Name: how dna phages replicate in bacteria
Uploaded: 2025-06-12T09:30:01.000Z
Duration: 1 min 26 s
Channel: JoVE

K12 Standards

Virginia  Standards of Learning

HIgh School

Biology

BIO.4

BIO.4.a

DNA Bacteriophages

Os bacteriófagos de DNA são vírus que ocorrem em várias formas e infectam bactérias injetando seu DNA. Eles podem ter DNA de fita simples chamado ssDNA ou DNA de fita dupla chamado genomas de dsDNA. Por exemplo, o fago ΦX174, um fago ssDNA icosaédrico, tem um pequeno genoma com genes sobrepostos. Isso permite que várias proteínas sejam codificadas por meio de diferentes quadros de leitura. Este fago se replica por meio da replicação do círculo rolante, formando um intermediário de fita dupla antes de gerar novos genomas. Finalmente, a progênie é liberada por lise do hospedeiro. Em contraste, M13, um fago filamentoso de ssDNA, sai da célula hospedeira por extrusão em vez de lise, permitindo a produção contínua de fagos enquanto mantém o hospedeiro vivo. Entre os fagos dsDNA, o fago T7 se replica bidirecionalmente, formando concatemers processados por uma enzima terminase para empacotamento do genoma. Por outro lado, Mu inicia a replicação por transposição, inserindo-se em vários locais no genoma do hospedeiro. Em seguida, ele extirpa e empacota seu genoma linear em novos vírions.

bacteriófagos de dna

Os bacteri&#243;fagos, ou fagos, s&#227;o v&#237;rus que infectam especificamente bact&#233;rias, utilizando seu material gen&#233;tico para sequestrar a maquinaria celular do hospedeiro a fim de se replicar. Os fagos de DNA empregam genomas de DNA de fita simples (ssDNA) ou de fita dupla (dsDNA). Esses fagos apresentam estrat&#233;gias de replica&#231;&#227;o e intera&#231;&#245;es com o hospedeiro altamente diversas, influenciando seus pap&#233;is ecol&#243;gicos e aplica&#231;&#245;es em biotecnologia e medicina.
Fagos ssDNA
Os fagos ssDNA, com seus genomas reduzidos, utilizam estrat&#233;gias &#250;nicas para maximizar a efici&#234;ncia gen&#233;tica. O fago &#934;X174, um v&#237;rus icosa&#233;drico de ssDNA, exemplifica isso com genes sobrepostos, nos quais diferentes quadros de leitura codificam m&#250;ltiplas prote&#237;nas. Essa estrat&#233;gia permite maximizar o uso do espa&#231;o gen&#233;tico em um genoma compacto. A replica&#231;&#227;o come&#231;a com a s&#237;ntese de uma fita complementar, formando uma intermedi&#225;ria de DNA de fita dupla conhecida como forma replicativa (FR). Essa FR serve como molde para a replica&#231;&#227;o por c&#237;rculo rolante, gerando novos genomas virais que s&#227;o ent&#227;o empacotados em v&#237;rions. Ap&#243;s a replica&#231;&#227;o, o fago lisa a c&#233;lula bacteriana, liberando os descendentes.
Por outro lado, o fago M13, um v&#237;rus filamentoso de ssDNA, adota uma estrat&#233;gia de libera&#231;&#227;o distinta. Em vez de empacotar os genomas rec&#233;m-sintetizados em v&#237;rions e liber&#225;-los por lise, os v&#237;rions do M13 s&#227;o montados na membrana bacteriana e secretados continuamente por um processo de extrus&#227;o, permitindo que a c&#233;lula hospedeira sobreviva e continue produzindo fagos. Essa caracter&#237;stica de produ&#231;&#227;o sustentada de fago &#233; amplamente utilizada em t&#233;cnicas de biologia molecular, como exposi&#231;&#227;o em fago (phage display) e tecnologias de DNA recombinante.
Fagos dsDNA
Em contraste com os fagos ssDNA, os fagos dsDNA adotam mecanismos de replica&#231;&#227;o mais elaborados, ampliando suas intera&#231;&#245;es com os hospedeiros bacterianos. O fago T7 utiliza um mecanismo de replica&#231;&#227;o bidirecional altamente eficiente. Uma vez dentro do citoplasma bacteriano, o T7 inicia a replica&#231;&#227;o a partir de um s&#237;tio de origem &#250;nico, prosseguindo em ambas as dire&#231;&#245;es. Notavelmente, o T7 depende de sua pr&#243;pria DNA polimerase codificada pelo fago, o que aumenta a velocidade de replica&#231;&#227;o. Al&#233;m disso, a RNA polimerase do T7 desempenha um papel crucial na coordena&#231;&#227;o da express&#227;o g&#234;nica e na efici&#234;ncia replicativa. As novas mol&#233;culas de DNA formam concat&#234;meros &#8212; longas cadeias cont&#237;nuas contendo m&#250;ltiplas unidades gen&#244;micas. Esses concat&#234;meros s&#227;o ent&#227;o processados por uma enzima terminase, que os cliva em segmentos do tamanho do genoma para encapsulamento em novas part&#237;culas de fago. Essa estrat&#233;gia eficiente de replica&#231;&#227;o tornou o T7 um sistema modelo na biologia sint&#233;tica e na engenharia gen&#233;tica.
O fago Mu, outro bacteri&#243;fago de dsDNA, replica-se por um mecanismo baseado em transposi&#231;&#227;o, ao inv&#233;s dos modelos convencionais de replica&#231;&#227;o por c&#237;rculo rolante ou bidirecional. Integra-se em v&#225;rios s&#237;tios dentro do genoma bacteriano e passa por m&#250;ltiplas rodadas de transposi&#231;&#227;o antes de se excisar para o empacotamento em novos v&#237;rions. A transposi&#231;&#227;o do fago Mu duplica o DNA hospedeiro nos s&#237;tios de inser&#231;&#227;o, frequentemente interrompendo genes, o que o torna uma ferramenta &#250;til para mutag&#234;nese e mapeamento gen&#244;mico bacteriano.

Bacteriófagos de DNA

Os bacteri&#243;fagos, ou fagos, s&#227;o v&#237;rus que infectam especificamente bact&#233;rias, utilizando seu material gen&#233;tico para sequestrar a ...

Education

JoVE Core

Microbiology

Microbiologia

Unit

Unidade

Viruses

Vírus

KEY TERMS AND CONCEPTS

TERMOS E CONCEITOS-CHAVE

how dna phages replicate in bacteria

DNA bacteriophages are viruses that infect bacteria and use bacterial cell machinery to make more copies of themselves. They carry either single-stranded DNA (ssDNA) or double-stranded DNA (dsDNA), and each group uses a different replication strategy. Their life cycles also shape how they interact with hosts and how scientists use them in biotechnology and medicine.

Some ssDNA phages keep their genomes very small and compact. The icosahedral phage ΦX174 shows this clearly because it uses overlapping genes, so different reading frames can code for different proteins. After infection, it first makes a complementary DNA strand. This creates a double-stranded replicative form, or RF, which then serves as the template for rolling circle replication.

Rolling circle replication produces new viral genomes that are packaged into virions. When replication ends, the phage lyses the bacterial host and releases the new particles. M13, another ssDNA phage, follows a different path. Its virions assemble at the bacterial membrane and are secreted continuously by extrusion, so the host cell stays alive and keeps making phages.

That steady release makes M13 useful in molecular biology. Scientists use it in phage display and in recombinant DNA work. These applications depend on the phage’s ability to keep producing particles without immediately killing the bacterium.

dsDNA bacteriophages use more elaborate replication systems. T7 begins replication at a unique origin site inside the bacterial cytoplasm and copies its DNA in both directions. It uses phage-encoded DNA polymerase, which helps replication move quickly. T7 RNA polymerase also helps coordinate gene expression and replication efficiency.

The new T7 DNA molecules form concatemers, which are long DNA strands that contain multiple genome copies. A terminase enzyme then cuts these strands into genome-sized pieces for packaging into new phage particles. This efficient system has made T7 a model for synthetic biology and genetic engineering.

Mu phage is another dsDNA bacteriophage, but it does not use a standard rolling circle or bidirectional pattern. Instead, it replicates through transposition, which means it inserts into different sites in the bacterial genome and makes multiple rounds of movement before it is excised for packaging. This process duplicates host DNA at the insertion site and can disrupt genes, which is why Mu is useful for mutagenesis and bacterial genome mapping.

How DNA Phages Replicate in Bacteria

introduction to virus

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size and structure of viral genomes

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viral replication: lysogenic cycle

Prophage Integration in Bacterial Cells

The lysogenic cycle shows how a bacteriophage can stay inside a bacterial cell without killing it right away. Temperate phages, such as bacteriophage lambda (λ), use this strategy to persist in Escherichia coli while the host cell remains alive. After attachment to the bacterial surface, the phage injects its genetic material into the cytoplasm. The linear phage genome then circularizes, which helps protect it from host nucleases. Next, phage-encoded integrase carries out recombination that...

dna bacteriophages

DNA bacteriophages are viruses that infect bacteria and use bacterial cell machinery to make more copies of themselves. They carry either single-stranded DNA (ssDNA) or double-stranded DNA (dsDNA), and each group uses a different replication strategy. Their life cycles also shape how they interact with hosts and how scientists use them in biotechnology and medicine. Some ssDNA phages keep their genomes very small and compact. The icosahedral phage ΦX174 shows this clearly because it uses...

viruses of archaea

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viruses with rna genomes

RNA Virus Replication Strategies

RNA viruses use several replication strategies based on their genome type. They are grouped as positive-strand, negative-strand, or double-stranded RNA viruses. Some RNA viruses also use reverse transcription, which adds another layer to how they copy their genetic material. Positive-strand RNA viruses have genomes that can act like messenger RNA, or mRNA, as soon as they enter a cell. This lets the virus begin making proteins right away. Bacteriophage MS2 infects Escherichia coli by attaching...

the antiviral system of bacteria and archaea: crispr

the-antiviral-system-of-bacteria-and-archaea-crispr

How CRISPR Remembers Viral Infections

CRISPR is an adaptive immune system in bacteria and archaea that helps protect cells from viral infection. It works by identifying foreign genetic material, remembering it, and stopping the same invader later. In many cases, the main targets are bacteriophages, which are viruses that infect bacteria. The first defense step begins during an initial infection. Cas proteins, which are CRISPR-associated proteins, detect foreign DNA by looking for specific sequences called Protospacer Adjacent...

crispr/cas9 genome editing

CRISPR-Cas9 and DNA Repair in Cells

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subviral agents

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Viroids, prions, and satellites are subviral agents that can cause infection even though they are not complete viruses. They resemble viruses in spread and disease, but each lacks one or more key viral parts, such as a capsid or the machinery needed for replication. Viroids are the simplest of these agents. They are circular, single-stranded RNA molecules with no protein coat. Viroids infect plants only and depend on host cell machinery to copy themselves. Host RNA polymerase replicates them...

key terms and concepts

Learn how DNA bacteriophages copy their genomes in bacteria, from ΦX174 and M13 to T7 and Mu, with clear examples of replication and packaging.

How DNA Phages Replicate in Bacteria | JoVE K12

JoVE Core Microbiology provides an engaging introduction to the microbial world and its influence on health, industry, and the environment. This comprehensive collection covers key concepts such as microbial structure, metabolism, genetics, and ecology. It introduces essential laboratory techniques and microscopy methods through visually engaging animations. Corresponding scientist-in-action videos bridge classroom concepts with real-world research and applications.

microbiology

Alabama Course of Study Science

9-12

Unity and Diversity

9-12.B.4.13.a

Introduction to Virus

Viruses are unique biological entities that blur the boundary between living and non-living systems. Although they lack cellular structure and metabolic ...

Size and Structure of Viral Genomes

Viral genomes exhibit remarkable diversity in size, structure, and composition, influencing their replication strategies and interactions with host cells. ...

Viral Replication: Lytic Cycle

Bacteriophages, or phages, are viruses that specifically infect bacteria. Among them, T-even bacteriophages, such as T4, exhibit a well-characterized ...

Viral Replication: Lysogenic Cycle

The lysogenic cycle is a crucial viral replication strategy that allows bacteriophages to persist within host cells without immediately destroying them. ...

Bacteriophages, or phages, are viruses that specifically infect bacteria, utilizing their genetic material to hijack host cellular machinery for ...

Viruses of Archaea

Archaeal viruses play a crucial role in the ecosystems of extremophilic archaea, particularly those belonging to the phyla Euryarchaeota and ...

Viruses with RNA Genomes

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The Antiviral System of Bacteria and Archaea: CRISPR

CRISPR stands for Clustered Regularly Interspaced Short Palindromic Repeats is a adaptive immune system found in bacteria and archaea that protects ...

CRISPR/Cas9 Genome Editing

The CRISPR-Cas system serves as a bacterial defense mechanism against invading genetic elements such as viruses and plasmids, forming the foundation for ...

Subviral Agents

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The student will investigate and understand that bacteria and viruses have an effect on living systems. Key ideas include  viruses depend on a host for metabolic processes;

Binary Fission

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Generation Time

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Bacterial Growth Curve

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Biofilms

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The student will investigate and understand that bacteria and viruses have an effect on living systems. Key ideas include the modes of reproduction/replication can be compared

BIO.4.b

Prokaryotic vs. Eukaryotic Cells

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Microbial Morphologies 

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Bacterial Cell Wall 

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Archaeal Cell Wall

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Cell Inclusions

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Endospores and Sporulation

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Nucleoid

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Surface Appendages of Archaea

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BIO.4.c

Types of Microorganisms

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Environmental Applications of Microorganisms

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Community DNA Extraction from Bacterial Colonies

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Detecting Environmental Microorganisms with the Polymerase Chain Reaction and Gel Electrophoresis

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Quantifying Environmental Microorganisms and Viruses Using qPCR

Source: Laboratories of Dr. Ian Pepper and Dr. Charles Gerba - The University of Arizona
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Isolation of Fecal Bacteria from Water Samples by Filtration

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The quality of water destined ...

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Detection of Bacteriophages in Environmental Samples

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Viruses are a unique group of ...

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Culturing and Enumerating Bacteria from Soil Samples

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Bacterial Growth Curve Analysis and its Environmental Applications

Source: Laboratories of Dr. Ian Pepper and Dr. Charles Gerba - The University of Arizona
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BIO.4.d

History of Microbiology

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Infection

When a pathogen enters the body and reproduces, it can cause an infection, damage body cells, and cause illness symptoms that eventually lead to disease. ...

Defense Mechanism Against Infection

Natural flora, body system defenses, and inflammation are natural barriers of the body against infectious agents regardless of previous exposure. Normal ...

The student will investigate and understand that bacteria and viruses have an effect on living systems. Key ideas include  the germ theory of infectious disease is supported by evidence.

BIO.4.e

How DNA Phages Replicate in Bacteria

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