YSU BIOL 3702 - Chapter 19 - Microbial Taxonomy and Phylogeny (7 pages)

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Chapter 19 - Microbial Taxonomy and Phylogeny



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Chapter 19 - Microbial Taxonomy and Phylogeny

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7
School:
Youngstown State University
Course:
Biol 3702 - Microbiology
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BIOL 3702 Lecture Outline Chapter 19 Microbial Taxonomy and Phylogeny Overview The extraordinary diversity of the microbes is fascinating yet very complex Due to the diverse nature of living organisms it is desirable to categorize them into groups based upon their similarities Taxonomy the science of biological classification Classification arrangement of organisms into groups or taxa s taxon based upon similarities or evolutionary relatedness Nomenclature assignment of names to taxonomic groups using special rules Identification determining to which recognized taxon a particular organism belongs Why is taxonomy important Permits the organization of huge amounts of information Allows predictions and hypotheses to be made upon this information Places organisms in useful groups with precise names that permit effective communication between investigators Essential for the identification of organisms The term systematics is often used in synonymy with taxonomy This term is better defined as the scientific study of organisms with the ultimate object of characterizing and arranging them in an organized manner Actually encompasses other disciplines including morphology ecology epidemiology biochemistry molecular biology and physiology Microbial Evolution Earth is estimated to be 4 6 billion years old First procaryotic cells as evident from fossilized remains appeared about 3 5 3 8 billion years ago and were likely anaerobic Subsequent evolution of cyanobacteria and oxygenic photosynthesis occurred 2 53 0 billion years ago Microbial diversity increased as an oxygen rich environment developed Carl Woese and colleagues studying rRNA sequences suggest that procaryotes divided into two distinct lineages early in the earth s evolution These workers also suggested that all living things can be placed into one of three domains Page 1 of 7 Copyright 2004 by Chester R Cooper Jr BIOL 3702 Lecture Outline Chapter 19 Domains placed above the phylum and kingdom levels of classification Bacteria procaryotic Archaea procaryotic Eucarya eucaryotic Eucaryotes arose from procaryotes 1 4 2 7 billion years ago Two hypotheses for the evolution of eucaryotic cells Organelles arose within procaryotes from the invagination of the plasma membrane Endosymbiotic hypothesis Fusion of ancient true bacteria and archaea to form a nucleus and a Golgi apparatus Mitochondria and chloroplasts develop later from a permanent symbiotic relationship with other bacteria e g cyanelle cyanobacterium living inside the protist Cyanophora paradoxa Taxonomic Ranks Classification of an organism requires that it be placed ranked in a group taxon and given a specific name Informal names lactic acid bacterium Formal names Lactobacillus acidophilus Groups are hierarchical in nature Classification of an organism requires that it be placed ranked in a group taxon and given a specific name Informal names lactic acid bacterium Formal names Lactobacillus acidophilus Groups are hierarchical in nature Categories used in any rank unites groups under it based upon common properties In procaryotes in ascending order some ranks have characteristic suffixes Species Note do not capitalize first letter Genus Family suffix aceae Order suffix iales Class Phylum Domain Page 2 of 7 Copyright 2004 by Chester R Cooper Jr BIOL 3702 Lecture Outline Chapter 19 Species basic taxonomic group In higher organisms a species is defined based upon sexual reproduction Not a good criteria for bacteria many procaryotes do not reproduce sexually Procaryotic species collection of strains that share many stable properties and differ significantly from other groups of strains Strain population of organisms that is distinct from other populations within a particular taxonomic category and is typically descended from a single organism or a pure culture Biovars biochemical or physiological Morphovars shape Serovars antigenic properties Type strain standard but not always the most representative member Genus a well defined group of one or more species that is clearly distinct from other genera Naming of microbes uses a binomial system developed by Carolus Linnaeus Genus Escherichia Species coli Abbreviated E coli but only after the full name epithet is used once never start a sentence with an abbreviation Classification Systems Two basic types of classification systems are used Phenetic classification Natural classification system that groups organisms together based upon mutual similarity of their phenotypic characteristics May be used to infer possible evolutionary relationships Phylogenetic phyletic classification Based solely on evolutionary relationships Has been difficult to use in the past for procaryotes due to a lack of a fossil record Modern methods instead use gene sequences e g RNA genes or their products proteins to estimate phylogenetic relationships Page 3 of 7 Copyright 2004 by Chester R Cooper Jr BIOL 3702 Lecture Outline Chapter 19 Taxonomic Characteristics Classical characteristics Morphology Physiological metabolic Ecological Genetic analysis Transformation Conjugation Plasmid content Molecular characteristics Proteins Sequencing Physical of conserved proteins kinetic and regulatory properties Nucleic acids Base composition Hybridization Sequencing of conserved genes e g rRNA because it is generally stable yet changes over long periods of time Microbial Phylogeny There are a number of methods used to assess the phylogeny of microbes Molecular chronometers assumes that changes in conversed proteins or genes occurs over time without destroying or altering the molecules function Phylogenetic trees compares molecular sequence differences of a conserved gene or protein between organisms to generate a tree that expresses the differences as an evolutionary distance Signature sequence particular groups of microbes will possess unique nucleotides at specific locations in 16S rRNA molecules Signature sequence particular groups of microbes will possess unique nucleotides at specific locations in 16S rRNA molecules Polyphasic taxonomy taxonomic scheme which employs a wide range of stable and accepted phenotypic and genotypic information Modern microbial taxonomists generally employ phylogenetic trees derived from rRNA comparisons Page 4 of 7 Copyright 2004 by Chester R Cooper Jr BIOL 3702 Lecture Outline Chapter 19 Divisions of Life Kingdom systems of classification Five kingdom system Whittaker 1960s based upon cell type organization and the means of nutrient


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