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Information about Classification

Published on September 5, 2010

Author: aditya0291


Chapter 10: Classification of Microorganisms : Chapter 10: Classification of Microorganisms Slide 2: Phylogeny: The Study of Evolutionary Relationships of Living Organisms Over 1.5 million different organisms have been identified to date. Many similarities among living organisms: Made up of cells surrounded by a plasma membrane. Use ATP as energy source. Store genetic information as DNA. Ribosomes are the site of protein synthesis. Both differences and similarities among organisms are caused by natural selection (Darwin, 1858). Organisms can be classified into taxonomic categories (taxa), based on the differences and similarities among them. Taxonomy : Taxonomy The science of classifying organisms Provides universal names for organisms Provides a reference for identifying organisms Systematics or phylogeny The study of the evolutionary history of organisms All Species Inventory (2001-2025) To identify all species of life on Earth Goals of Classification : Goals of Classification - Stability - Predictability Methods Of Classification : Methods Of Classification 1. Intuitive Method Old method, based on perception of individual, ambiguous method, attimes quite usual 2. Numerical Taxanomy Determination of characteristics of microorganisms, equal weightage to all characteristics, computer analysis,determination of % similarity %S= NS/ NS+ND NS= No of similar characteristics (+ve/ -ve) ND= No. of different characteristics High % S organisms fall in same group and groups with high %S are placed in larger groups Slide 6: Advantages: Great practical usefulnessRelatively unbiased High degree of predictability and stability 3. Genetic Relatedness: Based on hereditary material DNA (initially %G+C) Problems with the existing methods so improved techniques -- DNA homology expts: used for species level of classification, formation of heteroduplexes --Ribosomal RNA homology expts & ribosomal RNA oligonucleotide cataloging: study of nucleotide sequence of rRNA Slide 7: Phylogeny: The Study of Evolutionary Relationships of Living Organisms Ancient Greeks classified all living organisms into two groups Kingdom Plantae Kingdom Animalia In 1850s bacteria and fungi were incorrectly placed in the Plant Kingdom. In 1860s Kingdom Protista was proposed to include bacteria, fungi, algae, and protozoa, but many scientists still classified bacteria and fungi as plants. Intense disagreement over classification of bacteria and fungi persisted over 100 years. Slide 8: Phylogeny: The Study of Evolutionary Relationships of Living Organisms In 1930s electron microscopy made it clear that bacterial cells lacked a nucleus. The term procaryote was introduced in 1937. In 1959 Kingdom Fungi was established. In 1961 the current definition of the term procaryote was established. In 1968 the Kingdom Procaryotae was accepted by biologists. In 1969 Robert Whitaker proposed a five-kingdom system of biological classification for all living organisms. Slide 9: Five-Kingdom System of Biological Classification Proposed in 1969 by Robert Whitaker : 1. Kingdom Procaryotae (Monera): Oldest known cells. Lived over 3.5 billion years ago. Lack a nucleus and membrane bound organelles. The other four kingdoms are eucaryotes. Have a true nucleus and membrane bound organelles. 2. Kingdom Protista: Mostly unicellular, lack tissue organization. Most have flagella during life. 3. Kingdom Fungi: May be unicellular (yeasts) or multicellular (molds). Many are saprotrophs. 4. Kingdom Plantae: Multicellular, photosynthetic. 5. Kingdom Animalia: Multicellular, heterotrophs that ingest food through a mouth or oral cavity. Five-Kingdom Classification System : Five-Kingdom Classification System :  Phylogeny The Three Domain System Domain: In 1978 Carl Woese proposed this level of classification above kingdom. There are three domains based on the following distinguishing criteria: Cell wall composition Membrane lipids RNA sequence Protein synthesis Antibiotic sensitivity I. Domain Eubacteria: “True bacteria”. II. Domain Archaeabacteria: “Ancient bacteria” III. Domain Eucarya: All eucaryotes: Protista, Fungi, Plantae, and Animalia. :  Phylogeny: The Three Domain System Recent developments in molecular biology and biochemistry have revealed that there are two types of procaryotic cells, based on differences in their ribosomes, cell walls, and metabolism. 1. Eubacteria: “True bacteria”. Cell wall contains peptidoglycan. Sensitive to antibiotics. 2. Archaeabacteria: “Ancient bacteria” Cell walls lack peptidoglycan, resistant to antibiotics. Live in extreme environments Three kingdoms: 1. Methanogens: Strict anaerobes that produce methane. 2. Extreme Halophiles: Require high salt concentrations. 3. Thermoacidophiles: Live in hot, acidic environments. Phylogenetic Relationships of Procaryotes : Phylogenetic Relationships of Procaryotes Slide 15: Classification of Organisms Scientific Nomenclature Scientific nomenclature: Universal system for naming and classifying living organisms. Initially developed in the 18th century by Carl Linnaeus. Binomial nomenclature: Each organism (species) has a two part name. Names are either italicized or underlined. Genus name: Always capitalized, always a noun. May use initial. species name: Always lower case, usually an adjective. Names are usually derived from Latin (or Greek) or may have latinized endings. Examples: Homo sapiens (H. sapiens): Human Penicillium notatum (P. notatum): Mold that produces penicillin Canis familiaris (C. familiaris): Domestic dog Slide 16: Classification of Organisms Hierarchy of Taxonomic Categories DOMAIN Kingdom Phylum or Division (Bacteria) Class Order Family Genus species Slide 17: Please remember this: Dumb Kings Play Chess On Funny Green Squares Slide 18: Taxonomic Categories Division (Bacteria) Slide 19: Classification of Bacteria Scientific Nomenclature Bacterial species: a collection of bacterial cells which share an overall similar pattern of traits in contrast to other bacteria whose pattern differs significantly Bacterial strain: A subgroup of a bacterial species that has distinguishing characteristics. Identified by numbers, letters, or names that follow the scientific name. a culture derived from a single parent that differs in structure or metabolism from other cultures of that species (biovars, morphovars) Escherichia coli O157:H7: Strain that causes bloody diarrhea. type – a subspecies that can show differences in antigenic makeup (serotype or serovar), susceptibility to bacterial viruses (phage type) and in pathogenicity (pathotype). Bergey’s Manual: Provides a reference for identifying and classifying bacteria. Classification initially based on cell morphology, staining, metabolism, biochemistry, serology, etc. More recently, DNA, RNA, and protein sequence analysis are being used to study evolutionary relationships. Major Taxonomic Groups of Bacteria per Bergey’s manual : Major Taxonomic Groups of Bacteria per Bergey’s manual Gracilicutes – gram-negative cell walls, thin-skinned Firmicutes – gram-positive cell walls, thick skinned Tenericutes – lack a cell wall & are soft Mendosicutes – archaea, primitive procaryotes with unusual cell walls & nutritional habits Procaryotes: Lack Nucleus and Membrane-Bound Organelles : Procaryotes: Lack Nucleus and Membrane-Bound Organelles Slide 26: Classification of Viruses Viruses are not considered living organisms by most biologists, because they lack cells and their own anabolic machinery. Obligate intracellular parasites. Must have evolved after their host cell evolved. Viral species: Population of viruses with similar characteristics that occupies a particular ecological niche. Morphology Genes Enzymes

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