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Classification of
Micr oor ganisms

Taxonomy
 Organizing, classifying
and naming living things
 Formal system originated
by Carl von Linné (1701-
1778)
 Identifying and classifying
organisms according to
specific criteria
 Each organism placed
into a classification
system

Taxonomy
 Domain
 Kingdom
 Phylum
 Class
 Order
 Family
 Genus
 species

3 Domains
 Eubacteria
 true bacteria, peptidoglycan
 Archaea
 odd bacteria that live in extreme
environments, high salt, heat, etc. (usually
called extremophiles)
 Eukarya
 have a nucleus & organelles (humans,
animals, plants)

3 classification of microorganisms

Taxonomy
 4 main kingdoms:
 Protista
 Fungi
 Plantae
 Animalia
 Algae

Naming Micoorganisms
 Binomial (scientific) nomenclature
 Gives each microbe 2 names:
 Genus - noun, always capitalized
 species - adjective, lowercase
 Both italicized or underlined
 Staphylococcus aureus (S. aureus)
 Bacillus subtilis (B. subtilis)
 Escherichia coli (E. coli)

Evolution - living things
change gradually over
millions of years
 Changes favoring survival are retained and less
beneficial changes are lost
 All new species originate from preexisting
species
 Closely related organism have similar features
because they evolved from common ancestral
forms
 Evolution usually progresses toward greater
complexity

Insert figure 1.15
Woese-Fox System

Classification
Systems in the
Pr ocar yotae

Classification Systems
in the Procaryotae
1. Microscopic morphology
2. Macroscopic morphology – colony
appearance
3. Physiological / biochemical characteristics
4. Chemical analysis
5. Serological analysis
6. Genetic and molecular analysis
• G + C base composition
• DNA analysis using genetic probes
• Nucleic acid sequencing and rRNA analysis

Bacterial Taxonomy
Based on Bergey’s
Manual
 Bergey’s Manual of Determinative
Bacteriology – five volume resource
covering all known procaryotes
 classification based on genetic information –
phylogenetic
 two domains: Archaea and Bacteria
 five major subgroups with 25 different phyla

Major Taxonomic
Groups of Bacteria
 Vol 1A: Domain Archaea
 primitive, adapted to extreme habitats and
modes of nutrition
 Vol 1B: Domain Bacteria
 Vol 2-5:
 Phylum Proteobacteria – Gram-negative cell
walls
 Phylum Firmicutes – mainly Gram-positive
with low G + C content
 Phylum Actinobacteria – Gram-positive with
high G + C content

Diagnostic Scheme for
Medical Use

 Uses phenotypic qualities in
identification
 restricted to bacterial disease agents
 divides based on cell wall structure, shape,
arrangement, and physiological traits

Species and
Subspecies
 Species
 collection of bacterial cells which share an overall
similar pattern of traits in contrast to other bacteria
whose pattern differs significantly
 Strain or variety
 culture derived from a single parent that differs in
structure or metabolism from other cultures of that
species (biovars, morphovars)
 Type
 subspecies that can show differences in antigenic
makeup (serotype or serovar), susceptibility to
bacterial viruses (phage type) and in pathogenicity
(pathotype)

Archaea: The Other
Procaryotes
 Constitute third Domain Archaea
 Seem more closely related to Domain Eukarya than to
bacteria
 Contain unique genetic sequences in their rRNA
 Have unique membrane lipids and cell wall construction
 Live in the most extreme habitats in nature,
extremophiles
 Adapted to heat, salt, acid pH, pressure and
atmosphere
 Includes: methane producers, hyperthermophiles,
extreme halophiles, and sulfur reducers

Eukaryotes

 Protista
 Fungi
 Plantae
 Animalia
 Algae

Fungal Classification
 Sexual reproduction
 Spores are formed following fusion of male and
female strains and formation of sexual structure
 Sexual spores and spore-forming structures
are one basis for classification
 Zygospores
 Ascospores
 Basidiospores

Fungal Classification
 Subkingdom Amastigomycota
 Terrestrial inhabitants including those of
medical importance:

1. Zygomycota – zygospores; sporangiospores and
some conidia
2. Ascomycota – ascospores; conidia
3. Basidiomycota – basidiospores; conidia
4. Deuteromycota – majority are yeasts and molds;
no sexual spores known; conidia

Protozoan
Classification
 Difficult because of diversity
 Simple grouping is based on method of motility,
reproduction, and life cycle
1. Mastigophora – primarily flagellar motility, some
flagellar and amoeboid; sexual reproduction; cyst
and trophozoite
2. Sarcodina – primarily ameba; asexual by fission;
most are free-living
3. Ciliophora – cilia; trophozoites and cysts; most are
free-living, harmless
4. Apicomplexa – motility is absent except male
gametes; sexual and asexual reproduction; complex
life cycle – all parasitic

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3 classification of microorganisms

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