This document discusses taxonomy and classification of organisms. It describes how taxonomy involves classifying organisms into groups based on similarities and evolutionary relationships. There are three domains of life - Archaea, Bacteria, and Eukarya. Bacteria are prokaryotic cells that are classified based on characteristics like cell structure, staining properties, shape, and biochemical reactions. Proper classification and naming of bacteria according to taxonomic rules is important for effective communication among microbiologists and organizing biological knowledge.

1. BY MWEBAZA IVAN
Msci I
2013/HD07/767U
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2. TAXONOMY
Involves classification, nomenclature and identification
of organisms.
 classification is the arrangement of organisms into groups
based on their mutual similarity or evolutional relatedness.
 Nomenclature is the process of assigning names to a an
organism (and requires agreement for unambiguous usage of
such names)
 Identification is the practical process of determining that a
particular isolate belongs to a given recognized group.(
microbiologists are usually concerned with this in practice)
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3. DOMAINS OF LIFE
All life forms belong to three large groups/domains i.e.
Archaea, bacteria and eukarya (three domain system-
carl woese, 1977).
Eukarya-
 Have membrane bound organelles.
 DNA is linear and found on x-somes in nucleus.
 Transcription requires formation of mRNA and moves
outside of the nucleus.
 Have glycerol fatty acyl diester membrane lipids.
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4. ARCHAEA
 classified as separate from Bacteria by Carl woese in
1977 basing on rRNA gene sequences,
considered as prokaryotes along side Bacteria.
 Their transcription and translation enzymes are
more similar to those of eukaryotes than of bacteria.
 Have isoprenoid glycerol diether or diglycerol
tetraether lipids.
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5. BACTERIA
Have no membrane bound organelles,
Have single circular DNA.
Transcription and translation can be carried out
simultaneously.
Have diacyl glycerol diester lipids in their membranes.
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6. Importance of Bacterial taxonomy
 Helps in predictions and frame hypotheses for further
research based on knowledge of similar organisms.
 Easy communication among microbiologists
 Organization of knowledge.
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7. Classification of Bacteria
Bacteria are arranged into species, genera, families, orders
and phyla.
 The species is the basic group.
 A prokaryotic species is a collection of strains which share
many stable properties and differ significantly from other
groups.
 It should have similar G+C composition and 70% or greater
similarity as judged by DNA hybridization.
 Species should ideally be distinguishable phenotypically
from other species.
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8. STRAIN
A strain is a popn of organisms which are considered
to have descended from a single organism as found in a
natural habitat, in primary culture and in sub cultures.
Strains in a species may differ slightly e.g. biovars ,
morphovars , serovars.
Type strain is the first strain studied and more fully x-
terized than other strains.
A type strain must remain with in the genus of which
it is the nomenclatural type, only those strains very
similar to the type species are included in the species.
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9. Classification systems
Once taxonomically relevant x-tics have been collected, they
may be used to construct a classification:
 Natural classification (developed by Linnaeus), considers
just the overall similarity/observable traits,basically
anatomical traits (phenetic classification).
Numerical (Adansonian) classification, some how related
to phenetic though information about the properties of
organisms is converted into numerical form and compared
using computer programms , similarity or matching
coefficients and dendograms are constructed .( Robert
Sokal and Peter H.A.Sneath)
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10. Systems contd….
Phylogenic/phyletic classification
Involves study of evolutionary r/ships among
groups of organisms which are discovered through
molecular sequencing data and morphological data
matrices.
Polyphasic taxonomy.
This considers the phenotype,genotype, molecular
sequences, evolutionary x-tics , and ecological
behaviors in classification of the organisms
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11. Bacterial Nomenclature
 The rules are set in International code for the
nomenclature of Bacteria.
 Bacteria are named according to binomial system
developed by Carl Von Linne/Linnaeus
 A species is designated with two latinized names i.e. genus
and species
 The first name is capitalized, second is not capitalized
(Escherichia coli).
 Taxonomic names approved by the International
committee of systematic Bacteriology are considered
official and binding.
 Bergey’s Manual of systematic Bacteriology contains the
accepted system of prokaryotic taxonomy
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12. IDENTIFICATION OF MEDICALLY
IMPORTANT BACTERIA
Key parameters used:
 Cell wall (rigid, flexible, or absent).
 Intracellular or extracellular.
 Shape of the organism.
 Staining reaction.
 Spore forming abilities.
 Biochemical reactions.
 Genetics. (rRNA sequences, hybridization, gene probes)
 Cultural x-tics (diameter, outline, elevation,colour etc)
 The ability to grow in absence or presence of oxygen
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13. 10/1/2013
Bacteria
Thick
walled
Extracellu
lar
Gram
positive
Cocci
e.g.Strepto
coccus,Sta
phylococo
ccus
rods
Spore
forming
Aerobic
e.g.
bacillus
Anaerobic
e.g.clost
ridium
Non
spore
forming
Filament
ous e.g.
Actinom
yces,Nor
cardia
Non
Fillame
ntous-
Coryne
bacteriu
m,
Listeria
Acid fast e.g
Mycobacteriu
m
Gram
negative
Cocci-
Nisserias
rods
Fucultati
ve
straight
Resp organism-
Haemophillus,Bord
etella,Legionella
Zoonotic,-
Brucella,Pas
teurella,Yer
sinia
Enteric-
Escherichia,Entero
bacter,Serratia,Sal
monella
Curved-
Vibrio,H
elicobact
er
Aerobic-
pseudom
onas
Anaerobic-
Bacteriode
s
Obligate
intracellular
e.g.Rickettsia ,
Chlamydia
Flexible
thin walled
e.g.Trepon
ema,
Borreila
Wall less e.g.
Mycoplasma

14. References
 Microbiology 5th edition (Lansing M. Prescott)
 Lange microbiology and immunology review 10th
edition (Warren Levinson)
 Brocks biology of Microorganisms (Madigan,
Martinko etal..)
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