10. Bacterial Appendages and Secretion Systems

• polysaccharide + protein hydrophilic polymer
• repels viruses and hydrophobic anti-microbial compounds
• attaches to host tissues
• protects against phagocytosis and dessication
• participates in biofilm formation

• 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

• 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

• 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

• 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

• 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

• 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
• 

• 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

controlling the frequency of runs and tumbles to move toward attractants or away from repellents

• used for:
• twitching motility across surfaces
• bacterial conjugation
• adherence to host tissues

• 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

bacteria glide over surfaces by extending a sticky pilus and then retracting it to pull the cell body forward

• 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

• 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

• related to Type IV pili
• virulence proteins are exported into the periplasm by Sec system then secreted into extracellular space

• 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

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