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

- [Istruttore] Alcuni tipi di
virus chiamati batteriofagi

o mangiatori di batteri
infettano le cellule batteriche.

I fagi possono variare nella
forma e nel materiale genetico,

la più singolare è la
morfologia dei testa-coda

con DNA a doppio filamento.

Per iniziare il processo
d'infezione, ossia il suo ciclo di

vita, il fago si lega
innanzitutto a un batterio.

Più specificamente le proteine
dentro le fibre della coda

si legano a specifici
recettori sulla superficie.

La coda poi si contrae, iniettando il DNA

all'interno del citoplasma dell'ospite

e si traduce in un capside vuoto.

Per riprodursi, un modo è
di entrare nel ciclo litico,

una modalità di replicazione
che coinvolge il controllo

del meccanismo cellulare del batterio,

distruggendo il DNA ospite

e costringendolo a
produrre componenti virali.

Il DNA del fagi è protetto e copiato

e ulteriori set di proteine
vengono sintetizzati

per aiutare a formare nuovi virus.

Durante questa fase di auto-assemblaggio,

il genoma virale viene
impacchettato dentro la testa.

Il fago traduce anche le proteine

che degradano la parete
cellulare dell'ospite,

consentendo all'acqua di entrare.

Come risultato dell'espansione,
la cellula scoppia

e tale lisi del batterio

rilascia centinaia di nuovi fagi,

che ora possono trovare e
infettare la popolazione

di batteri nelle vicinanze.

Doss, Janis, Kayla Culbertson, Delilah Hahn, Joanna Camacho e Nazir Barekzi. "Una revisione della terapia fagica contro i patogeni batterici degli organismi acquatici e terrestri". Virus 9, n. 3 (18 marzo 2017). [<a href="https://doi.org/10.3390/v9030050" target="__blank">Sorgente</a>]

Abedon, Stephen T., Pilar García, Peter Mullany e Rustam Aminov. "Editoriale: Terapia fagica: passato, presente e futuro." Frontiere in Microbiologia 8 (2017). [<a href="https://doi.org/10.3389/fmicb.2017.00981" target="__blank">Sorgente</a>]

ciclo litico dei batteriofagi

I batteriofagi, noti anche come fagi, sono virus specializzati che infettano i batteri. Una caratteristica chiave dei fagi è la loro caratteristica morfologia "testa-coda". Un fago inizia il processo di infezione (cioè ciclo litico) legandosi all'esterno di una cellula batterica. L'attaccamento avviene tramite proteine nella coda del fago che si legano a specifiche proteine recettoriali sulla superficie esterna del batterio. La coda inietta il genoma del DNA del fago nel citoplasma batterico. Nel ciclo di replicazione litico, il fago utilizza il meccanismo cellulare del batterio per produrre proteine che sono fondamentali per la replicazione e la dispersione del fago. Alcune di queste proteine portano la cellula ospite a prendere acqua e scoppiare, o lisare, dopo che la replicazione dei fagi è completa, rilasciando centinaia di fagi che possono infettare nuove cellule batteriche.

<h4>Terapia di Fazò</h4>

Dall'inizio del XX secolo, i ricercatori hanno riconosciuto il valore potenziale dei batteriofagi littici nella lotta contro le infezioni batteriche nelle colture, nell'uomo e negli animali agricoli. Poiché ogni tipo di fago può infettare e sizzare solo tipi specifici di batteri, i fagi rappresentano una forma altamente specifica di trattamento antibatterico. Questa qualità è in contrasto con i farmaci antibiotici familiari che spesso prendiamo per le infezioni batteriche, che sono in genere trattamenti ad ampio spettro che uccidono sia i batteri patogeni che i batteri benefici. L'uso diffuso di antibiotici ad ampio spettro ha causato l'evoluzione della resistenza batterica a intere classi di questi farmaci, rendendo una volta letali infezioni potenzialmente letali. Poiché più batteri patogeni evolvono resistenza agli antibiotici, la terapia con fago a spettro stretto può diventare un'alternativa utile. Poiché i fagi sono altamente specifici nei batteri che infettano, l'evoluzione della resistenza ai fagi sarebbe anche limitata al particolare ceppo di batteri.

Tuttavia, è necessario superare diversi ostacoli affinché la terapia del fago diventi una valida alternativa agli antibiotici. Per esempio, l'alta specificità dei fagi è anche uno svantaggio, perché sarebbero necessari diversi fagi per ogni specie del patogeno batterico o anche ceppo di batteri all'interno di una specie patogena. Sarebbe quindi difficile produrre fagi per molte infezioni batteriche diverse su larga scala. Inoltre, a causa della specificità dei fagi, sarebbe necessario conoscere il particolare ceppo batterico che sta causando un'infezione o utilizzare un cocktail di più fagi diversi nel trattamento e sperare che uno di essi corrisponda ai batteri patogeni. Nonostante questi inconvenienti, la terapia del fago rimane un'area attiva di ricerca.

Ciclo litico dei batteriofagi

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...

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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