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BACTERIOLOGY > 9 - BACTERIAL MOTILITY AND TAXIS > Flashcards

9 - BACTERIAL MOTILITY AND TAXIS Flashcards

1
Q

Tactic response requires:

A

1) Motility - swimming

2) Sensory mechanism

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2
Q

Various forms of taxis:

A

Chemotaxis, aerotaxis, phototaxis, thermotaxis, pH taxis, magneto taxis

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3
Q

Different flagella arrangements:

A

Polar flagella (Vibrio Cholera, pseudomonas), peritrichous flagella (E.coli)

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4
Q

Basic components of flagella and their sizes:

A

Basal body, hook and filament - 10-15 um long, 14nm diameter

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5
Q

What is the filament made out of?

A

FliC, flagellen

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6
Q

What is the hook made of?

A

FlgE and hook associated proteins (HAPs) e.g. HAP2 - cap protein on growing filament - will move along as filament is made

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7
Q

How many different proteins make up the basal body?

A

26 different proteins

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8
Q

Where is FliC made?

A

Made in cell, and polymerises and assembles on the cell surface

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9
Q

What different rings are part of the basal body and where are they located ?

A 
L-ring, P-ring, MS-ring, and C ring.
L-ring = OM absent in g+ bacteria
P-ring = contacts PG layer
MS-ring = in CM 
C-ring = in cytoplasm
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10
Q

Which protein confer motor function?

A

Motor proteins (MotA and MotB) and switch proteins

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11
Q

How many mot proteins are there, and where are they located?

A

11 mot proteins, surrounding the MS ring

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12
Q

What does in motor protein unit consist of?

A

MotA4 and MotB2 = 1 unit

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13
Q

What protein does Mot interact with?

A

FliG

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14
Q

What proteins form the C ring? How many copies of the protein?

A

Switch proteins - FliG, FliC, FliN, FliM - 26 copies

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15
Q

Components that rotate and components that do not:

A

Rotate: C ring, MS ring, Rod-Hook-Filament

Do not Rotate: Mot proteins (P ring L ring)

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16
Q

Which aa in MotB are critical for rotation?

A

aa in MotB - Asp32

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17
Q

What chemical property plays a role rotation on aspartate residues in motB?

A

Dicarboxylic acid - 2 COOH groups, one in peptide bond and one can be protonated and has a role in pmf and generating rotational force

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18
Q

Other that aspartate what amino acids are involved in rotation in motB?

A

Proline173 and Proline22, mutation causes reduced rotation. Proline involved in rotation as can undergo conformational change

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19
Q

When aspartate is protonated it leads to a conformational change which is then transmitted to which protein?

A

Switch protein FliG, which then transmitted to the next switch protein in the MS ring - this is what generates rotational movement and force

20
Q

When peritrichous flagella rotate counter clockwise how do bacteria move?

A

Smooth swimming

21
Q

When peritrichous flagella rotate clockwise how do bacteria move?

A

Tumbling mode - not swimming smoothy - jittery motion on the spot

22
Q

Smooth swimming and tumbling cause the bacteria to move in a…

A

Random walk - switch between tumbling and smooth swimming

23
Q

What causes bias random walk?

A

Chemical in the environment e.g. glucose

24
Q

What changes during a bias random walk?

A

Extended time smooth swimming, more CCW rotation of flagella. Shows purposeful behaviour.

25
Q

What is chemotaxis?

A

Purposeful behaviour to or from a compound

26
Q

Describe experiment to show bias random walk/chemotaxis:

A

Capillary tube containing:
1) nutrient rich media
2) same nutrient poor medium as in growth vessel
3) toxin
was placed in a culture vessel containing nutrient poor medium. Then a viable cell count was taken.

27
Q

What were the results of the capillary tube experiment o show evidence of chemotaxis?

A

Significantly more bacteria above control (same nutrient poor media) when nutrient rich media in capillary tube, significantly less bacteria when toxin in tube. This shows bacteria must be displaying purposeful chemotaxis behaviour AND SENSING concentration.

28
Q

What does the frequency of tumbling depend on?

A

The frequency of tumbling depends on change in concentration of the stimulus

29
Q

What are two possible sensing mechanism?

A

1) Spatial sensing - sense change between front and back - discounted too small distance, change in conc would be very small
2) Temporal sensing - change in concentration of attractant or repellent with time cause switch between tumbling and smooth swimming behaviour

30
Q

Mechanism of temporal sensing requires:

A

1) memory - compare current and past measures
2) adaptation mechanism - adapt to high concs in order to detect higher ones - adaption is fundamental
* respond to change not absolute conc

31
Q

What are MCPs?

A

Methyl accepting chemotaxis proteins. They span the CM. Different bacteria have different MCPs as different environments require different detection.

32
Q

How many MCPs does E.coli have?

A

4 Tar, Tsr, Trg, Tap

33
Q

What does Tar sense?

A

Attractant: Asp Maltose
Repellent: Co Ni

34
Q

What does Tar sense?

A

Attractant: Serine
Repellent: Acetate, benzoate

35
Q

What does Trg sense?

A

Attractant: Galactose, ribose

36
Q

What does Tap sense?

A

Dipeptides

37
Q

What domains do MCPs have?

A

Sensing domain - periplasm

Signalling domain - cytoplasm

38
Q

Ternary Complex:

A

MCP, CheW, CheA

39
Q

Stabilised Ternary Complex occurs under what condition?

A

Forms under no attractant.

40
Q

Stabilied Ternary Complex

A

No attractant causes CheA activity - autokinase activity phosphorlates histidine by hydrolysing ATP. Then transfers P from CheA to CheY (A key signalling molecule). CheY-P binds to switch protein in C ring = flagella rotation CW and tumbling behaviour.
- So if no attractant = increased chance of tumbling (not binary)

41
Q

Ternary complex becomes destabilised under what conditions

A

Attractant bound = destabilised

42
Q

How is ternary complex destabilised

A

No longer mechanism to make CheY-P .
CheZ dephosphorylates an existing CheY
CheY-P no longer interacts with switch proteins.
No CW rotation of flagella
Increased CCW rotation and increase swimming

43
Q

How does bacteria know to keep moving toward something?

A

1st time interact = ternary destabilise and move toward
How does bacteria know to keep moving toward something?
- memory
- adaption

44
Q

Adaption mechanism

A

CheR is a methyl transferase and transfers Me to exposed glutamic residues on MCP.
Glutamic residue exposed due to attractant binding.
Methylation = restabilisation of ternary complex formation
- switch back to no attractant
- bacterium now adapted to concentration
To destabilise ternary complex needs to encounter increased conc of attractant.

45
Q

How to reset adaption mechanism of chemotaxis if go from high to low conc?

A

RESET IF BACTERIA MOVE TO LOWER CONC

methyl esterase CheB, removed Me from MCP, this destabilises ternary complex = attractant bound state = swimming.

46
Q

Are the MCP evenly distributed?

A

Not entirely, seem to be more at ‘front’ end opposed to flagella end.
Spatial separation between detection and activation

BACTERIOLOGY (3 decks)

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