Archaea

Archaea

Prokaryotic domain distinct from Bacteria and Eukarya; many inhabit extreme environments but are found worldwide.

16S rRNA Sequencing

Method that revealed archaea are abundant in soils, wetlands, oceans, and other habitats.

Methanogens

Archaea that produce methane and cannot tolerate oxygen.

Extremophiles

Organisms adapted to extreme environmental conditions.

Extreme Halophiles

Archaea that thrive in very high salt concentrations.

Hyperthermophiles

Archaea that grow optimally at extremely high temperatures.

Acidophiles

Archaea adapted to highly acidic environments.

Psychrophiles

Archaea adapted to very cold temperatures.

Extremely Halophilic Archaea

Require hypersaline to extremely hypersaline habitats (≥1.5 M NaCl).

Halobacterium

Extremely halophilic archaeal genus.

Haloferax

Extremely halophilic archaeal genus.

Natronobacterium

Extremely halophilic archaeal genus.

Methanogenesis

Production of methane (CH₄) by reduction of CO₂.

Role of Methanogenesis

Final step of organic matter degradation in anoxic environments.

Extreme Acidophiles

Archaea capable of growth at extremely low pH, sometimes below pH 0.

Chemolithotroph

Organism that obtains energy from oxidation of inorganic compounds.

Ferrous Iron (Fe²⁺) Oxidation

Conversion of Fe²⁺ to Fe³⁺ for energy generation.

Thermoplasma

Thermoacidophilic archaeal genus lacking a cell wall.

Picrophilus

Archaeal genus known for growth at extremely low pH.

Ferroplasma

Iron-oxidizing acidophilic archaeal genus.

Thaumarchaeota

Widespread archaea involved in ammonia oxidation.

Ammonia Oxidation

Aerobic conversion of NH₃ to NO₂⁻; first step of nitrification.

Most Common Archaea

Thaumarchaeota are among the most abundant archaea in soil and oceans.

Hyperthermophile Habitat

Geothermal, volcanic, sulfur-rich, and deep-sea environments.

Growth Above 100°C

Possible under high-pressure conditions where water remains liquid.

Korarchaeota

Hyperthermophilic archaeal lineage.

Crenarchaeota

Archaeal group containing many hyperthermophiles.

Nanoarchaeota

Small archaeal lineage associated with extreme environments.

Asgard Archaea

Archaeal group closely related to eukaryotes.

Thermosome

Archaeal chaperone protein that maintains proper protein folding at high temperatures.

Reverse DNA Gyrase

Enzyme that introduces positive supercoils to stabilize DNA at high temperatures.

High Intracellular K⁺

Helps stabilize DNA in hyperthermophiles.

Biphytanyl Tetraether Lipids

Membrane lipids that enhance thermal stability.

High rRNA G+C Content

Increases ribosomal stability at high temperatures.

Archaeal Shapes

Cocci, rods, curved rods, spirals, branched, and flat forms; no spirochetes.

Archaeal Plasma Membrane

Composed of ether-linked lipids rather than ester-linked lipids.

Phospholipid Monolayer

Single membrane layer formed by tetraether lipids in many archaea.

Ether Linkage

Heat- and chemical-resistant bond connecting archaeal lipids to glycerol.

Ester Linkage

Lipid bond found in bacterial and eukaryotic membranes.

Archaeal Cell Wall

Lacks peptidoglycan; usually composed of an S-layer.

S-Layer

Cell wall structure made of repeating protein or glycoprotein subunits.

Simple S-Layer Envelope

Most common archaeal cell envelope type.

Protein Sheath Envelope

S-layer with an additional outer protein layer.

Carbohydrate Layer Beneath S-Layer

Envelope containing a polysaccharide layer under the S-layer.

Carbohydrate Layer Instead of S-Layer

Cell envelope where polysaccharide replaces the S-layer.

Double Membrane Envelope

Rare archaeal envelope with two membranes.

Archaeal Cytoplasm

Contains inclusions, vacuoles, nucleoid, plasmids, and cytoskeleton.

Archaeal Ribosomes

More similar to eukaryotic ribosomes than bacterial ribosomes.

Response to Ribosomal Antibiotics

Generally resistant to antibiotics targeting bacterial ribosomes.

Nucleoid-Associated Proteins

DNA-binding proteins analogous to eukaryotic histones.

Histones

Proteins that package and organize DNA.

Nucleosome

DNA wrapped around a histone protein core.

Histone Core

Contains two copies each of H2A, H2B, H3, and H4.

Type IV Pili

Surface appendages involved in attachment and motility.

Archaella

Archaeal motility structures analogous to bacterial flagella.

Archaella Structure

Thinner and assembled differently than bacterial flagella.

Archaella Energy Source

Powered by ATP rather than proton motive force.

Bacterial Flagella Energy Source

Powered by proton motive force.