Differences between Archaebacteria and Eubacteria

American microbiologist and biophysicist Carl Richard Woese proposed three kingdom classification system in 1990. This classification system divides the life forms into three domains and six kingdoms.

The three domains are archaea, bacteria, eukaryote, and six kingdoms are Archaebacteria (ancient bacteria), Eubacteria (true bacteria), Protista, Fungi, Plantae, Animalia.

Woese classified them based on their differences in the 16S ribosomal RNA (rRNA) structure. 16S rRNA can be used for comparative analysis between prokaryotic and eukaryotic species. 

Carl Woese used the rRNA as an “Evolutionary Chronometer” – an evolutionary time clock.

The Archaea (Archaebacteria)

• Archaea are ancient bacteria - believed to have evolved just after the evolution of first life on earth.
• Archaea are prokaryotic cells. The cell walls of Archaea contain no peptidoglycan, hence Archaea are not sensitive to some antibiotics that affect the Bacteria.
• Archaea have membranes composed of branched hydrocarbon chains (many also containing rings within the hydrocarbon chains) attached to glycerol by ether linkages. 
• The ether-containing linkages in the Archaea membranes is more stable than the ester-containing linkages in the Eubacteria  and are better able to withstand higher temperatures and stronger acid concentrations. 
• Archaea often live in extreme environments and include methanogens, extreme halophiles, and hyperthermophiles.
• Archaea contain rRNA that is unique to the Archaea, distinctly different from the rRNA of Bacteria and Eukarya.

  Archaea are found in Volcanic hot springs- Grand Prismatic Spring of Yellowstone National Park

                            The very cold and ultra-salty Deep Lake in East Antarctica is home to haloarchaea.

Hydrothermal vents on the ocean floor, where the surrounding water can reach over 300° Celsius, are home  for some archaeal species.

The Bacteria (Eubacteria)

Bacteria (also known as eubacteria or "true bacteria") are prokaryotic cells that are common in human daily life. Eubacteria can be found almost everywhere and serve as antibiotic producers and food digesters, pathogens etc. 

Bacteria are prokaryotic cells. They have membranes composed of unbranched fatty acid chains attached to glycerol by ester linkages. 

The cell walls of Bacteria contain peptidoglycan. Bacteria are sensitive to  antibacterial antibiotics.

Bacteria contain rRNA that is unique.

Bacteria include mycoplasmas, cyanobacteria, Gram-positive bacteria, and Gram-negative bacteria.

Thus, in short, Archaebacteria are called ancient bacteria whereas the eubacteria are called true bacteria. Eubacteria are usually found in soil, water, living in and on of large organisms. Eubacteria are divided into two groups known as gram positive and gram negative bacteria. Archaebacteria are found in salt brines, ocean depths and hot springs.  Three types of archaebacteria are found: methanogens, halophiles and thermoacidophiles.

 Eu Bacteria and Archaea – The Major Differences

  

	ArchaeaBacteria	EuBacteria
	-Ancient bacteria-	-True bacteria-
Complexity	Simple in their organization	Complex than archaebacteria
Habitat	Can sustain in extremely harsh environment such as oceans, hot springs, marshlands, hot springs and gut of animals	Found everywhere - soil, organic matter, earth’s crust, water, bodies of animals and plants, radioactive wastes, hot springs
Size	0.1-15 μm in diameter	0.5-5 μm in diameter
Shape	spheres, rods, plates, spiral, flat or square-shaped	cocci, bacilli, vibrio, rods, filaments or spiral in shape
Cell wall	Pseudopeptidoglycan	Lipopolysaccharide/ Peptidoglycan with muramic acid
Membrane lipids	Ether-linked, branched, aliphatic chains, containing D-glycerol phosphate	Ester-linked, straight chains of fatty acids, containing L-glycerol phosphates
RNA	Consists of single RNA	Three types of RNA
RNA polymerase	Complex subunit pattern	Simple subunit pattern
Introns (a long stretch of noncoding DNA found between exons (or coding regions) in a gene)	Present in archaebacteria	Absent in eubacteria
Metabolism	Methanogenesis- exhibit neither glycolysis nor Kreb’s cycle	Autotrophy, Aerobic and Anaerobic Respiration, Fermentation and Photosynthesis-exhibit both glycolysis and Kreb’s cycle
Reproduction and Growth	Asexual Reproduction, by fragmentation, budding and binary fission	Other than binary fission, budding and fragmentation, eubacteria can produce spores in order to remain dormant during unfavorable conditions
Types	Methanogens, halophiles and thermophiles	Gram positive and Gram negative
Examples	Halobacterium, Thermoproteus, Pyrobaculum, Thermoplasma and Ferroplasma	Mycobacteria, Bacillus, E. coli, Pseudomonas, Clostridium etc

 Interesting Read

https://www.ck12.org/c/biology/archaea/lesson/Introduction-to-Archaea-Advanced-BIO-ADV/

https://www.science.org.au/curious/earth-environment/what-are-archaea