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Problem 1d
For bacteria that are F⁺, Hfr, F', and F⁻, perform or answer the following.
Which of these donors can transfer a donor gene to exconjugants?
Problem 1e
For bacteria that are F⁺, Hfr, F', and F⁻, perform or answer the following.
Describe the results of conjugation (i.e., changes in the recipient and the exconjugant) that allow detection of the state of the F factor in a donor strain.
Problem 1f
For bacteria that are F⁺, Hfr, F', and F⁻, perform or answer the following.
Describe a "partial diploid" and how it originates.
Problem 2
The flow diagram identifies relationships between bacterial strains in various F factor states. For each of the four arrows in the diagram, provide a description of the events involved in the transition.
Problem 3
Conjugation between an Hfr cell and an F⁻ cell does not usually result in conversion of exconjugants to the donor state. Occasionally, however, the result of this conjugation is two Hfr cells. Explain how this occurs.
- Bacteria transfer genes by conjugation, transduction, and transformation. Compare and contrast these mechanisms. In your answer, identify which if any processes involve homologous recombination and which if any do not.
Problem 4
Problem 5a
Explain the importance of the following features in conjugating donor bacteria:
the origin of transfer
Problem 5b
Explain the importance of the following features in conjugating donor bacteria:
the conjugation pilus
Problem 5c
Explain the importance of the following features in conjugating donor bacteria:
homologous recombination
Problem 5d
Explain the importance of the following features in conjugating donor bacteria:
the relaxosome
Problem 5e
Explain the importance of the following features in conjugating donor bacteria:
relaxase
Problem 5f
Explain the importance of the following features in conjugating donor bacteria:
T strand DNA
Problem 5g
Explain the importance of the following features in conjugating donor bacteria:
pilin protein
Problem 6
Describe the difference between the bacteriophage lytic cycle and lysogenic cycle.
Problem 7
Describe what is meant by the term site-specific recombination as used in identifying the processes that lead to the integration of temperate bacteriophages into host bacterial chromosomes during lysogeny or to the formation of specialized transducing phage.
Problem 8
What is a prophage, and how is a prophage formed?
Problem 9
How is the frequency of cotransduction related to the relative positions of genes on a bacterial chromosome? Draw a map of three genes and describe the expected relationship of cotransduction frequencies to the map.
Problem 10
Describe the differences between genetic complementation and recombination as they relate to the detection of wild-type lysis by a mutant bacteriophage.
Problem 11
Among the mechanisms of gene transfer in bacteria, which one is capable of transferring the largest chromosome segment from donor to recipient? Which process generally transfers the smallest donor segments to the recipient? Explain your reasoning for both answers.
Problem 12
What is lateral gene transfer? How might it take place between two bacterial cells?
Problem 13
Lateral gene transfer is thought to have played a major role in the evolution of bacterial genomes. Describe the impact of LGT on bacterial genome evolution.
Problem 14
Seven deletion mutations (1 to 7 in the table below) are tested for their ability to form wild-type recombinants with five point mutations (a to e). The symbol "+" indicates that wild-type recombination occurs, and "-" indicates that wild types are not formed. Use the data to construct a genetic map of the order of point mutations, and indicate the segment deleted by each deletion mutation.
Problem 15a
A 2013 CDC report identified the practice of routinely adding antibiotic compounds to animal feed as a major culprit in the rapid increase in the number of antibiotic-resistant strains. Agricultural practice in recent decades has encouraged the addition of antibiotics to animal feed to promote growth rather than to treat disease.
Speculate about the process by which feeding antibiotics to animals such as cattle might lead to an increase in the number of antibiotic-resistant strains of bacteria.
Problem 15b
A 2013 CDC report identified the practice of routinely adding antibiotic compounds to animal feed as a major culprit in the rapid increase in the number of antibiotic-resistant strains. Agricultural practice in recent decades has encouraged the addition of antibiotics to animal feed to promote growth rather than to treat disease.
How might the increase in antibiotic-resistant strains of bacteria in cattle be a threat to human health?
Problem 16a
Hfr strains that differ in integrated F factor orientation and site of integration are used to construct consolidated bacterial chromosome maps. The data below show the order of gene transfer for five strains.
Hfr Strain Order of Gene Transfer (First → Last)
Hfr A oriT–thr–leu–azi–ton–pro–lac–ade
Hfr B oriT–mtl–xyl–mal–str–his
Hfr C oriT–ile–met–thi–thr–leu–azi–ton
Hfr D oriT–his–trp–gal–ade–lac–pro–ton
Hfr E oriT–thi–met–ile–mtl–xyl–mal–str
Identify the overlaps between Hfr strains. Identify the orientations of integrated F factors relative to one another.
Problem 16b
Hfr strains that differ in integrated F factor orientation and site of integration are used to construct consolidated bacterial chromosome maps. The data below show the order of gene transfer for five strains.
Hfr Strain Order of Gene Transfer (First → Last)
Hfr A oriT–thr–leu–azi–ton–pro–lac–ade
Hfr B oriT–mtl–xyl–mal–str–his
Hfr C oriT–ile–met–thi–thr–leu–azi–ton
Hfr D oriT–his–trp–gal–ade–lac–pro–ton
Hfr E oriT–thi–met–ile–mtl–xyl–mal–str
Draw a consolidated map of the bacterial chromosome. (Hint: Begin by placing the insertion site for Hfr A at the 2 o'clock position and arranging the genes thr–leu–azi- . . . in clockwise order.)
Problem 17
Five Hfr strains from the same bacterial species are analyzed for their ability to transfer genes to F⁻ recipient bacteria. The data shown below list the origin of transfer (oriT) for each strain and give the order of genes, with the first gene on the left and the last gene on the right. Use the data to construct a circular map of the bacterium.
Hfr Strain Genes Transferred
Hfr 1 oriT met ala lac gal
Hfr 2 oriT met leu thr azi
Hfr 3 oriT gal pro trp azi
Hfr 4 oriT leu met ala lac
Hfr 5 oriT trp azi thr leu met
Problem 18a
An interrupted mating study is carried out on Hfr strains 1, 2, and 3 identified in Problem 17. After conjugation is established, a small sample of the mixture is collected every minute for 20 minutes to determine the distance between genes on the chromosome. Results for each of the three Hfr strains are shown below. The total duration of conjugation (in minutes) is given for each transferred gene.
Hfr strain 1 oriT met ala lac gal
Duration (min) 0 2 8 13 17
Hfr strain 2 oriT met leu thr azi
Duration (min) 0 2 7 10 17
Hfr strain 3 oriT gal pro trp azi
Duration (min) 0 3 8 14 19
For each Hfr strain, draw a time-of-entry profile.
Problem 18b
An interrupted mating study is carried out on Hfr strains 1, 2, and 3 identified in Problem 17. After conjugation is established, a small sample of the mixture is collected every minute for 20 minutes to determine the distance between genes on the chromosome. Results for each of the three Hfr strains are shown below. The total duration of conjugation (in minutes) is given for each transferred gene.
Hfr strain 1 oriT met ala lac gal
Duration (min) 0 2 8 13 17
Hfr strain 2 oriT met leu thr azi
Duration (min) 0 2 7 10 17
Hfr strain 3 oriT gal pro trp azi
Duration (min) 0 3 8 14 19
Using the chromosome map you prepared in answer to Problem 17, determine the distance in minutes between each gene on the map.
Problem 18c
An interrupted mating study is carried out on Hfr strains 1, 2, and 3 identified in Problem 17. After conjugation is established, a small sample of the mixture is collected every minute for 20 minutes to determine the distance between genes on the chromosome. Results for each of the three Hfr strains are shown below. The total duration of conjugation (in minutes) is given for each transferred gene.
Hfr strain 1 oriT met ala lac gal
Duration (min) 0 2 8 13 17
Hfr strain 2 oriT met leu thr azi
Duration (min) 0 2 7 10 17
Hfr strain 3 oriT gal pro trp azi
Duration (min) 0 3 8 14 19
Explain why azi is the last gene of strain 2 to transfer in the 20 minutes of conjugation time. How many minutes of conjugation time would be needed to allow the next gene on the map to transfer from Hfr strain 2?
