Genetics Ch. 9 [II]
discovery of generalized transduction
- set up a U tube and noticed that prototrophs were formed so it was NOT contact dependent - the "factor" (temperate phage) moved through the filter and moved genes
merodiploid
-partially diploid - caused by F-duction
co-transduction of genes
1. close together on the chromosome (1 infection) 2. carried by 2 different phages (simultaneous infection)
Steps of Generalized transduction
1. phage enters cell and breaks bacterial DNA 2. assembly of WT and transducing phages (w/ bacterial genes in head) 3. lysis 4. infection of recipient bacterium with transducing phage 5. genetic exchange of donor gene with recipient gene by DCO 6. stable transduced bacterium produced by recombination 7. linear fragments degraded
interrupted-mating
2 strains (use one that you know is sensitive to something -HfrH- and one you know is resistant to something...in the end, you only want the F⁻ - resistant one) mixed together, allowed to conjugate 2. bacteria grown under diff. media conditions to determine phenotype 3. about 100 min to transfer all genes 4. map the genes (distance measured in minutes)
F'
F factor can be removed from bacteria chromosome and when doing so, takes part of the chromosome with it-- called F'
F-duction
F' factor- F'(lac) - 2 circles of DNA- making the bacteria partially diploid (merodiploid)
Hfr strain
High-frequency recombination strain of E. coli - The F factor can integrate into the bacteria chromosome forming an Hfr strain - then, when Hfr bacteria conjugate with F⁻ bacteria, part of the bacterial chromosome will be transferred (can be used to map bacterial chromosome
tranduction
a process by which bacteriophages (phage vectors) transfer genes from one bacterium (donor) to another (recipient) - may undergo genetic recomb w/homologous region of recipient's chromosome
bacteriophage (T2)
can carry genes from former host to new host (at most 1%)
F factor
conjugative plasmid that can copy itself into an F⁻ bacteria via conjugation pilus (that it forms)
generalized vs. specialized transduction
generalized: any genes can be transferred between bacteria specialized: only specific genes can be transferred
complete media
in addition to minimal media ingredients, includes vitamins, AA, etc.
Lysogenic vs. Lytic
lysogenic: phage embeds its DNA into the host chromosome, replicates many times, excises its DNA and joins lytic lytic: phage inserts its DNA into host cell and replicates only its DNA and then makes translates itself and bursts cell open
transductants
recombinant recipient
mixing of complementary auxotrophic and phototrophic bacteria
showed that genes are not transferred through the media, but that they are contact dependent
phototrophs
strains that do not need nutritional supplementation - ex: bacteria are able to make leucine by itself rather than having it on the plate
auxotrophs
strains unable to synthesize essential nutrients, need nutritional supplementation - may be caused by a mutation preventing the production of something
how to map transduction data
the higher the %, the closer they are together
minimal media
the nutrients required for the growth of WT bacteria - carbon source, salts, trace elements
transformation
transfer of extracellular DNA into cells - DNA is taken up and recombines with bacterial chromosome (heteroduplex formation) - the more tightly linked the genes, the more likely they will be transformed together - can use to map genes (similar to radiation hybrid technique for humans)
phage
virus that can infect bacteria