week 11 - bacterial motility Flashcards
Structure of bacterial flagellum
- Long thin appendaged
- Helical filament
o Composed of flagellin - Hook
- Basal body
o L ring – anchored in OM
o P ring – anchored in peptidoglycan
o MS and C rings – anchored in CM
o Rod – connects the MS ring and the hook
o Fli proteins - Mot protein complex
energy conservation
- Electrochemical gradients
- Cell biology
o Higher eukaryotes use Na+ electrochemical gradients to create ionic gradients across membranes and drive transport processes, prokaryotes use proton gradients
Need energy to rotate flagella - Not from ATP
- Proton motive force
Flagella rotation
- Rotary motor
- Mot proteins from an ion conducting complex
- Protons move across CM, through Mot complex
o Specific amino acid channel - Proton binding to (or dissociate from) Mot triggers conformational change
- Drives rotation of basal body and rod
- Up to 300 revolutions per sec
- Up to 60 cell lengths per sec
Mot proteins surround whole thing
The change in shape drives rotation
flagella and flagellum distinction
Flagellum
* Modified cilia
* Whips
Flagella
* rotates
arrangements of flagella (on external surface of bacteria)
- Peritrichous
o Flagella at many locations on cell
o Escherichia coli, Salmonella spp
arrangements of flagella (on external surface of bacteria)
- polar
o Flagella at one end of cell
o Pseudomonas spp
MOVEMENT:
Peritrichous flagella
- Runs (moving steadily in one direction)
o Counter clockwise (CCW) rotation
o Helical flagella form a bundle
o Propel bacterium forward - Tumble (reverse direction)
o Clockwise rotation
o Filaments separate
o Random movement - Return to CCW
o Moves in a new direction
MOVEMENT:
Peritrichous flagella
combination of runs and tumbles allows…
advantageous movement
- Directed movement
- Towards something good
- Away from something bad
MOVEMENT:
polar flagella
- Counter clockwise rotation
o Propel bacterium forward (pushing)
CCW forwands
CW backwards
chemotaxis:
peritrichous e.g. e. coli
no attractant present
- Swims randomly
- Runs – forward motion
- Tumbles – changing direction
chemotaxis:
peritrichous e.g. e. coli
attractant bear
- Runs in favourable direction are longer
- Tumbles in unfavourable conditions are more frequent
- Runs longer if conditions improve
- If conditions bad more tumbles
o As trying to find favourable conditions
How are chemical gradients sensed?
- Bacteria sense a temporal gradient
(Time as moving conditions better / worse)
o Sense a change in concentration (over time)
o Receptors – methyl-accepting chemotaxis proteins (MCPs)
o Affects autophoshorylation of cytoplasmic proteins CheA CheY - Repellents increase phosphorylation
o CheY-P interacts with flagella motor
o Induces CW rotation
o Tumbling - Attractants decrease phosphorylation
o CheY (not phosphorylated) cant bind to flagellar motor
o Runs
Receptors dense in the membrane where they are needed
Fimbriae (pili)
- Filamentous
- Composed of protein
- Shorter and thinner than flagella
- Found in both Gram negatives and Gram positives
- Important in:
o Motility
o Adhesion
o Pathogenicity
These act together
Type four pilus (T4P)
- Adhesin at tip (dark blue)
- Filament composed of pilin subunits
- Secretin in outer membrane
- Two ATPases
o Extension (gets longer out of cell)
o Retraction
Repeated units of the same structure
helical structure
energy provided by ATP
PILINS the bit that sticks to surfaces
MOVEMENT ON SURFACES:
twitching motility
- Pilus is extended
o Extension ATPase - Pilus tip attaches to surface
o Anchors bacteria - Pilus is retracted
o Retraction ATPase
Pulls bacteria closer to point of attachment - Cell moves closer to site of adhesion
In context of disease: bacteria moves along surfaces towards each other
