Describe what the two staining results of an archael cell wall mean.
- If positive, then there is often a thick homogenous layer.
- If it stains negative, then there is often a surface layer of protein or glycoproteins.
Describe the differences of the archael cell wall in regards to bacteria.
- Very different biochemically
- Lack muramic acid
- Lack D-amino acids
- Resistant to lysozyme and beta-lactam antiobiotics
- Some contain pseudomurein
What are pseudomureins found in the archael cell walls?
They are peptidoglycan-like polymer.
Describe the difference in plasma membrane structure between prokaryotes/eukaryotes and archaea.
Bacteria/Eukaryotes
Fatty acids attached to glycerol by ester linkages
Archaea
- Branched chain hydrocarbons attached to glycerol by ether linkages.
- Some have diglycerol tetraethers.
- The Archael membrane may be mono-layered (found in extreme thermophiles) or bilayered.
List all of the characteristics of the chromosome in Archaea.
- One chromosome per cell
- Closed circular double-stranded DNA
- Generally smaller than bacterial chromosomes
- Some have histones that bind DNA to form nucleosome-like structures
- DNA replication proteins seem to be similar to eukaryotic proteins (DNA polymerase, etc).
Describe some of the genetic characteristics of Archaea.
- Have few plasmids
- mRNAs may be polygenic. There is no evidence of RNA splicing.
- Promoters similar to bacterial promoters
- tRNAs contain modified bases not found in bacterial or eukaryotic tRNAs
- Initiator tRNA is methionine-tRNA
- Ribosome size is 70S. Shapes variable, differing from both bacterial and eukaryotic ribosomes
- Elongation factor 2 similar to that of eukaryotes
Distinguish between Extreme Halophiles, Thermophiles, and Methanogens.
[Archaea]
Extreme Halophiles and Thermophiles
- Use modified Entner-Doudoroff to catabolize glucose
- Pyruvate->acetyl CoA catalyzed by pyruvate oxidoreductase
- Have functional TCA cycle
- Have respiratory chains
- Use reverse Embden-Meyerhoff for gluconeogenesis
- Biosynthetic pathways similar to those of other organisms
- Some use glycogen as major reserve material
Methanogens
- Do not catabolize glucose significantly
- Pyruvate-acetyl CoA catalyzed by pyruvate oxidoreductase
- NO TCA cycle
- NO evidence for respiratory chains
- Use reverse Embden-Meyerhoff for gluconeogenesis
- Biosynthetic pathways similar to those of other organisms
- Some fix nitrogen
- Some use glycogen as major reserve material
Archaea taxonomy is divided into which two phyla?
Euryarchaeota and Crenarchaeota
Describe the lovely characteristics of Phylum Crenarchaeota.
[Archaea]
- Most are extremely thermophilic
- Many are acidophiles
- Many are sulfur-dependent
- For some, sulfur is used as electron acceptor in anaerobic respiration
- For some, sulfur is used as electron source (chemolithotrophs)
- Almost all are strict anaerobes
- Grow in geothemally heated water or soils that contain elemental sulfur
- Include organotrophs and lithotrophs (sulfur-oxidizing and hydrogen-oxidizing)
Describe the characteristics of Phylum Eurarchaeota.
(Archaea)
- Consists of many classes, orders, and families
- Often divided informally into fice major groups
- Methanogens
- Halobacteria
- Thermoplasms
- Extremely thermophilic
- Sulfate-reducers
Who are the methanogens and what’s so darn special about them?
[Archaea]
- They live in anaerobic environments that are rich in organic matter
- e.g. animal rumens, anaerobic sludge digesters, or withing anaerobic protozoa
- Ecologically, they are important in wastewater treatment as they can oxidize iron (contributes significantly to corrosion of iron pipes).
- They can also produce significant amounts of methane. Methane can be used as clean burning fuel and an energy source. It is a greenhouse gas and MAY contribute to global warming.
What’s so damn cool about the Halobacteria?
[Archaea]
- They are extreme halophiles. They require at least 1.5M NaCl with an optimal growth near 3-4M NaCl
- They are aerobic, respiratory, chemoheterotrophs with complex nutritional requirements
- Can cause spoilage of salted foods!
- Has unique type of photosynthesis
- Not chlorophyll based
- Uses modified cell membrane (purple membrane)
- Absorption of light by bacteriorhodopsin drives proton transport, creating PMF for ATP synthesis
List the chracteristics of the Thermoplasms.
[Archaea]
- Thermoacidophiles
- Grow in refuse piles of coal mines (55-59*C, pH 1-2)
- They lack cell walls
- Contain diglycerides and glycoproteins
- They have various cell shapes depending on the temperature (irregular filament at 59*C and spherical at lower temperatures)
- They may be flagellate and motile
- Cell membrane is strengthened by diglycerol tetraethers, lipopolysaccharides, and glycoproteins
The sulfate-reducing archaea can seem to be of alien nature at first glance. What is it about them that makes it seem so?
- Irregular coccoid cells
- Cell walls consist of glycoprotein subunits
- Extremely thermophilic
- Optimum 83*C
- Isolated from marine hydrothermal vents
- Metabolism
- Can be lithotrophic (H2) or organotrophic (lactate or glucose)
- Uses sulfate, sulfite, or thiosulfite as electron acceptor
