Bacterial immunity Flashcards
(90 cards)
what type of phages infect in a vegetative state and virion maturation occurs before release?
type 1
Obligately lytic, professionally lytic, strictly lytic, virulent
what phages infect in a vegetative state and virions mature during release?
type 2
chronic and non temperate phages
what phages infect in a vegetative state or as a prophage and virions mature before release?
type 3
lytic and temperate
what phages infect in a vegetative state or as a prophage and virions mature during release?
type 4
chronic and temperate
how are temperate phages, virulent mutants, and professionally lytic phages genetically related?
Temperate phage: phage that is genetically able to display lysogenic cycles as well as productive cycles
Virulent mutant: phage that is one or just a few genetic changes separated from a temperate phage ancestor
Professionally lytic: phage that is unrelated or extremely distantly related to temperate phages (no ability to integrate)
give three generic examples of the aims of anti-virus systems
- prevent infection - block entry
- prevent replication - cleave or block DNA and RNA
- prevent spreading - dormancy and suicide
what bacterial immune defenses are there for the degredation of phage nucleic acids?
- CRISPR-Cas systems
- Restriction modification systems
- Argonaute systems (pAgo)
what bacterial immune defenses are there for abortive infection?
- Signalling systems (CBASS, Pycsar, Thoeris)
- Retron systems
- Toxin-antitoxin systems
- Others (eg PrrC, Bacterial gasdermins)
What bacterial immune defenses are ther for inhibition of DNA and RNA synthesis?
- Chemical defense (prokaryotic viperin pVips, secondary metabolites (anthracyclines, aminoglycosides))
- Nucleotide depletion (dCTP deaminase, dGTPase)
how common are R-M systems?
R-M systems are present in about three quarters of bacterial genomes
what are restriction-modification systems?
consist of a modification enzyme that epigenetically methylates a specific DNA sequence, and a restriction endonuclease (restriction enzyme) that cuts DNA lacking this epigenetic mark.
IN general R-M systems have two distinct functions, what are they
what do the R and M stand for
- A DNA methyltransferase (Mod) that modifies DNA, at the target site to protect endogenous DNA
- A restriction endonuclease (Res) that cleaves foreign DNA at unmethylated target sites
what does SAM do in restriction modification systems
SAM serves as the methyl donor in cytosine methylation
what proportion of bacterial genomes have R-M systems?
R-M systems are present in about three quarters of bacterial genomes
what are the three major groups of restriction modification systems?
on what basis are they categorised?
type 1
type 2
type 3
subunit composition, cleavage position, sequence specificity, cofactor requirements
what elements are involved in type 1 R-M system?
enzymes, hydrolysis, cut site, type of protein
- Hetero-oligomeric enzymes
- require ATP hydrolysis for restriction
- cut DNA at sites remote from the recognition sequence
- DEAD-box proteins
what features are involved in type 2 R-M systems?
- ENase and MTase separate enzymes
- cut DNA within recognition sequence
give an example of a type 1 R-M system?
EcoKI
what elements are involved in type 3 R-M systems?
- heterooligomeric ENase
- ATP required for restriction
- cut DNA close to recognition sequence
- DEAD-box proteins
give an example of a type 2 R-M system
EcoRI
give an example of a type 3 R-M system?
StyLTI
what enzymatic reaction occurs in type 1, 2 and 3 R-M systems
In each instance, a methyltransferase (MTase) transfers a methyl group (CH3) from S-adenosyl-L-methionine (SAM) to the unmodified nucleotide, producing a methylated nucleotide and S-adenosyl-homocysteine (SAH).
how do type IV systems differ from type 1-3?
Type IV R-M systems have no methyltransferase, and are composed only of a restriction endonuclease that cleaves methylated foreign DNA
how do R-M systems cause cell death?
The REase attacks the unmodified host genome, resulting in cell death.