Cell wall

The Gram stain for bacteria allows differentiation according to thickness of the layer of peptidoglycan (murein, im) in the cell wall. Bacteria that stain heavily (Gram +ve) have a thick monolayer of peptidoglycan compared to the thin or absent layer of peptidoglycan in (bilayer) bacteria that do not take up the stain (Gram -ve). The cell walls of Archaeobacteria contain no peptidoglycan (murein), rather they contain pseudomurein, complex carbohydrates, or protein-glycoproteins.

S-layers comprise one of the most common surface structures on archaea and bacteria. These surface layers have now been identified in hundreds of different species belonging to all major phylogenetic groups of bacteria, and they represent a feature common to almost all archaea (recent compilation 133). S-layers are monomolecular crystalline arrays of proteinaceous subunits (125, 131, 132).

Tables  Cell walls of Prokaryotes  Comparisons of Eubacteria, Archaea, and Eukaryotes  Electron acceptors for respiration and methanogenesis in prokaryotes  Glycolysis in bacteria  Lithotrophic prokaryotes  Structure of bacteriochlorophylls  Comparison of plant and bacterial photosynthesis :

Diagrams: Eubacteria : peptidoglycan : gram + gram - peptidoglycan : Gram + : Gram - : P. aeruginosa comp-mod : gram -ve : antimicrobials gram + gram - : cell walls gram + gram - mycobacteria : comparison gram + / gram - cell walls : b-w g+ g- : Archaea : Gram positive archaeal cell wall : Gram negative archaeal cell wall : Unusual cell wall of Deinococcus radiodurans :

: S-layer Freeze etched sem :

The structure of secondary cell wall polymers: how Gram-positive bacteria stick their cell walls together.
The cell wall of Gram-positive bacteria has been a subject of detailed chemical study over the past five decades. Outside the cytoplasmic membrane of these organisms the fundamental polymer is peptidoglycan (PG), which is responsible for the maintenance of cell shape and osmotic stability. In addition, typical essential cell wall polymers such as teichoic or teichuronic acids are linked to some of the peptidoglycan chains. In this review these compounds are considered as 'classical' cell wall polymers. In the course of recent investigations of bacterial cell surface layers (S-layers) a different class of 'non-classical' secondary cell wall polymers (SCWPs) has been identified, which is involved in anchoring of S-layers to the bacterial cell surface. Comparative analyses have shown considerable differences in chemical composition, overall structure and charge behaviour of these SCWPs. This review discusses the progress that has been made in understanding the structural principles of SCWPs, which may have useful applications in S-layer-based 'supramolecular construction kits' in nanobiotechnology.
Schaffer C, Messner P. The structure of secondary cell wall polymers: how Gram-positive bacteria stick their cell walls together. (Free Full Text Article) Microbiology. 2005 Mar;151(Pt 3):643-51.

Molecular organization of selected prokaryotic S-layer proteins.
Regular crystalline surface layers (S-layers) are widespread among prokaryotes and probably represent the earliest cell wall structures. S-layer genes have been found in approximately 400 different species of the prokaryotic domains bacteria and archaea. S-layers usually consist of a single (glyco-)protein species with molecular masses ranging from about 40 to 200 kDa that form lattices of oblique, tetragonal, or hexagonal architecture. The primary sequences of hyperthermophilic archaeal species exhibit some characteristic signatures. Further adaptations to their specific environments occur by various post-translational modifications, such as linkage of glycans, lipids, phosphate, and sulfate groups to the protein or by proteolytic processing. Specific domains direct the anchoring of the S-layer to the underlying cell wall components and transport across the cytoplasma membrane. In addition to their presumptive original role as protective coats in archaea and bacteria, they have adapted new functions, e.g., as molecular sieves, attachment sites for extracellular enzymes, and virulence factors.
Claus H, Akca E, Debaerdemaeker T, Evrard C, Declercq JP, Harris JR, Schlott B, Konig H.
Molecular organization of selected prokaryotic S-layer proteins. Can J Microbiol. 2005 Sep;51(9):731-43.
Glycoproteins in prokaryotes. [Arch Microbiol. 1997] PMID: 9382700
Structural research on surface layers: a focus on stability, surface layer homology domains, and surface layer-cell wall interactions. [J Struct Biol. 1998] PMID: 10049812
Prokaryotic glycosylation. [Proteomics. 2001] PMID: 11680871
Glycobiology of surface layer proteins. [Biochimie. 2001] PMID: 11522387
Stress genes and proteins in the archaea. [Microbiol Mol Biol Rev. 1999] PMID: 10585970
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S-Layer proteins.
Cell walls are an important structural component of prokaryotic organisms and essential for many aspects of their life. Particularly, the diverse structures of the outermost boundary layers strongly reflect adaptations of organisms to specific ecological and environmental conditions (6).
Over the past 3 decades of research, it has become apparent that one of the most common surface structures on archaea and bacteria are monomolecular crystalline arrays of proteinaceous subunits termed surface layers or S-layers (125, 131, 132). Since S-layer-carrying organisms are ubiquitous in the biosphere and because S-layers represent one of the most abundant cellular proteins, it is now obvious that these metabolically expensive products must provide the organisms with an advantage of selection in very different habitats (133). This minireview provides a brief survey of the current state of our knowledge about S-layers with a particular focus on molecular biological and genetic aspects. Other recent reviews (5, 7, 127, 133, 135) are recommended for a more detailed introduction to and treatises on this subject.
Sara M, Sleytr UB. S-Layer proteins. (Free Full Text Article) J Bacteriol. 2000 Feb;182(4):859-68.

Prokaryotic glycosylation. [Proteomics. 2001] PMID: 11680871
Common history at the origin of the position-function correlation in transcriptional regulators in archaea and bacteria. [J Mol Evol. 2001] PMID: 11523004
[Homologous protein domains in superkingdoms Archaea, Bacteria, and Eukaryota and the problem of the origin of eukaryotes] [Izv Akad Nauk Ser Biol. 2005] PMID: 16212260
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Cell wall polymers in Archaea (Archaebacteria).
The distribution of the various cell wall and cell envelope (S-layer) polymers among the main lineages of the domain Archaea (Archaebacteria) and the chemical composition and primary structure of polymers forming rigid cell wall sacculi is described. Differences between bacteria and archaea in their sensitivity to antibiotics which inhibit cell wall synthesis in bacteria are discussed.
Kandler O, Konig H. Cell wall polymers in Archaea (Archaebacteria). Cell Mol Life Sci. 1998 Apr;54(4):305-8.

beta-Lactamases are absent from Archaea (archaebacteria). [Microb Drug Resist. 1996] PMID: 9158771
Structure of anionic carbohydrate-containing cell wall polymers in several representatives of the order actinomycetales. [Biochemistry (Mosc). 2000] PMID: 11092967
Anionic polymers in cell walls of gram-positive bacteria. [Biochemistry (Mosc). 1997] PMID: 9360295
The response of selected members of the archaea to the gram stain. [Microbiology. 1996] PMID: 8885405
Life's third domain (Archaea): an established fact or an endangered paradigm? [Theor Popul Biol. 1998] PMID: 9733652
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The Archaea

The Archaea (formerly Archaeobacteria, or Mendosicutes) constitute a recently recognized phylogenetic domain. While Eubacteria and Archaea are similar in structure, they have a different metabolism and genotype. A defining physiological characteristic of Archaea is their ability to live in extreme environments. Thus, these organisms are called “extremophiles” and, unlike Eubacteria and Eukarya, they depend for survival on environmental conditions such as high salinity, extremes of temperature, unusual chemical substrates, or high pressure.

Archaea can be distinguished from bacteria in that their cell walls do not have murein—a peptidoglycan-containing muramic acid. Their plasma membranes are ~4-5 nm in thickness, and are unique in including isopranyl ether lipids – branched isoprenoid hydrocarbons that are linked to glycerol by di-/tetraether bonds. The glycerol diethers are associated with bilayer membranes, whereas the glycerol tetraethers are associated with monolayer membranes. Archaea with mixtures of di- & tetraethers have mixed mono- & bilayer- membranes. Hyperthermophiles have increased membrane fluidity due to branched glycerol tetraethers, and often lack a cell wall. Psychrophiles have lipids comprising mainly unsaturated fatty acids. The plasma membrane of Archaea also contains sulfolipids.

The cell walls of most Archaea comprise a multilayered sacculus (sheet) that surrounds the plasma membrane and provides resistance to osmotic shock. This enables the Archaea (except Thermoplasma) to maintain high intracellular osmotic pressures (15-20 atm). The cells wall may comprise peptidoglycans (Methanobacterium) in which the chief sugars are N-acetyl talosaminouronic acid (NAT or T) and GlcNAc (NAG or G). These are linked to each other by lysozime insensitive (b1->3) glycosidic bond. The T units are linked to L-aminoacid containing oligopeptides by a penicillin-insensitive transpeptidase. In other genera, the cell wall may comprise only non-sulfated polysaccharides (Methanosarcina), only sulfated polysaccharides (Halococcus), only proteins (Methanomicrobium and Methanococcus), or negatively charged aminoacid-containing peptides (Halobacteria).

Images: tem -thermophilic archaeobacteria, line-up


Phylogenetic taxonomy of the Archaea (right), based on 16s rRNA trees.

The Bacteria (eubacteria) were the first prokaryotes recognized. (see phylogeny)

In 1977, Woese and Fox discovered the Archaea based upon their phylogenetic relationships to the Bacteria and the Eucarya. The yellow asterisk indicates the progenote, and the junction between teal and purple lines, the Last Common Ancestor, or Cenancestor.

Woese, Free Full Text Article: Toward a natural system of organisms

(left) The Domain Archaea is divided into three Phyla: Crenarchaeota, Euryarchaeota, and Nanoarchaeota. A brief phylogenetic relationship of Crenarchaeota and Euryarchaeota are shown in the tree diagram (top right), and a more detailed cladogram is shown below. (click to enlarge)




From the Taxonomicon, based on Systema Naturae, 2000:
Domain Archaea (Woese, Kandler & Wheelis, 1990)
Phylum Crenarchaeota
Class Thermoprotei
Order Thermoproteales™ Zillig & Stetter, 1982
Order Desulfurococcales
Order Sulfolobales Stetter, 1989

Phylum Euryarchaeota (Woese, Kandler & Wheelis, 1990)
Class Methanobacteria
Class Methanococci
Class Halobacteria
Class Thermoplasmata
Class Thermococci
Class Archaeoglobi Garrity & Holt, 2002
Class Methanopyri

Phylum Nanoarchaeota Huber et al., 2002
Genus Nanoarchaeum™ Huber et al., 2002

The Archaea: A Personal Overview of the Formative Years: "The simple method of growing methanogenic cells in an anaerobic pressurized atmosphere of hydrogen and carbon dioxide was pivotal to the discovery of the Archaea, for hydrogen and carbon dioxide could be replenished with safe containment of high levels of 32P and without exposure of cells to oxygen or contamination.

In November 1977, Woese and Fox proposed that ribosomal RNA sequence characterization could be used to define three "aboriginal lines of descent" (Woese and Fox, 1977). One line, the typical bacteria, was designated "eubacteria." "archaebacteria" was proposed as a name for the methanogen line, and the term "urkaryotes" was proposed for the cytoplasmic component of eukaryotic cells. So the methanogens were Archaebacteria. The name Archaebacteria was suggested by David Nanney. In a way, the term was unfortunate because the case was being made that the methanogens were "old" (i.e., represented a very ancient divergence in evolution), so that they were no more related to bacteria than to eukaryotes. On the other hand, they were bacteria. (Over a decade later, Woese, Kandler, and Wheelis would propose the name "Archaea" for the Archaebacteria [Woese et al., 1990]. By that time, much evidence had accumulated showing the Archaea clearly belonged on the eukaryotic line of descent, and it would be less confusing if the word "bacteria" in Archaebacteria was deleted.)"

more detail: Physiology of the Archaea :

Free Full Text Article : Phylogenetic structure of the prokaryotic domain: The primary kingdoms. Woese CR, Fox GE. Proc Natl Acad Sci U S A. 1977 Nov;74(11):5088-90.

1995 Commentary Archaea: narrowing the gap between prokaryotes and eukaryotes pdf

Information on Archaea:
Information on Archaea from the American Society for Microbiology
An Introduction to Archaea from the Department of Plant Biology at University of California, Berkeley
USGS Microbiology Laboratory, Columbus, Ohio
USGS Microbiology Research: Activity, Biogeochemistry, and Transport in Water
U.S. Environmental Protection Agency's Microbiology Home Page
U.S. Department of Energy's Microbial Genome Program
Archaea Taxonomy from the National Institutes of Health

News:
A hydrogen-based subsurface microbial community dominated by methanogens: Nature
Scientist May Have Discovered a Model for Extraterrestrial Life, Washington Post
Found: Life on Earth That Could Exist on Mars, New York Times (by Associated Press)
Scientists Find New Kind of Microbe, New York Times (by Associated Press)
UMass Researchers Find Environment on Earth that Mimics Mars Geochemically and Supports Ancient Life Form, NASA Press Release