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Classification of Microorganisms

Introduction

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

1. Living organisms are currently classified into three domains. A domain can beprovided into kingdoms.

2. In this system, plants, animals, fungi, and protists belong to the Domain Eukarya.3. Bacteria (with peptidoglycan) form a second domain.4. Archaea (with unusual cell walls) are placed in the Domain Archaea.

A Phylogenetic Hierarchy

1. Organisms are grouped into taxa according to phylogenetic relationships (from acommon ancestor).

2. Some of the information for eukaryotic relationships is obtained from the fossilrecord.3. Prokaryotic realtionships are determined by rRNA sequencing.

Classification Of Organisms

Scientific Nomenclature

1. According to scientific nomenclature, each organism is assigned two names, orbinomial : a genus and a specific epithet, or species.

2. Rules for the assignment of names to bacteria are established by theInternational Committee on Systematic Bacteriology.

3. Rules for naming fungi and algae are published in the International Code ofBotanical Nomenclature.

4. Rules for naming protozoa are found in the International Code of ZoologicalNomenclature.

The Taxonomic Hierarchy

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1. A eukaryotic species is a group of organisms that interbreeds but does not breedwith individuals of another species.

2. Similiar species are grouped into a genus; similiar genera are group into afamily; families into an order; orders into a class; classes into a division orphylum; phyla into a kingdom; and kingdoms into domains.

Classification of Prokaryotes

1. Bergey's Manual of Systematic Bacteriology is the standard reference onbacterial classification.

2. A group of bacteria derived from a single cell is called a strain.3. Closely related strains constitute a bacterial species.

Classification of Eukaryotes

1. Eukaryotic organisms may be classified into the Kingdom Fungi, Plantae, orAnimalia.

2. Protists are mostly unicellular organisms; these organisms are currently beingassigned 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 andcannot grow without a host cell.

2. A viral species is a population of viruses with similar characteristics that occupiesa particular ecological niche.

Methods Of Classifying And Identifying Microorganisms

1. Bergey' s Manual of Determinative Bacteriology is the standard reference forlaboratory identification of bacteria.

2. Morphological characteristics are useful in identifying microorganisms, especiallywhen aided by differential staining techniques.

3. The presence of various enzymes, as determined by biochemical tests, is usedin identifying microorganisms.

4. Serological tests, involving the reactions of microorganisms with specificantibodies, are useful in determining the identity of strains and species, as

well as relationships among organisms. ELISA and Western blotting areexamples of serological tests.

5. Phage typing is the identification of bacterial species and strains by determiningtheir susceptibility to various phages.

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.

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9. The number and sizes of DNA fragments, or DNA fingerprints, produced byrestriction enzymes are used to determine genetic similarities.

10. The sequence of bases in ribosomal RNA can be used in the classification oforganisms.

11. The polymerase chain reaction (PCR) can be used to detect small amounts ofmicrobial DNA in a sample.

12. Single strands of DNA and RNA, from related organisms will hydrogen-bond toform a double-stranded molecule; this bonding is called nucleic acidhybridization.

13. Southern blotting and DNA probes are examples of hybridization techniques.14. Dichotomous keys are used for the identification of organisms. Cladograms

show phylogenetic relationships among organisms.