Name: how phages infect and burst bacteria
Uploaded: 2019-03-11T09:21:23.000Z
Duration: 1 min 30 s
Channel: JoVE

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From Molecules To Organisms: Structures And Processes

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Lytic Cycle of Bacteriophages

Some types of viruses called bacteriophages, or bacteria eaters, only infect bacteria cells. While phages can vary in their shape and genetic material the most unique in this class is the head-tail morphology with double-stranded DNA.

To begin the injection process, termed its lifecycle, the phage first attaches to a bacterium. More specifically, proteins within the tail fibers bind to specific receptors on the surface. The tail then contracts injecting the DNA inside the cytoplasm of the host and results in an empty capsid.

To reproduce, one possibility is to enter the lytic cycle, a mode of replication that involves taking over the bacterium&#39;s cycle machinery destroying the host DNA enforcing it to produce viral components.

The phages DNA is protected and copied and additional sets of proteins are synthesized to aid in forming new viruses. During this self-assembly phase the viral genom is packaged inside the head.

The phage even translates proteins that degrade the host&#39;s cell wall allowing water to enter.&nbsp;As a result of the expansion, the cell bursts and such lices of the bacterium releases hundred of new phages which can now find and infect the population of bacteria nearby.

lytic cycle of bacteriophages

Bacteriophages, also known as phages, are specialized viruses that infect bacteria. A key characteristic of phages is their distinctive &ldquo;head-tail&rdquo; morphology. A phage begins the infection process (i.e., lytic cycle) by attaching to the outside of a bacterial cell. Attachment is accomplished via proteins in the phage tail that bind to specific receptor proteins on the outer surface of the bacterium. The tail injects the phage&rsquo;s DNA genome into the bacterial cytoplasm. In the lytic replication cycle, the phage uses the bacterium&rsquo;s cellular machinery to make proteins that are critical for the phage&rsquo;s replication and dispersal. Some of these proteins cause the host cell to take in water and burst, or lyse, after phage replication is complete, releasing hundreds of phages that can infect new bacterial cells.

<h4>Phage Therapy</h4>

Since the early 20th century, researchers have recognized the potential value of lytic bacteriophages in combating bacterial infections in crops, humans, and agricultural animals. Because each type of phage can infect and lyse only specific types of bacteria, phages represent a highly specific form of anti-bacterial treatment. This quality stands in contrast to the familiar antibiotic drugs that we often take for bacterial infections, which are typically broad-spectrum treatments that kill both pathogenic and beneficial bacteria. The widespread use of broad-spectrum antibiotics has caused the evolution of bacterial resistance to whole classes of these drugs, rendering once treatable infections potentially deadly. As more pathogenic bacteria evolve resistance to antibiotics, narrow-spectrum phage therapy may become a useful alternative. Because phages are highly specific in the bacteria that they infect, the evolution of resistance to phages would also be limited to the particular strain of bacteria.

However, several obstacles must be overcome for phage therapy to become a viable alternative to antibiotics. For instance, the high specificity of phages is also a drawback, because different phages would be needed for each species of the bacterial pathogen or even strain of bacteria within a pathogenic species. It would, therefore, be difficult to produce phages for many different bacterial infections at a large scale. Furthermore, because of phage specificity, it would be necessary to either know the particular bacterial strain that is causing an infection or use a cocktail of multiple different phages in the treatment and hope that one of them matches the pathogenic bacteria. Despite these drawbacks, phage therapy remains an active area of research.

Bacteriophages, also known as phages, are specialized viruses that infect bacteria. A key characteristic of phages is their distinctive ...

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how phages infect and burst bacteria

Bacteriophages, or phages, are viruses that infect bacteria. They have a distinctive head-tail shape. In the lytic cycle, a phage first attaches to the outside of a bacterial cell. Tail proteins bind to specific receptor proteins on the bacterium’s surface.

After attachment, the phage tail injects its DNA genome into the bacterial cytoplasm. The phage then uses the bacterium’s cellular machinery to make proteins needed for replication and dispersal. When phage replication is complete, some of these proteins cause the host cell to take in water and burst, or lyse. This releases hundreds of new phages that can infect other bacterial cells.

Lytic bacteriophages have also drawn interest for phage therapy. Since the early 20th century, researchers have studied them for use against bacterial infections in crops, humans, and agricultural animals. Phages are highly specific, so each type infects only certain bacteria. That makes them different from many broad-spectrum antibiotics, which can kill both harmful and helpful bacteria.

This specificity can be useful when antibiotic resistance becomes a problem. Widespread antibiotic use has led some bacteria to evolve resistance to whole classes of drugs, making once-treatable infections potentially deadly. Resistance to phages would be limited to the particular strain of bacteria. Even so, phage therapy has challenges. Different phages may be needed for each species or strain, and treatment may require knowing the exact bacterial strain or using a cocktail of several phages. Despite these limits, phage therapy remains an active area of research.

How Phages Infect and Burst Bacteria

what are viruses?

How Viruses Infect Cells and Multiply

Viruses infect cells and make new copies by using a host cell’s own machinery. A virus is a tiny infectious particle with an RNA or DNA genome inside a protective protein coat. It cannot reproduce on its own, so it must enter a cell to make more viruses. After infection, the virus sheds its protein coat and uses the host cell to transcribe and translate its genetic material. The cell then assembles many new viral particles. In many cases, these new viruses rupture the host cell and kill it.

viral structure

How Virus Shapes Help Infection

Viruses have specific structures that help them infect host cells and trigger immune responses. Each virus has a core that contains either a DNA-based or RNA-based genome. That core is surrounded by a protective protein coat called the capsid. The capsid is made of smaller subunits called capsomeres. The capsid and the genome-containing core together are called the nucleocapsid. Viruses are often grouped by capsid design. Most viruses have either icosahedral or helical capsids, but some have...

Bacteriophages, or phages, are viruses that infect bacteria. They have a distinctive head-tail shape. In the lytic cycle, a phage first attaches to the outside of a bacterial cell. Tail proteins bind to specific receptor proteins on the bacterium’s surface. After attachment, the phage tail injects its DNA genome into the bacterial cytoplasm. The phage then uses the bacterium’s cellular machinery to make proteins needed for replication and dispersal. When phage replication is complete, some of...

lysogenic cycle of bacteriophages

Prophage Integration in Bacteria

The lysogenic cycle shows how bacteriophages can infect bacteria without killing the host right away. In this cycle, the phage genome joins the bacterial genome. The integrated phage DNA is called a prophage, and the bacterium copies it each time it replicates. Some prophages can switch back into the lytic cycle. This change can happen after DNA damage or even without an obvious outside trigger. When the prophage is induced, the phage begins making new virus particles again. Prophages can...

retrovirus life cycles

How Retroviruses Replicate in Host Cells

Retroviruses replicate by copying their RNA genome into DNA inside a host cell. After entry, the viral enzyme reverse transcriptase makes a double-stranded DNA copy from the single-stranded RNA genome. The viral DNA is then carried into the nucleus and inserted into the host genome by integrase. Once integrated, the retroviral DNA is transcribed whenever the host genome is transcribed. This produces new viral RNA that can be copied and used again. The new RNA moves into the cytoplasm, where it...

viral recombination

How Viruses Swap Genes and Spread

Viral gene swapping can happen when more than one virus infects the same cell. After the viruses break open and expose their genomes for replication, matching regions can pair up and exchange sequences. This process is called recombination. Viruses with segmented genomes can also swap whole segments, which is called reassortment. These changes can help create new diseases. Some diseases can infect more than one species. Pigs can be infected by some human and bird viruses, along with the...

viral mutations

How Virus Mutations Drive Outbreaks

Virus mutations can change how quickly a virus evolves and spreads. A mutation is a change in the sequence of bases in DNA or RNA. Some mutations happen when the genome is copied. They are caused by errors made by polymerase enzymes, which replicate DNA or RNA. RNA viruses often change faster than DNA viruses because RNA polymerase does not proofread its work. That means RNA-based genomes, such as HIV, can gather mutations more quickly. Mutation and recombination give viruses the raw material...

key terms and concepts

Trace the lytic cycle of bacteriophages, from attachment and DNA injection to bacterial lysis, and see why phages are studied for targeted phage therapy.

How Phages Infect and Burst Bacteria | JoVE K12

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How Phages Infect and Burst Bacteria

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