2.6 Movement of Bacterial Cells

Question 1

Motility

Answer 1

• the ability to propel your own movement
• nonmotile bacteria can still move around they just can’t control their own movement.
• many bacteria are motile they have different movement strategies/mechanisms have evolved.
• not all bacteria are motile, Yersinia Pestis and cocci

Question 2

Movement using Flagella

Answer 2

• flagella is a large, complex, multi-protein machine that powers bacterial movement.

-The flagellum includes a long, thick filament that acts like a propeller. It is rotated using a motor that is anchored in the cell envelope.

• rotation of the flagellum propels the cell through fluids, enabling the bacterium to swim through fluids.
• flagella can also be used for swarming, coordinated multicellular moments across a solid surface.

Question 3

Different Arrangements of Flagella

Answer 3

• Flagella can be built at different positions along the cell- different bacteria have different numbers/arrangements.
• some bacteria only produce flagella at the cell pole. Either single or multiple, generally at one pole, but some have them at both.
• other bacteria have multiple flagella scattered around cell poles and bodies.

Arrangements: are based on location and tristichous
- Perirtichous - many across pole and body. (e. coli and salmonella)
- Monotrichous or Polar - single or at one pole.
-Lophotrichous -many at one pole
-Amphitrichous - flagella at both poles.
- Atrichous -no flagella

Question 4

Flagella movement: peritichous

Answer 4

• Flagella rotate in both directions -
• longer runs- counterclockwise rotation, helical bundle formed at tail of cell. This helps cell move forward.it is a default for going counterclockwise.

-short tumbles - one or more flagella rotate clockwise and bundle falls apart• The bacteria tumbles, assumes new, random orientation. Will eventually switch back to counterclockwise.

• motor switching from counterclockwise to clockwise dictates direction of movement.

Question 5

Flagellar movement: Monotrichous

Answer 5

• Bacteria with a reversible flagellum: rotation in opposite direction reverses the direction of movement.
• other bacteria have unidirectional flagella. Here, rotation stops/starts. random movement during stops changes the direction of the bacterium.

-the bacteria will randomly reorient as they stop, the bacteria will be spinning or not spinning.

Question 6

Flagella Strutcure

Answer 6

• it is massive, there are 50 different proteins involved in the structure of a flagellum.
• 3 segments of the flagellum:
  1. Filament - long thin propeller, that drives the movement.
  2. Hook - Adaptor that connects filament to the basal body. It is the motor spinning the propeller.
  3. Basal Body - core of the structure. Powers rotation of filaments. It is below the hook.

Question 7

The Flagellar Motor

Answer 7

• it harnesses proton motive force to drive the rotation.
• central rod passes through a series of rings: MS ring (cytoplasmic membrane), C ring (cytoplasm), P ring (peptidoglycan), L ring (outer membrane)
• stator couples the flow of protons to the rotation of the MS ring, basically behaving as a proton turbine. selectively allowing H+ to form proton motive force which causes the spinning of flagella.
• MS ring rotates the rod and ultimately the hook and filament.
• L/P rings act like bearings to help rotation.

-C ring is important for generating torque, switching motor direction, and flagellin secretion.

Question 8

Gram Positive bacteria

Answer 8

• it lacks P/L rings
• it only has C and MS rings
• gram-positive bacteria do not have an outer membrane so you need an enzyme to chew up the peptidoglycan so it can smoothly go through the cell membrane and move.

Question 9

Flagellar Filament - Flagellin

Answer 9

• The long filament that drives movement is made of thousands of copies of a single protein called flagellin.
• filament is 5-10 micrometer longand 20 nm wide
• the filament is rigid (prevent form whipping around), helical and hollow
• it is free at one end (out in the environment) and the other end is connected to the motor by a rod and hook.
• flagellin as the filament is conserved in bacterial flagella but its sequences vary.
• Flagellin is detected by our immune systems, it is an important antigen.
• often used in stereotyping, if we see an H antigen we know that it is apart of a flagella, just like we know that the O antigen is apart of the LPS.

Question 10

Synthesis of Flagellum

Answer 10

• the flagellar structure is built from the inside out, the innermost stuff assembles first.
• Flagellin (filament) grows from outside. Is produced in the cytoplasm and secreted through the flagellum the hollow filament. new subunit assembles at the end (outside of the cell) with the help of cap proteins. (sits on the top and moves up, it prevents the flagella from moving away.
• Type III secretion system uses to export flagellin: a related system is used as a protein toxin injection system by certain pathogens. (way to secrete proteins outside of the cell)

Question 11

Variations of Flagellar Motility

Answer 11

• Gram-positive rings, different flagella numbers/locations, unidirectional motor rotation.
• some bacteria have motors that use Na+ gradient instead of the proton motive force to drive rotation. (high salt environment and allows to power flagella)
• Spirochetes have a flagellum (axial filament) that resides in periplasm - rotation results in corkscrew motion of the entire bacterium –> useful in a viscous liquid, it spins within the cell envelope.
• Flagellar motility if often highly regulated - even motile bacteria can adopt a trichous/non-motile state.

Question 12

Taxis

Answer 12

• the directed movement of bacteria
• it is accomplished by a “bias random walk” (the bacteria walk in different directions, and are biased in which direction it move in)
• the bacteria will tumble if it is going in the wrong direction and then will be moving in the counterclockwise position.

Question 13

Chemotaxis in E.coli

Answer 13

• Chemotaxis: movement in the direction of gradients of increasing or decreasing concentration to particular chemicals.
• chemoreceptors detect specific chemicals and then they transfer info onto proteins that control the direction of the motor.
• if the bacterium moves forward with desirable nutrient, tumbles are inhibited (longer runs =less frequent tumbles)
• if moving away = shorter runs, more frequent tumbles. (tumble is promoted when bacteria go in the wrong direction, and then go back to long runs that are counterclockwise. )

Question 14

Some other types of taxis

Answer 14

• They just have different receptors that detect different kinds of signals.
• Photoreceptors: move toward or away from light

-Aerotaxis: directed motility in response to oxygen. It protects the concentration of oxygen.

Question 15

Other Types of Motlity

Answer 15

• some bacteria can move using other types of motility (non-flagellar)
• this includes twitching motility, in which a Type IV pilus attaches to a surface and then retracts.
• like grappilng hook.