. Retrieved July 1, 2008, from http://www.merriam-webster.com/dictionary/archaea
  6. ^ DeLong EF (1998). "Everything in moderation: archaea as 'non-extremophiles'". Curr. Opin. Genet. Dev. 8 (6): 649–54. DOI:10.1016/S0959-437X(98)80032-4. PMID 9914204. 
  7. ^ Theron J, Cloete TE (2000). "Molecular techniques for determining microbial diversity and community structure in natural environments". Crit. Rev. Microbiol. 26 (1): 37–57. DOI:10.1080/10408410091154174. PMID 10782339. 
  8. ^ Schmidt TM (2006). "The maturing of microbial ecology" (PDF). Int. Microbiol. 9 (3): 217–23. PMID 17061212. 
  9. ^ Gevers D, Dawyndt P, Vandamme P, et al (2006). "Stepping stones towards a new prokaryotic taxonomy". Philos. Trans. R. Soc. Lond., B, Biol. Sci. 361 (1475): 1911–6. DOI:10.1098/rstb.2006.1915. PMID 17062410. 
  10. ^ a b Robertson CE, Harris JK, Spear JR, Pace NR (2005). "Phylogenetic diversity and ecology of environmental Archaea". Curr. Opin. Microbiol. 8 (6): 638–42. PMID 16236543. 
  11. ^ Huber H, Hohn MJ, Rachel R, Fuchs T, Wimmer VC, Stetter KO. (2002). "A new phylum of Archaea represented by a nanosized hyperthermophilic symbiont". Nature 417 (6884): 27–8. DOI:10.1038/417063a. PMID 11986665. 
  12. ^ Barns SM, Delwiche CF, Palmer JD, Pace NR (1996). "Perspectives on archaeal diversity, thermophily and monophyly from environmental rRNA sequences". Proc. Natl. Acad. Sci. U.S.A. 93 (17): 9188–93. DOI:10.1073/pnas.93.17.9188. PMID 8799176. 
  13. ^ Elkins JG, Podar M, Graham DE, et al (June 2008). "A korarchaeal genome reveals insights into the evolution of the Archaea". Proc. Natl. Acad. Sci. U.S.A. 105 (23): 8102–7. DOI:10.1073/pnas.0801980105. PMID 18535141. 
  14. ^ Baker, B.J., Tyson, G.W., Webb, R.I., Flanagan, J., Hugenholtz, P. and Banfield, J.F. (2006). "Lineages of acidophilic Archaea revealed by community genomic analysis. Science". Science 314 (6884): 1933 – 1935. DOI:10.1126/science.1132690. PMID 17185602. 
  15. ^ de Queiroz K (2005). "Ernst Mayr and the modern concept of species". Proc. Natl. Acad. Sci. U.S.A. 102 Suppl 1: 6600–7. DOI:10.1073/pnas.0502030102. PMID 15851674. 
  16. ^ Eppley JM, Tyson GW, Getz WM, Banfield JF (2007). "Genetic exchange across a species boundary in the archaeal genus ferroplasma". Genetics 177 (1): 407–16. DOI:10.1534/genetics.107.072892. PMID 17603112. 
  17. ^ Papke RT, Zhaxybayeva O, Feil EJ, Sommerfeld K, Muise D, Doolittle WF (2007). "Searching for species in haloarchaea". Proc. Natl. Acad. Sci. U.S.A. 104 (35): 14092–7. DOI:10.1073/pnas.0706358104. PMID 17715057. 
  18. ^ Kunin V, Goldovsky L, Darzentas N, Ouzounis CA (2005). "The net of life: reconstructing the microbial phylogenetic network". Genome Res. 15 (7): 954–9. DOI:10.1101/gr.3666505. PMID 15965028. 
  19. ^ Hugenholtz P (2002). "Exploring prokaryotic diversity in the genomic era". Genome Biol. 3 (2): REVIEWS0003. DOI:10.1186/gb-2002-3-2-reviews0003. PMID 11864374. 
  20. ^ Rappé MS, Giovannoni SJ (2003). "The uncultured microbial majority". Annu. Rev. Microbiol. 57: 369–94. DOI:10.1146/annurev.micro.57.030502.090759. PMID 14527284. 
  21. ^ Schopf J (2006). "Fossil evidence of Archaean life" (PDF). Philos Trans R Soc Lond B Biol Sci 361 (1470): 869–85. DOI:10.1098/rstb.2006.1834. PMID 16754604. 
  22. ^ Chappe B, Albrecht P, Michaelis W (July 1982). "Polar Lipids of Archaebacteria in Sediments and Petroleums". Science 217 (4554): 65–66. DOI:10.1126/science.217.4554.65. PMID 17739984. 
  23. ^ Brocks JJ, Logan GA, Buick R, Summons RE (1999). "Archean molecular fossils and the early rise of eukaryotes". Science 285 (5430): 1033–6. DOI:10.1126/science.285.5430.1033. PMID 10446042. 
  24. ^ Rasmussen B, Fletcher IR, Brocks JJ, Kilburn MR (October 2008). "Reassessing the first appearance of eukaryotes and cyanobacteria". Nature 455 (7216): 1101–4. DOI:10.1038/nature07381. PMID 18948954. 
  25. ^ Hahn, Jürgen; Pat Haug (1986). "Traces of Archaebacteria in ancient sediments". System Applied Microbiology 7 (Archaebacteria '85 Proceedings): 178–83. 
  26. ^ Wang M, Yafremava LS, Caetano-Anollés D, Mittenthal JE, Caetano-Anollés G (2007). "Reductive evolution of architectural repertoires in proteomes and the birth of the tripartite world". Genome Res. 17 (11): 1572–85. DOI:10.1101/gr.6454307. PMID 17908824. 
  27. ^ Ciccarelli FD, Doerks T, von Mering C, Creevey CJ, Snel B, Bork P (2006). "Toward automatic reconstruction of a highly resolved tree of life". Science 311 (5765): 1283–7. DOI:10.1126/science.1123061. PMID 16513982. 
  28. ^ Woese CR, Gupta R (1981). "Are archaebacteria merely derived 'prokaryotes'?". Nature 289 (5793): 95–6. DOI:10.1038/289095a0. PMID 6161309. 
  29. ^ Woese C (1998). "The universal ancestor". Proc. Natl. Acad. Sci. U.S.A. 95 (12): 6854–9. DOI:10.1073/pnas.95.12.6854. PMID 9618502. 
  30. ^ Gupta RS (2000). "The natural evolutionary relationships among prokaryotes". Crit. Rev. Microbiol. 26 (2): 111–31. DOI:10.1080/10408410091154219. PMID 10890353. 
  31. ^ Gribaldo S, Brochier-Armanet C (2006). "The origin and evolution of Archaea: a state of the art". Philos. Trans. R. Soc. Lond., B, Biol. Sci. 361 (1470): 1007–22. DOI:10.1098/rstb.2006.1841. PMID 16754611. 
  32. ^ a b Woese CR (March 1994). "There must be a prokaryote somewhere: microbiology's search for itself". Microbiol. Rev. 58 (1): 1–9. PMID 8177167. 
  33. ^ Lake JA (January 1988). "Origin of the eukaryotic nucleus determined by rate-invariant analysis of rRNA sequences". Nature 331 (6152): 184–6. DOI:10.1038/331184a0. PMID 3340165. 
  34. ^ Gouy M, Li WH (May 1989). "Phylogenetic analysis based on rRNA sequences supports the archaebacterial rather than the eocyte tree". Nature 339 (6220): 145–7. DOI:10.1038/339145a0. PMID 2497353. 
  35. ^ Yutin N, Makarova KS, Mekhedov SL, Wolf YI, Koonin EV (May 2008). "The deep archaeal roots of eukaryotes". Mol. Biol. Evol. 25: 1619. DOI:10.1093/molbev/msn108. PMID 18463089. 
  36. ^ Nelson KE, Clayton RA, Gill SR, et al (1999). "Evidence for lateral gene transfer between Archaea and bacteria from genome sequence of Thermotoga maritima". Nature 399 (6734): 323–9. DOI:10.1038/20601. PMID 10360571. 
  37. ^ Lake JA. (1988). "Origin of the eukaryotic nucleus determined by rate-invariant analysis of rRNA sequences". Nature 331 (6152): 184–6. DOI:10.1038/331184a0. PMID 3340165. 
  38. ^ a b
  39. ^ Barns, Sue and Burggraf, Siegfried. (1997) Crenarchaeota. Version 01 January 1997. in The Tree of Life Web Project
  40. ^ Walsby, A.E. (1980). "A square bacterium". Nature 283 (5742): 69–71. DOI:10.1038/283069a0. 
  41. ^ Hara F, Yamashiro K, Nemoto N, et al (2007). "An actin homolog of the archaeon Thermoplasma acidophilum that retains the ancient characteristics of eukaryotic actin". J. Bacteriol. 189 (5): 2039–45. DOI:10.1128/JB.01454-06. PMID 17189356. 
  42. ^ Trent JD, Kagawa HK, Yaoi T, Olle E, Zaluzec NJ (1997). "Chaperonin filaments: the archaeal cytoskeleton?". Proc. Natl. Acad. Sci. U.S.A. 94 (10): 5383–8. DOI:10.1073/pnas.94.10.5383. PMID 9144246. 
  43. ^ Hixon WG, Searcy DG (1993). "Cytoskeleton in the archaebacterium Thermoplasma acidophilum? Viscosity increase in soluble extracts". BioSystems 29 (2–3): 151–60. DOI:10.1016/0303-2647(93)90091-P. PMID 8374067. 
  44. ^ Hall-Stoodley L, Costerton JW, Stoodley P (2004). "Bacterial biofilms: from the natural environment to infectious diseases". Nat. Rev. Microbiol. 2 (2): 95–108. DOI:10.1038/nrmicro821. PMID 15040259. 
  45. ^ Kuwabara T, Minaba M, Iwayama Y, et al (November 2005). "Thermococcus coalescens sp. nov., a cell-fusing hyperthermophilic archaeon from Suiyo Seamount". Int. J. Syst. Evol. Microbiol. 55 (Pt 6): 2507–14. DOI:10.1099/ijs.0.63432-0. PMID 16280518. 
  46. ^ Nickell S, Hegerl R, Baumeister W, Rachel R (2003). "Pyrodictium cannulae enter the periplasmic space but do not enter the cytoplasm, as revealed by cryo-electron tomography". J. Struct. Biol. 141 (1): 34–42. DOI:10.1016/S1047-8477(02)00581-6. PMID 12576018. 
  47. ^ Horn C, Paulmann B, Kerlen G, Junker N, Huber H (Aug 1999). "In vivo observation of cell division of anaerobic hyperthermophiles by using a high-intensity dark-field microscope". J. Bacteriol. 181 (16): 5114–8. PMID 10438790. 
  48. ^ Rudolph C, Wanner G, Huber R (May 2001). "Natural communities of novel archaea and bacteria growing in cold sulfurous springs with a string-of-pearls-like morphology". Appl. Environ. Microbiol. 67 (5): 2336–44. DOI:10.1128/AEM.67.5.2336-2344.2001. PMID 11319120. 
  49. ^ a b Thomas NA, Bardy SL, Jarrell KF (2001). "The archaeal flagellum: a different kind of prokaryotic motility structure". FEMS Microbiol. Rev. 25 (2): 147–74. DOI:10.1111/j.1574-6976.2001.tb00575.x. PMID 11250034. 
  50. ^ Rachel R, Wyschkony I, Riehl S, Huber H (March 2002). "The ultrastructure of Ignicoccus: evidence for a novel outer membrane and for intracellular vesicle budding in an archaeon" (PDF). Archaea 1 (1): 9–18. PMID 15803654. 
  51. ^ a b Koga Y, Morii H (2007). "Biosynthesis of ether-type polar lipids in archaea and evolutionary considerations". Microbiol. Mol. Biol. Rev. 71 (1): 97–120. DOI:10.1128/MMBR.00033-06. PMID 17347520. 
  52. ^ De Rosa M, Gambacorta A, Gliozzi A (Mar 1986). "Structure, biosynthesis, and physicochemical properties of archaebacterial lipids". Microbiol. Rev. 50 (1): 70–80. PMID 3083222. 
  53. ^ Albers SV, van de Vossenberg JL, Driessen AJ, Konings WN (September 2000). "Adaptations of the archaeal cell membrane to heat stress". Front. Biosci. 5: D813–20. DOI:10.2741/albers. PMID 10966867. 
  54. ^ Damsté JS, Schouten S, Hopmans EC, van Duin AC, Geenevasen JA (October 2002). "Crenarchaeol: the characteristic core glycerol dibiphytanyl glycerol tetraether membrane lipid of cosmopolitan pelagic crenarchaeota". J. Lipid Res. 43 (10): 1641–51. DOI:10.1194/jlr.M200148-JLR200. PMID 12364548. 
  55. ^ Koga Y, Morii H (November 2005). "Recent advances in structural research on ether lipids from archaea including comparative and physiological aspects". Biosci. Biotechnol. Biochem. 69 (11): 2019–34. DOI:10.1271/bbb.69.2019. PMID 16306681. 
  56. ^ Hanford MJ, Peeples TL (January 2002). "Archaeal tetraether lipids: unique structures and applications". Appl. Biochem. Biotechnol. 97 (1): 45–62. DOI:10.1385/ABAB:97:1:45. PMID 11900115. 
  57. ^ Macalady JL, Vestling MM, Baumler D, Boekelheide N, Kaspar CW, Banfield JF (October 2004). "Tetraether-linked membrane monolayers in Ferroplasma spp: a key to survival in acid". Extremophiles 8 (5): 411–9. DOI:10.1007/s00792-004-0404-5. PMID 15258835. 
  58. ^ Golyshina OV, Pivovarova TA, Karavaiko GI, et al (May 2000). "Ferroplasma acidiphilum gen. nov., sp. nov., an acidophilic, autotrophic, ferrous-iron-oxidizing, cell-wall-lacking, mesophilic member of the Ferroplasmaceae fam. nov., comprising a distinct lineage of the Archaea". Int. J. Syst. Evol. Microbiol. 50 Pt 3 (3): 997–1006. PMID 10843038. 
  59. ^ Sára M, Sleytr UB (2000). "S-Layer proteins". J. Bacteriol. 182 (4): 859–68. DOI:10.1128/JB.182.4.859-868.2000. PMID 10648507. 
  60. ^ Engelhardt H, Peters J (1998). "Structural research on surface layers: a focus on stability, surface layer homology domains, and surface layer-cell wall interactions". J Struct Biol 124 (2–3): 276–302. DOI:10.1006/jsbi.1998.4070. PMID 10049812. 
  61. ^ a b Kandler, O.; König, H. (1998). "Cell wall polymers in Archaea (Archaebacteria)" (PDF). Cellular and Molecular Life Sciences (CMLS) 54 (4): 305–308. DOI:10.1007/s000180050156. 
  62. ^ Howland, John L. (2000). The Surprising Archaea: Discovering Another Domain of Life. Oxford: Oxford University Press, 32. ISBN 0-19-511183-4. 
  63. ^ Ng SY, Chaban B, Jarrell KF (2006). "Archaeal flagella, bacterial flagella and type IV pili: a comparison of genes and posttranslational modifications". J. Mol. Microbiol. Biotechnol. 11 (3–5): 167–91. DOI:10.1159/000094053. PMID 16983194. 
  64. ^ Bardy SL, Ng SY, Jarrell KF (February 2003). "Prokaryotic motility structures". Microbiology (Reading, Engl.) 149 (Pt 2): 295–304. DOI:10.1099/mic.0.25948-0. PMID 12624192. 

Further reading

  • Howland, John L. (2000). The Surprising Archaea: Discovering Another Domain of Life. Oxford: Oxford University Press. ISBN 0-19-511183-4. 
  • Martinko JM, Madigan MT (2005). Brock Biology of Microorganisms, 11th, Englewood Cliffs, N.J: Prentice Hall. ISBN 0-13-144329-1. 
  • Garrett RA, Klenk H (2005). Archaea: Evolution, Physiology and Molecular Biology. WileyBlackwell. ISBN 1-40-514404-1. 
  • Cavicchioli R (2007). Archaea: Molecular and Cellular Biology. American Society for Microbiology. ISBN 1-55-581391-7. 
  • Blum P (editor) (2008). Archaea: New Models for Prokaryotic Biology. Caister Academic Press. ISBN 978-1-904455-27-1. 
  • Lipps G (2008). "Archaeal Plasmids", Plasmids: Current Research and Future Trends. Caister Academic Press. ISBN 978-1-904455-35-6. 

External links

Wikispecies may have information related to: Archaea
Wikimedia Commons has media related to: Archaea
Look up Archaea in Wiktionary, the free dictionary.

General

Classification

Genomics

v • d • e
Biological classification of Life
Prokaryota
Archaea · Bacteria
Eukaryota
v • d • e
Extremophiles
Categories
Notable extremophiles
Related articles
This page uses content from Wikipedia. The original article was at Archaea.
The list of authors can be seen in the page history. The text of this Wikinfo article is available under the GNU Free Documentation License and the Creative Commons Attribution-Share Alike 3.0 license.

English | Română | edit

Retrieved from "http://www.wikinfo.org/index.php/Archaea"
Personal tools