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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
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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
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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
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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
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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
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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
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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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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
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chemotaxis
controlling the frequency of runs and tumbles to move toward attractants or away from repellents
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pili or fimbriae
- used for:
- twitching motility across surfaces
- bacterial conjugation
- adherence to host tissues
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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
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Pilus retraction
bacteria glide over surfaces by extending a sticky pilus and then retracting it to pull the cell body forward
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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
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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
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Type II secretion systems
- related to Type IV pili
- virulence proteins are exported into the periplasm by Sec system then secreted into extracellular space
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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
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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
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