Bacterial Conjugation

Watch the animation on the left side of the screen to see how bacteria share genes that encode resistance to antibiotics. This demonstration has been adapted from an animation developed by HHMI international research scholar B. Brett Finlay, Ph.D., for the 1999 Holiday Lectures on Science, 2000 and Beyond: Confronting the Microbe Menace.

To view the animation, manipulate the controls at the bottom of the view screen. Expect several pauses as the text in this panel updates to describe the relevant step in the animation.

Part 1: The bacterial genome

The animation begins with two bacteria meeting. Each one contains its own chromosome. Above the chromosome of one bacterium (bacterium A) is a plasmid, a portion of the bacterial genome that is separate from the chromosome. The plasmid of bacterium A is also known as Resistance (R) factor. It contains genes that encode different traits and can, as you will see, be transferred from one bacterium to another, and even between different species! In the case of this animation, the R factor encodes a molecule that provides resistance to the antibacterial drug X.

To view a version of this animation that includes audio narration, click here.

Part 2: The bacterial sex pilus

Bacteria transfer genetic material through the sex pilus. The bacterium that contains the R factor creates the pilus, a tube that extends from the surface of the bacterial cell wall and connects bacterium A to bacterium B.

Part 3: The transfer of the bacterial DNA

The two DNA strands of the R factor are separated and one of them moves across the sex pilus. As the plasmid enters bacterium B, complementary DNA synthesis occurs in both bacteria to generate double-stranded DNA. At the end of the process, a portion of bacterium A's genome has been duplicated in bacterium B.

Part 4: Bacterium obtains multidrug resistance

Once the R factor has been incorporated into the genome of bacterium B, the bacterium expresses a molecule on its surface that provides resistance to drug X.

Bacterial Conjugation Background

Most bacteria contain a single chromosome that carries the cell's genetic information. In addition, bacteria often contain small circular, double-stranded DNA molecules called plasmids. Plasmids are not connected to the main bacterial chromosomes and replicate independently. Plasmids usually contain genes, such as those coding for antibiotic resistance and the production of toxins, that are not crucial to the survival of the bacterium under normal environmental conditions.

Plasmids can be passed on from one bacterium to the other in a process called conjugation. Conjugation is one of the mechanisms by which bacteria can aquire new genetic material and, as a result, new traits.

Bacterial Conjugation Animation Teaching Tips

The animations in this section have a wide variety of classroom applications. Use the tips below to get started but look for more specific teaching tips in the near future. Please tell us how you are using the animations in your classroom by sending e-mail to grantswww@hhmi.org.

1. Use the animations to make abstract scientific ideas visible and concrete.

2. Explain important scientific principles through the animations. For example, the biological clocks animations can be used to demonstrate the fundamentals of transcription and translation.

3. Make sure that students learn the material by repeating sections of the animations as often as you think necessary to reinforce underlying scientific principles. You can start, restart, and play back sections of the animations.

4. Urge students to use the animations in accordance with their own learning styles. Students who are more visually oriented can watch the animations first and read the text later, while others might prefer to read the explanations first and then view the graphics.

5. Incorporate the animations into Web-based learning modules that you create to supplement your classroom curricula.

6. Encourage students to incorporate the animations into their own Web-based projects.

Bacterial Conjugation Credits

Director: Dennis Liu, Ph.D.

Scientific Direction: B. Brett Finlay, Ph.D.

Scientific Content: Laura Bonetta, Ph.D.

Animators: Eric Keller, Satoshi Amagai, Ph.D.