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Animation Illustrating Genetic Exchange as a Result of Bacterial Transformation

  • 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 as a result of bacterial transformation.
  • Publication Date : December 2014
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Summary

Transformation is a form of genetic recombination in which a DNA fragment from a dead, degraded bacterium enters a competent recipient bacterium and is exchanged for a piece of DNA of the recipient.

Introduction

Transformation usually involves only homologous recombination, a recombination of homologous DNA regions having nearly the same nucleotide sequences. For many bacteria this involves similar bacterial strains or strains of the same bacterial species, while others will take up any DNA and recombine with any that has significant homology.

During transformation, DNA fragments (usually about 10 genes long) are released from a dead degraded bacterium and bind to DNA-binding proteins on the surface of a competent living recipient bacterium. Depending on the bacterium, either both strands of DNA penetrate the recipient, or a nuclease degrades one strand of the fragment and the remaining DNA strand enters the recipient. This DNA fragment from the donor is then exchanged for a piece of the recipient's DNA by means of RecA proteins and other molecules and involves breakage and reunion of the paired DNA segments (1). Transformation 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: Introduction

Transformation is a form of genetic recombination in which a DNA fragment from a dead, degraded bacterium enters a competent recipient bacterium and is exchanged for a piece of DNA of the recipient.

Slides 3 and 4

Transformation begins when a donor bacterium dies and is degraded. The chromosome is fragmented and the plasma membrane and cell wall break apart.

Slides 5 and 6

DNA fragments (usually about 10 genes long) are released from a dead degraded bacterium and bind to DNA binding proteins on the surface of a competent living recipient bacterium.

Slides 7 and 8

A nuclease usually degrades one strand of the donor fragment and the remaining complementary DNA strand enters the recipient.  Competence-specific single-stranded DNA-binding proteins bind to the donor DNA strand to prevent it from being degraded in the cytoplasm.

Slides 9 and 10

The single strand of donor bacterial DNA pairs up with the region of homologous recipient DNA, a region having nearly the same nucleotide sequence. RecA proteins, as well as other molecules, promote genetic exchange between the donor's DNA and that of the recipient.  This involves breakage and reunion of the pared DNA segments

Slides 11 and 12

The excised strand of DNA cannot replicate and is eventually degraded.

Slide 13

Differences in the nucleotide sequences between the homologous regions of the donor and recipient DNA can activate the DNA repair systems of the bacterium.  Either the donor or the recipient DNA can be repaired during this process.

Slides 14 and 15

If the repair occurs in the previously inserted donor DNA, then as the donor nucleotides are removed they will be replaced with nucleotides complementary to the recipient's DNA.  The bacterium will once again have DNA identical to that of the original recipient bacterium. Therefore the genotype and phenotype of the recipient will remain unchanged.

Slides 16 and 17

On the other hand, if the repair occurs in the homologous area of the recipient's DNA, then as the recipient nucleotides are removed, they will be replaced by nucleotides complementary to the donor's DNA and the bacterium will permanently contain genes from the initial donor bacterium, and the recipient's genotype and phenotype will change.

Reference

1. deVries J, Wackernagel W. 2002. Integration of foreign DNA during natural transformation of Acinetobacter sp. by homology-facilitated illegitimate recombination. Proc. Natl. Acad. Sci. US 99: 2094-2099.

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