Prescott's Microbiology
11th Edition
ISBN: 9781260211887
Author: WILLEY, Sandman, Wood
Publisher: McGraw Hill
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Chapter 16.2, Problem 1MI
How would you screen for a tryptophan auxotroph? How would you select for a mutant that is resistant to the antibiotic ampicillin but sensitive to tetracycline (assume the parental stain is resistant to both antibiotics)?
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Two auxotrophic triple Escherichia coli strains (A: met- phe- ade- val+ bio+ thr+ and B:
met+ phe+ ade+ val- bio- thr-) are mixed in LB liquid medium, diluted and then spread on
LB solid rich medium. Six colonies are observed:
Then, replicates are performed on 6 different media (minimum medium + glucose + indicated
substances). The results are shown below. Determine the genotype of the 6 colonies observed.
Which ones are from strain A? From strain B? Which hypotheses can explain these results
and which one do you prefer?
met phe
val bio
Abbreviations:
met ade
val thr
phe ade
bio thr
Met: methionine; Phe: phenylalanine; Ade: adenine; Val: valine; Bio: biotin; Thr: threonine.
The strain of λ phage t is cI857. That tells you that the cI DNA segment is disabled by a specific mutation. What is the exact genetic change in cI857? What specific property of the cI gene product does this mutation change, and how does this help titering for a plaque assay?
Why is replica plating used to isolate an auxotrophic mutant from a prototrophic parent?
Chapter 16 Solutions
Prescott's Microbiology
Ch. 16.1 - Retrieve, Infer, Apply List three ways in which...Ch. 16.1 - Compare and contrast the means by which the...Ch. 16.1 - Give examples of intragenic and extragenic...Ch. 16.1 - Retrieve, Infer, Apply Sometimes a point mutation...Ch. 16.1 - Retrieve, Infer, Apply Why might a missense...Ch. 16.2 - How would you screen for a tryptophan auxotroph?...Ch. 16.2 - Why is a small amount of histidine added to the...Ch. 16.2 - Retrieve, Infer, Apply Describe how replica...Ch. 16.2 - Retrieve, Infer, Apply Why are mutant selection...Ch. 16.2 - Retrieve, Infer, Apply Briefly discuss how...
Ch. 16.2 - Describe how you would isolate a mutant that...Ch. 16.2 - Prob. 5CCCh. 16.3 - How is mismatch repair similar to DNA polymerase...Ch. 16.3 - How is damaged DNA recognized by the UvrAB...Ch. 16.3 - Prob. 1CCCh. 16.3 - Retrieve, Infer, Apply What role does DNA...Ch. 16.3 - Retrieve, Infer, Apply When E. coli cells are...Ch. 16.3 - Explain how the following DNA alterations and...Ch. 16.4 - An antibiotic-resistance gene located on a...Ch. 16.4 - What four fates can DNA have after entering a...Ch. 16.4 - How does homologous recombination differ from...Ch. 16.5 - What features are common to all types of...Ch. 16.5 - How does a transposon differ from an insertion...Ch. 16.5 - What is simple (cut-and-paste) transposition? What...Ch. 16.5 - What effect would you expect the existence of...Ch. 16.6 - Prob. 1MICh. 16.6 - What is bacterial conjugation and how was it...Ch. 16.6 - For F+, Hfr, and F strains of E. coli, indicate...Ch. 16.6 - Describe how F+ F and Hfr conjugation processes...Ch. 16.6 - Compare and contract F+ F and F F conjugation.Ch. 16.7 - According to this model, what would happen if DNA...Ch. 16.7 - Prob. 1CCCh. 16.7 - Describe how transformation occurs in S....Ch. 16.7 - Discuss two ways in which artificial...Ch. 16.8 - Compare the number of transducing particles that...Ch. 16.8 - Why cant the gal and bio genes be transduced by...Ch. 16.8 - Describe generalized transduction and how it...Ch. 16.8 - What is specialized transduction and how does it...Ch. 16.8 - How might one tell whether horizontal gene...Ch. 16.8 - Why doesnt a cell lyse after successful...Ch. 16.8 - Describe how conjugation, transformation, and...Ch. 16.9 - As a replicative transposon, what would happen if...Ch. 16 - Prob. 1RCCh. 16 - Prob. 2RCCh. 16 - Prob. 3RCCh. 16 - Prob. 4RCCh. 16 - Prob. 5RCCh. 16 - Prob. 6RCCh. 16 - Mutations are often considered harmful. Give an...Ch. 16 - Mistakes made during transcription affect the cell...Ch. 16 - Suppose that transduction took place when a U-tube...Ch. 16 - Suppose that you carried out a U-tube experiment...Ch. 16 - Prob. 5ALCh. 16 - Prob. 6ALCh. 16 - Prob. 7AL
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- Are the bands indicated in Step 6 (SDS-PAGE) likely visualized by western blot or by a general protein stain (such as Coomassie or silver)?arrow_forwardWith regard to studying the mechanism of conjugation,what is the purpose of using a U-tube?arrow_forwardWhat is the purpose of using Triton X in hemolytic assay.arrow_forward
- You co-culture the following bacterial strains: an Hfr prototroph and an F- auxotroph for the genes mal, met, mtl, and xyl. You interrupt conjugation at various time points and place the mixtures on media plates lacking each of the nutrients. Based on the results shown on the right, what is the order of these four genes along the bacterial chromosome? Explain your reasoning.arrow_forwardYou are counting plaques on your plaque assay plates made from serial dilutions of your high titer lysate. Your 10-5 plate has 615 plaques although some are butting up against each other so it is difficult to get an accurate count. Your 10-6 plate has 42 plaques, and your 10-7 plate has only 1 plaque. Which plate would probably yield the most accurate titer calculation of your phage and why is it more trustworthy than the others?arrow_forwardYou co-culture the following bacterial strains: an Hfr prototroph and an F- auxotroph for the genes mal, met, mtl, and xyl. You interrupt conjugation at various time points and place the mixtures on media plates lacking each of the nutrients. Based on the results shown in the image, what is the order of these four genes along the bacterial chromosome? Please explain!arrow_forward
- If an E. coli auxotroph X could grow only on a medium containing leucine, and an auxotroph Y could grow only on a medium containing threonine. (i) Write the genotype of both E. coli strains. (ii) How would you test whether DNA from X could transform Y?arrow_forwardWhat order should the steps be in for this culture method?arrow_forwardChoose two genes from Figure 4.6 and draw a graph to represent the change in transcription over time.arrow_forward
- A plaque assay is performed beginning with 1 mL of a solution containing bacteriophages. This solution is serially diluted 4 times by combining 0.1 mL of each sequential dilution with 9.9 mL of liquid medium. Then 0.1 mL of the final dilution is plated in the plaque assay and yields 21 plaques. What is the initial density of bacteriophages in the original 1 mL? Recall that initial phage density = (plaque number/mL) ×× (dilution factor).arrow_forwardResults from a Kirby Bauer antibiotic assay on a Gram-negative bacterial culture are described as follows: A) the bacterium is resistant to penicillin, an antibiotic that targets synthesis of the peptidoglycan cell wall and B) the bacterium is resistant to tetracycline, an antibiotic that targets the small subunit of the ribosome, inhibiting protein synthesis. Which of the results represents intrinsic resistant and which represents acquired resistants?arrow_forwardPrototrophy is often the phenotype selected to detecttransformants. Prototrophic cells are used for donorDNA extraction; then this DNA is cloned and the clonesare added to an auxotrophic recipient culture. Successfultransformants are identified by plating the recipientculture on minimal medium and looking for colonies.What experimental design would you use to make surethat a colony that you hope is a transformant is not, infact,a. a prototrophic cell that has entered the recipientculture as a contaminant?b. a revertant (mutation back to prototrophy by a secondmutation in the originally mutated gene) of theauxotrophic mutation?arrow_forward
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