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

K12 Standards

Louisiana Student Standards for Science

High School

Life Sciences

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

From Molecules To Organisms: Structures And Processes

HS-LS1-8

Lysogenic Cycle of Bacteriophages

- Quando è presente un grosso
numero di batteriofagi,

possono iniziare un modello
alternativo di riproduzione,

il ciclo lisogenico, in cui
i fagi possono riprodursi

senza uggidere il loro ospite.

Il ciclo comincia come il ciclo litico,

il fago attacca la cellula ospite

e inietta il suo DNA.

Una volta dentro, il DNA
del fago si ricombina

e si integra con il genoma del batterio,

formando un profago.

Il profago in sé non è attivo

e non genera la produzione di altri fagi.

Piuttosto, quando la
cellula ospite si divide,

si replica con il DNA dell'ospite.

Castro, Vinicius Silva, Ricardo César Tavares Carvalho, Carlos Adam Conte-Junior e Eduardo Eustáquio Souza Figuiredo. "Shiga-Tossina che produce Escherichia coli: patogenicità, supershedding, metodi diagnostici, occorrenza e focolai di origine alimentare". Recensioni complete in Food Science and Food Safety 16, n. 6 (2017): 1269–80. [<a href="https://doi.org/10.1111/1541-4337.12302" target="__blank">Sorgente</a>]

Melton-Celsa, Angela R. "Classificazione, struttura e funzione della tossina Shiga (Stx)." Spettro di microbiologia 2, n. 2 (2014). [<a href="https://doi.org/10.1128/microbiolspec.EHEC-0024-2013" target="__blank">Sorgente</a>]

ciclo lisogeno dei batteriofagi

In contrasto con il ciclo litico, i fagi che infettano i batteri attraverso il ciclo lisogenico non uccidono immediatamente la loro cellula ospite. Invece, combinano il loro genoma con il genoma ospite, permettendo ai batteri di replicare il DNA dei faghi insieme al genoma batterico. La copia incorporata del genoma del fago è chiamata profago. Alcune proscioni possono riattivare ed entrare nel ciclo litico. Ciò si verifica spesso in risposta a una perturbazione, come il danno al DNA, ma può anche trasparire in assenza di spunti esterni.

<h4>Conversione lisogenica</h4>

In alcuni casi, i geni codificati dai profagi possono alterare il fenotipo del batterio infetto, un processo noto come conversione lisogenica. Alcuni fagi codificano proteine o tossine chiamate fattori di virulenza che possono facilitare le infezioni batteriche. Attraverso la conversione lisogenica, i batteri normalmente non patogeni possono diventare altamente virulenti tramite infezione da un fago che trasporta fattori di virulenza.

Ad esempio, tali fagi sono in gran parte responsabili della patogenicità delle specie batteriche che causano il botulismo (Clostridium botulinum), la diftheria (Corynebacterium diphtheriae) e il colera (Vibrio cholerae). Senza conversione lisogenica, questi batteri di solito non causano malattie.

Un esempio particolarmente studiato di conversione lisogenica è quello del ceppo Escherichia coli O157:H7. Diversi massicci richiami di cibo sono dovuti alla contaminazione da E. coli O157:H7. Questo ceppo di E. coli è stato infettato da un fago che codifica tossina simile a Shiga (Stx), che può causare sanguinamento intestinale e insufficienza renale. Nel ciclo lisogenico, Stx non è prodotto, ei batteri non causano malattie. Il fago deve rientrare nel ciclo litico per la produzione di Stx. Purtroppo, alcuni antibiotici possono innescare l'induzione del profago e la conseguente produzione di Stx, rendendo difficile il trattamento di queste infezioni. La ricerca attuale sta studiando nuove terapie che impediscono l'avvio della propagazione.

Ciclo lisogeno dei batteriofagi

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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