Horizontal Gene Transfer

Horizontal gene transfer is the movement of genetic material between organisms other than by inheritance from parent to offspring, a process that makes bacterial genomes remarkably dynamic.

Definition

Horizontal gene transfer is the acquisition of genetic material by an organism from a source other than its parent, encompassing transformation, transduction, and conjugation in prokaryotes.

Scope

This topic covers the three principal mechanisms of prokaryotic gene transfer: natural transformation, in which cells take up free DNA; transduction, in which bacteriophages carry DNA between cells; and conjugation, in which DNA passes through direct cell-to-cell contact. It also addresses recombination of transferred DNA and the evolutionary and applied consequences of gene flow among microbes.

Core questions

• What are the main mechanisms by which bacteria exchange DNA?
• How is transferred DNA stably incorporated into the recipient genome?
• Why does horizontal gene transfer accelerate microbial evolution?
• How does gene transfer contribute to the spread of resistance and virulence?

Key concepts

• Natural transformation and competence
• Transduction by bacteriophages
• Conjugation and the F factor
• Homologous recombination of transferred DNA
• Gene flow and microbial evolution

Key theories

Mechanisms of genetic exchange

Bacteria acquire genes by transformation, transduction, and conjugation, three distinct routes that allow DNA to move between cells and be incorporated by recombination, providing variation independent of vertical inheritance.

Mechanisms

In transformation, competent cells take up free DNA from the environment and integrate it by recombination. In transduction, a bacteriophage packages host DNA and delivers it to a new cell during infection. In conjugation, a donor cell transfers DNA, often a plasmid, to a recipient through a specialized appendage and direct contact. In each case the incoming DNA may be maintained on a plasmid or recombined into the chromosome.

Clinical relevance

Horizontal gene transfer is a major route for the dissemination of antibiotic resistance and virulence genes among bacteria, including between different species, and is also exploited as a tool for introducing DNA into microbes in research and biotechnology.

History

Frederick Griffith's 1928 transformation experiments and the later identification of DNA as the transforming principle, together with Lederberg and Tatum's discovery of conjugation in 1946 and the description of transduction, established that bacteria exchange genes by several distinct mechanisms.

Key figures

• Frederick Griffith
• Joshua Lederberg
• Edward Tatum

Seminal works

• madigan2018
• willey2020

Frequently asked questions

How does horizontal gene transfer differ from normal inheritance?

Normal, or vertical, inheritance passes genes from a parent cell to its offspring during reproduction. Horizontal gene transfer moves genes between organisms that are not parent and offspring, so a bacterium can acquire new genes from unrelated cells.