10. Bacterial Appendages and Secretion Systems

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  1. capsules
    • polysaccharide + protein hydrophilic polymer
    • repels viruses and hydrophobic anti-microbial compounds
    • attaches to host tissues
    • protects against phagocytosis and dessication
    • participates in biofilm formation
  2. bacterial flagella
    • 14-20 nm wide, up to 10um long
    • helical polymer of flagellin protein
    • enables cell to swim through liquid
    • anchored in cell membrane by a rotary motor
    • flagellar rotation acts like a boat propeller
  3. Tethered E.coli experiment
    • end of flagellum attached to slide using an antibody
    • as flagellar motor turns, see it as rotation of the cell body
    • motor is driven by proton gradient across the cytoplasmic membrane
  4. parts of the base
    • MS ring - anchor in the cytoplasmic membrane
    • P ring - anchor in PG
    • L ring - anchor in outer membrane
    • C ring - proteins associated with inner face of cytoplasmic membrane
  5. How do flagella move and what determines direction of rotation?
    • MotA and MotB - stator, don't rotate
    • other proteins - rotor, do rotate
    • MotB- bound to PG layer and MotA
    • protons pass through a channel in the MotA protein - causes push on FliG
    • FliM and FliN determine direction rotor turns
  6. In what direction are the flagella built?
    • base is built from inside to outside
    • flagellin monomers are added at the far end of the filament, under the cap
    • flagellar components exit through a channel in the axis of the filament, monomers assemble under the cap
    • flagella are lost by mechanical shearing
  7. transcriptional cascade of genes for flagellar proteins
    • early class II genes:
    • σ factor - transcription factor that promotes expression of the class III genes
    • FlgM, the anti-σ factor - a protein that binds to the σ factor and blocks its action

    • when body-hook complex is complete, FlgM is exported via the flagellar - morphological checkpoint
    • channel, allowing the σ factor to promote transcription of the flagellin
    • and cap export through the flagellar channel is powered by an ATPase in the C ring
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  8. flagella rotation direction
    • CCW- run, multiple flagella form bundle and work together to propel forward
    • CW - tumble, individual filaments are pushed out of the bundle and stop working together
  9. chemotaxis
    controlling the frequency of runs and tumbles to move toward attractants or away from repellents
  10. pili or fimbriae
    • used for:
    • twitching motility across surfaces
    • bacterial conjugation
    • adherence to host tissues
  11. type IV pili
    • extend and retract, are used for surface motility
    • pilus proteins exported into cytoplasmic membrane using Sec system
    • assembled pilus travels through OM in channel made of PilQ subunits
    • pilin subunits hydrophobic - stay attached to IM until assembly
    • subunits added at end near cytoplasmic membrane
    • PilF- powers pilus assembly
    • PilT- powers pilus retraction
  12. Pilus retraction
    bacteria glide over surfaces by extending a sticky pilus and then retracting it to pull the cell body forward
  13. PAP pili - Type I pilus
    • confer strong adherence, not for secretion or motility
    • subunits transferred to the periplasm through Sec pathway
    • they bind to chaperone PapD that prevents degradation and promotes pilus assembly by PapC
    • PapH - termination subunit
    • PapA - main pilus subunit
  14. Type I secretion systems
    • related to ABC transporters
    • substrate is pumped directly out of the cell into the extracellular space, without entering periplasm - makes channel through periplasm
    • substrates include proteins and antibiotics
  15. Type II secretion systems
    • related to Type IV pili
    • virulence proteins are exported into the periplasm by Sec system then secreted into extracellular space
  16. Type III secretion systems
    • related to the flagellar hook-basal body complex
    • virulence proteins are secreted directly from the bacterial cytoplasm into the cytoplasm of the host cell
    • needle structure punctures host cell membrane
  17. Type IV secretion systems
    related to conjugation systems

    • 1) A. tumefaciens - T-DNA complex (protein + DNA) exported directly into the host cytoplasm
    • T pilus is used for attachment

    • 2) B. pertussis - toxin is secreted to the extracellular space
    • then it is exported to periplasm through the Sec system before being sent across the OM
Card Set:
10. Bacterial Appendages and Secretion Systems
2011-10-05 03:31:09
PMB 112 midterm1

general microbiology midterm 1
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