2.4: Microbial Locomotion

Question 1

what is the most common device bacteria use to move

Answer 1

flagellum

Question 2

what are flagellum

Answer 2

• hollow protein filaments
• allow motility

Question 3

flagellum are not visible with brightfield microscope, what are some special techniques needed to view it?

Answer 3

• flagella stain
• dark-field
• TEM (transmission electron microscope)

Question 4

what are the 4 different flagellum types, used for identification

Answer 4

• Monotrichous -single flagellum
• Amphitrichous - flagella at opposite sides
• Lophotrichous -Multiple flagella in a single tuft
• Peritrichous -Flagella distributed around the cell

Question 5

Describe the 3 parts of flagellar structure

Answer 5

1. Filament -Rigid helical protein ~20 um long, composed of identical protein subunits -flagellin
2. Hook-Flexible coupling between filament and basal body
3. Basal Body (motor) -consists of central rod that passes through a series of rings:
   * L-Ring- LPS layer
   * P ring -Peptidoglycan
   * MS ring -Membrane
   * C-ring-cytoplasm (associated with cytoplasmic membrane)

Question 6

what are the 4 rings the basal body passes through (and what layer of envelope they’re found)

Answer 6

• L ring -found in LPS layer (in outer leaflet of outer membrane in gram negatives)
• P ring -Peptidoglycan -middle of periplasm
• MS ring -Membrane (embedded in-integral protein)
• C-ring-cytoplasm (peripheral proteins) associated with membrane by the MS ring of cytoplasm)

they’re rougly named for layer of envelope they’re found in

Question 7

where does the energy to turn the flagella come from

Answer 7

* the proton motive force -gradient of protons (H+) across the cytoplasmic membrane
-high [H+] outside (periplasm is considered outside for gram negative bc of outer membrane presence. outer membrane not a permeability barrier)
-low [H+] inside
* Mot proteins form a channel that allows H+ to move into the cytoplasm, providing the energy needed to turn the flagellum

(mot proteins > think motor)

Question 8

what’s the difference between the movement of eukaryotic flagella and prokaryotic

Answer 8

• eukaryotic flagella moves back and forth like a whip to pull the cell forward
• prokaryotic flagella turns like a propellor to push the cell forward

Question 9

describe the steps of flagellar synthesis

Answer 9

1. The basal body is made first and assembled into the cytoplasmic membrane and periplasm with rod and rings.
2. The hook is added to the basal body
3. flagellin proteins are synthesized in the cytoplasm (to build filament)
   -fed through a 3 nm channel in the flagellum
   -a cap protein adds new flagellin unit to the growing filament, flagellum grows from its tip (as flagellin is added capping protein moves further out)

Question 11

what do all filaments of prokaryotes (fimbriae, flagella etc) have in common?

Answer 11

• grow from the tip
• hollow
• anchored in the cytoplasmic membrane (cuz filaments are protein)

Question 12

what does flagellar rotation and speed depend on the …

Answer 12

depends on the PMF

Question 13

how many times can a flagella rotate per second

Answer 13

up to 300 times per second

Question 14

how many cell lengths does the flagella propel the cell per second

Answer 14

60 cell lengths per second

compared to cell length move very fast

Question 15

describe the pattern of movement by flagella (peritrichous)

Answer 15

• forward motion occurs when all flagella rotate counter-clockwise in a bundle -Run -occurs for a pretty constant period of time
• periodically, the flagella will reverse direction and rotate clockwise-called a tumble.
• this causes the flagella bundle to open, and the cell to reorient in a random new direction
• after a short time, a return to counter-clockwise rotation begins a new run and leads the cell off in its new direction (this run will approx be equivalent to previous run)

random changes in run usually ends with no net movement of population just individual cells moving in like circles

Question 16

what’s different about archaea flagella compared to bacteria flagella

Answer 16

• the rigid filament is thinner than that of bacteria
• there are fewer protein types that form the basal body (and they’re different)
• rotation of the filament is driven by ATP
• while they look similar and have same function, they are NOT related!

Question 17

Archaea flagella are not related to bacteria’s. What is archaea flagella actually related to?

Answer 17

Type IV pilus (used for twitching motility)

Question 18

what is taxis

Answer 18

directed movement in reponse to chemical or physical gradients

Question 19

Chemotaxis

Answer 19

directed movement in response to chemicals, toward an attractant or away from a repellent

Question 20

phototaxis

Answer 20

directed movement in response to light

Question 21

what is aerotaxis

Answer 21

directed movement in response to oxygen

Question 22

osmotaxis

Answer 22

directed movement in reponse to ionic strength

(like osmolarity has to do with concentration of ions in solvent)

Question 23

Hydrotaxis

Answer 23

directed movement in response to water

Question 24

for chemotaxis what are attractants and repellants sensed by

Answer 24

chemoreceptors

Question 25

what happens in the absence of a chemical attractant (in e. coli ex.)? what is this called?

Answer 25

* E. coli will move in a series of runs and tumbles * individual cells will all seem to move in random directions but there will be no net movement of population * called **random walk**

Question 26

when does chemotaxis occur

Answer 26

when there is a concentration gradient

Question 27

explain chemotaxis example of what happens when attractant Glucose is present

Answer 27

* The cell still exhibits series of runs and tumbles * If it senses that the concentration of glucose in an area is increasing: -the tumble is delayed -and the run lasts longer * there is a net movement of cells toward the attractant (even thought some individual cells will be headed in the wrong direction) * this is called biased random walk

Question 28

what happens in chemotaxis when a cell tumbles in wrong direction away from attractant ex: glucose and it senses glucose is conc. decreasing

Answer 28

it will run for the normal amount of time (and not longer but not shorter than normal time).

Question 29

what happens if the cell senses that the concentration of a repellent like hydrogen sulfide is increasing?

Answer 29

If the cell senses the repellent increasing (is going towards the repellent) it will run for the normal amount of time.

Question 30

how is chemotaxis measured? (to find whether bacteria are attracted to or repelled by chemical)

Answer 30

* a capillary tube containing a chemical is inserted into a medium containing motile bacteria (overtime chemical will diffuse through capillary and some bacteria will swim in. -chemical gradient forms surrounding the tip of the capillary -after short time, count the number of bacteria in the capillary and in the medium -if bacteria number is higher in the capillary, the chemical is attractant -if number is lower in capillary, chemical is repellent, but would not be 0 in capillary bc of random walk

Question 31

how does surface motility contrast to flagellar motility

Answer 31

It's considerably slower than flagellar motility and requires surface contact, while flagellar motility allows for movement in liquid.

Question 32

what are the 3 different mechanisms of surface motility? describe them

Answer 32

* **excretion of slime** -loosely bound polysaccharide creates slime layers and some excrete enough slime to move. *** twitching motility** -requires type IV pili, which extent from one pole of the cell, and attach to a surface -ATP hydrolysis causes the pilus to retract dragging the cell forward * **Gliding** -smooth movement across the long axis of the cell without help from external propelling structures

Question 33

what are the 3 sets of proteins are involved in gliding motility? and where they located?

Answer 33

* stationary "gliding motors" -anchored in CM * Helical protein track -in peptidoglycan layer * Extracellular adhesion proteins -on surface of outer membrane

Question 34

how does gliding motility work

Answer 34

* Gliding motors use energy from PMF to rotate, causing displacement of the helical track, moving the adhesion proteins. * causes cell to rotate on its axis and it is propelled forward

Question 35

which domain does gliding motility

Answer 35

Several bacteria (but not archaea)

Question 36

which domains do twitching motility?

Answer 36

* many bacteria and some archaea