Classification of microbes (and other living things)
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Classification of microbes (and other living things)
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Major events in the history of life:life was originally microscopic and
unicellular
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Taxonomy: the science of naming and classifying organisms (Carolus Linnaeus)
Phylogeny: evolutionary history
Systematics: the science of classification basedon evolutionary history of organisms
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Linnaean classification system is used today (with modifications)
• Binomial (“scientific name”)– Genus and species
names (specific epithet)
• Hierarchical classification
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How is classification achieved?
• Observation– Similarities and differences– Fossil record
• Molecular analysis – DNA – Ribosomal RNA– Mitochondrial DNA– Proteins
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Ideas about classification have changed
• Linnaeus- plants and animals (1735)• Where do bacteria and fungi belong?
– Von Nägeli- with plants (1857)– Haeckel- Kingdom Protista (1866)
• Whitaker – five kingdoms (1969)• Woese- domains (1978)
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Classification may change again
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Classification by RNA sequence data
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Phenotypes (physical differences) between the domains
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Classification of prokaryotes
• Morphology (Gram-staining)• Nutrition• Metabolism• Environmental niche• rRNA sequences (all living cells have them)• Reference: Bergey’s Manual of Systematic
Bacteriology; Bergey’s Manual of Determinative Bacteriology)
• Most prokaryotes have not been discovered!
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Microbial identification
• Differential media• Biochemical testing• Serology• Phage typing• Genetic testing
– rRNA sequencing
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A dichotomous key
• Classic tool for identification
• Most of these tests can be administered simultaneously
• Different keys can be developed for groups of bacteria
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How do you make bacteria look different?
Genomic analysis Phage typing
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Archaea: “extreme bacteria”
• Discovered in late 1970’s• Species live at extreme temperature, pH,
have unusual metabolic properties• Hard to study
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Classification of eukaryotes• Plantae- mosses, ferns, conifers, flworing plants
(some algae)– multicellular, photosynthetic
• Animalia- sponges, worms, various vertebrates and invertebrates– multicellular, ingest nutrients
• Fungi (1959)- yeasts, molds, mushrooms– Absorb nutrients, form hyphae if multicellular
• Protists- unicellular organisms– Don’t fit anywhere else!
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Classification of viruses
• Not cellular, so are not classified in hierarchical system
• Viral species- population of viruses with similar characteristics and that occupy a particular ecological niche
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Summary
• Eukaryotes are much more diverse than prokaryotes
• Some have evolved much more recently than others
• All are “successful” in their niche• Classification is an ongoing process• Genetic and phenotypic differences are
considered in classification