Name: prophage integration in bacteria
Uploaded: 2019-03-11T09:21:23.000Z
Duration: 43 s
Channel: JoVE

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Life Sciences

from-molecules-to-organisms-structures-and-processes

From Molecules To Organisms: Structures And Processes

HS-LS1-8

Lysogenic Cycle of Bacteriophages

- [Instructeur] Wanneer grote aantallen bacteriofagen aanwezig zijn, kunnen ze in een alternatieve replicatiemodus komen, de lysogene cyclus, waar fagen zich kunnen voortplanten zonder hun gastheer te doden. Deze cyclus begint net als de lytische cyclus. De fagie hecht zich eerst aan de gastheercel en injecteert zijn DNA.

Echter, eenmaal binnen, het faag-DNA recombineert en integreert met het bacteriële genoom en vormt een profage. De profage zelf is niet actief en drijft de productie van nieuwe fagen niet aan. In plaats daarvan, wanneer de gastheercel zich verdeelt, wordt hij samen met het gastheer-DNA gerepliceerd.

lysogene cyclus van bacteriofagen

In tegenstelling tot de lytische cyclus doden fagen die bacteriën infecteren via de lysogene cyclus hun gastheercel niet onmiddellijk. In plaats daarvan combineren ze hun genoom met het gastheergenoom, waardoor de bacteriën het faag-DNA samen met het bacteriële genoom kunnen repliceren. De ingebouwde kopie van het faaggenoom wordt de profaag genoemd. Sommige profeten kunnen opnieuw worden geactiveerd en in de lytische cyclus terechtkomen. Dit gebeurt vaak als reactie op een verstoring, zoals DNA-schade, maar kan ook plaatsvinden als er geen externe signalen zijn.

Lysogene conversie

In sommige gevallen kunnen de door profeten gecodeerde genen het fenotype van de geïnfecteerde bacterie veranderen, een proces dat bekend staat als lysogene conversie. Sommige fagen coderen voor eiwitten of toxinen die virulentiefactoren worden genoemd en die bacteriële infecties kunnen vergemakkelijken. Door lysogene omzetting kunnen normaal gesproken niet-pathogene bacteriën zeer virulent worden via infectie door een faag die virulentiefactoren draagt.

Dergelijke fagen zijn bijvoorbeeld grotendeels verantwoordelijk voor de pathogeniteit van de bacteriesoorten die botulisme (Clostridium botulinum), difterie (Corynebacterium diphtheriae) en cholera (Vibrio cholerae) veroorzaken. Zonder lysogene omzetting veroorzaken deze bacteriën gewoonlijk geen ziekte.

Een bijzonder goed bestudeerd voorbeeld van lysogene omzetting is dat van de Escherichia coli stam O157:H7. Verschillende massale terugroepacties van voedsel zijn het gevolg van besmetting met E. coli O157:H7. Deze stam van E. coli is geïnfecteerd door een faag die codeert voor Shiga-achtig toxine (Stx), dat darmbloedingen en nierfalen kan veroorzaken. In de lysogene cyclus wordt geen Stx geproduceerd en veroorzaken de bacteriën geen ziekten. De faag moet opnieuw de lytische cyclus ingaan voordat Stx kan worden geproduceerd. Helaas kunnen bepaalde antibiotica de inductie van de profaag en de daaruit voortvloeiende Stx-productie veroorzaken, waardoor de behandeling van deze infecties moeilijk wordt. Huidig onderzoek onderzoekt nieuwe therapieën die de initiatie van de profaag voorkomen.

Lysogene cyclus van bacteriofagen

In contrast to the lytic cycle, phages infecting bacteria via the lysogenic cycle do not immediately kill their host cell. Instead, they combine their ...

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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 also change the traits of the bacteria they infect. This effect is called lysogenic conversion. In this process, phage genes can give bacteria virulence factors, such as toxins or proteins that help infection. As a result, bacteria that were usually harmless can become much more harmful after phage infection.

This kind of conversion helps explain the disease-causing power of Clostridium botulinum, Corynebacterium diphtheriae, and Vibrio cholerae. It also plays a major role in Escherichia coli O157:H7, a strain linked to food recalls. In this strain, the phage carries the gene for Shiga-like toxin, or Stx, which can cause intestinal bleeding and kidney failure. Stx is not produced during lysogeny, and the bacteria do not cause disease until the phage enters the lytic cycle.

Treatment can be complicated because some antibiotics may trigger prophage induction and lead to Stx production. That is why current research is looking for new therapies that stop prophages from starting the lytic cycle.

Prophage Integration in 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...

lytic cycle of bacteriophages

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...

lysogenic cycle of bacteriophages

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

Learn how bacteriophages integrate into bacterial DNA, form prophages, and can change bacterial traits through lysogenic conversion and toxin genes.

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Prophage Integration in Bacteria

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