Highly diverse with respect to morphology, physiology, reproduction, and ecology
Best known for growth in anaerobic, hypersaline, pH extremes, and high-temperature habitats (although found across all ecosystems)
They exploit extreme environments.
They're found everywhere, in normal environments as well.
Also found in marine arctic temperature and tropical waters
Not a significant cause of diseases in humans.
Archaeal Cell Morphology
Examples include Methanosarcina mazei (a coccus that forms clusters) and Thermoproteus tenax (a branched archaeal cell).
Filamentous archaeon and Bacterial biofilm morphologies exist.
Bacterial vs. Archaeal Cells (Table 4.1)
Comparison of Bacterial and Archaeal Cells
Property differs between bacteria and archaea which are:
Plasma membrane lipids
Cell wall constituents
Inclusions present
Ribosome size
Chromosome structure
Plasmids present
External structures
Capsules or slime layers
Key Differences:
Plasma membrane lipids: Bacteria have ester-linked phospholipids and hopanoids forming a lipid bilayer; some have sterols. Archaea have glycerol diethers forming lipid bilayers; glycerol tetraethers form lipid monolayers.
Cell wall constituents: Bacteria have peptidoglycan in nearly all; some lack cell walls. Archaea lack peptidoglycan; some consist of S-layer only, others combine S-layer with polysaccharides or proteins, and some lack cell walls.
Ribosome size: Both Bacteria and Archaea have 70S ribosomes.
Chromosome structure: Both typically have circular, double-stranded (ds) DNA. Bacteria usually have a single chromosome.
External structures: Both have flagella. Bacteria have fimbriae (pili) common, while Archaea have pili and piluslike structures common.
Capsules or slime layers: Common in Bacteria, rare in Archaea.
Important Differences Between Bacteria and Archaea Cell Envelopes
Plasma membrane lipids: Bacteria have ester-linked phospholipids and hopanoids forming a lipid bilayer. Archaea have glycerol diethers forming lipid bilayers; glycerol tetraethers form lipid monolayers, branched isoprene subunits.
Cell wall: Bacteria have peptidoglycan in nearly all, some lack a cell wall, and some have an S-layer. Archaea always lack peptidoglycan and have diverse cell-wall chemistry with combinations of S-layer, polysaccharide, or proteins.
Capsules and slime layers: Common in Bacteria and rare in Archaea.
Archaeal Cell Envelopes
Differ from bacterial envelopes in the molecular makeup and organization
S layer may be only component outside plasma membrane
Some lack cell wall
Capsules and slime layers are rare
Archaeal Membranes
Composed of unique lipids
isoprene units (five carbon, branched)
ether linkages rather than ester linkages to glycerol
Some have a monolayer structure instead of a bilayer structure
Archaeal Membrane Lipids
Archaea have branched-chain hydrocarbons attached to glycerol by ether linkages.
Different from Bacteria and Eukarya, which have fatty acids attached to glycerol by ester linkages.
Archaeal isoprene-derived hydrocarbons are made by a different set of biosynthetic pathways and enzymes.
Archaeal membranes have polar phospholipids, sulfolipids, glycolipids, and other unique lipids
Archaeal Lipids and Membranes
Bacteria/Eukaryotes:
Fatty acids attached to glycerol by ester linkages
Archaea:
Branched-chain hydrocarbons (isoprene)
attached to glycerol by ether linkages
Some have diglycerol tetraethers
Ether linkage is stronger than ester linkage between archaeal and bacterial lipids.
Archaeal Lipids and Membranes
Bacteria/Eukaryotes: Fatty acids attached to glycerol by ester linkages.
Archaea: Branched chain hydrocarbons attached to glycerol by ether linkages.
Branched carbon precursors exist.
Pseudopeptidoglycan Repeating Unit
Methanogens make pseudopeptidoglycan
Pseudopeptidoglycan is composed of two sugars:
N-acetylglucosamine (NAG or GlcNAc)
N-acetyltalosaminuronic acid (TalANAc)
There is no peptidoglycan in archaea.
one class of archal bacteria only can produce methane using L-isomers, as opposed to D-isomers, as a waste product.
Archaeal Cell Surfaces
Cell envelopes
varied S layers attached to plasma membrane
pseudomurein (peptidoglycan-like polymer for some archaea)
complex polysaccharides, proteins, or glycoproteins found in some other species
There is no reason to produce or develop antibiotics, considering polysaccharides and no pathogens
Archaeal Cell Wall Properties
All lack peptidoglycan; methanogens have pseudomurein
Pseudomurein may be outermost layer, similar to Gram-positive microorganisms
Nearly all archaea have an S-layer.
S layer is glycoprotein matrix outside the membrane and separated by pseudomurein.
The lack of peptidoglycan makes archaea resistant to all antibiotics that target peptidoglycan biosynthesis.
S-layers in both Archaea and Bacteria
TEM image of a freeze-etched and metal-shadowed preparation of (a) an archaeal cell (from Methanocorpusuculum sinense), and (b) a bacterial cell (from Desulfotomaculum nigrificans).
Archaeal Motility
Flagella are thinner than bacteria.
Some made of more than one type of protein.
Filament is not hollow.
Rotation:
Powered by ATP hydrolysis instead of proton motive force.
Direction moves the cell forward or backward rather than runs and tumbles.
Swimming motility has extremely fast speeds.
Archae swim a lot faster than bacteria with a different set of motor proteins.