MIcrobiology Module 2

  1. Shapes of Some Prokaryotes (Slide 2)
    Shapes: Cocci (Spherical), Bacilli (Rod-like), Vibrios (Comma-shaped), Spirilla (Spirals), or Spirochete (Cork-screw)

    Cell can stick together after dividing to form pairs (Diplo), tetrads, chains (strepto), grape-like clusters (Staphylo-), filaments

    Size range from 0.05 um diameter to >500um

    E.Coli is a typical bacillus at 1X 3 um
  2. Parts of bacterial envelope of Gram Positive vs. Gram Negative bacteria (Slide 4)
    Envelope contains plasma membrane (PM or CM), cell wall made of murein (type of peptidoglycan) and sometimes an S-layer

    Gram (+) Positive have CM and cell

    Gram (-) have CM but have thinner cell wall and another structure (OM) and the space between the 2 membranes (periplasmic space)

    OM may be considered part of cell wall
  3. The Bacterial Plasma Membrane ( Slide 5)
    Basic structure of CM is phospholipid bilayer w/fatty acids face inward and glycerol phosphates point outward toward cytoplasm or outside of cell

    Hopanoids (related to cholesterol) act for fluidity buffers. Interact w/fatty acids within the membrane

    • Lipid composition depend on microbe and its environment
    • Fluidity determined by level of saturation of FA-at a given temperature the greater the number of double bonds (unsaturation) the more fluid the membrane
  4. Bacterial Cell Wall: Structure of Murein (Slide 6)
    Murein: Consists of layers, each layer comprised of alternating NAG and NAM (lysozyme-sensitive linkage)

    Each NAM has an attached short peptide that may be X-linked to another NAM short peptide on an adjacent layer (via transpeptidase)

    Gram Positive bacteria: X-link of D-Ala is to gly interbridge, then bridge is X-linked to L-Lys. Walls have many layers (20-80nm) (10-40 layers)

    Gram Negative bacteria: NO interbridges, Use DAP (Diaminopimelic Acid) linked to D-Ala and have fewer layers (2-7nm)

    In Gram Positive: Crystal violet binds to CM. Ethanol hits cell wall and causes all layers to collapse. Crystal violet gets stuck in collapsed layers

    Gram negative allows for ethanol to get to CM and wash out crystal violet
  5. Gram Positive Cell Wall Features (Slide 7)
    Teichoic Acid are covalently attached to cell wall (or lipoteichoic acids attached to CM)

    Teichoic acids give negative charge to cell wall, but function is unclear

    All cell walls of Gram + or - microbes protect cells from swelling excessively in hypotonic environments
  6. Gram Negative Outer Membrane (Slide 8)
    Inner leaflet of OM is continuation of CM

    Lipopolysaccharide (LPS) is major component of outer leaflet of OM

    LPS is comprised of lipid A, core polysaccharide and O antigen

    Lipid A (Endotoxin) is responsible for septic shock associated w/ Gram (-) bacterial infections

    OM much more permeable to solutes than PM due to presence of porins
  7. S-Layers (Slide 9)
    Found in some bacteria (Gram + and -) and archaea (can sometime take place of cell walls)

    Self assembling, crystalline structures of a single protein of glycoprotein

    Model systems for studies of nanotechnology

    Campylobacter use them to shield cells from immune system
  8. Capsules and Slime Layers (Slide 10)
    Extracellular structures composed of Hi MW polysaccharides or polypeptide

    Only found on some microbe. Used for attachment, protection from immune system or for protection against dessication

    Important virulence factors

    Slime layer part of gliding non-directed) motility in some species

    Glycocalyx refers to region of slime found between organisms
  9. Archaeal Envelopes (Slide 11)
    Closely related to Gram Positive (+) bacteria

    Cell walls are non-murein always. Variable in structure

    CMs contain branched lipids derived from isoprene, that are ether-linked to glycerol phosphate, no LPS in Gram Negative (-) Archaea

    Hyperthermophiles contain C40 monolayers (stable at hi temp.) other archaea contain lipid bilayers or combinations, depending on environment
  10. Prokaryotic Appendages (Slide 12)
    Flagella are most important. Most common form of prokaryotic directed motion. Used for chemotaxis

    Pili (Fimbriae) are used mainly for adhesion. Buy may be used along w/slime production to create a type of twitching (non-directed) motility

    Types and numbers of flagella and pili are used in classification
  11. Classification based on Flagella (Slide 13)
    Monotrichous Polar Flagellation: One flagella at end of cell

    Lophotrichoud Flagellation: Tuft of flagella at one end of cell

    Peritrichous Flagellation: Flagella all around cell
  12. Structure of Flagella (Slide 14)
    Semi-rigid, multi-component structures. Found in both Gram positive and negative cells.

    Prokaryotic and eukaryotic flagella differ

    In Prokaryotes: Flagella are anchored by rings assembled in each layer of the cell envelope (Basal Body)

    Flagella are assembled from inside to outside via hollow internal tube-like structure

    Filament is made of flagellin subunit (H antigens used for classification)
  13. How Flagellated Cells Move (Slide 15)
    Each flagella is semi rigid and movement occurs by turning whole structure (propeller mechanism)

    Torque is generated by movement of H+ into cell using Mot proteins

    Rotations of flagella can be either clockwise (backward or tumbles) or counterclockwise (forward) and can be reversed by Fli proteins

    Movement is in response to conc. of repellents or attractancts in environment (chemotaxis), pH taxis, phototaxis
  14. Endoflagella of spirochetes (Slide 16)
    Axial filament/fibrils wraps around cell w/in periplasmic space

    When flagella rotates, spirochetes move forward in corkscrew motion, allowing them to invade into tissues to cause disease
  15. Pili/Fimbriae (Slide 17)
    Short, filamentous structures (usually gram - microbes) used for attachments to substrata or to other microbes in conugation (Sex pili)

    Some involved in non-directed crawling motion called twitching motility but typically not involved in locomotion

    Filaments are made of proteins called pilins
  16. Nucleoid (Slide 19)
    Not rigid structure, area where DNA is found

    Prokaryotes typically have singular chromosome but no nuclear membrane

    Chromosome is condensed by proteins in special area (Nucleoid)

    Transcription and translation occur simultaneously
  17. Plasmids (Slide 20)
    Common extra-chromosomal circular DNAs that replicate autonomously in cytoplasm

    Size varies from 1kn to over 1000kb

    Copy number varies from 1 to >1000

    Plasmids have auxillary (non-essential) functions
  18. Prokaryotic Ribosomes (Slide 21)
    Site of translation. Prokaryotic cytoplasm is packed with ribosomes. contain 10-20X more ribosomes than eukaryotes

    Prokaryotic ribosomes (70S) consist of 2 subunits, are functionally similar but structurally diff. than eukaryotic ribosomes (80S) and are differentially inhibited by antibiotics

    Eukaryotic cells contain prokaryotic-type ribosomes in mitochondria and chloroplasts
  19. Prokaryotic Cytoskeleton (Slide 22)
    ALL prokaryotes have cytoskeletal elements analogous to those found in eukaryotes

    Functions: Cell division, protein localization and cell shape determination

    Mbl (Similar to actin)
  20. Gas Vesicles (Slide 23)
    Found in bacteria and archaea

    totally impermeable to water, but permeable to gases

    Purpose if for buoyancy ( NOT STORAGE)

    Usually found in photosynthetic organisms

    Vary in number from several to several hundred and vary in size
  21. Cell In
    Membrane delineated structures with specific functions

    Include: storage granules, inclusion bodies, carboxysomes, magnetosomes

    Most are separated from cytoplasm by membrane
  22. PHA (polyhydroxyalkanoates) (Slide 25)
    Commonly formed and used for storage of excess organic fuel molecules

    PHB (Poly-B-hydroxybuterate) is most common PHA

    Glycogen inclusions also occur

    PHAs are enclosed in lipid membrane to form storage vesicles

    Other types of molecules (phosphate, sulfur) are also stored in granules
  23. Magnetosomes (Slide 26)
    -some: Refer to a membrane delineated structrue

    Particles containing Fe(3)O(4) or Fe(3)S($=4). Essentially contains iron

    Work as magnet and allow cells to align along earth's magnetic pole

    Surrounded by invaginations of CM

    Carboxysomes contain high levels of enzymes used to fix CO2 into carbohydrate

    Enterosomes (intestinal) contain high levels of specific enzymes involved in special metabolic pathways in gut bacteria
  24. Endospores (Slide 27)
    Specific structures found in few microbes. Critically important.

    Location: Terminal, subterminal or central, characteristic of the species that make endospores

    Endosporulation occurs when times get tough and cell cannot survive (Cell does not survive endospore formation)

    Endospores resistant to dessication, heat, radiation, and chemicals and may survive for centuries

    Endospores contain high levels of Calcium, dipicolinic acid, and SASPs (small, acid-soluble proteins) that bind to and protect DNA. Very low water content and are metabolically inactive.
Card Set
MIcrobiology Module 2
Module 2