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Animation Illustrating Genetic Exchange in Bacteria as a Result of Generalized Transduction

  • Authors: Gary Kaiser 1, Erica Suchman 2
  • VIEW AFFILIATIONS HIDE AFFILIATIONS
    Affiliations: 1: Biology Department, The Community College of Baltimore County, Catonsville Campus, Baltimore, MD, 21228; 2: Colorado State University, Fort Collins, Colorado, 80523
  • Citation: Gary Kaiser, Erica Suchman. 2014. Animation illustrating genetic exchange in bacteria as a result of generalized transduction.
  • Publication Date : December 2014
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Summary

Generalized transduction is a form of genetic recombination in which a DNA fragment or a plasmid is carried from one bacterium and inserted into another by a bacteriophage called a transducing phage. Once inserted, the DNA fragment can subsequently be exchanged for a piece of the recipient's DNA by homologous recombination.

Introduction

During the replication of lytic bacteriophages and temperate bacteriophages, occasionally the bacteriophage capsid accidently assembles around a small fragment of bacterial DNA. When this bacteriophage, called a transducing particle, infects another bacterium, it injects the fragment of donor bacterial DNA it is carrying into the recipient where it can subsequently be exchanged for a piece of the recipient's DNA by homologous recombination (1,2). Generalized transduction occurs in a variety of bacteria, including Staphylococcus, Escherichia, Salmonella, and Pseudomonas (1). Transduction is one of the ways that bacteria can exchange genetic material in the environment, and serves as an important mechanism for horizontal gene transfer that results in increased bacterial genetic diversity.

Methods

Adobe Flash Professional CS5.5 was used in constructing this animation. Illustrations were drawn using Adobe Illustrator CS5.1 and imported into Adobe Flash Professional CS5.5.

Discussion

Slides 1 and 2

Generalized transduction begins when a bacteriophage adsorbs (binds to a receptor) on a susceptible bacterium.

Slides 3 and 4

The genome of the bacteriophage is "injected" into the host bacterium when the phage capsid proteins force the genome through the cell wall of the bacterium.

Slides 5 and 7

The bacteriophage uses the bacterium's metabolic machinery to replicate.  A bacteriophage-coded enzyme degrades the bacterial DNA into fragments in the process of "stealing" nucleotides for phage genome production. Occasionally a bacteriophage capsid will assemble around a fragment of the donor bacterium's DNA if the fragment is of a similar size to the bacteriophage's genome.  This is possible because bacteriophages do not use packaging signals, and hence can package any piece of DNA that is roughly the correct size.

Slides 8 and 9

Eventually the bacterium is lysed and bacteriophages are released and are now able to infect new susceptible bacteria. Note that the one bacteriophage in this example is carrying a fragment of double-stranded DNA for the donor bacterium (arrow). Typically between 50 and 200 bacteriophages are produced within a single infected bacterium. Only four are shown here.

Slides 10 and 11

The bacteriophage carrying the donor bacterium's DNA, now called a transducing phage, adsorbs (binds to a receptor) on a susceptible recipient bacterium.

Slides 12 and 13

The transducing phage inserts the donor bacterium's DNA it is carrying into the recipient bacterium when the phage capsid proteins force the genome through the cell wall of the recipient bacterium.

Slides 14 and 15

Homologous recombination occurs and the donor bacterium's DNA is exchanged for some of the recipient's DNA.  As the bacterium replicates, each daughter cell will now carry this new genetic material. (Note:  Bacterial plasmids can also be carried from one bacterium to another by generalized transduction if they are of a similar size to the bacteriophage's genome.)

References

1. Thierauf AI, Perez G, Maloy AS. 2009. Generalized transduction.  Method  Mol Biol 501:267-86.

2. Mann BA, Slauch JM. 1997. Transduction of Low-Copy Number Plasmids by Bacteriophage P22. Genetics 146: 447-456.

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