MICROBIOLOGY QUICK LEARN-Classification of microorganisms-basics

1. MICROBIOLOGY QUICK LEARN
CLASSIFICATION OF MICROORGANISMS
Ms Saajida Sultaana Mahusook

2. • Living organisms are diverse whether it is plants, animals or
microbes. They play important roles in nature.
• Arranging these microbes in order or hierarchy based on its
similarity or differences (in any characteristics), makes it easier to
know and get access to all the microbes. So it is necessary to
classify the organisms.
• Greek Philosopher Aristotle classified the living things as plants and
animals around 2000 years ago.
• John Ray defined species as similar patterns and genera for the
group containing closely related species.
• Carolous Linnaeus proposed the science of taxonomy- the basic
rules for taxonomic categories or taxa, binomial nomenclature.

3. Taxonomy
Taxonomy [Greek taxis, arrangement, and nomos, law] is defined
as the science of biological classification. Taxonomy is orderly
arranging organisms under study into groups of larger units.
It consists of three interrelated parts namely
Classification
Classification is
the orderly
arrangement of
organisms into
groups
or taxa (s., taxon)
based on mutual
similarity (Phenetic)
or evolutionary
relatedness(Phyloge
netic).
NomenclatureNomenclature is
concerned with
the assignment
of names to
taxonomic groups
in agreement
with published
rules.
Identification
Identification is
the practical
side of taxonomy,
the process of
determining that
a particular
isolate belongs to
a recognized
taxon.

4. Levels of Classification (Taxonomic hierarchy)
• Introduced by Linnaeus
• The main taxa/ groups in a classification are organized into several
descending ranks starting with Kingdom and ending with species.
• Techniques for identifying or determining taxonomical characters
o Morphology
o Physiology and
metabolism
o Ecology
o Genetic analysis

5. Divisions of Life
Kingdom systems of classification
-Three-kingdom system (Ernest Haeckel, 1866) – Plants, animals and Protista to include
unicellular organisms.
- Five-kingdom system (Whittaker, 1960s) - based upon cell type, organization, and the
means of nutrient acquisition (Monera, Protista, Fungi, Plantae, Animalia)
- Six-kingdom system - differs from five-kingdom system by dividing prokaryotes into
bacteria and archaea (Bacteria, Archaea, Protista, Fungi, Plantae, Animalia)
- Eight-kingdom system (Cavalier-Smith) - further division of the protists using rRNA data
and grouping organisms into two empires (Eucaryota and Bacteria) containing a total of
eight kingdoms [(Bacteria, Archaea), (Archezoa, Protista, Plantae, Chromista, Fungi,
Animalia)]

6. Five Kingdom Classification

7. Five Kingdom Classification
• Proposed by RH Whittaker in 1969.
• The main criteria of the five kingdom classification was cellular
organization(structure, body), mode of nutritional pattern of
organisms.
• This system places all living things into one of the five basic
kingdoms.
o Monera or Prokaryote
o Protista
o Fungi
o Plantae
o Animalia

10. THREE DOMAIN SYSTEM
• Proposed by Carl Woese and Fox, is an evolutionary model of phylogeny
based on differences in the sequences of nucleotides in the cell's
ribosomal RNAs (rRNA), as well as the cell's membrane lipid structure and
its sensitivity to antibiotics.
• Comparing rRNA structure is especially useful. Because rRNA molecules
throughout nature carry out the same function, their structure changes
very little over time.
• Therefore similarities and dissimilarities in rRNA nucleotide sequences
are a good indication of how related or unrelated different cells and
organisms are.
• The system proposes that a common ancestor cell gave rise to three
different cell types, each representing a domain. The three domains are
o Archaea
o Bacteria
o Eukarya

11. The Archaea (Archaebacteria)
• Archaea are prokaryotic cells.
• The cell walls of Archaea contain no peptidoglycan.
• The Archaea have membranes composed of branched hydrocarbon
chains (many also containing rings within the hydrocarbon chains)
attached to glycerol by ether linkages.
• Archaea are not sensitive to some antibiotics that affect the Bacteria,
but are sensitive to some antibiotics that affect the Eukarya.
• Archaea contain rRNA that is unique to the Archaea and distinctly
different from the rRNA of Bacteria and Eukarya.
• Archaea often live in extreme environments and include methanogens,
extreme halophiles, and hyperthermophiles.

12. The Bacteria (Eubacteria)
• Bacteria (also known as eubacteria or "true bacteria") are
prokaryotic cells.
• Their membranes are composed of unbranched fatty acid chains
attached to glycerol by ester linkages.
• The cell walls of Bacteria contain peptidoglycan.
• Bacteria are sensitive to traditional antibacterial antibiotics but
are resistant to most antibiotics that affect Eukarya.
• Bacteria contain rRNA that is unique to the Bacteria as indicated
by the presence molecular regions distinctly different from the
rRNA of Archaea and Eukarya.
• They include pathogenic and non-pathogenic bacteria living in
soil, water, etc.
• Bacteria include mycoplasmas, cyanobacteria, Gram-positive
bacteria, and Gram-negative bacteria.

13. The Eukarya (Eukaryotes)
• Eukarya includes eukaryotic cells.
• Like the Bacteria, they have membranes composed of straight
(unbranched) fatty acid chains attached to glycerol by ester
linkages.
• Not all Eukarya possess cells with a cell wall, but for
those Eukarya having a cell wall, that wall contains no
peptidoglycan. Cell wall is present in plants and fungi.
• Eukarya are resistant to traditional antibacterial antibiotics but
are sensitive to most antibiotics that affect eukaryotic cells.
• Eukarya contain rRNA that is unique to the Eukarya as indicated
by the presence molecular regions distinctly different from the
rRNA of Archaea and Bacteria.
• The domain includes Protists(algae and protozoan), Fungi, Plants
and animals.

14. Reference:
• Microbiology by Professor Dushyant Kumar Sharma
• https://nptel.ac.in/courses/102103015/34
• https://bio.libretexts.org/Bookshelves/Microbiology/Book%3A_Microbiology_(Kais
er)/Unit_1%3A_Introduction_to_Microbiology_and_Prokaryotic_Cell_Anatomy/1
%3A_Fundamentals_of_Microbiology/1.3%3A_Classification_-
_The_Three_Domain_System
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