Prokaryotic Profiles The Bacteria and Archaea. Chapter 3

Transcription

1 Prokaryotic Profiles The Bacteria and Archaea Chapter 3

2 Prokaryotic Form and Function Prokaryotes can be distinguished from eukaryotes by: the way their DNA is packaged (lack of nucleus and histones) the makeup of their cell wall (peptidoglycan and other unique chemicals) their internal structure (lack of membrane-bounded organelles)

3 The Structure of the Prokaryotic Cell All bacterial cells possess: - a cell membrane - cytoplasm - ribosomes - a cytoskeleton - one (or a few) chromosome(s) Most bacterial cells possess: - a cell wall - a surface coating called a glycocalyx

4 The Structure of the Prokaryotic Cell Some but not all bacterial cells possess: - flagella, pili, and fimbriae - an outer membrane - plasmids - inclusions - Endospores (or simply spores) - intracellular membranes

5 Prokaryotic Cell Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. In All Bacteria Cell (cytoplasmic) membrane A thin sheet of lipid and protein that surrounds the cytoplasm and controls the flow of materials into and out of the cell pool. Bacterial chromosome or nucleoid Composed of condensed DNA molecules. DNA directs all genetics and heredity of the cell and codes for all proteins. Ribosomes Tiny particles composed of protein and RNA that are the sites of protein synthesis. Actin cytoskeleton Long fibers of proteins that encircle the cell just inside the cell membrane and contribute to the shape of the cell. Cytoplasm Water-based solution filling the entire cell. In Some Bacteria Fimbriae Fine, hairlike bristles extending from the cell surface that help in adhesion to other cells and surfaces. uter membrane Extra membrane similar to cell membrane but also containing popolysaccharide. Controls flow of materials, and portions of it are toxic to mammals when released. Cell wall A semirigid casing that provides structural support and shape for the cell. Pilus An elongated, hollow appendage used in the transfer of DNA to other cells. Capsule (tan coating) A coating or layer of molecules external to the cell wall. It serves protective, adhesive, and receptor functions. It may fit tightly or be very loose and diffuse. Also called slime layer and glycocalyx. Inclusion/Granule Stored nutrients such as fat, phosphate, or glycogen deposited in dense crystals or particles that can be tapped into when needed. Plasmid Double-stranded DNA circle containing extra genes. Flagellum Specialized appendage attached to the cell by a basal body that holds a long, rotating filament. The movement pushes the cell forward and provides motility. In Some Bacteria (not shown) Endospore (not shown) Dormant body formed within some bacteria that allows for their survival in adverse conditions. Intracellular membranes (not shown) Science Photo Library RF/Getty Images

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7 Prokaryotic Shapes and Arrangements Most prokaryotes exist as unicellular organism sometimes they can act as a group colonies or in biofilms n average, prokaryotic cells are 1 μm (microns can range from μm ( nanobes ) to 750 μm Cells of one species may vary in shape and size this is pleomorphism caused by variations in cell wall structure

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9 Arrangement of Cocci Resulting from Different Planes of Cell Division Division in one plane Diplococcus (two cells) Streptococcus (variable number of coci in chains) Division in two perpendicular planes Tetrad (cocci in packets off our) Sarcina (packet of 8 64 cells) Division in several planes Irregular clusters (number of cells varies) (a) (b) Staphylococci and Micrococci` (c)

10 External Structures Flagella The Prokaryotic Propellers Bacterial locomotion Three distinct parts Filament Comprised of many proteins Basal body Rod Hook Rings uter membrane Cellwall Cell membrane 360 o rotation (a) Noreen R. Francis, Gina E. Sosinsky, Dennis Thomas and David J. DeRosier, Isolation, Characterization and Structure of Bacterial Flagellar Motors Containing the Switch Complex, Journal of Molecular Biology, Vol 235, Issue 4, 27 January 1994, Pages (b)

11 Flagellar Arrangements Monotrichous: single flagellum Lophotrichous: small bunches or tufts of flagella Amphitrichous: flagella at both poles of the cell Peritrichous: flagella dispersed randomly over the surface of the cell

12 Bacterial Movement Bacteria move in response to chemical signals (chemotaxis) Receptors bind extracellular molecules, which triggers flagellum to rotate Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Straight Tumble (a) General motility of a singular flagellum Runs: smooth linear movement toward a stimulus Tumbles: flagellar rotation reverses, causing the cell to stop and change its course Straight (b) Peritrichous motility Tumble

13 Prokaryotic Appendages Fimbriae: used for attachment Pili: used for attachment and genetic exchange during conjugation Fimbriae Pili

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15 Glycocalyx Composed of polysaccharides, proteins or both Varies in thickness / take on form of slime layer or capsule Used to avoid phagocytosis and for adhesion (biofilms) Surface First colonists rganic surface coating Glycocalyx (a) Glycocalyx slime Cells stick to coating. As cells divide, they form a dense mat bound together by sticky extracellular deposits. Additional microbes are attracted to developing film and create a mature community with complex function. Catheter surface Cell cluster (b) b: Science VU Charles W. Stratton/Visuals Unlimited

16 Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Capsule Bound more tightly to the cell, denser and thicker than a slime layer Visible by negative staining Produces a sticky (mucoid) character to colonies Encapsulated bacterial cells generally have greater pathogenicity Capsule Cellbody (a) (a): John D. Cunningham/Visuals Unlimited; b: Fig 1 from Brett J. Pellock, Max Teplitski, Ryan P. Boinay, W. Dietz Bauer, and Graham C. Walker, A LuxR Homolog Controls Production of Symbiotically Active Extracellular Polysaccharide II by Sinorhizobium meliloti. Journal of Bacteriology, September15, 2002, Vol. 184, No. 18, p Reproduced with permission from American Society for Microbiology. (b)

17 Cell Envelope Lies outside of the cytoplasm Composed of two or three basic layers: cell membrane cell wall outer membrane in some bacteria

18 Peptidoglycan Cell Wall Repeating framework of long glycan (sugar) chains cross-linked by short peptide (protein) fragments Present in most bacteria Provides strength to resist rupturing due to osmotic pressure (a) The peptidoglycan can be seen as a crisscross network pattern similar to a chainlink fence. G M M G G M Glycan chains M M G G M M M (b) It contains alternating glycans (G and M) bound together in long strands. The G stands for N-acetyl glucosamine, and the M stands for N-acetyl muramic acid. G G M Peptide cross-links M G M G M M G M CH 2 H M G CH G 2 H M G H3C C H H3C C H C C Tetrapeptide L alanine L alanine D glutamate D glutamate L lysine L lysine glycine D alanine D alanine glycine glycine glycine glycine G Interbridge (c) A detailed view of the links between the muramic acids. Tetrapeptide chains branching off the muramic acids connect by interbridges also composed of amino acids. It is this linkage that provides rigid yet flexible support to the cell and that may be targeted by drugs like penicillin.

19 Thick peptidoglycan Gram Positive Cell Teichoic acid and lipoteichoic acid ne membrane Wall teichoic acid Lipoteichoic acid Gram-Positive Envelope Peptidoglycan Cell membrane Membrane proteins

20 Thin peptidoglycan Lipopolysaccharide (endotoxin) Gram-Negative Two membranes / outer and inner Lipoproteins Porin proteins Porins Lipopolysaccharides uter membrane layer Phospholipids Peptidoglycan Cell membrane Membrane proteins Periplasmic space Membrane protein Gram Negative Cell

21 The Gram Stain: Developed by Hans Christian Gram (1884) Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Step 1. Crystal violet First, crystal violet is added to the cells in a smear. It stains them all the same purple color. Microscopic Appearance of Cell Gram (+) Gram ( ) Chemical Reaction in Cell Wall (very magnified view) Gram (+) Gram ( ) Both cell walls affix the dye 2. Gram s iodine Then, the mordant, Gram s iodine, is added. This is a stabilizer that causes the dye to form large complexes in the peptidoglycan meshwork of the cell wall. The thicker gram-positive cell walls are able to more firmly trap the large complexes than those of the gram-negative cells. Dye complex trapped in wall No effect of iodine 3. Alcohol Application of alcohol dissolves lipids in the outer membrane and removes the dye from the peptidoglycan layer only in the gram-negative cells. 4. Safranin (red dye) Because gram-negative bacteria are colorless after decolorization, their presence is demonstrated by applying the counterstain safranin in the final step. McGraw-Hill Companies, Inc. Crystals remain in cell wall Red dye masked by violet uter membrane weakened; wall loses dye Red dye stains the colorless cell

22 Acid-Fast Bacteria Mycobacterium sp. and Nocardia sp. Cell wall contain a form of peptidoglycan but also Contain mycolic acid (a wax) Gram-positive staining however Use an acid-fast stain to stain these type of bacteria Key to ID important pathogens causing: tuberculosis leprosy

23 Cell-Wall Deficient Bacteria Cell membrane stabilized by sterols, makes them resistant to lysis i.e. Mycoplasma pneumoniae ther cell-wall deficient types called L forms are linked to infections Mutation or chemical treatment Gram- Positive (a) Cell wall (peptidoglycan) Cell membrane Peptidoglycan lost Protoplast Cell membrane Mutation or chemical treatment uter membrane uter membrane Gram- Negative (b) Peptidoglycan Cell membrane Peptidoglycan lost Spheroplast Cell membrane

24 Lipopolysaccharide Case File Artwork Located in the outermost layer of the outer membrane (M) in gramnegative bacteria Lipid A is the factor which = endotoxin Endotoxins cause fever and systemic shock

25 Cytoplasmic Membrane A lipid bilayer with proteins embedde Case File Artwork bacterial cell membranes contain primarily phospholipids (30% 40% of the membrane mass) and proteins (60% 70% of the membrane mass) Provides a site for metabolic reaction contains enzymes of respiration and ATP synthesis since prokaryotes lack mitochondria Another major action of the cell membrane is to regulate the passage of nutrients into and out of the cell

26 The Cytoplasm Case File Artwork 70-80% water Soluble proteins, salts, carbohydrates Site of nearly all chemical reactions Contains the DNA in the nucleoid

27 Bacterial DNA Case File Artwork DNA of most bacteria exists in the form of a single circular bacterial chromosome DNA is aggregated in a dense area of the cell called the nucleoid Many bacteria contain other, nonessential pieces of DNA called plasmids

28 Prokaryotic Ribosome Two subunits (30S and 50S) Total size is 70S (versus 80S in eukaryotes) 60% rrna and 40% protein Translates mrna into proteins Large subunit (50S) Small subunit (30S) Ribosome (70S)

29 Inclusions or Granules: Storage Bodies Case File Artwork Non-membrane bound granules Usually for storage of nutrients The Cytoskeleton Peptidoglycan layer determines shape of many bacteria thers use protein fibers composed of actin and tubulin to alter cell shape

30 Bacterial Endospores (or simply spore) Dormant bodies Case File Artwork Heat resistance due to calcium and dipicolinic acid content Cortex, spore coats protect against radiation and chemicals Metabolically active vegetative cells can undergo sporulation Sporulation is not a reproductive function for most bacteria When spores of Clostridium sp. are embedded in a wound with dead tissue, they can germinate, grow, and release toxins

31 A Typical Sporulation Cycle in Bacillus Species Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Spore coats 1 Chromosome Vegetative cell begins to be depleted of nutrients. Cortex Chromosome Core of spore Cell wall 9 8 Cell membrane Germination: spore swells and releases vegetative cell. 2 Exosporium Spore coat Cortex Core Frees pore is released with the loss of the sporangium. 3 Forespore Sporangium 4 7 Mature endospore Cortex Chromosome is duplicated and separated. Cell is septated into a sporangium and forespore. Sporangium engulfs forespore for further development. Early spore 6 5 Cortex and outer coat layers are deposited. George Chapman/Visuals Unlimited Sporangium begins to actively synthesize spore layers around forespore.

32 Archaea Prokaryotic microorganisms Many are found in extreme environments (i.e. psychrophiles) Different from members of the domains Bacteria and Eukarya in terms of: cell structure, metabolism, genetics Able to survive in extreme environments / metabolize ammonia, methane, hydrogen! Table 3.2 Comparison of Three Cellular Domains Characteristic Bacteria Archaea Eukarya Cell type Prokaryotic Prokaryotic Eukaryotic Chromosomes Single, or few circular Single, circular Several, linear Types of ribosomes Contains unique ribosomal RNA signature sequences Number of sequences shared with Eukarya Protein synthesis similar to Eukarya 70S S but structure is similar to 80S S + (all) + Presence of peptidoglycan in cell wall + Cell membrane lipids Fatty acids with ester linkages Long-chain, branched hydrocarbons with ether linkages Fatty acids with ester linkages Sterols in membrane (some exceptions) +

33 Classification Systems For differentiating and identifying unknown microbial species i.e. Bergey s Manual of Determinative Bacteriology (phenotypic data) For studying prokaryotic relationships and origins i.e. Bergey s Manual of Systematic Bacteriology (rrna sequencing data)

34 Scientific classification Kingdom: Phylum: Class: Eubacteria Firmicutes Cocci Streptococcus pyogenes S. pyogenes bacteria at 900x magnification. rder: Lactobacillales Family: Streptococcaceae Genus: Species: S. pyogenes Binomial name Streptococcus Streptococcus pyogenes Rosenbach 1884

35 Prokaryotic Classification Systems Case File Artwork Bergey s Manual of Determinative Bacteriology organizes the prokaryotes into four major divisions based on cell wall structure: Gracilicutes: gram-negative cell walls and thus are thin-skinned Firmicutes: gram-positive cell walls that are thick and strong Tenericutes: lack a cell wall and thus are soft Mendosicutes: archaea with unusual cell walls

36 Species and Subspecies in Prokaryotes Case File Artwork Theoretically, a collection of bacterial cells, all of which share an overall similar pattern of traits and 70% 80% of their genes Members of given species can show variations subspecies, strain, or type are terms used to designate bacteria of the same species that have differing characteristics serotype refers to representatives of a species that stimulate a distinct pattern of antibody (serum) responses in their hosts

37 Concept Check Which of the following structures are possessed by some but not all prokaryotes? A. Ribosomes B. A cell membrane C. ne or more chromosomes D. Flagella

38 Concept Check Which of the following bacterial appendages is not used for attachment? A. Slime layer B. Flagellum C. Pilus D. Fimbriae

39 Concept Check The outer membrane contributes an extra barrier in gram-positive bacteria that makes them impervious to some antimicrobial chemicals, so they are generally more difficult to inhibit or kill than are gram-negative bacteria. A. True B. False

40 Concept Check Where in a prokaryotic cell would you find the genetic material? A. Nucleus B. Nucleolus C. Nucleocapsid D. Nucleoid

41 Concept Check Which of the follow do members of the domains Bacteria and Archaea both possess? A. Linear DNA B. A nucleus C. 70S ribosomes D. Fatty acids with ether linkages

42 Concept Check You identify a bacterium as gram-negative using the Gram stain method. In Bergey s Manual of Determinative Bacteriology, this bacterium belongs to the: A. Gracilicutes B. Firmicutes C. Tenericutes D. Mendosicutes