Micr 3240 - Chemotaxis + Motility

Swimming

-in liquid media 3D
-using flagella + pili

Floating

-up or down in water column 3D
-using gas vesicles

Swarming

-on solid media 3D
-using flagella

Gliding

-across solid media 2D
-using adhesins to rotate body CCW

Twitching

-across 2D relative other objects
-using pili

Sliding

-across 2D media
-powered by cell growth elongation

Analyzing Motility

-tether flagella to glass slip with anti-flagella antibodies
-cinematography = see tracks
-tracking microscope = 3D movement
-dark field microscopy = see flagella

Chemotaxis factors

1. high sensitivity
2. wide dynamic range
3. precise adaptation

flagella structure

-Rotor: FliG subunits
-Stator: Mot A+B proteins
-Motor switch: FliM

FliG

forms rotor of flagella

MotAB

stator of flagella
-forms proton pore, connecting exterior to interior

MotB

-stabilizes interaction with peptidoglycan
-holds base of model to cell wall

MotA

important in anchoring

FliM

motor switch
-controls direction of flagella

Tumble direction

CW

Run direction

CCW

random walk

flagella reversal in response to stimuli
-direction after tumble is random
-becomes bias as attractant conc increases

-away from attractant = more tumbles

MCP

short receptor metal-accepting chemotaxis protein
-on flagella

CheA

sensor kinase for chemotaxis

CheW

coupling/transmitting signal

CheY

response regulator

CheZ

Phosphatase

CheR

Methyl Transferase

CheB

Methyl Esterase

Kinase ON

-unoccupied receptors --> more tumbling
1. A autophospho His
2. A phospho Y
3. Y interacts with FliM -> CW direction
4. Z rapidly dephospho Y -> more runs

Kinase OFF

-occupied receptors -> more running
1. Bound MCP causing dimer like structure
2. inactivates A
3. Y not phosphorylated
4. FliM not interacted with -> keeps CCW directions
5. Z dephospho any Y-P

Kinase On reasons

1. non bound attractant receptor
2. bound repellant receptor
3. methylation

Kinase Off reasons

1. bound attractant receptor

sensory adaptation

diminished sensitivity from constant stimulation
-cant sense conc gradient
-receptors must be reset + memory made

CheR/B mechanism

-CheR adds methyl to Glu residues: OFF to ON state
-reverses attractant binding motility
-CheB removes methyl: ON to OFF state (dimer) -> respond to low attractant conc

Smooth Swimming mutants

CheA, W, Y, R

Tumbly Mutants

CheZ and B