Lecture 12 Flashcards
1
Q
What are the two main types of movement exhibited by bacteria?
A
Bacteria exhibit random movement and directed movement.
2
Q
What structures do most bacteria use for motility?
A
Most bacteria use flagella or pili for motility.
3
Q
Define taxis in the context of bacterial motility.
A
Taxis refers to directed movement in response to a stimulus.
4
Q
What is positive taxis?
A
Positive taxis is movement towards a stimulus, such as nutrients.
5
Q
Provide an example of negative taxis.
A
Negative taxis is movement away from a stimulus, such as toxic substances.
6
Q
What is chemotaxis?
A
Chemotaxis is the movement towards or away from attractants/repellents in response to chemical stimuli.
7
Q
What are flagella?
A
Flagella are long helical surface structures used by bacteria for motility in liquid environments.
8
Q
What are the dimensions of flagella?
A
Flagella typically have a diameter of 20 nanometers and can be up to 20 micrometers long.
9
Q
How does flagellar swimming occur?
A
Flagellar swimming results from the rapid rotation of flagella.
10
Q
Why is water considered viscous for microbes?
A
Water is considered viscous for microbes because it significantly impedes their movement.
11
Q
What is the typical rotation speed of flagella?
A
Flagella can rotate at speeds ranging from 100 to 1000 times per second.
12
Q
What is the maximum speed at which bacteria can swim using flagella?
A
Bacteria can swim at speeds of up to 100 micrometers per second using flagella.
13
Q
How can flagella be different across different bacteria?
A
Bacteria exhibit variation in the number and distribution of flagella.
14
Q
What does “atrichous” mean in terms of flagella?
A
Atrichous bacteria have no flagella.
15
Q
Define “monotrichous” in the context of flagella.
A
Monotrichous bacteria have a single flagellum located at one pole.
16
Q
What is the characteristic feature of lophotrichous bacteria?
A
Lophotrichous bacteria have a tuft of flagella at one or both poles. (looks like little hair on a cartoon characters head)
17
Q
Describe the arrangement of flagella in amphitrichous bacteria.
A
Amphitrichous bacteria have a single flagellum at both poles.
18
Q
What is the distribution pattern of flagella in peritrichous bacteria?
A
Peritrichous bacteria have flagella distributed over their surface.
19
Q
What is the function of the basal body in flagellum structure?
A
The basal body attaches the flagellum to the cell envelope and contains the motor responsible for rotation.
20
Q
Describe the filament of the flagellum.
A
The filament is a long helical structure that extends from the surface of the cell. Rotation of the filament moves the cell.
21
Q
What is the function of the hook in flagellum structure?
A
The hook is a flexible, bent structure that transmits rotation from the basal body to the filament.
22
Q
In which types of bacteria are basal bodies present? (Gram pos or Gram neg)
A
Basal bodies are present in both Gram-negative and Gram-positive bacteria.
23
Q
Describe the protein structure of the basal body.
A
The basal body is composed of a central rod and several rings.
24
Q
What rings are embedded in the cell envelope of most Gram-negative bacteria?
A
Most Gram-negative bacteria have L, P, and MS rings embedded in the cell envelope.
25
Where is the C ring located in bacteria?
The C ring is located in the cytoplasm of bacteria.
26
Do most gram-negatives have a C ring? If so, where?
Yes, most gram-negs have a C ring in the cytoplasm
27
What are the functions of the basal body in bacteria?
The basal body is responsible for transporting subunits during flagellum assembly and for motor functions, rotating the hook and filament.
28
What is the role of the basal body in the export functions of bacteria?
The basal body plays a role in exporting proteins necessary for various cellular functions.
29
What components make up the basal body as a motor?
The basal body as a motor consists of a rotor (including a rod and MS ring), bushings or bearings (P and L rings), and a stator (composed of MotA and MotB proteins).
30
How is rotation of the basal body typically powered?
Rotation of the basal body is typically powered by the proton motive force.
31
What is the function of the proton channel formed by MotA and MotB proteins?
The proton channel formed by MotA and MotB proteins facilitates the flow of protons, contributing to the proton motive force that powers rotation.
32
What role does the switch (C ring) play in flagellar motors?
The switch, represented by the C ring, determines the direction of rotation of the flagellar motor.
33
In what order does the assembly of the flagellum occur?
The assembly of the flagellum begins with the basal body, followed by the hook, and then the filament.
34
How are subunits added to the distal end of the flagellum during assembly?
Subunits are exported up the hollow core of the flagellum and added to the distal end during assembly.
35
What protein makes up the filament of the flagellum?
The filament of the flagellum is made of thousands of flagellin proteins.
36
How is the filament of the flagellum assembled?
The filament is assembled in a helical pattern, with flagellin proteins being incorporated under a cap protein.
37
Techoic acids are a type of microbe-associated molecular pattern (MAMP). How does the innate immune system recognize MAMPs?
a) using antibodies
b) using complement proteins
c) using dendritic cells
d) using pattern-recognition receptors
d)
using pattern-recognition receptors on surface of bacterial cells
38
Why are flagella considered major immune targets?
Flagella are considered major immune targets because they are exposed on the surface of bacteria.
39
How does the innate immune system recognize flagellin?
The innate immune system recognizes flagellin through Toll-like receptor 5 (TLR5).
40
What happens when flagellin binds to Toll-like receptor 5 (TLR5)?
When flagellin binds to Toll-like receptor 5 (TLR5), it activates NF-κB, a transcription factor.
41
What is the role of NF-κB in the immune response?
NF-κB activation leads to the production of pro-inflammatory cytokines, contributing to the immune response.
42
How are flagella targeted by the adaptive immune system?
Flagella are targeted by the adaptive immune system as they are recognized as major antigenic structures.
43
Provide an example of a bacterium where flagellar antigens are targeted by the adaptive immune system.
E. coli O157:H7 is an example of a bacterium where flagellar antigens, specifically H7, are targeted by the adaptive immune system.
44
What is the significance of the large number of protein subunits, such as flagellin, in flagella?
The large number of protein subunits in flagella increases the likelihood of antibody formation.
45
What is the consequence of antibody binding to flagellar antigens?
Antibody binding to flagellar antigens leads to phagocytosis, which is the process of engulfing and destroying the bacteria by immune cells.
46
What is observed in some bacteria once they enter the host environment regarding flagella production?
Some bacteria stop producing flagella once they enter the host environment.
47
How do some bacteria alternate between different flagellins?
Some bacteria alternate between different flagellins through phase variation, which involves a reversible change in phenotype.
48
Describe phase variation. Include key terms phenotype and genetic content.
Phase variation is a process through which some bacteria can alternate between different flagellins. This involves a reversible change in phenotype, but the genetic content stays roughly the same throughout this.
49
Provide an example of a bacterium that exhibits phase variation in flagellins.
Salmonella enterica is an example of a bacterium that exhibits phase variation in flagellins, specifically FljB and FliC.
50
What mechanism underlies phase variation in flagellins?
Phase variation in flagellins is often mediated by a reversible inversion of the promoter region, which involves recombination events.
51
What is the significance of phase variation in terms of immune evasion?
Phase variation allows bacteria to evade the host immune response by altering their surface antigens, making it difficult for the immune system to recognize and target them effectively.
52
What is the behavior of bacteria when there is no chemical gradient present?
When there is no chemical gradient present, bacteria move in a random walk.
53
Describe the random walk of bacteria.
Bacteria swim forward in a straight line, known as a "run," and occasionally reorient themselves in a new random direction, known as a "tumble."
54
What is the significance of the random walk in bacterial movement?
The random walk allows bacteria to explore their environment efficiently, facilitating the search for chemical gradients and resources.
55
What occurs during a bacterial "run"?
During a "run," bacteria swim forward in a straight line.
56
What happens during a bacterial "tumble"?
During a "tumble," bacteria reorient themselves in a new random direction.
57
How does the direction of flagellum rotation determine the movement of the cell?
The direction of flagellum rotation determines whether the cell is running or tumbling.
58
What happens when the flagellum rotates counterclockwise in a monotrichous bacterium?
When the flagellum rotates counterclockwise in a monotrichous bacterium, the cell runs forward in a straight line.
59
What occurs when the flagellum rotates clockwise in a monotrichous bacterium?
When the flagellum rotates clockwise in a monotrichous bacterium, the cell tumbles and changes its direction.
60
How does flagellum rotation affect the movement of peritrichous bacteria?
In peritrichous bacteria, the direction of flagellum rotation determines the overall movement of the cell. If most flagella rotate counterclockwise, the cell runs forward; if most flagella rotate clockwise, the cell tumbles and changes its direction.
61
What is the significance of flagellum rotation in bacterial movement?
Flagellum rotation allows bacteria to switch between running and tumbling behaviors, enabling them to navigate their environment effectively.
62
What happens to bacterial movement in a chemical gradient?
In a chemical gradient, some directions become advantageous for bacterial movement.
63
Describe the movement of bacteria in a biased random walk.
In a biased random walk, bacteria move in a random manner, but the direction of movement is biased towards regions of higher chemical concentration.
64
How do bacteria respond if the direction is favorable in a chemical gradient?
If the direction is favorable in a chemical gradient, bacteria exhibit longer runs with fewer tumbles.
65
What occurs if the direction is unfavorable in a chemical gradient?
If the direction is unfavorable in a chemical gradient, bacteria experience more frequent tumbles.
66
What is the significance of biased random walks in chemotaxis?
Biased random walks allow bacteria to efficiently navigate towards regions of higher chemical concentration, increasing their chances of finding nutrients or avoiding harmful substances.
67
How do chemical stimuli impact the direction of rotation in bacterial flagella?
Chemical stimuli impact the direction of rotation in bacterial flagella through the action of methyl-accepting chemotaxis proteins (MCPs).
68
What are methyl-accepting chemotaxis proteins (MCPs)?
Methyl-accepting chemotaxis proteins (MCPs) are chemoreceptors located in the cytoplasmic membrane of bacteria.
69
What is the role of MCPs in bacterial chemotaxis?
MCPs play a crucial role in bacterial chemotaxis by detecting different chemical attractants and repellents in the environment.
70
How do different MCPs contribute to chemotaxis?
Different MCPs are specialized to sense specific attractants or repellents, allowing bacteria to respond appropriately to their surrounding chemical environment.
71
What is the default direction of rotation for flagella?
By default, flagella rotate counterclockwise.
72
What is favored when flagella rotate counterclockwise?
When flagella rotate counterclockwise, it favors runs, where the bacterium moves forward in a straight line.
73
How can methyl-accepting chemotaxis proteins (MCPs) signal flagella to change direction?
MCPs can signal flagella to change direction by altering their conformation upon binding to specific ligands.
74
What occurs when a ligand binds to the ligand-binding domain of an MCP?
When a ligand binds to the ligand-binding domain of an MCP, it changes the conformation of the MCP's signaling domain.
75
What is the role of CheW in the signaling pathway of MCPs?
CheW is bound to the signaling domain of MCPs and its activity is impacted by the presence of ligands, influencing the direction of flagellar rotation and bacterial movement.
76
What happens if no attractant ligand is bound to a methyl-accepting chemotaxis protein (MCP)?
If no attractant ligand is bound to an MCP, the cell perceives the direction as "bad" and aims to tumble to reorient itself.
77
What is the first step in response to no attractant bound to MCP?
CheW detects no attractant bound to MCP, initiating the signaling cascade.
78
What is the signaling pathway triggered in bacteria when no attractant ligand is bound to a methyl-accepting chemotaxis protein (MCP)?
1. CheW detects no attractant bound to MCP.
2. CheW causes kinase CheA to be auto-phosphorylated.
3. CheA-P phosphorylates CheY.
4. CheY-P binds to the flagellum switch, causing clockwise (CW) rotation of the flagella.
5. Over time, CheY-P is dephosphorylated by CheZ. This turns off the clockwise bias.
79
What happens if an attractant ligand is bound to a methyl-accepting chemotaxis protein (MCP), indicating a "good" direction for the bacterial cell to continue running forward?
1. CheW detects the attractant bound to MCP.
2. CheW does not induce auto-phosphorylation of CheA.
3. CheY remains unphosphorylated, preventing its binding to the flagellum switch.
4. Counterclockwise (CCW) rotation of the flagella is favored, allowing the cell to maintain its forward movement.
80
What is excitation in bacterial chemotaxis?
Excitation in bacterial chemotaxis refers to the process where input from many methyl-accepting chemotaxis proteins (MCPs) influences the direction of flagellar rotation.
(they all work together to have a global impact on whether the flagella goes CW or CCW)
81
How does ligand binding to MCPs affect flagellar rotation?
Ligand binding to MCPs causes a counterclockwise (CCW) bias in flagellar rotation.
82
What happens when more MCPs have bound ligand? (in terms of CheY-P)
When more MCPs have bound ligand, less CheY-P is formed.
83
What are the consequences of excitation on bacterial movement?
Excitation leads to longer runs and fewer tumbles, facilitating the bacterium's movement in the direction of higher ligand concentration.
84
What effect does ligand binding to MCP have on CheA autophosphorylation?
Ligand binding to MCP decreases CheA autophosphorylation.
85
How does ligand binding to MCP impact the amount of CheY-P?
Ligand binding to MCP decreases the amount of CheY-P.
86
What occurs a few seconds after ligand binds to MCP?
A few seconds after ligand binds, MCP is methylated by CheR.
87
What is the function of CheR in bacterial chemotaxis?
CheR is responsible for methylating methyl-accepting chemotaxis proteins (MCPs).
88
How does methylation of MCP affect CheA autophosphorylation?
Methylation of MCP increases CheA autophosphorylation.
89
What effect does methylation of MCP have on the amount of CheY-P?
Methylation of MCP increases the amount of CheY-P.
90
Which of the following would cause a bacterial cell to tumble?
a) Higher amounts of CheY-P
b) More attractant bound to MCP
c) Less CheA autophosphorylation
d) CCW flagellar rotation
a)
91
How does methylation of methyl-accepting chemotaxis proteins (MCPs) impact flagellar rotation?
Methylation of MCPs offsets the impact of ligand binding on flagellar rotation by removing the counterclockwise (CCW) bias.
92
What happens if the ligand leaves after methylation of MCP?
If the ligand leaves after methylation of MCP, the methylated MCP still enhances CheA activity, causing a clockwise (CW) bias in flagellar rotation.
93
How do bacteria typically measure concentration gradients for chemotaxis?
How do bacteria typically measure concentration gradients for chemotaxis?
94
What information do bacteria use to assess current concentration gradients?
Bacteria assess current concentration gradients based on the number of methyl-accepting chemotaxis proteins (MCPs) with ligands.
95
How do bacteria assess past concentration gradients?
Bacteria assess past concentration gradients based on the number of methylated MCPs.
96
What accounts for the difference in assessing current and past concentration gradients?
The difference results from the approximately 2-second delay of methylation after ligand binding.
97
What does the ability of bacteria to measure temporal gradients allow them to do?
The ability of bacteria to measure temporal gradients allows them to swim up or down concentration gradients.
98
What happens when ligand concentration increases in the environment, and how does it affect bacterial movement in a concentration gradient?
- Increasing ligand concentration leads to more ligands binding to methyl-accepting chemotaxis proteins (MCPs).
- This results in more MCPs being methylated, although the methylation process is delayed.
- The overall effect is a counterclockwise (CCW) bias in flagellar rotation, leading to longer runs and fewer tumbles.
- This bias allows bacteria to swim up a concentration gradient.
99
What occurs when ligand concentration decreases in the environment, and how does it influence bacterial movement in a concentration gradient?
- Decreasing ligand concentration leads to fewer ligands binding to methyl-accepting chemotaxis proteins (MCPs).
- Methylation of MCPs may increase due to the delay in the process or stay the same.
- The overall result is a clockwise (CW) bias in flagellar rotation, resulting in shorter runs and more frequent tumbles.
- This bias allows bacteria to swim down a concentration gradient.
100
How are methyl-accepting chemotaxis proteins (MCPs) demethylated over time, and what is the consequence of demethylation?
MCPs are demethylated by CheB over time.
Once an MCP is demethylated, ligand binding will again result in a counterclockwise (CCW) bias in flagellar rotation.
101
What is the importance of demethylation in bacterial chemotaxis?
Demethylation makes it possible for bacteria to respond to gradients.
For example, increasing attractant concentration normally causes a counterclockwise (CCW) bias in flagellar rotation.
However, if demethylation did not occur, more attractant binding wouldn't cause a CCW bias, thus highlighting the significance of demethylation in enabling bacteria to appropriately respond to changing environmental conditions.
102
How can bacteria move on solid media using flagella?
Bacteria can move on solid media using flagella through a type of motility called swarming motility.
103
What is swarming motility?
Swarming motility is a type of bacterial movement on solid surfaces facilitated by flagella.
104
What other bacterial structure can be utilized for movement on solid media besides flagella?
Besides flagella, bacteria can also use pili for movement on solid media.
105
What type of bacterial movement on solid surfaces involves the use of pili?
Twitching motility is a type of bacterial movement on solid surfaces that involves the use of pili.
106
What is the significance of motility on solid surfaces for bacteria?
Motility on solid surfaces allows bacteria to colonize and explore their environment, aiding in processes such as biofilm formation and pathogenicity.
107
What is swarming in the context of bacterial motility?
Swarming refers to the coordinated movement of groups of bacteria (rafts) across solid surfaces.
108
What are the requirements for swarming motility?
Swarming motility requires multiple flagella, usually peritrichous, and the presence of surfactants.
109
How do surfactants contribute to swarming motility?
Surfactants reduce the surface tension between the bacterial cells and the solid surface, facilitating the movement of bacteria across the surface.
110
What role do flagella play in swarming motility?
Flagella play a crucial role in swarming motility by providing the motile force necessary for the coordinated movement of bacteria.
111
What distinguishes swarming motility from non-swarming motility?
Swarming motility involves the coordinated movement of groups of bacteria across solid surfaces, whereas non-swarming motility refers to individual bacterial movement without the formation of rafts or coordinated groups.
112
If a bacteria is incapable of demethylation, what will be the bias of the direction it travels?
If a bacteria is incapable of demethylation, there will be no CCW bias. This is because it has to remove methyl groups in order to detect concentration gradients and change accordingly.
113
What would happen if a repellent were to bind to an MCP?
a) The cell would tumble less frequently
b) The MCP would have a CW bias
c) The MCP would be demethylated
d) Less CheY-P would be formed
b)
because it wants to avoid a repellent, therefore wants to tumble (CW bias)
114
What is Proteus mirabilis known for?
Proteus mirabilis is a common cause of catheter-associated urinary tract infections (UTIs).
115
How does Proteus mirabilis contribute to urinary tract infections?
Proteus mirabilis bacteria swarm along catheters, allowing them to enter the urinary tract and cause infections.
116
What issue can arise due to the swarming behavior of Proteus mirabilis along catheters?
The swarming behavior of Proteus mirabilis along catheters can lead to the formation of crystalline biofilms that block urethral catheters.
117
How do swarmer cells of Proteus mirabilis differ from regular cells?
Swarmer cells of Proteus mirabilis produce thousands of flagella and become 20-50 times longer than regular cells.
118
What structures do swarmer cells of Proteus mirabilis form on surfaces?
Swarmer cells of Proteus mirabilis form multicellular rafts on surfaces, facilitating their swarming motility.
119
What is twitching motility?
Twitching motility is a type of surface motility in bacteria that involves the extension and retraction of type IV pili.
120
How do bacteria move during twitching motility?
During twitching motility, the pilus extends, binds to the surface, and then retracts, pulling the cell toward the attachment site in a jerky motion.
121
What are type IV pili used for in twitching motility?
Type IV pili are used by bacteria for twitching motility to attach to inert surfaces or other cells.
122
What is the significance of twitching motility for bacteria?
Twitching motility allows bacteria to colonize new environments, which is important for processes such as host colonization by pathogens.
123
How does twitching motility differ from other forms of bacterial motility?
Twitching motility involves a jerky motion where the bacteria extend and retract type IV pili to move along surfaces, while other forms of motility, such as flagellar-driven swimming, involve smoother movements through liquid environments.
124
How does the pilus extend during twitching motility?
The pilus extends by adding subunits, such as pilins (e.g., PilA), to the base.
125
What occurs after the pilus adheres to the surface during twitching motility?
After adhering to the surface, the pilus then rapidly retracts.
126
How fast are pilins removed from the base of the pilus during twitching motility?
Pilins are removed from the base of the pilus at a rate of approximately 1500 per second.
127
What is the significance of rapid pilus retraction during twitching motility?
Rapid pilus retraction during twitching motility allows bacteria to move along surfaces effectively and efficiently.
128
If there’s still attractant bound to an MCP, why wouldn’t the cell want to favour runs over tumbles?
As a bacterium swims up a concentration gradient, it will initially have some attractants binding to its MCPs (causing a CCW bias).
After a couple of seconds, those MCPs will be methylated, offsetting the CCW bias. However, if the bacterium is indeed swimming up an attractant concentration gradient, there will also be more attractants molecules around, and these attractants can bind to other MCPs.
So, while the MCPs that initially had attractants bound (and are now methylated and are unbiased), the other MCPs that have new attractant molecules bound to them will have their own CCW bias. So, in spite of the methylation (which will increase CheA autophosphorylation, etc), the other MCPs with attractants bound which haven’t been methylated yet will tend to decrease CheA autophosphorylation.
