bacteriophage and the environment-lecture 26 Flashcards
What are bacteriophages?
Most abundant biological entity Head contains genome Tail fibers bind to cell surface Tail pumps genetic material into host individual virus cell- Virion
Describe the lytic cycle
Phage lands on bacterium, binds to surface(ADSORPTION) injection of genome into cytosol genome cyclizes and replicates genome packaged into cupsids lysis of bacterial cell
How are phages different from eukaryotic viruses
Have DNA genomes instead of RNA genomes
lack lipid envelopes because bacteria have cell wall and eukaryotes don’t
non-segmented vs. 8 piece in euks
What is the range of bacteriophages and how do we detect them?
Dispersal by water currents, animals, aerosols (no form of locomotion)
very specific phage/genus combinations
Detect via filteration and microscopy, lab isolation (plaques), or DNA sequencing
What is the lysogenic pathwiay?
infection-> integration, genome cyclizes -> phage genome is integrated
lysogen: bacterial cell that harbors phage
lysogeny->lytic pathway if stress/DNA damage
When and how does the phage decide which pathway to do?
phages detect quorum sensing to determine population density
high prey availability-> lysis
low prey availability-> lysogeny
What are some other phage lifestyles, besides lysis and lysogeny?
- non integrating prophages (act like plasmid)
- > don’t integrate into genomes, lyse eventually
- pseudolysogeny
- > associated with starvation states, phage waits till nutrients available to lyse
-nonlytic replication cycles (inoviridae) aka carrier state-> never lyse cell
What are some ways that the host evolves against phages?
prevent adorption silencing by lysogen repressor cleavage by RM or CRISPR kill infected cell assembly interference
Describe the restriction modification system of defense.
- sequence specific nucleases recognize sites on phage DNA
- methyl’s modifies and protects those sites in bacterial genome
- easy for phage to escape if methyl’s gets ti phage DNA before nucelase
- restriction endonuclease cute phage DNA
Methyl Transferase can methylate phage genome to make it REase resistant
describe the CRISPR-Cas systems of defense.
Adaptive Immunity
The Crispr-Cas genome has spacers of phage DNA (like a vaccination record), forms complexes that search for same genome
Crispr->cRNA->binds to cas nuclease
binds to phage DNA then cleaves
Describe the subverting anti-phage defense mechanisms
Ocr: Anti-Restriction protein (made in infection)
- mimics DNA to inhibit restriction endonuclease (binds to restriction endonuclease to inhibit phage recognition)
Anti-Crispr proteins (prevent CRISPR system)
made in early phage infection
works via diverse mechanisms
often bind to bas nucleases and prevent them from recognizing target DNA
sometimes modify or degrade Cas proteins
How is a phage genome structure?
Phage genome contains multiple stages: the late lytic stage (viral capsid proteins, cell lysis), early lytic (DNA replication), lysogeny (lytic repressor, integrase)
- phage moron genes ass more onto the core genome-> nonessential but confer advantage
- most evident during lysogeny
How can phage moron genes alter metabolism?
Cyanophages infect cyanobacteria (moron genes)
Cyanophage moron genes hyper stimulate photosynthesis to maximize virus production
–> maximize phage production
How do phage moron genes impact virulence? What are the notable phages?
Shiga Toxin of E.Coli and shigella has StxA and StxB phage encoded toxins that cause food borne illness and dysentary
Chlorera toxin(CTX) of Vibrio Cholera
Bostulinum toxin (botox) of clostridium botulinum
What is interphage warfare?
Superinfection exclusion systems
- > prevent second phage from binding
- mostly expressed by prophages
- prevent re-infection of cells already infected with phage
- some phage have anti-phage defenses targeting other phages! RM or CRISPR
