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Classification of Microorganisms – Chapter 9

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1 Classification of Microorganisms – Chapter 9
Taxonomy The science of classifying organisms Provides universal names for organisms Provides a reference for identifying organisms Phylogeny The study of the evolutionary history of organisms

2 The Three-Domain System

3 Taxonomic Hierarchy

4 Species Definition Eukaryotic species:
A group of closely related organisms that breed among themselves and produce offspring that can produce offspring Viral species: Population of viruses with similar characteristics that occupies a particular ecological niche

5 Prokaryotic species: A population of cells with similar characteristics Based on: morphology biochemistry genetics Strain: Genetically different cells within a species

6 Domain Eukarya Animalia: Multicellular; no cell walls; chemoheterotrophic Plantae: Multicellular; cellulose cell walls; usually photoautotrophic Fungi: Unicellular or multicellular; cell wall structure varies; Chemoheterotrophic Protista: A catchall for eukaryotic organisms that do not fit other kingdoms; Predominantly unicellular

7 References • Bergey’s Manual of Determinative Bacteriology
Provides identification schemes for identifying bacteria and archaea Morphology, differential staining, biochemical tests • Bergey’s Manual of Systematic Bacteriology Provides phylogenetic information on bacteria and archaea Based on rRNA sequencing • Approved Lists of Bacterial Names Lists species of known prokaryotes Based on published articles

8 Identification Methods
Morphological characteristics: More useful for identifying eukaryotes than prokaryotes Differential staining: Gram staining Acid-fast staining Special staining Negative staining (Endo)spore staining

9 Identification Methods
Biochemical tests: Determines presence of specific bacterial See Animations → Dichotomous Key (chapter 10 Microbiology Place CD or website)

10 Miniaturized Rapid Identification – “Enterotube”
Vitek 2 – a more advanced miniaturized rapid identification system

11 Serology Combine known antiserum + unknown bacterium or bacterial antigens Slide agglutination ELISA Western blot

12 Another antibody-antigen test
Rapid “Strep” throat test Detects Group A streptococci (i.e. Streptococcus pyogenes) in minutes.

13 Flow Cytometry Can identify different cell types
Fluorescently labelled antibodies are attached to cells Computer detects cells

14 Genetics DNA fingerprinting Electrophoresis of enzymatic digests
rRNA sequencing

15 Nucleic Acid Hybridization: DNA chip


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