CBG Lecture 19: Bacterial Transduction Flashcards
define bacteriophage
a virus that infects bacteria
define lysogenic cycle
phage integrates into chromosome and is replicated along with the bacterial DNA
define lytic cyccle
the phage replicates in the host cell, releasing a new gen of viruses when the infected cell lyses
define virulent phage
reproduces only through lytic cycle
kills host
define prophage
a temperate bacteriophage integrated into the chromosome of the host bacterium
define temperate phage
can use lytic or lysogenic cycle
define plaque
a clear patch on bacterial lawn showing where cells have been lysed by phage infection
what two phages did Hershey and Rotman use
h-r+ and h+r-
wgucg E.coli strains can h- infect
E.coli strains B and B/2
which phage can infect E.coli B and B/2
h-
what happens when h- infects E.coli strains B and B/2
clear
which strain can h+ infect
strain B E.coli
what infects strain B E.coli
h+ and h=
what happens when h+ infects strain B
cloudy plaques
which infection gives clear plate
when h- infects E.coli strains B and B/2
which infection gives cloudy plaque
when h+ infects strain B
what does r- do
lyses cells rapidly giving large plaques
what does r+ do
lyses cells slowly giving small plaques
how are large plaques formed
by r- lysing cells rapidly
how are small plaques formed
by r+ lysing cells slowly
why do you cross h-r+ with h+r- in B strain bacteria
because this is the only strain which both phages can infect
why is high concn of phage used
to ensure multiple infections occur
when experimenting with phages, how do you ensure multiple infections occur
high concn of phage use
what is genotype of clear and small
h- r+
what is genotype of clear and large
h- r-
what is genotype of cloudy and small
h+ r+
what is genotype of cloudy and large
h+ r-
what is phenotype of h- r+
clear and small
what is phenotype of h+ r+
cloudy and small
what is phenotype of h+ r-
cloudy and large
what is phenotype of h-r-
clear and large
what causes triggering of lytic from lysogenic cycle
stressors
eg. UV - excises the phage DNA
what do plaques show
where cells have been lysed
what types of transduction are there
generalised
specific
what is generalised transduction
phages carry any part of the bacterial chromosomes
what can cotransduction be useful for
mapping genes (like cotransformation) - a headful of DNA is transferred at a time
what type of transduction where phages carry any part of the bact chromosome
generalised
what is specialisd transduction
phages carry only restricted parts of the bacterial chromosome
compare specialised transduction to generalized
in generalised phages carry ANY part of bact chrom and it involves the lytic cycle but in specialised transduction the lysogenic cycle is involved and specific genes are transferred - those next to phage attachment sites
give example of a phage used in specialised transduction
lamda phage
how can phages be excised from bact chrom
production of initial lysate then rare abnormal outlooping
which genes are transferred in specialised transduction
those next to phage attachment sites
what can transfer of genes be via
lysogenic incorporation into the bacterial chromosome or by recombination
what are the two ways that excision can appear
production of initial lysate
transduction by initial lysate
what is a bacterial lawn
the field of bacteria formed when all the individual colonies on a petri dish agar plate merge
what did hershey and rotman do
h-r+ and h+r- crossing to map phage genes
what did Lederberg and zinder do
can recombination occur in salmonella as it does in E.coli
what is production of initial lysate
produced via outlooping - involved in the excision of phage from bacterial chrom
what is transduction of initial lysate involved in
new genetic material in recipient cell
name some phages that show generalised transduction
p1 and p22
where does lamda phage insert betwen
specialised transducer which inserts between the gal and bio genes in the E.coli host chrom
how does lamda phage excise out of bact chrom
lamda phage is a specialised transducer and normally excises out of bact chrom via an outlooping mechanism that is precisely the reverse of its integration
when can lamda phage transduce
only when an occasional faulty outlooping includes the gal or bio genes into the phage cycle
what is a lysate
A popn of progeny phages
what is a known temperate phage of salmonella
P22 - it fits in the filter of U tube
what is zygotic induction
The sudden release of a lysogenic phage from an Hfr chromosome when the prophage enters the Fâ cell, and the subsequent lysis of the recipient cell.
how is the prophage attached to the bacterial genome
reciprocal recombination of lamda phage into E.coli chromsome = takes place between a specific attachement site of the circular lamda DNA and specific region on bac chrom between the gal and bio genes
what can specialised transduction prodeuce
normal labda, or abnormal lamda d gal - the transducing particle
when does transduction occur
when newly forming phages acquire host genes and transfer them to other bacterial cells
what is specialised transduction due to
faulty separation of the prophage from the bacterial chrom so the new phage includes both phage and bacterial genes = the transducing phage can transfer only specific host genes
