A Survey of Prokaryotic Cells and Microorganisms

Transcription

1 Chapter 4 A Survey of Prokaryotic Cells and Microorganisms Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

2 Characteristics of Cells and Life All living things (single and multicellular) are made of cells that share some common characteristics: Basic shape spherical, cubical, cylindrical Internal content cytoplasm, surrounded by a membrane DNA chromosome(s), ribosomes, metabolic capabilities Two basic cell types: eukaryotic and prokaryotic 2

3 Characteristics of Cells Eukaryotic cells: animals, plants, fungi, and protists Contain membrane-bound organelles that compartmentalize the cytoplasm and perform specific functions Contain double-membrane bound nucleus with DNA chromosomes Prokaryotic cells: bacteria and archaea No nucleus or other membrane-bound organelles Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display Prokaryotic Ribosomes Chromosome Eukaryotic Ribosomes Nucleus Mitochondria Cell wall Flagellum Cell membrane Flagellum Cell membrane 3

4 Characteristics of Life Reproduction and heredity genome composed of DNA packed in chromosomes; produce offspring sexually or asexually Growth and development Metabolism chemical and physical life processes Movement and/or irritability respond to internal/external stimuli; self-propulsion of many organisms Cell support, protection, and storage mechanisms cell walls, vacuoles, granules and inclusions Transport of nutrients and waste 4

5 Structure of a bacterial cell Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Fimbriae Ribosomes Cell wall Cell membrane Capsule Slime layer Cytoplasmic matrix Mesosome Actin filaments Chromosome (DNA) Pilus Inclusion body Flagellum 5

6 4.3 Prokaryotic Profiles 6

7 External Structures Appendages Two major groups of appendages: Motility flagella and axial filaments (periplasmic flagella) Attachment or channels fimbriae and pili Glycocalyx surface coating 7

8 3 parts: Flagella Filament long, thin, helical structure composed of protein flagellin Hook curved sheath Basal body stack of rings firmly anchored in cell wall Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Filament Hook Outer membrane L ring Cell wall Basal body Rod Rings Periplasmic space Rings Cell membrane 8 (a) 22 nm (b)

9 Rotates 360 o Flagella Functions in motility of cell through environment Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. (a) (c) (b) 9

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11 Flagellar Arrangements Monotrichous single flagellum at one end Lophotrichous small bunches emerging from the same site Amphitrichous flagella at both ends of cell Peritrichous flagella dispersed over surface of cell 11 11

12 Flagellar Responses Guide bacteria in a direction in response to external stimulus: Chemical stimuli chemotaxis; positive and negative Light stimuli phototaxis Signal sets flagella into motion clockwise or counterclockwise: Counterclockwise results in smooth linear direction run Clockwise tumbles Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Key Tumble (T) Run (R) Tumble (T) T T T T R (a) No attractant or repellent R (b) Gradient of attractant concentration 12

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14 Periplasmic Flagella Internal flagella, enclosed in the space between the outer sheath and the cell wall peptidoglycan Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. (a) PF PC OS Outer sheath (OS) Protoplasmic cylinder (PC) Produce cellular motility by contracting and imparting twisting or flexing motion (b) Periplasmic flagella (PF) Cell membrane Peptidoglycan 14

15 Fimbriae Fine, proteinaceous, hairlike bristles emerging from the cell surface Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Function in adhesion to other cells and surfaces (a) Eye of Science/Photo Researchers, Inc. E. coli cells G Intestinal microvilli Dr. S. Knutton from D.R. Lloyd and S. Knutton, Infection and Immunity, January 1987, p ASM (b) 15

16 Pili Rigid tubular structure made of pilin protein Found only in gram-negative cells Function to join bacterial cells for partial DNA transfer called conjugation Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Fimbriae Pili 16 L. Caro/SPL/Photo Researchers, Inc.

17 Glycocalyx Coating of molecules external to the cell wall, made of sugars and/or proteins Two types: 1. Slime layer - loosely organized and attached 2. Capsule - highly organized, tightly attached Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Slime layer (a) (b) Capsule 17

18 Functions of the Glycocalyx Protect cells from dehydration and nutrient loss Inhibit killing by white blood cells by phagocytosis, contributing to pathogenicity Attachment - formation of biofilms Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Colony without a capsule Colonies with a capsule Cell body Capsule (a) Kathy Park Talaro (b) John D. Cunningham/Visuals Unlimited 18 18

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20 Biofilm on a catheter Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Catheter surface Fungal cells Staphylococci Janice Carr/CDC 20

21 The Cell Envelope External covering outside the cytoplasm Composed of two basic layers: Cell wall and cell membrane Maintains cell integrity Two different groups of bacteria demonstrated by Gram stain: Gram-positive bacteria: thick cell wall composed primarily of peptidoglycan and cell membrane Gram-negative bacteria: outer cell membrane, thin peptidoglycan layer, and cell membrane 21

22 Tetrapeptide Structure of Cell Walls Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Determines cell shape, prevents lysis due to changing osmotic pressures Peptidoglycan is the primary component: Unique macromolecule composed of a repeating framework of long glycan chains cross-linked by short peptide fragments (a) The peptidoglycan of a cell wall is a huge, 3-dimensional lattice work that is actually one giant molecule to surround and support the cell. (b) This shows the molecular pattern of peptidoglycan. It has alternating glycans (NAG and NAM) bound together in long strands. The NAG stands for N-acetyl glucosamine, and the NAM stands for N-acetyl muramic acid. Adjacent muramic acid molecules on parallel chains are bound by a cross-linkage of peptides (green spheres) (c) An enlarged view of the links between the NAM molecules. Tetrapeptide chains branching off the muramic acids connect by amino acid Interbridges. The amino acids in the interbridge can vary or may be lacking entirely. It is this linkage that provides rigid yet flexible support to the cell. NAG O H 3 C C C CH 2 OH O NAM O H L alanine NH C D glutamate O O NAG NAG H 3 C CH 2 OH O NAM O CH 3 CH 3 O C C H L alanine NH C D glutamate L lysine O O NAG L lysine D alanine glycine glycine glycine glycine glycine D alanine 22 Interbridge

23 Tetrapeptide Structure of Cell Walls Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. CH 2 OH CH 2 OH NAG O O NAM O O NAG NAG O O NAM O O NAG H 3 C C H NH H 3 C C H NH C C O C C O CH 3 CH 3 L alanine (a) The peptidoglycan of a cell wall is a huge, 3-dimensional lattice work that is actually one giant molecule to surround and support the cell. L alanine D glutamate L lysine D alanine glycine glycine glycine glycine glycine D glutamate L lysine D alanine Interbridge (b) This shows the molecular pattern of peptidoglycan. It has alternating glycans (NAG and NAM) bound together in long strands. The NAG stands for N-acetyl glucosamine, and the NAM stands for N-acetyl muramic acid. Adjacent muramic acid molecules on parallel chains are bound by a cross-linkage of peptides (green spheres) (c) An enlarged view of the links between the NAM molecules. Tetrapeptide chains branching off the muramic acids connect by amino acid Interbridges. The amino acids in the interbridge can vary or may be lacking entirely. It is this linkage that provides rigid yet flexible support to the cell. 23

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25 Gram-Positive Cell Wall nm thick peptidoglycan Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Includes teichoic acid and lipoteichoic acid: function in cell wall maintenance and enlargement during cell division; move cations across the cell envelope; stimulate a specific immune response Peptidoglycan Cell membrane Gram (+) Some cells have a periplasmic space, between the cell membrane and cell wall (a) S.C Holt/Biological Photo Service Cell membrane Cell wall (peptidoglycan) 25

26 Gram-Negative Cell Wall Inner and outer membranes and periplasmic space between them contains a thin peptidoglycan layer Outer membrane contains lipopolysaccharides (LPS) Lipid portion (endotoxin) may become toxic when released during infections May function as receptors and blocking immune response Contain porin proteins in upper layer regulate molecules entering and leaving cell Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Cell membrane Peptidoglycan Outer membrane Gram ( ) T. J. Beveridge/Biological Photo Service Cell membrane Periplasmic space Peptidoglycan Cell wall Outer membrane (b) 26

27 Envelope Structures of Gram-Positive and Gram-Negative Bacterial Cell Walls Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Lipoteichoic acid Wall Teichoic acid Lipopolysaccharides Porin proteins Phospholipids Outer membrane layer Peptidoglycan Periplasmic space Cell membrane Membrane proteins Lipoproteins Periplasmic space Membrane protein Peptidoglycan Teichoic acid Phospholipid Membrane proteins Lipopolysaccharide Porin Lipoprotein 27

28 Comparison of Gram-Positive and Gram-Negative Cell Walls 28

29 The Gram Stain Differential stain that distinguishes cells with a gram-positive cell wall from those with a gramnegative cell wall Gram-positive - retain crystal violet and stain purple Gram-negative - lose crystal violet and stain red from safranin counterstain Important basis of bacterial classification and identification Practical aid in diagnosing infection and guiding drug treatment 29

30 The Gram Stain Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Microscopic Appearance of Cell Chemical Reaction in Cell (very magnified view) Step 1 Crystal Violet (primary dye) Gram (+) Gram ( ) Gram (+) Gram ( ) Both cell walls stain with the dye. 2 Gram siodine (mordant) Dye crystals trapped in cell No effect of iodine 3 Alcohol (decolorizer) Crystals remain in cell. Outer wall is weakened; cell loses dye. 4 Safranin (red dye counterstain) Red dye has no effect. Red dye stains the colorless cell. 30

31 Nontypical Cell Walls Some bacterial groups lack typical cell wall structure, i.e., Mycobacterium and Nocardia Gram-positive cell wall structure with lipid mycolic acid (cord factor) Pathogenicity and high degree of resistance to certain chemicals and dyes Basis for acid-fast stain used for diagnosis of infections caused by these microorganisms Some have no cell wall, i.e., Mycoplasma Cell wall is stabilized by sterols Pleomorphic 31

32 Cell Membrane Structure Phospholipid bilayer with embedded proteins fluid mosaic model Functions in: Providing site for energy reactions, nutrient processing, and synthesis Passage of nutrients into the cell and discharge of wastes Cell membrane is selectively permeable Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Glycolipid Carbohydrate receptor Integral protein Integral protein Phospholipid Peripheral protein 32

33 Inside the Bacterial Cell Cell cytoplasm: Dense gelatinous solution of sugars, amino acids, and salts 70-80% water Serves as solvent for materials used in all cell functions 33

34 Nucleoid Chromosome Single, circular, doublestranded DNA molecule that contains all the genetic information required by a cell Plasmids Free small circular, doublestranded DNA Not essential to bacterial growth and metabolism Used in genetic engineering - readily manipulated and transferred from cell to cell Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Courtesy of Michael J. Daly 34

35 Bacterial Ribosome Ribosomes Made of 60% ribosomal RNA and 40% protein Consist of two subunits: large and small Prokaryotic differ from eukaryotic ribosomes in size and number of proteins Site of protein synthesis Found in all cells Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Large subunit (50S) Ribosome (70S) Small subunit (30S) 35

36 Bacterial Internal Structures Inclusions and granules Intracellular storage bodies Vary in size, number, and content Bacterial cell can use them when environmental sources are depleted Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. MP (a) (b) D. Balkwill and D. Maratea 36

37 Bacterial Internal Structures Cytoskeleton Many bacteria possess an internal network of protein polymers that is closely associated with the cell wall Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Actin filaments 37 Rut CARBALLIDO-LOPEZ/I.N.R.A. Jouy-en-Josas, Laboratoire de Génétique Microbienne

38 Bacterial Internal Structures Endospores Inert, resting, cells produced by some G+ genera: Clostridium, Bacillus, and Sporosarcina Have a 2-phase life cycle: Vegetative cell metabolically active and growing Endospore when exposed to adverse environmental conditions; capable of high resistance and very longterm survival Sporulation - formation of endospores Hardiest of all life forms Withstands extremes in heat, drying, freezing, radiation, and chemicals Not a means of reproduction 38 Germination - return to vegetative growth

39 Sporulation cycle Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Exosporium Core Spore coats 1 Vegetative cell Cortex Chromosome SJ Jones, CJ Paredes, B Tracy, N Cheng, R Sillers, RS Senger, ET Papoutsakis, "The transcriptional program underlying the physiology of clostridial sporulation," Genome Biol., :R114 Cell wall Cell membrane 2 9 Germination spore swells and releases vegetative cell. Chromosome is duplicated and separated. 8 Free spore is released with the loss of the sporangium. Exosporium Spore coat Cortex Core Sporulation Cycle Forespore 3 Cell is septated into a sporangium and forespore. Sporangium 7 4 Mature endospore Sporangium engulfs forespore for further development. 5 6 Cortex and outer coat layers are deposited. Sporangium begins to actively synthesize spore layers around forespore. 39 Cortex Early spore

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41 Endospores Dehydrated, metabolically inactive Thick coat Longevity verges on immortality, 250 million years Resistant to ordinary cleaning methods and boiling Pressurized steam at 120 o C for minutes will destroy 41

42 Bacterial Shapes, Arrangements, and Sizes Vary in shape, size, and arrangement but typically described by one of three basic shapes: Coccus spherical Bacillus rod Coccobacillus very short and plump Vibrio gently curved Spirillum helical, comma, twisted rod, Spirochete spring-like 42

43 Common bacterial shapes Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. (a) Coccus (b) Rod/Bacillus (c) Vibrio Janice Carr/CDC Janice Carr/CDC From Jacob S. Teppema, In vivo adherence and colonization of Vibrio cholerae strains that differ in hemagglutinating activity and motility, Journal of Infection and Immunity, 55(9): , Sept Reprinted by permission of American Society for Microbiology (d) Spirillum (e) Spirochete (f) Branching filaments Photo by De Wood. Digital colorization by Chris Pooley VEM/Photo Researchers, Inc. Science VU/Frederick Mertz/Visuals Unlimited Key to Micrographs (a) Micrococcus luteus (22,000 ) (b) Legionella pneumophila (6500 ) (c) Vibrio cholerae (13,000 ) (d) Aquaspirillum (7,500 ) (e) Spirochetes on a filter (14,000 ) (f) Streptomyces species (6500 ) 43

44 Variation in cell shape and size within a single species Pleomorphism Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Metachromatic granules Some species are noted for their pleomorphism Palisades arrangement Metachromatic granules A.M. Siegelman/Visuals Unlimited Palisades arrangement 44

45 Bacterial Arrangements Arrangement of cells is dependent on pattern of division and how cells remain attached after division: Cocci: Singles Diplococci in pairs Tetrads groups of four Irregular clusters Chains Cubical packets (sarcina) Bacilli: Diplobacilli Chains Palisades Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. (a) Division in one plane (b) Division in two perpendicular planes (c) Division in several planes Staphylococci and Micrococci Diplococci (two cells) Tetrad (cocci in packets of four) Irregular clusters (number of cells varies) Streptococci (variable number of cocci in chains) Sarcina (packet of 8 64 cells) 45

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47 Classification Systems for Prokaryotes 1. Microscopic morphology 2. Macroscopic morphology colony appearance 3. Bacterial physiology 4. Serological analysis 5. Genetic and molecular analysis 47

48 Bacterial Taxonomy Based on Bergey s Manual Bergey s Manual of Determinative Bacteriology five volume resource covering all known prokaryotes Classification based on genetic information phylogenetic Two domains: Archaea and Bacteria Five major subgroups with 25 different phyla 48

49 Bergey s Classification Scheme 49

50 Major Taxonomic Groups of Prokaryotes Domain Archaea primitive, adapted to extreme habitats and modes of nutrition Domain Bacteria: Phylum Proteobacteria Gram-negative cell walls Phylum Firmicutes mainly Gram-positive with low G + C content Phylum Actinobacteria Gram-positive with high G + C content 50

51 Universal phylogenetic tree Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Bacteria Heliobacterium Archaea Zea (corn) Eukarya 51

52 Diagnostic Scheme for Medical Use Uses phenotypic qualities in identification Restricted to bacterial disease agents Divides bacteria based on cell wall structure, shape, arrangement, and physiological traits 52

53 Medically Important Bacteria 53

54 Species and Subspecies Species a collection of bacterial cells which share an overall similar pattern of traits in contrast to other bacteria whose pattern differs significantly Strain or variety a culture derived from a single parent that differs in structure or metabolism from other cultures of that species (biovars, morphovars) Type a subspecies that can show differences in antigenic makeup (serotype or serovar), susceptibility to bacterial viruses (phage type) and in pathogenicity (pathotype) 54

55 Prokaryotes with Unusual Characteristics Free-living nonpathogenic bacteria Photosynthetic bacteria use photosynthesis, can synthesize required nutrients from inorganic compounds Cyanobacteria (blue-green algae) Green and purple sulfur bacteria Gliding, fruiting bacteria 55

56 Cyanobacteria (blue-green algae) Gram-negative cell walls Extensive thylakoids with photosynthetic chlorophyll pigments and gas inclusions Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 20 microns (a) (a2) (a3) Stromatolite (b) 10 mm (c) Thylakoid membranes 56 (d)

57 Green and Purple Sulfur Bacteria Photosynthetic Contain photosynthetic pigment bacteriochlorophyll Do not give off oxygen as a product of photosynthesis 57

58 Gliding and Fruiting Bacteria Gram-negative Glide over moist surfaces Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 58 GBF-German Research Center for Biotechnology, Braunschweig, Germany

59 Unusual Forms of Medically Significant Bacteria Obligate intracellular parasites Rickettsias Very tiny, gram-negative bacteria Most are pathogens Obligate intracellular pathogens Cannot survive or multiply outside of a host cell Rickettsia rickettisii Rocky Mountain spotted fever Nucleus Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Rickettsial cells Baca and Paretsky, Microbiological Reviews, 47(20);133, fig. 16, June 1983 ASM Vacuole 59

60 Unusual Forms of Medically Significant Bacteria Chlamydias Tiny Obligate intracellular parasites Not transmitted by arthropods Chlamydia trachomatis severe eye infection and one of the most common sexually transmitted diseases Chlamydia pneumoniae lung infections 60

61 Archaea: The Other Prokaryotes Constitute third Domain Archaea More closely related to Eukarya than to Bacteria Contain unique genetic sequences in their rrna Have unique membrane lipids and cell walls 61

62 Archaea Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Live in the most extreme habitats in nature, extremophiles Adapted to heat, salt, acid ph, pressure, and atmosphere Includes: methane producers, hyperthermophiles, extreme halophiles, and sulfur reducers (a) 5 mm 62 (b) Dr. Mike Dyall-Smith, University of Melbourne