Carl Woese’s Classification – Three Domain Classification

Written by SouravBio · 6 minutes read >

Carl Woese’s Classification. Before 1969, there was two-kingdom classification, in which life was divided into two kingdoms such as, Animal Kingdom and the Plant Kingdom.

The two-kingdom classification system did not last too long because this two-kingdom classification can not differentiate between the eukaryotes and prokaryotes; neither unicellular and multicellular; nor photosynthetic and the non-photosynthetic.

Between 1969 – 1990 the five-kingdom classification system was introduced. In this classification system life was divided into five-kingdom such as Monera, Protista, Plantae, Fungi, Animalia. This classification system divides the life based on their anatomy, morphology, embryology, and cell structure.

There were several limitations of five kingdom classification such as this classification system does not mention about viruses, even this classification does not mention about how organisms within Kingdoms or between kingdoms may be related to each other via evolutionary relationships among the kingdoms.
After 1990, The Domain kingdom classification system or Carl Woese’s Classification or Six Kingdoms and Three Domains Classification was introduced. This classification system is based on the genetic characteristics (rather than phenotypic ones) with respect to evolutionary relatedness (phylogeny) of organisms that may prove more stable and predictable.

Carl Woese’s Classification

Carl Woese’s Classification
  • Carl Woese’s Classification is also known as the Three-domain system.
  • This three kingdom classification system was first proposed by an American microbiologist and biophysicist Carl Richard Woese in 1990.
  • This classification system divides the life forms into three domains and six kingdoms, that is why it also called the Six Kingdoms and Three Domains Classification.
  • 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.
  • In 1987 Carl Woese of the University of Illinois (USA) proposed a phylogenetic classification of prokaryotic species, which was based on the differences in their nucleotide sequence of 16S rRNA molecules. Later he concludes that 16S rRNA can be used for comparative analysis between prokaryotic and eukaryotic species.
  • This provides a tree of relatedness based on common ancestry or genealogy because both prokaryotic and eukaryotic cells contain small subunit rRNA (SSU rRNA).
  • Carl Woese used the rRNA as an “Evolutionary Chronometer” – an evolutionary time clock.

Why is rRNA a good ‘Chronometer’?

  • rRNA is universally distributed –  all species have rRNA
  • rRNA is functionally similar in different organisms – it participates in synthesis of protein.
  • rRNA changes its sequence slowly – optimum for looking across long periods of time.
  • rRNA sequences can be aligned, or matched up, between 2 organisms.

Domains of Carl Woese’s Classification

Carl Woese’s Classification

1. Domain Archaea

  • They are prokaryotic cells with no nuclear membrane.
  • Archaea has a distinct biochemistry, and RNA markers from bacteria.
  • They have isoprenoid glycerol diether or diglycerol tetraether lipids in their membranes.
  • They contain archaeal rRNA.
  • Archaea lacks peptidoglycan in their cell wall.
  • They are not sensitive to those antibiotics, those are used for the treatment of bacteria. But they are sensitive to some antibiotics that are affecting the Eukarya.
  • Archaea contain ether linkages in their membrane, which is formed between branched hydrocarbon chains and glycerol.
  • They can thrive in extreme environments such as high temperatures, low temperatures, stronger acid concentrations, etc. because they have a more stable ether linkage as compared to ester-containing linkages in the Bacteria and Eukarya 
Carl Woese’s Classification
Ether and Ester Linkage in membrane of bacteria and Archaea

Phyla of Archaea

Archaea has three major phyla such as;

  1. Crenarchaeota
  • This phylum is consist of those microorganisms which are lived in extremely high temperature and extremely low temperature.
  • Some of Crenarchaeota can thrive above the boiling point of water which is also called hyperthermophilic such as Sulfolobus, Acidianus, Pyrolobus.
  • Some of Crenarchaeota can live in frigid waters for example those microorganisms are lived in Antarctic.
  1. Euryarchaeota 
  • Euryarchaeota inhabit extreme environments of one or the other.
  • Some of them are extremely halophiles, which means they can alive or inhibit highly saline environments. An example of extremely halophile is Halobacterium.
  • Some of them help in methane production, they are called methane-producing bacteria such as Methanobacterium, Methanosarcina.
  • Some Euryarchaeota can inhibit extremely acidic environments they are called as acidophilic, such as Thermoplasma, Ferroplasma and Picrophilus

Note! A new euryarchaeote has been isolated from Ace Lake of Antarctica called Methanogenium

  1. Konarchaeota
  • This phyla is not yet officially recognized taxonomically.
  • Konarchaeota contains those organisms that are discovered from a single hot spring, Obsidian Pool, present in Yellowstone National Park (USA).
  • The mixed laboratory cultures of Konarchaeota indicate that they are hyperthermophilic.

2. Domain Bacteria

  • These are prokaryotic cells.
  • They also contain a nucleus without any membrane.
  • These are also known as eubacteria or “true bacteria”
  • Their membrane contains diacyl glycerol diester lipids.
  • All bacteria are not pathogenic some of them play beneficial roles by producing antibiotics and food.
  • They contain ester linkages in their membranes. This linkage is formed between unbranched fatty acid chains and glycerol.
  • Unlike the Archaea and Eukarya, the bacterial cell wall contains peptidoglycan.
  • They are sensitive to all antibacterial drugs but they are resistant to most of the antibiotics that affect the Eukarya.
  • They contain a unique bacterial rRNA which is distinctly different from the rRNA of Archaea and Eukarya.

 Phyla of Bacteria

  1. Proteobacteria: Includes all Enteric bacteria such as E. coli, Salmonella typhus, Legionella, Heliobacter pylorii (cause of many ulcers), Neisseria gonorrhea (cause of gonorrhea). These are closely related to eukaryotic mitochondria.
  2. Cyanobacteria: These include all Photosynthetic ‘blue-green’ bacteria which produces O2 gas.
  3. Eubacteria: These include Clostridium (tetanus, botulism), Bacillus, mycoplasma (walking pneumonia).
  4. Chlamydias: These include Parasites: Giardia, Chlamydia (STD).
  5. Spirochaetes: These include Spiral bacteria that cause syphilis, Lyme disease.

3. Domain Eukarya

  • They are eukaryotic cells.
  • Eukarya contains a membrane-bounded nucleus.
  • Eukarya contain ester linkages in their membranes. This linkage is formed between unbranched fatty acid chains and glycerol.
  • The cell wall of Eukarya contains no peptidoglycan.
  • They can inhibit the antibacterial antibiotics but sensitive to antibiotics that affect eukaryotic cells.

Kingdoms of Eukarya

Eukarya has four kingdoms, such as,

  1. Protista: These are single-celled eukaryotes found on land, in water, or living inside other organisms. The Protista includes Euglena, Amoeba, Paramecium etc.
  2. Fungi: These are unicellular or multicellular organisms with eukaryotic cell types. Their mode of nutrition is absorption. The fungi include Mushrooms, bread molds, water molds, yeasts, etc.
  3. Plantae: They are multicellular and eukaryotic cells. The Plantae includes Flowering plants, gymnosperms (conifers), ferns, mosses, etc.
  4. Animalia: Animalia are multicellular and eukaryotic cells. These include sponges, jellyfish, corals, fish, worms, insects, and vertebrates, etc.

FAQ on Carl Woese’s Classification

Q1. Explain why a two three and five Kingdom system is no longer acceptable for classification?

 Before 1969, there was two-kingdom classification, in which life was divided into two kingdoms such as, Animal Kingdom and the Plant Kingdom.

The two-kingdom classification system did not last too long because this two-kingdom classification can not differentiate between the eukaryotes and prokaryotes; neither unicellular and multicellular; nor photosynthetic and the non-photosynthetic.

Between 1969 – 1990 the five-kingdom classification system was introduced. In this classification system life was divided into five-kingdom such as Monera, Protista, Plantae, Fungi, Animalia. This classification system divides the life based on their anatomy, morphology, embryology, and cell structure.

There were several limitations of five kingdom classification such as this classification system does not mention about viruses, even this classification does not mention about how organisms within Kingdoms or between kingdoms may be related to each other via evolutionary relationships among the kingdoms.
After 1990, The Domain kingdom classification system or Carl Woese’s Classification or Six Kingdoms and Three Domains Classification was introduced. This classification system is based on the genetic characteristics (rather than phenotypic ones) with respect to evolutionary relatedness (phylogeny) of organisms that may prove more stable and predictable.

There were several limitations or drawbacks of these classifications that is why they don’t last too long. (Follow my previous articles )

Q2. What are the 3 domains of classification?

The three domains of Carl Woese’s Classification are the Archaea, the Bacteria, and the Eukarya.

Q3. How are the 3 domains of life related?

Three domains of living things, archaea, bacteria, and eukarya, are organized by shared characteristics fundamental to life: cellular organization, biochemistry, and molecular biology.

Q4. What are the 3 domains and 6 kingdoms?

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

References

Writer and Founder of Microbiologynote.com. I am from India and my main purpose is to provide you a strong understanding of Microbiology. Microbiologynote.com shares notes related to different branches of microbiology.

3 thoughts on “Carl Woese’s Classification – Three Domain Classification”

  1. Magnificent goods from you, man. I have understand your stuff previous
    to and you are just extremely wonderful. I actually like what you
    have acquired here, certainly like what you’re
    stating and the way in which you say it. You make it enjoyable and you still take
    care of to keep it smart. I can not wait to read much more from you.
    This is really a tremendous site.

    Reply

Leave a Comment

Subscribe Us

Subscribe Us to Get instant update, free ebook From Microbiologynote.com.

About Us

Microbiolgynote.com is an educational blog. Share notes related to different branches of Microbiology and botany, zoology.Explore

Contact Us

For Image copright realated issue or found any broke link please feel free and contact with us; contact@microbiologynote.com

Share
Reply
3 responses