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Questions and Answers
The Type VI Secretion System (T6SS) is described as a 'spring-loaded javelin'. Which aspect of its function is BEST emphasized by this analogy?
The Type VI Secretion System (T6SS) is described as a 'spring-loaded javelin'. Which aspect of its function is BEST emphasized by this analogy?
- The continuous and cyclical nature of toxin delivery, ensuring sustained impact on the target cell.
- The rapid and forceful expulsion of effector proteins into adjacent cells, causing immediate harm. (correct)
- The energy-efficient process of toxin secretion, minimizing metabolic burden on the bacterial cell.
- The selective targeting of specific host cell receptors, ensuring minimal collateral damage.
Photorhabdus Virulence Cassette Nanosyringes (PVCs) and Type VI Secretion Systems (T6SS) share genetic similarities, yet PVCs are described as not being 'recycled'. What is the MOST significant implication of this difference in terms of bacterial strategy?
Photorhabdus Virulence Cassette Nanosyringes (PVCs) and Type VI Secretion Systems (T6SS) share genetic similarities, yet PVCs are described as not being 'recycled'. What is the MOST significant implication of this difference in terms of bacterial strategy?
- PVCs are primarily used for long-range interactions, while T6SS are limited to cell-to-cell contact. (correct)
- PVCs are less efficient in toxin delivery compared to T6SS due to the lack of component reuse.
- PVC production is more energetically costly for bacteria than T6SS assembly and operation.
- PVCs require more complex regulatory mechanisms for toxin loading compared to T6SS.
If a bacterium were to employ both Type III Secretion Systems (T3SS) and Photorhabdus Virulence Cassette Nanosyringes (PVCs) as virulence mechanisms, what would be the MOST likely functional distinction in their application during host infection?
If a bacterium were to employ both Type III Secretion Systems (T3SS) and Photorhabdus Virulence Cassette Nanosyringes (PVCs) as virulence mechanisms, what would be the MOST likely functional distinction in their application during host infection?
- T3SS would be active during the early stages of infection, and PVCs would become dominant during chronic infection.
- T3SS would be deployed against bacterial competitors, and PVCs would be reserved for host cell cytotoxicity.
- T3SS would be primarily used for initial host cell attachment, while PVCs would facilitate intracellular invasion.
- T3SS would be utilized for manipulating host cell processes from a close range, whereas PVCs could target distant immune cells. (correct)
The development of 'NanoSyrinx' technology for cancer treatment, inspired by PVCs, LEAST directly leverages which inherent characteristic of PVCs?
The development of 'NanoSyrinx' technology for cancer treatment, inspired by PVCs, LEAST directly leverages which inherent characteristic of PVCs?
Considering the '16 gene operons' responsible for PVC production, what is the MOST significant evolutionary advantage of organizing these genes in operons for bacteria employing PVCs?
Considering the '16 gene operons' responsible for PVC production, what is the MOST significant evolutionary advantage of organizing these genes in operons for bacteria employing PVCs?
Neutrophils, macrophages, and dendritic cells are all phagocytic cells. Despite their shared ability to perform phagocytosis, what PRIMARY functional distinction differentiates their roles in the context of bacterial infection?
Neutrophils, macrophages, and dendritic cells are all phagocytic cells. Despite their shared ability to perform phagocytosis, what PRIMARY functional distinction differentiates their roles in the context of bacterial infection?
Bacterial pathogens employ strategies to 'evade recognition' or 'deal with the process' of phagocytosis. Which of the following bacterial mechanisms would be BEST categorized as 'dealing with the process' rather than 'evading recognition'?
Bacterial pathogens employ strategies to 'evade recognition' or 'deal with the process' of phagocytosis. Which of the following bacterial mechanisms would be BEST categorized as 'dealing with the process' rather than 'evading recognition'?
Considering the diverse secretion systems (T3SS, T6SS, PVCs) and strategies to counter phagocytosis, what overarching principle BEST describes the evolutionary arms race between bacterial pathogens and host immune systems?
Considering the diverse secretion systems (T3SS, T6SS, PVCs) and strategies to counter phagocytosis, what overarching principle BEST describes the evolutionary arms race between bacterial pathogens and host immune systems?
Flashcards
Type VI Secretion System
Type VI Secretion System
A secretion system that utilizes a spring-loaded mechanism to stab adjacent cells with toxins.
PVC Nanosyringes
PVC Nanosyringes
Molecular machines that act like nano-scale hypodermic syringes to inject toxin into the target cell.
Phagocytosis
Phagocytosis
A central immune mechanism where cells engulf and destroy pathogens.
Pathogen Defense
Pathogen Defense
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Photorhabdus Virulence Cassette Nanosyringes (PVCs)
Photorhabdus Virulence Cassette Nanosyringes (PVCs)
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Phagocytosis is performed?
Phagocytosis is performed?
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PVC Function
PVC Function
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Type VI assembly
Type VI assembly
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Study Notes
Type III Secretion System
- Evolved from the flagella apparatus
- Forms a macromolecular needle
- Extends from the bacterial cytoplasm, through the Gram-negative envelope, to the extracellular space
- The tip inserts into the host cell membrane
- Protein toxins (effectors) are injected directly into the host cell cytoplasm
- Used by many Gram-negative bacteria to deliver a range of toxins called effectors
- Multiple effectors can be delivered, and these can have diverse and subtle effects
- Yersinia uses T3SS to deliver Yop proteins to remodel host cellular processes
Type VI Secretion System
- Similar to a stabbing device
- Injects toxins into neighboring cells
- Assembled inside the bacterium's cytoplasm on the membrane
- Actuates like a spring-loaded javelin that shoots out into the target cell
- After firing, it disassembles and protein subunits are recycled
- Discovered as a mechanism for competition between bacteria
- Used to inject toxins into host cells during infection
Photorhabdus Virulence Cassette Nanosyringes (PVCs)
- Multi-protein molecular machines
- Act as nano-scale hypodermic syringes
- Bacterium produces these nanosyringes loaded with a protein toxin
- Nanosyringes released from the cell seek out a target host cell and inject the toxin
- Have specificity binding fibers which provide targeting
- Genetically related to T6SS
- Once released don't require cell-to-cell contact
- Cannot be recycled
- Made by 16 gene operons
- Can load different toxin proteins
- Different variants evolved to target different host/cell types
Pathogen Strategies - Cell Invasion
- Cell surface components for adhesion and entry
- Structural defenses against immunity
- Active combat using invasive enzymes and toxins for nutrient acqusition
- General strategies include dealing with phagocytosis
Dealing with Phagocytosis
- Central to immunity
- Done by Neutrophils, Macrophages, and Dendritic cells
- Bacteria can evade recognition or use strategies to deal with the process
- Indirect inhibition of phagocytosis includes the prevention of opsonisation
- Direct inhibition involves the injection of an inhibitor via type III secretion and/or induction of apoptosis
- Survival strategies include intracellular survival in phagocytes and inhibition by intracellular survival in phagocytes
Communication Interference
- Some bacteria can spy by binding host cytokines and then modify their behavior accordingly.
- Others suppress cytokine synthesis, cutting off communication lines.
- Vibrio cholerae suppresses TNF-α and IL-12 using Cholera toxin.
- Yersinia pestis uses YopJ/P to suppress TNF-α.
- E. coli uses Lymphostatin to suppress IL-2, IL-4, IL-5, and IFN-γ.
- Salmonella typhimurium interferes with IL-2 signaling.
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Description
Type III Secretion System (T3SS) injects toxins into host cells. It evolved from flagella. Type VI Secretion System functions as a stabbing device to inject toxins into neighboring cells. It was discovered as a mechanism for competition between bacteria.
