LIFESCI 4 Lecture Notes - Lecture 14: Auxotrophy, Asha, Erythromycin
LIFESCI 4 - Lecture 14 - Midterm Review
Clicker 1
- Selection: use methionine as marker for F- and lactose as marker for Hfr (everything that
is previous to those markers cannot be used due to the genotypes of F- and Hfr)
- Selection markers: et lacm ++
- Select for Met+ to kill the most F- strains (to select for Met+, we should
NOT put methionine into the plate)
- Select for Lac+ to kill the most Hfr strains
- Optimization: add in all the other amino acids that were not used as markers
- + lysine
- + arginine
- + galactose (sugar source) → since we used lactose (sugar source) as one of the
markers, we should add in galactose as well to save the most exconjugants
- Answer: Minimal Media + lactose + galactose + lysine + arginine
Clicker 2
Selection Media: MM + lactose + galactose
Which is/are the selection marker(s)?
A) Lac+
B) Gal+
C) Lac+ and gal+
D) Lac+ or gal+
E) Can’t tell
Explanation:
- If both sugars are in minimal media, only one of them are being selected, the other one
is added to save whatever strains the first sugar are selecting against
- With this plate, only strains with genotype would dieac gall −−
Clicker 3
Selection Media: MM + lactose + galactose
Which genotype(s) will be able to grow on the above media?
A) Lac+ gal+
B) Lac+ gal-
C) Lac- gal+
D) Two of these above
E) A + B + C
Explanation:
- Either one sugar is selected when both sugars are put in minimal media
- The only strain that cannot grow is , so all three strains (A B C) can grow onac gall −−
this minimal media
Clicker 4
Selection Media: MM + lactose
Which genotype(s) will be able to grow on the above media?
A) Lac+ gal+
B) Lac+ gal-
C) Lac- gal+
D) Two of these above
F) A + B + C
Explanation:
- If plate contains lactose, then lac+ is selected for, galactose can be (+)/(-)
- Can be lac+ gal- or lac+ gal+
Clicker 5
Selection Media: MM + galactose
Which genotype(s) will be able to grow on the above media?
A) Lac+ gal+
B) Lac+ gal-
C) Lac- gal+
D) Two of these above
E) A + B + C
Explanation:
- If plate contains galactose, then gal+ is selected for, lactose can be (+)/(-)
- Can be lac+ gal+ or lac- gal+
Clicker 6
Your F+ strain has a single auxotrophic mutation (his-), is able to use both lactose and galactose,
and is sensitive to erythromycin and resistant to streptomycin. Your F- strain asha single
auxotrophic mutation (arg-), is unable to use either lactose or galactose, and is resistant to
erythromycin and sensitive to streptomycin.
Hfr strain A is derived from the F+ strain described above. The order of markers transferred by
HfrA is: (first) his str arg gal ery lac (last).
a) Your master plate should select for the greater possible number of exconjugants.
Assume you are using Minimal Media (MM). Circle ONE answer for each.
The carbon source(s) on the master plate should be:
glucose
The master plate should include:
both ery and str
The master plate should include:
both arg and his
Explanation:
- First, write out the genotype of HfrA and F-:
- Hfr: is lac gal ery str argh − + +s R +
- F-: is lac gal ery str argh + − −R s −
- Selecting markers:
- Str can be used to select against F- (+str)
- Ery can be used to select against Hfr (+ery)
- Optimizing the exconjugants:
- Add in all the amino acids that are not used as markers
- (+arg)
- (+his)
- Choosing carbon source:
- Since no sugars are used as a marker, glucose should be the
carbon source to maximize number of exconjugants since it
doesn’t select against any strains
b) You make replica plates of the following compositions. Assume each plate has glucose
unless gal and or lac is added instead.
Document Summary
Lifesci 4 - lecture 14 - midterm review. Selection: use methionine as marker for f- and lactose as marker for hfr (everything that is previous to those markers cannot be used due to the genotypes of f- and hfr) Select for met+ to kill the most f- strains (to select for met+, we should. Select for lac+ to kill the most hfr strains. Optimization : add in all the other amino acids that were not used as markers. + galactose (sugar source) since we used lactose (sugar source) as one of the markers, we should add in galactose as well to save the most exconjugants. Answer: minimal media + lactose + galactose + lysine + arginine. Which is/are the selection marker(s): lac, gal, lac+ and gal, lac+ or gal, can"t tell. If both sugars are in minimal media, only one of them are being selected, the other one is added to save whatever strains the first sugar are selecting against.
