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
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
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 firstname.lastname@example.org.
Use the animations to make abstract scientific ideas visible and
Explain important scientific principles through the animations. For
example, the biological clocks animations can be used to demonstrate
the fundamentals of transcription and translation.
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.
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.
Incorporate the animations into Web-based learning modules that you
create to supplement your classroom curricula.
Encourage students to incorporate the animations into their own Web-based
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.