Archaea

Greek-archaios means ancient

Introduction• Diverse group• Gram Positive or Gram Negative• Spherical, lobed, rod-shaped, spiral, cubodial,

triangular, plate shaped, irregularly shaped,• Pleomorphic• Present as a single cells, or aggregates / filaments• Multiplication- binary fission, fragmentation and

other mechanisms• Physiologically diverse-aerobic, facultative

anaerobes, strictly anaerobes

• Chemolithoautotroph, organotroph• Psychrophiles, mesophiles and hyperthermophiles

(can grow above 1000 c)

Ecology• They live in an extreme environment• Area with very high or low temperature, PH• Area with high salt concentration• Area with high concentration of methane• Area with no oxygen (anoxic)

Volcanic eruptions

Amazing Geyser Landscape inNevada

the vivid red brine (teaming with halophilicarchaebacteria) of Owens

Halophiles in sea

Great Salt Lake of Utah

methanogens may thrive in hot springs

Archaeal Cell Wall• Lack muramic acid and D- amino acids• Eg. methanogens have peudomurein (a

peptidoglycan like polymer that is cross-linkedwith L-amino acids

• Some contain a complex carbohydrate similar tochondroitin sulfate of animal connective tissue

• Hyperthermophile and methanogens have protencell wall

Archaeal membrane• Branched chain hydrocarbon attached to glycerol

by ether• Thermophile archaea have long tetraether in their

cell membrane. Also pentacyclic rings in HC ofsome (help maintain the delicate liquid crystallinebalance of membrane of membrane at hightemperature)

• Other lipids- polar phospholipid, sulfolipid,glycolipid.

Major Archaeal groupsMethanogenic archaea

Archaeal sulfate reducers

Extremely halophilic archaea

Cell wall-less archaea

Methanogenic Archaea• Strict anaerobes• Produces methane as a major metabolic end

product• Convert sulfur to hydrogen sulphide wth no energy

production• They possess co-enzyme M, factor 420/430,

methanopterin• Eg. Metanobacterim, Methanococcus,

Methanomicrobium, Methanosarcina

Archaeal sulfate reducers• Irregular gram-negative coccoid cells• Strictly anaerobe and extremely thermophilic• Hydrogen sulfide is formed from thiosulfate and

sulfate• Heterotrophic in nature, autotrophic growth with

thiosulfate and hydrogen• Forms traces of methane• Possess factor 420 and methanopterin• Eg. Archeoglobus

Extremely halophilic archaea• Rods, cocci, irregular shaped (pyramid, cube etc)• Stain gram-positive and gram-negative• Chemoorganoheterotroph• Lack peptidogycan• Most spp. require sodium chloride (> or =15M)• Mostly produce bright red colonies• Some unpigmented• Neutrophilic to alkalophilic• Generally mesophilic, one sp. is thermophilic• Possess bacteriorhodopsin and halorhodopsin (

and can use light energy to produce ATP

Cell wall-less Archaea• Pleomorphic cell lacking cell wall• Thermoacidophilic and chemoorganotrophic• Facultaive anaerobes• Mannose-rich glycoprotein and a lipoglycan

Extremely thermophilic elementary sulfur• Gram negative rods, filaments or cocci• Obligatory thermophile (70-1100 c)• Usually strictly anaerobe, some are aerobic and

facultative• Acidophilic and neutrophilic• Autotrophic or heterotrophic• Reduction of sulfur to hydrogen sulfide –

anaerobically and hydrogen sulfide or elementalsulfur oxidized to sulfuric acid aerobically

• eg. Desulfurococcus, Sulfolobus, Thermococcus

Economic Importance• Thermophiles grow in heated water and soil rich in

elemental sulfur and these environment are scatteredall over the world. Eg. Sulfur rich hot springs inYellowstone National Park

• Methanogens produce methane using sewage sludge,which is a clean burning fuel(pollution free energy)

• Methane production can contribute to global warming• Halophiles are used in the production of many salted

food products, including soysauce• Thermoplasma oxidizes iron sulfide (in piles of coal

mines) to sulfuric acid. As a result piles become hotand acidic

Yellowstone National Park