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

From Molecules To Organisms: Structures And Processes

HS-LS1-8

Lytic Cycle of Bacteriophages

- [Instructor] Algunos tipos de virus

llamados bacteriófagos,

o comedores de bacterias,

solo infectan las células bacterianas.

Si bien los fagos pueden variar

en su forma y material genético,

el más singular de esta clase

es la morfología de la cola de cabeza

con el ADN de doble cadena.

Para comenzar el proceso de inyección,

denominado su ciclo de vida,

el fago primero se adhiere a una bacteria.

Más específicamente,

las proteínas dentro de
las fibras de la cola

se unen a receptores
específicos en la superficie.

La cola luego se contrae

al inyectar el ADN en el interior
del citoplasma del huésped

y se traduce en una cápside vacía.

Para reproducirse,

una posibilidad es
ingresar al ciclo lítico,

un modo de replicación que consiste

en hacerse cargo de la maquinaria
del ciclo de la bacteria,

destruyendo el ADN del huésped

y obligándolo a producir
componentes virales.

El ADN del fago está protegido y copiado

y se sintetizan conjuntos
adicionales de proteínas

para ayudar a formar nuevos virus.

Durante esta fase de autoensamblaje,

el genoma viral se empaqueta
dentro de la cabeza.

El fago incluso traduce proteínas

que degradan la pared celular del huésped

permitiendo que el agua ingrese.

Como resultado de la expansión,
los estallidos celulares

y tales piojos de la bacteria

liberan cientos de fagos nuevos

que ahora pueden encontrar e infectar

a la población de bacterias cercanas.

Doss, Janis, Kayla Culbertson, Delilah Hahn, Joanna Camacho y Nazir Barekzi. "Una revisión de la terapia con fagos contra patógenos bacterianos de organismos acuáticos y terrestres". Virus 9, no. 3 (18 de marzo de 2017). [<a href="https://doi.org/10.3390/v9030050" target="__blank">Fuente</a>]

Abedon, Stephen T., Pilar García, Peter Mullany y Rustam Aminov. "Editorial: Terapia con fagos: pasado, presente y futuro". Frontiers in Microbiology 8 (2017). [<a href="https://doi.org/10.3389/fmicb.2017.00981" target="__blank">Fuente</a>]

ciclo lítico de bacteriófagos

Los bacteriófagos, también conocidos como fagos, son virus especializados que infectan bacterias. Una característica clave de los fagos es su morfología distintiva de "cabeza-cola". Un fago comienza el proceso de infección (es decir, ciclo lítico) adhiriéndose al exterior de una célula bacteriana. La unión se logra mediante proteínas en la cola del fago que se unen a proteínas receptoras específicas en la superficie exterior de la bacteria. La cola inyecta el genoma de ADN del fago en el citoplasma bacteriano. En el ciclo de replicación lítica, el fago utiliza la maquinaria celular de la bacteria para producir proteínas que son críticas para la replicación y dispersión del fago. Algunas de estas proteínas hacen que la célula huésped absorba agua y explote o se lisa una vez completada la replicación de los fagos, liberando cientos de fagos que pueden infectar nuevas células bacterianas. <h4>Terapia con fagos</h4> Desde principios del siglo XX, los investigadores han reconocido el valor potencial de los bacteriófagos líticos en la lucha contra infecciones bacterianas en cultivos, humanos y animales agrícolas. Debido a que cada tipo de fago puede infectar y lisar sólo tipos específicos de bacterias, los fagos representan una forma muy específica de tratamiento antibacteriano. Esta cualidad contrasta con los conocidos antibióticos que a menudo tomamos para las infecciones bacterianas, que suelen ser tratamientos de amplio espectro que matan tanto las bacterias patógenas como las beneficiosas. El uso generalizado de antibióticos de amplio espectro ha provocado la evolución de la resistencia bacteriana a clases enteras de estos medicamentos, haciendo que infecciones que alguna vez fueron tratables sean potencialmente mortales. A medida que más bacterias patógenas desarrollan resistencia a los antibióticos, la terapia con fagos de espectro reducido puede convertirse en una alternativa útil. Debido a que los fagos son altamente específicos en las bacterias que infectan, la evolución de la resistencia a los fagos también estaría limitada a la cepa particular de bacterias. Sin embargo, deben superarse varios obstáculos para que la terapia con fagos se convierta en una alternativa viable a los antibióticos. Por ejemplo, la alta especificidad de los fagos también es un inconveniente, porque se necesitarían fagos diferentes para cada especie de bacteria patógena o incluso cepa de bacteria dentro de una especie patógena. Por lo tanto, sería difícil producir fagos para muchas infecciones bacterianas diferentes a gran escala. Además, debido a la especificidad de los fagos, sería necesario conocer la cepa bacteriana particular que está causando una infección o usar un cóctel de múltiples fagos diferentes en el tratamiento y esperar que uno de ellos coincida con la bacteria patógena. A pesar de estos inconvenientes, la terapia con fagos sigue siendo un área activa de investigación.

Ciclo lítico de bacteriófagos

Los bacteriófagos, también conocidos como fagos, son virus especializados que infectan a las bacterias. Una característica clave de los fagos es su ...

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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...

lytic cycle of bacteriophages

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.

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How Phages Infect and Burst Bacteria

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