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

- [Instructor] Cuando un
gran número de bacteriófagos

están presentes, pueden entrar
en un modo de reproducción

alternativa, el ciclo lisogénico,
donde los fagos se pueden

reproducir sin matar a su anfitrión.

Este ciclo comienza muy
parecido al ciclo lítico.

El fago primero se adhiere
a la célula anfitrión

e inyecta su ADN-

Sin embargo, una vez que está
adentro, el DBA del fago se

recombina e integra
con el genoma bacterial

formando un profago.

El profago en sí mismo no está activo

y no impulsa la producción
de nuevos fagos.

Mas bien, cuando la célula
anfitrión se divide,

se replica junto con el ADN anfitrión.

Castro, Vinicius Silva, Ricardo César Tavares Carvalho, Carlos Adam Conte-Junior y Eduardo Eustáquio Souza Figuiredo. "Escherichia coli productora de toxina Shiga: patogenicidad, superexcreción, métodos de diagnóstico, ocurrencia y brotes transmitidos por los alimentos". Comprehensive Reviews in Food Science and Food Safety 16, no. 6 (2017): 1269–80. [<a href="https://doi.org/10.1111/1541-4337.12302" target="__blank">Fuente</a>]

Melton-Celsa, Angela R. "Clasificación, estructura y función de la toxina Shiga (Stx)". Microbiology Spectrum 2, no. 2 (2014). [<a href="https://doi.org/10.1128/microbiolspec.EHEC-0024-2013" target="__blank">Fuente</a>]

ciclo lisogénico de bacteriófagos.

A diferencia del ciclo lítico, los fagos que infectan bacterias a través del ciclo lisogénico no matan inmediatamente a su célula huésped. En cambio, combinan su genoma con el genoma del huésped, lo que permite a las bacterias replicar el ADN del fago junto con el genoma bacteriano. La copia incorporada del genoma del fago se llama profago. Algunos profagos pueden reactivarse y entrar en el ciclo lítico. Esto suele ocurrir en respuesta a una perturbación, como un daño en el ADN, pero también puede ocurrir en ausencia de señales externas. <h4>Conversión lisogénica</h4> En algunos casos, los genes codificados por los profagos pueden alterar el fenotipo de la bacteria infectada, un proceso conocido como conversión lisogénica. Algunos fagos codifican proteínas o toxinas llamadas factores de virulencia que pueden facilitar las infecciones bacterianas. A través de la conversión lisogénica, las bacterias normalmente no patógenas pueden volverse muy virulentas mediante la infección por un fago que porta factores de virulencia. Por ejemplo, estos fagos son en gran medida responsables de la patogenicidad de las especies bacterianas que causan el botulismo (Clostridium botulinum), la difteria (Corynebacterium diphtheriae) y el cólera (Vibrio cholerae). Sin conversión lisogénica, estas bacterias no suelen causar enfermedades. Un ejemplo particularmente bien estudiado de conversión lisogénica es el de la cepa O157:H7 de Escherichia coli. Varias retiradas masivas de alimentos se han debido a la contaminación por E. coli O157:H7. Esta cepa de E. coli ha sido infectada por un fago que codifica la toxina similar a Shiga (Stx), que puede provocar hemorragia intestinal e insuficiencia renal. En el ciclo lisogénico, no se produce Stx y las bacterias no causan enfermedades. El fago debe volver a entrar en el ciclo lítico para que se produzca Stx. Desafortunadamente, ciertos antibióticos pueden desencadenar la inducción del profago y la consiguiente producción de Stx, lo que dificulta el tratamiento de estas infecciones. La investigación actual está investigando nuevas terapias que impidan el inicio del profago.

Ciclo lisogénico de bacteriófagos.

A diferencia del ciclo lítico, los fagos que infectan a las bacterias a través del ciclo lisogénico no matan inmediatamente a su célula huésped. En su lugar, combinan su ...

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KEY TERMS AND CONCEPTS

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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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HS-LS1-4

Prophage Integration in Bacteria

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