Question

What are the two types of bacteriophase infection?

Short answer

The two types of bacteriophage infections are lytic infection and lysogenic infection. In lytic infection, the bacteriophage replicates inside the bacterial cell and kills the host, releasing new bacteriophages to infect other cells. In lysogenic infection, the bacteriophage integrates its genetic material into the host's genome and remains dormant, replicating passively with the host until certain factors trigger it to switch to the lytic cycle.

Step-by-step solution

Introduction to bacteriophages

Bacteriophages are viruses that infect and replicate within bacteria. These viruses are specific to their bacterial host, and they can play a significant role in controlling bacterial populations in various environments. There are two primary types of bacteriophage infections: lytic infection and lysogenic infection. Now let's discuss each type in detail.

Lytic infection

Lytic infection is a kind of bacteriophage infection in which the bacteriophage enters a bacterial cell, replicates, and produces many copies of itself. The new bacteriophages then burst out of the bacterial cell (by killing the host), which releases the viral progeny to infect other bacterial cells. In a lytic infection, the bacteriophages are called virulent phages. The main steps in the lytic infection cycle are adsorption, penetration, replication, assembly, and lysis: 1. Adsorption: The bacteriophage attaches to specific receptors on the bacterial cell surface. 2. Penetration: The bacteriophage injects its genetic material (DNA or RNA) into the bacterial cell. 3. Replication: The viral genes take control of the bacterial cell, and new bacteriophages are produced. 4. Assembly: The newly synthesized bacteriophage components are assembled into complete viruses. 5. Lysis: The bacterial cell is lysed, and the newly formed bacteriophages are released to infect more bacterial cells.

Lysogenic infection

A lysogenic infection occurs when the bacteriophage integrates its genetic material into the bacterial cell's genome instead of immediately replicating, producing new phages, and destroying the host. In this case, the viral DNA (called a prophage) is passively copied and inherited by daughter cells during bacterial cell division. The lysogenic infection cycle can continue for many generations, and the prophage can be maintained for a long time. Moreover, certain external factors such as UV radiation or stress can eventually induce the prophage to switch to a lytic infection cycle, called induction. The bacteriophages that undergo lysogenic infection are called temperate phages. In summary, the two types of bacteriophage infections are the lytic and lysogenic infections.

Key concepts

lytic infection

During a lytic infection, a bacteriophage takes control of a bacterial cell and forces it to reproduce new phages. This process causes the bacterial cell to burst, releasing the newly created viruses.
The cycle starts with the bacteriophage attaching to the bacterial surface, using its receptors to lock on tightly.
After attachment, the bacteriophage injects its genetic material into the host, hijacking the bacteria's machinery to replicate its own components.

• The copied parts are then assembled into complete viral forms inside the bacterial cell.
• Finally, the cell undergoes lysis, which is when it bursts and releases these viral progeny.

This entire sequence can be summarized by five key steps: adsorption, penetration, replication, assembly, and lysis.
All of this makes lytic infections quite brutal for the host bacterium and enables the rapid spread of phages to multiple cells.

lysogenic infection

In contrast to lytic infections, lysogenic infections involve a more subtle interaction between bacteriophage and bacteria.
Here, the bacteriophage integrates its DNA into the bacterial genome, becoming known as a prophage. Rather than taking over the host immediately, the prophage remains dormant, replicating alongside the host's DNA.
This dormancy means when the bacterial cell divides, it splits and passes on the viral DNA to its daughter cells.

• This way, the viral DNA is silently replicated without destroying the host.
• The process allows the virus to persist in a population of bacteria over many generations.

Certain conditions, like environmental stress, can trigger the prophage to exit the lysogenic cycle, entering the lytic cycle to produce new phages.
This conversion is referred to as induction, marking a shift from dormancy to active multiplication.

bacterial cell

Bacterial cells are the primary hosts for bacteriophages, acting as both shelters and factories for viral reproduction.
Bacteria have a cell wall, membrane, and various internal components that are hijacked during a phage infection.
Bacteriophages have specific receptors on the bacterial cell surface that they recognize and attach to, starting the infection process.

• The integrity of the bacterial cell wall is crucial as it's this structure that eventually bursts open during lysis.
• The bacterial DNA and cellular machinery are pivotal during the replication phase, being commandeered to produce viral components.

Bacteria often possess mechanisms to resist phage attacks, such as CRISPR systems, highlighting the evolutionary arms race between host and virus.
This constant battle shapes both bacterial and viral adaptations.

virulent phages

Virulent phages are the types of bacteriophages responsible for lytic infections.
They are highly efficient in taking over bacterial cells and rapidly producing new viral particles.
Upon attachment, they inject their genetic material, quickly commandeering the host's resources.

• This aggressive infection strategy ensures that the host cell is destroyed, leading to cell lysis.
• Virulent phages rely on the complete exploitation of their host's machinery for survival and replication.

Due to their destructive nature, virulent phages are key players in regulating bacterial populations in nature.
Despite their efficiency, the lethal takeover strategy means that virulent phages must constantly find new hosts, making them completely reliant on a steady supply of susceptible bacteria.