Archaea

Prokaryotes

Organisms lacking a membrane-bound nucleus, divided into bacteria and archaea based on this characteristic.

Archaea

Morphologically similar to bacteria but more closely related to Eukaryota, with unique membrane structures and flagella.

Archaeal membranes

Chemically and structurally diverse. Semi-rigid lattice of pseudomurein, sugars, proteins or glycoproteins. S layer is a very common arrangement

1,2-sn-glycerol aka D-glycerol

found in bacterial and eukaryotic membranes

2,3-sn glycerol aka L-glycerol

archaeal membranes

difference between bacterial and archaeal phospholipids

Bacterial phospholipids contain ester linkages and unbranched fatty acids whereas archaeal phospholipids contain ether linkages and branched isoprene lipids

bacterial flagella

Thicker, helical, hollow filaments which rotate. Produced by adding flagellin to the tip

archaeal flagella

Similar in appearance but non-homologous to bacterial flagella. Grow by addition to the base

similarities between bacteria and archaea

contain plasmids, are unicellular and arrange their genes in operons

similarities between archaea and eukaryotes

insensitive to antibiotics, sensitive to diphtheria toxin, arrange DNA by histones and have complex DNA and RNA polymerases

5 major groups of archaea

Euryarchaeota, Crenarchaeota, Thaumarchaeota, Korarchaeota and Nanoarchaeota

Key Euryarchaeota genera

Halobacterium, Haloferax and Natronobacterium

Euryarchaeota habitat

high temperature, high salt or high acid content eg artificial saline habitats, solar salt evaporation ponds and salt lakes

properties of Euryarchaeota

• binary fission

• non motile, obligate aerobes

• very thick glycoprotein cell wall stabilised by sodium ions

• coloured due to bacteriorhodopsin

Halobacterium osmotic balance

Pump potassium ions into cell so intracellular [K+] exceeds extracellular [Na+] to maintain positive water balance

How do halophiles typically maintain osmotic balance?

Accumulation or synthesis of compatible solutes such as glycerol. Highly acidic, contain fewer hydrophobic amino acids and lysine residues.

Key genera of Methanogenic archaea

Methanobacterium, Methanocaldococcus and Methanosarcine

properties of methanogens

• obligate anaerobes

• very diverse cell wall chemistries eg pseudomurein or methanocondroitin

• 11 substrates of 3 different classes converted to methane by pure cultures

• can convert glucose to methane in cooperative reactions with anaerobic bacteria

Thermoplasmatales (taxonomic order within Euryarchaeota)

Includes thermophilic and acidophilic genera like Thermoplasma and Ferroplasma

key genera of thermopasmatales (taxonomic order within Euryarchaeota)

Thermoplasma, Picrophilus and Ferroplasma

Thermoplasma

thermophilic, acidophilic chemoorganotrophs. Facultative aerobes via sulphur respiration. Found in self-heating coal piles.

Thermoplasma unique membrane structure

contains glycoproteins, no sterols and lipoglycan. Tetraether lipid monolayer membrane with mannose and glucose

Ferroplasma

Chemolithotrophic, acidophilic. Oxidise Fe(II) to Fe(III) generating acid. Grow in mine tailings containing pyrite

Picophilus

Extreme acidophiles, grow optimally at pH 0.7

key Thermococcales and Methanopyrus genera (hyperthermophilic Euryarchaeota)

Thermococcus, Pyrococcus and Methanopyrus

Thermococcus and Pyrococcus

highly motile and indigenous to anoxic thermal waters. Uses in biotechnology include PCR.

Key crenarchaeota genera

Sulfolobus, Acidianus, Thermoproteus and Pyrobaculum

Sulfolobales

aerobic chemolithotrophs which oxidise reduced sulphur or iron. Grow in sulphur-rich acidic hot springs

Acidianus

live in acidic sulphur hot springs, use elemental sulphur aerobically and anaerobically

How do thermophilic species increase thermostability?

• high cytoplasmic solute concentration for protein monomer stability

• heat stable molecules eg non heme iron proteins

• DNA gyrase to introduce +ve supercoils (hyperthermophiles)

• high polyamine levels

• dibiphytanul tetraether type lipids which form monolayer

• higher GC content

Hyperthermophiles

Organisms with high temperature tolerance, using heat-stable molecules and unique adaptations for survival in extreme environments.

H₂ oxidation

common to many hyperthermophiles, may have been first energy yielding metabolism