FN - Bacteriophages I Flashcards
What are the types of microbial interactions in a community? (3)
Cooperation – Microbes work together to benefit the community.
Competition – Microbes compete for resources and survival.
Predation – Some microbes prey on others for nutrients.
What are two examples of microbial cooperation?
Public goods sharing – Microbes collectively create resources that benefit all, even non-contributors (like a community garden).
Cross-feeding – One microbe’s metabolic byproducts serve as nutrients for another (one’s waste is another’s treasure).
What are two examples of microbial competition?
Cheating – Some microbes benefit from cooperative efforts without contributing.
Resource competition – Organisms compete for limited nutrients and space, sometimes through direct aggression or efficiency.
What are some forms of microbial predation? (3)
Solitary hunting – A single predator captures and consumes prey.
Group hunting – Predators work together to catch prey.
Interference – One microbe harms or hinders another, often using toxins.
What is the difference between microbiota and microbiome?
Microbiota – The community of living microbes, including bacteria, archaea, fungi, algae, and small protists.
Microbiome – The microbiota plus its “theatre of activity” (microbial structures, metabolites, etc.).
Viruses/phages, plasmids, mobile genetic elements - Part of the microbiome, but not of the microbiota.
What role do viruses play in microbial communities? (4)
- Control bacterial populations and influence microbial evolution.
- Represent the most abundant biological entities on Earth.
- Store vast genetic diversity (shown in virome studies).
- Shape microbial ecology and geochemical cycles.
What are the two life cycles of bacteriophages?
Lytic Cycle – Immediate destruction of host cells.
Lysogenic Cycle – Viral DNA integrates into host genome and replicates until triggered to enter the lytic cycle.
What are the steps of the lytic cycle? (5)
- Attachment – The phage binds to the bacterial surface.
- Genome Entry – Phage injects DNA into the bacterial cytoplasm.
- Replication – Host machinery replicates phage DNA and proteins.
- Assembly – New phages are assembled.
- Lysis – The bacterial cell bursts, releasing new phages.
What are the steps of the lysogenic cycle? (6)
- Attachment – The phage binds to the bacterial surface.
- Genome Entry - Phage injects DNA into the bacterial cytoplasm.
- Integration – Phage DNA integrates into bacterial genome (prophage).
- Cell Division – The prophage replicates along with the bacterial chromosome.
- Environmental Trigger – Stress can cause the prophage to be excised.
- Lytic Cycle Activation – The phage enters the lytic cycle and destroys the host.
What is the difference between virulent and temperate phages?
Virulent phages - only undergo lytic cycle
Temperate phages - can undergo lysogenic and lytic cycle
What are the key steps of bacteriophage infection mechanisms? (4)
- Attachment – Retracted long tail fibers extend to recognize specific receptors on the bacterial surface.
- Base Plate Contact – The base plate of the phage binds to the bacterial cell wall.
- Tail Sheath Contraction – The sheath contracts, forcing the central tube through the bacterial wall.
- Genome Delivery – The tail tube injects the phage’s DNA into the bacterial cytoplasm.
How do bacteriophages recognize their bacterial hosts? (3)
- Receptor Binding Proteins (RBPs)– Phages use RBPs to identify specific receptors on bacteria.
- Host Receptors – These include lipopolysaccharides (LPS) or outer membrane proteins (OMPs).
- Host Range – Different phages have different RBPs, which determine which bacterial species they can infect.
What are three major bacteriophage morphotypes?
- Myophage – Contractile tail sheath that shortens during infection.
- Siphophage – Long, flexible, non-contractile tail.
- Podophage – Short tail.
How do flagellotropic phages infect bacteria? (3)
- They use flagella to bind to moving bacteria.
- Use curled tail fibres that wrap around the flagellum and travel toward the cell pole.
- This increases the chance of locating the receptor for infection.
What is unique about Pseudomonas phage phi6 genome entry? (2)
- Unlike most phages, its entire capsid enters the bacterial cell.
- This is to protect its dsRNA genome from host ribonucleases.
How does Pseudomonas phage phi6
enter and replicate inside a bacterial cell? (5)
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Pilus Attachment & Retraction – The phage uses the protein spikes that protrude from its capsid to adsorb to the side of a pilus in the bacteria.
— Phage uses pili retraction to get closer to the outer membrane of the cell. - Membrane Fusion – Phage protein P6 fuses its lipid envelope with the bacterial outer membrane.
- Genome Entry – The nucleocapsid enters, and an exposed endopeptidase digests through the peptidoglycan layer.
- Capsid Protection – The phage sheds its outer capsid, leaving an inner capsid that protects its dsRNA.
- RNA Synthesis & Translation – RdRP in the capsid transcribes positive-sense RNA, which exits into the cytoplasm for protein translation and phage replication.
What is the difference between positive-sense and negative-sense viral RNA?
- Positive-sense RNA – Can be immediately translated by host ribosomes.
- Negative-sense RNA – Must be converted to positive-sense RNA by an RNA polymerase before translation.
