Classification of Microorganisms, Carl Woese, Bacteria, Archeae, Eukarya

1. THREE DOMAINS OF LIFE
Preparaed By:
Mr. K. Sanjay,
M.Sc., Microbiology,
Sacred Heart College
[Autonomous],
Tirupattur.
Head of the Department:
Dr. P. Saran Raj, M.Sc., M.Phil., Ph.D., NET
Head of Department of Microbiology,
Sacred Heart College[Autonomous],
Tirupattur.

2. Discovery
• The term “Domain” was introduced by American Microbiologist
and bio-physicst Carl woese et al., in 1990.
• Together with the proposal of a natural classification system for all
life on earth, including microorganisms, which had previously
escaped any attempt of classification based on evolutionary
relationships.

3.  Organisms can be classified into one of three
domains
 based on differences in the sequences of
nucleotides in the cell's ribosomal RNAs (rRNA),
the cell's membrane lipid structure, and its
sensitivity to antibiotics.
 The three domains are the Archaea, the Bacteria,
and the Eukarya.
Three Domains of Life:

4. • Archaea are prokaryota cells,
• Typically characterized by membrane lipids that are
branched hydrocarbon chains attached to glycerol by ether
linkages.
• The presence of these ether linkages in Archaea adds to their
ability to withstand extreme temperatures and
highly acidic conditions, but many archaea live in mild
environments.
• Halophiles, organisms that thrive in highly salty environments,
and hyperthermophiles, organisms that thrive in extremely hot
environments, are examples of Archaea.
Archaea:

5. Archaea evolved many cell sizes, but all are relatively small.
Their size ranges from 0.1 μm to 15 μm diameter and up to
200 μm long.
They are about the size of bacteria, or similar in size to
the mitochondria found in eukaryotic cells.
Members of the genus Thermoplasma are the smallest of the
Archaea

6. Even though bacteria are prokaryotic cells just like Archaea,
their membranes are made of phospholipid bilayers.
Cyanobacteria and mycoplasmas are two examples of
bacteria.
They characteristically do not have ether linkages like
Archaea, and they are grouped into a different category—and
hence a different domain.
Bacteria

7. There is a great deal of diversity in this domain.
Confounded by that diversity and horizontal gene transfer
It is next to impossible to determine how many species of
bacteria exist on the planet or to organize them in a tree-
structure,
Without cross-connections between branches.

8.  Members of the domain Eukarya—called
eukaryotes
 Have membrane-bound organelles (including a
nucleus containing genetic material) and are
represented by
 Five kingdoms: Plantae, Protozoa, Animalia,
Chromista, and Fungi.
Eukarya: