5. Genetics of Bacteria and Viruses

Transduction

5. Genetics of Bacteria and Viruses

Transduction

2:52 minutes

Problem 3Klug - 12th Edition

Textbook Question

Price et al. [(1999). J. Bacteriol. 181:2358–2362] conducted a genetic study of the toxin transport protein (PA) of Bacillus anthracis, the bacterium that causes anthrax in humans. Within the 2294-nucleotide gene in 26 strains they identified five point mutations—two missense and three synonyms—among different isolates. Necropsy samples from an anthrax outbreak in 1979 revealed a novel missense mutation and five unique nucleotide changes among ten victims. The authors concluded that these data indicate little or no horizontal transfer between different B. anthracis strains.

What is meant by 'horizontal transfer'?

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Horizontal transfer, also known as horizontal gene transfer (HGT), refers to the movement of genetic material between organisms other than through vertical transmission (from parent to offspring).

In bacteria, horizontal transfer can occur through mechanisms such as transformation, transduction, and conjugation.

Transformation involves the uptake of naked DNA from the environment by a bacterial cell.

Transduction is the process by which bacterial DNA is transferred from one bacterium to another by a virus (bacteriophage).

Conjugation involves the direct transfer of DNA between two bacterial cells that are temporarily joined.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Horizontal Gene Transfer

Horizontal gene transfer (HGT) refers to the process by which an organism incorporates genetic material from another organism without being its offspring. This mechanism allows for the exchange of genes between different species, contributing to genetic diversity and the evolution of traits such as antibiotic resistance. In bacteria, HGT can occur through transformation, transduction, or conjugation, significantly impacting their adaptability and survival.

Point Mutations

Point mutations are changes in a single nucleotide base pair in the DNA sequence of a gene. These mutations can be classified as missense mutations, which result in a different amino acid being incorporated into a protein, or synonymous mutations, which do not change the amino acid sequence. Understanding point mutations is crucial for studying genetic variation and the functional consequences of genetic changes in organisms.

Bacillus anthracis and Anthrax

Bacillus anthracis is a bacterium that causes anthrax, a serious infectious disease. It can form spores that survive in harsh conditions, making it a potent pathogen. The study of its genetic variations, such as those identified in the toxin transport protein, helps researchers understand the epidemiology of anthrax and the genetic factors that contribute to its virulence and transmission among hosts.

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Textbook Question

In this chapter, we have focused on genetic systems present in bacteria and on the viruses that use bacteria as hosts (bacteriophages). In particular, we discussed mechanisms by which bacteria and their phages undergo genetic recombination, which allows geneticists to map bacterial and bacteriophage chromosomes. In the process, we found many opportunities to consider how this information was acquired. From the explanations given in the chapter, what answers would you propose to the following questions? How do we know that bacteriophages recombine genetic material through transduction and that cell-to-cell contact is not essential for transduction to occur?

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Textbook Question

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.

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Textbook Question

A triple-auxotrophic strain of E. coli having the genotype phe⁻ met⁻ ara⁻ is used as a recipient strain in a transduction experiment. The strain is unable to synthesize its own phenylalanine or methionine, and it carries a mutation that leaves it unable to utilize the sugar arabinose for growth. The recipient is crossed to a prototrophic strain with the genotype phe⁺ met⁺ ara⁺. The table below shows the selected marker and gives cotransduction frequencies for the unselected markers. Selected Selected Colonies Containing the Marker Unselected Marker (%) _ phe⁺ met⁺ ara⁺ met⁺ 4 - 7 phe⁺ - 2 51 met⁺, phe⁺. - - 79 ara⁺ 68 5 - Use the cotransduction data to determine the order of these genes.

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Textbook Question

A triple-auxotrophic strain of E. coli having the genotype phe⁻ met⁻ ara⁻ is used as a recipient strain in a transduction experiment. The strain is unable to synthesize its own phenylalanine or methionine, and it carries a mutation that leaves it unable to utilize the sugar arabinose for growth. The recipient is crossed to a prototrophic strain with the genotype phe⁺ met⁺ ara⁺. The table below shows the selected marker and gives cotransduction frequencies for the unselected markers. Selected Selected Colonies Containing the Marker Unselected Marker (%) _ phe⁺ met⁺ ara⁺ met⁺ 4 - 7 phe⁺ - 2 51 met⁺, phe⁺. - - 79 ara⁺ 68 5 - Identify the compounds present in each of the selective media.

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Textbook Question

The phage P1 is used as a generalized transducing phage in an experiment combining a donor strain of E. coli of genotype leu⁺ phe⁺ ala⁺ and a recipient strain that is leu⁻ phe⁻ ala⁻. In separate experiments, transductants are selected for leu⁺ (Experiment A), for ala⁺ (Experiment B), and for phe⁺ (Experiment C). Following selection, transductant genotypes for the unselected markers are identified. The selection experiment results below show the frequency of each genotype. Experiment A Experiment B Experiment C phe⁻ ala⁻ 26% leu⁻ ala⁻ 65% leu⁻ phe⁻ 71% phe⁺ ala⁻ 50% leu⁺ ala⁻. 48% leu⁺ phe⁻ 21% phe⁻ ala⁺ 19% leu⁻ ala⁺ 0% leu⁻ phe⁺ 0% phe⁺ ala⁺ 3% leu⁺ ala⁺ 4% leu⁺ phe⁺ 3% In Experiment B, why are there no transductants with the genotype leu⁻ ala⁺?

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Textbook Question

The phage P1 is used as a generalized transducing phage in an experiment combining a donor strain of E. coli of genotype leu⁺ phe⁺ ala⁺ and a recipient strain that is leu⁻ phe⁻ ala⁻. In separate experiments, transductants are selected for leu⁺ (Experiment A), for ala⁺ (Experiment B), and for phe⁺ (Experiment C). Following selection, transductant genotypes for the unselected markers are identified. The selection experiment results below show the frequency of each genotype. Experiment A Experiment B Experiment C phe⁻ ala⁻ 26% leu⁻ ala⁻ 65% leu⁻ phe⁻ 71% phe⁺ ala⁻ 50% leu⁺ ala⁻. 48% leu⁺ phe⁻ 21% phe⁻ ala⁺ 19% leu⁻ ala⁺ 0% leu⁻ phe⁺ 0% phe⁺ ala⁺ 3% leu⁺ ala⁺ 4% leu⁺ phe⁺ 3% Diagram the crossover events that form each of the transductants in Experiment A.

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Textbook Question

The phage P1 is used as a generalized transducing phage in an experiment combining a donor strain of E. coli of genotype leu⁺ phe⁺ ala⁺ and a recipient strain that is leu⁻ phe⁻ ala⁻. In separate experiments, transductants are selected for leu⁺ (Experiment A), for ala⁺ (Experiment B), and for phe⁺ (Experiment C). Following selection, transductant genotypes for the unselected markers are identified. The selection experiment results below show the frequency of each genotype. Experiment A Experiment B Experiment C phe⁻ ala⁻ 26% leu⁻ ala⁻ 65% leu⁻ phe⁻ 71% phe⁺ ala⁻ 50% leu⁺ ala⁻. 48% leu⁺ phe⁻ 21% phe⁻ ala⁺ 19% leu⁻ ala⁺ 0% leu⁻ phe⁺ 0% phe⁺ ala⁺ 3% leu⁺ ala⁺ 4% leu⁺ phe⁺ 3% Determine the order of genes on the donor chromosome.

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Textbook Question

The phage P1 is used as a generalized transducing phage in an experiment combining a donor strain of E. coli of genotype leu⁺ phe⁺ ala⁺ and a recipient strain that is leu⁻ phe⁻ ala⁻. In separate experiments, transductants are selected for leu⁺ (Experiment A), for ala⁺ (Experiment B), and for phe⁺ (Experiment C). Following selection, transductant genotypes for the unselected markers are identified. The selection experiment results below show the frequency of each genotype. Experiment A Experiment B Experiment C phe⁻ ala⁻ 26% leu⁻ ala⁻ 65% leu⁻ phe⁻ 71% phe⁺ ala⁻ 50% leu⁺ ala⁻. 48% leu⁺ phe⁻ 21% phe⁻ ala⁺ 19% leu⁻ ala⁺ 0% leu⁻ phe⁺ 0% phe⁺ ala⁺ 3% leu⁺ ala⁺ 4% leu⁺ phe⁺ 3% What compound or compounds are added to the minimal medium to select for transductants in Experiments A, B, and C?

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Multiple Choice

True or False:Transduction uses viruses to transfer foreign DNA into bacteria

Specialized transduction differs from generalized transduction because specialized transduction is defined by what?

A cotransduction experiment was performed with two bacteria strains. The first train has the genotype l+ g m+ while the second strain has the genotype of l g+ m. The researchers found that 46 colonies had cotransduced m+ with l+, while only 25 colonies had cotransduced g with l+. Using this information determine which of the following gene pairs are closest together.

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