Bacterial Transformation: Videos & Practice Problems

Bacterial transformation is a form of horizontal gene transfer where competent cells uptake free or naked DNA from their environment. This process occurs in four steps: binding of double-stranded DNA to cell receptors, entry of a single strand into the cell, integration into the bacterial chromosome via homologous recombination, and rebuilding the complementary strand. This mechanism allows for the acquisition of traits such as antibiotic resistance, enhancing the adaptability of bacteria in various environments.

Bacterial Transformation

In this video, we're going to begin our lesson on bacterial transformation, a type of horizontal gene transfer. Recall from our previous lesson videos once again that transformation is a type of horizontal gene transfer characterized by the uptake of free or naked DNA in the environment by the cell. The cell is able to uptake free or naked DNA from the environment, and that is called transformation. Now, in order for a cell to transform DNA, it must be what is known as a competent cell. A competent cell is really describing a really complex physiological state. Competent cells are cells that have the ability to transform DNA from the environment, in other words, to uptake naked DNA from the environment. If a cell is not competent, then it will not be able to transform DNA.

If we take a look at our image down below, notice that it's distinguishing competent cells versus noncompetent cells. Notice the cell that's over here on the left is a totally competent cell. Competency is describing a really complex physiological state, but in the end, competent cells have the ability to transform or uptake DNA from the environment. Notice that this cell is able to transform naked DNA from the environment. This naked DNA is just this bare DNA that you see here, and it's able to transform or uptake that naked DNA. The naked DNA is able to make its way into the cell because the cell is competent. However, a cell that is not competent, like this one over here, notice is not able to uptake DNA. It's not able to transform DNA, and so the DNA is not able to get into the cell if it's not competent. Only competent cells are capable of transformation.

Cells can actually be competent or cells can be induced to be competent by chemical treatment. Transform or uptake external DNA. This here concludes our brief or our brief intro to bacterial transformation and competent cells, and we'll be able to learn more about transformation as we continue to move forward in our course. So, I'll see you all on our next video.

Mechanism of Natural Transformation

In this video, we're going to discuss the mechanism of natural transformation, which is one of the types of horizontal gene transfer. Cells that are naturally competent and able to transform or uptake DNA can regularly transform or uptake DNA from the environment when that DNA is available. The reason that DNA might be available in the environment is because maybe a nearby cell lysed or ruptured and released its DNA into the environment. Thus, natural transformation can really occur in a series of 4 steps that we have numbered down below: 1, 2, 3, and 4.

In these images, the blue structure represents a bacterial cell, and the circular structure inside represents the chromosome of the bacteria—the original DNA that belongs to that bacteria. You'll notice that this little segment of DNA represents the free naked DNA that is going to be transformed by the cell or uptake into the cell. This free naked DNA, in many cases, will contain genes. In this case, it contains an antibiotic resistance gene for antibiotic x, where x is just any antibiotic, just for the sake of an example. The antibiotic resistance gene is found in this external piece of DNA. This external piece of DNA is a double stranded DNA molecule, indicated as dsDNA, representing double stranded DNA.

The double stranded DNA molecule in the free naked DNA will simply bind to cell surface receptors on the surface of the bacterial cell. The ssDNA mentioned represents single stranded DNA. The single stranded DNA is going to enter the cell, and the complement strand, the other strand, is going to get degraded. You can see here that one of the strands is going to be broken up and degraded, whereas the other strand is actually going to enter the cell.

The single stranded DNA that enters the cell is then going to integrate into the host cell's chromosome, and it does this via homologous recombination. You can see this little single stranded piece of DNA that has entered and been transformed is going to integrate into the chromosome via homologous recombination. You can see the integration here. In the 4th and final step, the cell is going to rebuild the complement strand, the other strand that was degraded. It rebuilds that, so now we have a double stranded region back in place. This antibiotic resistance gene has now been incorporated into the chromosome, and so now the cell has resistance to antibiotic x because it obtained this antibiotic resistance gene through horizontal gene transfer, through natural transformation.

This concludes our brief lesson on the mechanism of natural transformation. We'll be able to get some practice applying these concepts as we move forward. I'll see you all in our next video.

What does it mean when a bacterial cell is naturally competent?

• A. The bacterial cell is able to transform its chromosomal DNA into RNA.
• B. The bacterial cell is able to transform DNA from their environment.
• C. The bacterial cell is able to degrade viral DNA from attacking viruses.
• D. The bacterial cell is able to take in naked DNA and incorporate that DNA into its genome.
• E. A and C.
• F. B and D.

Answer: (F)

Bacterial cells can become competent in two ways, which are:

• A. Spontaneously.
• B. Instinctively.
• C. Horizontally.
• D. Induced.
• E. A and D.
• F. A and C.
• G. B and C.

Answer: (E)

DNA transformation in bacteria is an important tool for DNA modification and cloning experiments. If the DNA being transformed by the bacteria contains antibiotic resistance genes, how does this help the scientists?

• A. Antibiotics will kill any bacteria that did not naturally transform the transferred DNA.
• B. It allows the scientists to identify which bacterial cells are competent and which cells are not.
• C. It allows scientists to remove all bacteria that have not incorporated the experimental genes into their genome.
• D. All of the above are reasons why antibiotic resistance is commonly used in transformation experiments.

Answer: (D)

Here’s what students ask on this topic:

What is bacterial transformation and how does it occur?

Bacterial transformation is a form of horizontal gene transfer where competent cells uptake free or naked DNA from their environment. This process occurs in four main steps: (1) Binding of double-stranded DNA to cell surface receptors, (2) Entry of a single strand of DNA into the cell while the complementary strand is degraded, (3) Integration of the single-stranded DNA into the bacterial chromosome via homologous recombination, and (4) Rebuilding of the complementary strand to form a stable double-stranded DNA. This mechanism allows bacteria to acquire new traits, such as antibiotic resistance, enhancing their adaptability in various environments.

What is a competent cell in the context of bacterial transformation?

A competent cell is a bacterial cell that has the physiological ability to uptake free or naked DNA from its environment. Competency is a complex physiological state that enables the cell to bind, uptake, and integrate external DNA into its own chromosome. Cells can naturally be competent or can be induced to become competent through chemical treatments. Only competent cells are capable of undergoing transformation, making this state crucial for the process of horizontal gene transfer.

What are the steps involved in natural transformation?

Natural transformation involves four key steps: (1) Binding of double-stranded DNA to cell surface receptors, (2) Entry of a single strand of DNA into the cell while the complementary strand is degraded, (3) Integration of the single-stranded DNA into the host cell's chromosome via homologous recombination, and (4) Rebuilding of the complementary strand to form a stable double-stranded DNA. This process allows the bacterial cell to acquire new genetic traits, such as antibiotic resistance, from the environment.

How does bacterial transformation contribute to antibiotic resistance?

Bacterial transformation can contribute to antibiotic resistance by allowing bacteria to uptake and integrate DNA that contains antibiotic resistance genes from their environment. When a competent cell uptakes such DNA, it can incorporate the resistance gene into its own chromosome through homologous recombination. This newly acquired gene can then be expressed, providing the bacterium with resistance to specific antibiotics. This mechanism enables bacteria to rapidly adapt to antibiotic pressures in their environment.

Can all bacterial cells undergo transformation?

No, not all bacterial cells can undergo transformation. Only competent cells, which are in a specific physiological state, have the ability to uptake and integrate free or naked DNA from their environment. Some bacteria are naturally competent, while others can be induced to become competent through chemical treatments. Non-competent cells lack the necessary mechanisms to bind, uptake, and integrate external DNA, and therefore cannot undergo transformation.