Question

Define the term prophage.

Short answer

Answer: A prophage is a phage genome integrated into the bacterial host's DNA, becoming part of the bacterial chromosome and replicating along with the host bacteria. In the bacterial life cycle, the prophage remains dormant during the lysogenic cycle and does not destroy the host cell. However, under certain conditions, it can revert to the lytic cycle, producing new phage particles and destroying the host cell. Additionally, the presence of prophage DNA can provide benefits to the host bacteria, such as increased resistance to stressors.

Step-by-step solution

Defining a Prophage

A prophage is a phage (a virus that infects bacteria) genome that has been integrated into the bacterial host's DNA. It becomes a part of the bacterial chromosome and can replicate along with the host bacteria.

Explaining the Role of Prophage in the Bacterial Life Cycle

The prophage is in a dormant state within the bacterial host during the lysogenic cycle. It remains inactive and does not destroy the host cell. However, under certain conditions such as stress or DNA damage, the prophage can revert to a lytic cycle, where it will start to produce new phage particles, leading to the destruction of the host cell. During the lysogenic cycle, the presence of the prophage DNA can potentially provide additional benefits or traits to the host bacteria, such as increased resistance to environmental stressors.

Key concepts

Lysogenic Cycle

The lysogenic cycle is a process where a bacteriophage, a virus that specifically infects bacteria, incorporates its genetic material into the host bacterium's DNA. This integrated viral DNA is referred to as a prophage. In this cycle, the prophage remains dormant within the bacterial genome and does not cause harm to the host cell.

While embedded in the bacterial DNA, the prophage replicates in tandem with the host cell's division process. This means the viral genetic material gets passed on to the bacterial offspring without active virus production. Typically, the lysogenic phase can last for many generations.

• Prophage remains inactive, not producing new viral particles.
• Host cell remains alive, continuing normal functions.
• Environmental triggers can switch the cycle to the lytic phase, causing virus particle production and eventually the destruction of the host cell.

The lysogenic cycle is significant as it can alter the bacterial cell's characteristics, providing potential advantages such as increased resistance to harsh environments.

Bacterial Genetics

Bacterial genetics involves the study of genes, hereditary information, and genetic variation in bacterial populations. Bacteria are simple organisms, yet they exhibit complex genetic behaviors, such as horizontal gene transfer and lysogeny.

Bacteria typically reproduce asexually through binary fission, creating identical copies of themselves. However, genetic diversity can occur via other mechanisms:

• Transformation, where bacteria take up foreign DNA from their surroundings.
• Conjugation, involving the transfer of genetic material between two bacteria.
• Transduction, where a bacteriophage introduces new genetic material into the bacterial genome.

The integration of a prophage into the bacterial genome represents a form of genetic variation. This interaction can introduce new genes and traits, sometimes offering the host cell survival advantages or new capabilities. Such genetic changes can drive bacterial evolution and impact bacterial population dynamics.

Virus Integration

Virus integration is the process by which viral genetic material becomes part of the host cell's DNA. In bacteriophages, this occurs when the phage DNA integrates into the bacterial chromosome, transforming into a prophage. This integration is a crucial aspect of the lysogenic cycle.

During virus integration, the following occurs:

• The bacteriophage attaches to the bacterial cell and injects its DNA.
• Instead of taking over the host cell's machinery immediately, the phage DNA integrates into the host's genome.
• This integrated DNA, or prophage, gets replicated along with the host cell's DNA during cell division.

Integration effectively makes viral genetic material a part of the host cell's genetic library. It allows the virus to maintain a low profile until conditions favor a shift to the lytic cycle, where new viral particles are produced, leading to host cell destruction. This ingenious strategy aids the virus in surviving through unfavorable external conditions and ensures its propagation through bacterial populations.