Bacteriophage: Filamentous Phage Infections: Videos & Practice Problems

Filamentous phages, characterized by their long, fiber-like structure, cause productive infections in bacterial cells without lysing them. They attach to the pilus of a host bacterium, allowing their DNA to enter. The phage genome is then synthesized, leading to the production of new phage particles, which are released through a process called extrusion. Although the host cell remains alive, its growth is inhibited, demonstrating the phage's impact on bacterial physiology. Understanding this process is crucial for applications in phage therapy and microbial ecology.

Bacteriophage: Filamentous Phage Infections

In this video, we're going to continue to talk about bacteriophages by focusing specifically on filamentous phage infections. Now, filamentous phages are bacteriophages, or phages, that take the shape of long fibers, also known as filaments, which is where they get their name from. These filamentous phages cause productive infections in bacterial cells. Recall that productive infections just mean that it's going to be actively generating new phages. However, filamentous phages do not kill or lyse the cell. Instead of lysing the cell, these filamentous phage particles exit the cell without causing lysis, and they do so as they assemble in a process known as extrusion. Although filamentous phages do not kill or lyse the cell, they still cause the infected cells to grow slower than the uninfected cells, making them still harmful to the infected cells.

If we take a look at our example down below, we can look at a specific example of a filamentous phage, M13 phage replication. In the very first step of a filamentous phage infection, we have attachment. During attachment, the filamentous phage, which has these long filaments and is a relatively longer structure, attaches specifically to the pilus of a host bacterium. You can see here the pilus of a host bacterium and the filamentous phage attaching to that pilus. In step 2, we have genome entry. This is when the genome of the filamentous phage enters the host cell. The genome, or the DNA of the filamentous phage, enters the host cell via the pilus of the bacterial cell.

In step 3, we have synthesis. During the synthesis step, the phage genome is synthesized and replicated, and phage proteins are also synthesized. Here, it is shown that the phage DNA replicates inside the bacterium, and phage components, including phage proteins, are created inside the bacterium. The viral capsid proteins, these little green proteins, accumulate on the inside of the membrane while the phage DNA is also being synthesized and replicated.

In the 4th and final stage, what we have is release through the process of extrusion. During this process, you have the release of the virus and the assembly of the virus simultaneously. You can see these new phages being released here. Once again, with a filamentous phage infection, the cell itself is not going to lyse; it is not going to die. Thus, it will be able to continuously produce these filamentous phage particles. This concludes our brief introduction to filamentous phage infections, and we'll be able to get some practice applying these concepts as we move forward in our course. I'll see you all in our next video.

Filamentous phages are unique in their ability to do what?

• A. To build and release new phages without killing the host cell.
• B. To cause the host cell to replicate and synthesize new viral DNA and viral proteins.
• C. To cause the host cell to lyse or burst open releasing new, infectious phages.
• D. To perform the lysogenic and lytic cycles within the host cell at the same time.

Answer: (A)

Some filamentous phages infect the host bacterium using the bacterium's pilus. How does this process work?

• A. The phage uses the pilus to begin the process of entering the bacterium via endocytosis.
• B. The phage uses the pilus to trigger cell lysis to release the newly created filamentous phages.
• C. The phage transfers its viral DNA through the pilus into the bacterium.

Answer: (C)

Here’s what students ask on this topic:

What are filamentous phages and how do they differ from other bacteriophages?

Filamentous phages are a type of bacteriophage characterized by their long, fiber-like structure. Unlike other bacteriophages that often lyse the host cell to release new phage particles, filamentous phages do not kill or lyse the bacterial cell. Instead, they cause productive infections where new phages are continuously produced and released through a process called extrusion. This allows the host cell to remain alive, although its growth is inhibited. This non-lytic nature differentiates filamentous phages from lytic phages, which destroy the host cell during the release of new viral particles.

How do filamentous phages attach to and enter bacterial cells?

Filamentous phages attach to bacterial cells by specifically binding to the pilus of the host bacterium. The pilus is a hair-like appendage on the surface of the bacterial cell. Once attached, the phage's DNA enters the host cell through the pilus. This process is the initial step in the infection cycle, allowing the phage genome to enter the bacterial cytoplasm where it can begin replication and synthesis of new phage components.

What is the process of extrusion in filamentous phage infections?

Extrusion is the process by which new filamentous phage particles are released from the host bacterial cell without causing cell lysis. During extrusion, the assembly of new phage particles occurs simultaneously with their release. The phage components, including the viral capsid proteins and replicated DNA, are assembled into new phages, which then exit the cell through the bacterial membrane. This allows the host cell to remain intact and continue producing new phages, although its growth rate is slowed.

What impact do filamentous phages have on their bacterial host cells?

Filamentous phages impact their bacterial host cells by inhibiting their growth. Although the host cell is not lysed and remains alive, the continuous production and release of new phage particles through extrusion slow down the cell's growth rate. This can be detrimental to the bacterial cell's overall health and function, even though it is not immediately lethal. The persistent infection can affect the bacterial cell's physiology and its ability to thrive in its environment.

What are the applications of understanding filamentous phage infections in phage therapy and microbial ecology?

Understanding filamentous phage infections has significant applications in phage therapy and microbial ecology. In phage therapy, filamentous phages can be used to target and control bacterial populations without causing widespread cell lysis, which can be beneficial in treating bacterial infections while minimizing damage to beneficial microbiota. In microbial ecology, studying filamentous phages helps researchers understand the dynamics of bacterial populations and their interactions with phages in natural environments. This knowledge can inform strategies for managing bacterial communities in various settings, including agriculture, industry, and environmental conservation.