Download Classification of Microorganisms

Classification of Microorganisms
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Taxonomy
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Provides universal names for organisms
Provides a reference for identifying organisms
Systematics or phylogeny
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The science of classifying organisms
The study of the evolutionary history of organisms
All Species Inventory (2001-2025)
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To identify all species of life on Earth
Three Domains
- Archaea
- Eukarya
- Bacteria (Eubacteria)
Endosymbiotic Theory
- origin of mitochondria and chloroplasts
- one ancient prokaryotic cell engulfed by another
- they lived symbiotically
- over the eons, endosymbionts specialized for energy production
Classification
Traditional taxonomy was developed to classify larger multicellular animals (and plants) which possessed many different
observable characteristics. Bacteria are microscopic with few and often similar morphologies. Also, “species” refers to
members of a particular group that interbreed. Bacteria do not reproduce sexually and produce offspring. Nevertheless
bacteria are classified and named according to the standard Genus species nomenclature.
These names often try to incorporate observed characteristics, origin of discovery, even the discoverer.
Staphylococcus aureus
Legionella pneumophilia
Species Definition
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Eukaryotic species:
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A group of closely related organisms that breed among themselves
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Prokaryotic species:
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A population of cells with similar characteristics
Clone: Population of cells derived from a single cell
Strain: Genetically different cells within a clone
Viral species:
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Population of viruses with similar characteristics that occupies a particular ecological niche
Domain: Eukarya
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Animalia: Multicellular; no cell walls; chemoheterotrophic
Plantae: Multicellular; cellulose cell walls; usually photoautotrophic
Fungi: Chemoheterotrophic; unicellular or multicellular; cell walls of chitin; develop from spores or hyphal
fragments
Protista: A catchall for eukaryotic organisms that do not fit other kingdoms
Identification Methods
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Morphological characteristics: Useful for identifying eukaryotes
Differential staining: Gram staining, acid-fast staining
Biochemical tests: Determines presence of bacterial enzymes
Serology
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Combine known antiserum + unknown bacterium
Slide agglutination
ELISA
Western blot
uses antibodies and cell surface antigens
Genetics
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DNA base composition
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DNA fingerprinting
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Guanine + cytosine moles% (GC)
Electrophoresis of restriction enzyme digests
rRNA sequencing
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Polymerase Chain Reaction (PCR)
DNA base composition - % G + C
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-the % G + C content is stable from generation to generation
-closely related organisms will have similar G + C content
-unrelated species will have very different G + C content
This method can determine that organisms are unrelated but not conclusively related. Why?
DNA homology - examine the similarity of base pair sequences.
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- DNA hybridization is used to determine homology. The greater the degree of hybridization, the greater the
homology; thus the more related the organisms are.
- Southern blotting - use radioactively labeled DNA probes to hybridize to suspect organism’s DNA
- like pieces of DNA will hybridize indicating probable ID
Methods
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DNA Fingerprinting
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- compare restriction fragments
- the more closely related the organisms, the more similar the fragment pattern
Polymerase Chain Reaction (PCR)
- technique for amplification of DNA
- amplified DNA can be tested using techniques
Dichotomous Key
- identification scheme
- usually a series of questions concerning characteristics: yes/no or either/or
- bacterial dichotomous key = flow chart
Study Objectives
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Define taxonomy and phylogeny.
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Compare and contrast the three domains of life.
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Explain the endosymbiotic theory.
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Compare and contrast species definition with respect to eukaryotes, prokaryotes and viruses.
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Describe the general principle of serology and describe how those techniques (ELISA, agglutination, Western
blot) can be used to identify/classify organisms.
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Describe the general principle of comparing DNA base composition and describe how those techniques
(%G+C, hybridization, Southern blot, fingerprinting, PCR) can be used to identify/classify organisms.
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Describe a dichotomous key.
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