Chapter 10 Lecture Figures
Lecture Figures
Lecture Figures
Bio 225 materials
Bio 225 Materials

Classification of Microorganisms




  1. Taxonomy is the science of the classification of organisms, with the goal of showing relationships among organisms.
  2. Taxonomy also provides a means of identifying organisms.


The Study Of Phylogenetic Relationships


  1. Phylogeny is the evolutionary history of a group of organisms.
  2. The taxonomic hierarchy shows evolutionary, or phylogenetic, relationships among organisms.
  3. Bacteria were separated into the Kingdom Prokaryotae in 1968.
  4. Living organisms were divided into five kingdoms in 1969.


The Three Domains (Figure 10.1)


  1. Living organisms are currently classified into three domains.  A domain can be divided into kingdoms.
  2. In this system, plants, animals, fungi, and protists belong to the Domain Eukarya. (Table 10.1)
  3. Bacteria (with peptidoglycan) form a second domain.
  4. Archaea (with unusual cell walls) are placed in the Domain Archaea.


Table 10.2

A Phylogenetic Hierarchy


  1. Organisms are grouped into taxa according to phylogenetic relationships (from a common ancestor).
  2. Some of the information for eukaryotic relationships is obtained from the fossil record.
  3. Prokaryotic relationships are determined by rRNA sequencing, although some fossils of prokaryotes exist. (Figure 10.4)


Classification Of Organisms


Scientific Nomenclature


  1. According to scientific nomenclature, each organism is assigned two names, or binomial : a genus and a specific epithet, or species. Table 10.3
  2. Rules for the assignment of names to bacteria are established by the International Committee on Systematic Bacteriology.
  3. Rules for naming fungi and algae are published in the International Code of Botanical Nomenclature.
  4. Rules for naming protozoa are found in the International Code of Zoological Nomenclature.        


The Taxonomic Hierarchy


  1. A eukaryotic species is a group of organisms that interbreeds but does not breed with individuals of another species.
  2. Similiar species are grouped into a genus; similiar genera are group into a family; families into an order; orders into a class; classes into a division or phylum; phyla into a kingdom; and kingdoms into domains. (Figure 10.5)


Classification of Prokaryotes


  1. Bergey's Manual of Systematic Bacteriology is the standard reference on bacterial classification.
  2. A group of bacteria derived from a single cell is called a strain.
  3. Closely related strains constitute a bacterial species. Table 10.4, Figure 10.6


Classification of Eukaryotes


  1. Eukaryotic organisms may be classified into the Kingdom Fungi, Plantae, or Animalia.
  2. Protists are mostly unicellular organisms; these organisms are currently being assigned to kingdoms.
  3. Fungi are absorptive chemoheterotrophs that develop from spores.
  4. Multicellular photoautotrophs are placed in the Kingdom Plantae.
  5. Multicellular ingestive heterotrophs are classified as Animalia.


Classification of Viruses


  1. Viruses are not placed in a kingdom.  They are not composed of cells and cannot grow without a host cell.
  2. A viral species is a population of viruses with similar characteristics that occupies a particular ecological niche.


Methods Of Classifying And Identifying Microorganisms


  1. Bergey' s Manual of Determinative Bacteriology is the standard reference for laboratory identification of bacteria.
  2. Morphological characteristics are useful in identifying microorganisms, especially when aided by differential staining techniques (Gram staining and acid fast stains can suggest a course of treatment before the organism is positively identified). (Figure 10.7)
  3. The presence of various enzymes, as determined by biochemical tests, is used in identifying microorganisms. (Figure 10.8) Rapid identification can be accomplished with specific sets of biochemical tests. (Figure 10.9)
  4. Serological tests, involving the reactions of microorganisms with specific antibodies, are useful in determining the identity of strains and species, as well as relationships among organisms.  Slide agglutination (Figure 10.10), ELISA (Figure 10.11), and Western blotting (Figure 10.12) are examples of serological tests.
  5. Phage typing is the identification of bacterial species and strains by determining their susceptibility to various phages. (Figure 10.13)
  6. Fatty acid profiles can be used identify some organisms.
  7. Flow cytometry measures physical and chemical characteristics of cells.
  8. The percentage of GC base pairs in the nucleic acid of cells can be used in the classification of organisms.
  9. The number and sizes of DNA fragments, or DNA fingerprints, produced by restriction enzymes are used to determine genetic similarities. (Figure 10.14)
  10. The sequence of bases in ribosomal RNA can be used in the classification of organisms.
  11. The polymerase chain reaction (PCR) can be used to detect small amounts of microbial DNA in a sample.
  12. Single strands of DNA and RNA, from related organisms will hydrogen-bond to form a double-stranded molecule; this bonding is called nucleic acid hybridization. (Figure 10.15)
  13. Southern blotting and DNA probes, including DNA chips, are examples of hybridization techniques. (Figure 10.16, Figure 10.17) Summary: (Figure 10.18)
  14. Dichotomous keys are used for the identification of organisms.  Cladograms show phylogenetic relationships among organisms. Table 10.5