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DNA Bacteriophages01:26

DNA Bacteriophages

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Bacteriophages, or phages, are viruses that specifically infect bacteria, utilizing their genetic material to hijack host cellular machinery for replication. DNA bacteriophages employ single-stranded DNA (ssDNA) or double-stranded DNA (dsDNA) genomes. These phages exhibit diverse replication strategies and host interactions, influencing their ecological roles and applications in biotechnology and medicine.ssDNA BacteriophagesssDNA phages, with their small genomes, utilize unique strategies to...
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Lytic Cycle of Bacteriophages01:30

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Bacteriophages, also known as phages, are specialized viruses that infect bacteria. A key characteristic of phages is their distinctive “head-tail” morphology. A phage begins the infection process (i.e., lytic cycle) by attaching to the outside of a bacterial cell. Attachment is accomplished via proteins in the phage tail that bind to specific receptor proteins on the outer surface of the bacterium. The tail injects the phage’s DNA genome into the bacterial cytoplasm. In the...
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Viral Replication: Lysogenic Cycle01:16

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The lysogenic cycle is a crucial viral replication strategy that allows bacteriophages to persist within host cells without immediately destroying them. This process is primarily observed in temperate phages, such as bacteriophage lambda (λ), which infects Escherichia coli. The cycle allows the viral genome to persist across bacterial generations while keeping host cells viable.Integration of the Viral GenomeUpon infection, bacteriophage lambda attaches to the bacterial surface and injects...
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Lysogenic Cycle of Bacteriophages00:43

Lysogenic Cycle of Bacteriophages

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In contrast to the lytic cycle, phages infecting bacteria via the lysogenic cycle do not immediately kill their host cell. Instead, they combine their genome with the host genome, allowing the bacteria to replicate the phage DNA along with the bacterial genome. The incorporated copy of the phage genome is called the prophage. Some prophages can re-activate and enter the lytic cycle. This often occurs in response to a perturbation, such as DNA damage, but can also transpire in the absence of...
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Viral Replication: Lytic Cycle01:20

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Bacteriophages, or phages, are viruses that specifically infect bacteria. Among them, T-even bacteriophages, such as T4, exhibit a well-characterized lytic replication cycle in Escherichia coli (E. coli). This process ensures the rapid proliferation of the virus while ultimately leading to the destruction of the bacterial host.Attachment and DNA InjectionThe infection process begins with the recognition and binding of the T4 phage to the E. coli cell surface. Tail fibers of the phage...
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Plasmids

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Plasmids are extrachromosomal DNA molecules found in bacteria, archaea, and some eukaryotic microbes like yeast. These small, circular DNA structures typically contain fewer than 30 genes, although some may exist linearly. Plasmids vary in their number within a cell, known as copy number. Single-copy plasmids are present in one copy per cell and multi-copy plasmids are present in multiple copies, reaching over 100 copies per cell.Plasmids usually replicate independently of the chromosomal DNA...
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Updated: Sep 13, 2025

Phage Phenomics: Physiological Approaches to Characterize Novel Viral Proteins
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Phage Phenomics: Physiological Approaches to Characterize Novel Viral Proteins

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The prototypic crAssphage is a linear phage-plasmid.

Danica T Schmidtke1, Angela S Hickey2, Jakob Wirbel3

  • 1Department of Microbiology and Immunology, Stanford University, Stanford, CA, USA.

Cell Host & Microbe
|July 29, 2025
PubMed
Summary
This summary is machine-generated.

The human gut virus crAssphage (Caudovirales) exists as a phage-plasmid, persisting extrachromosomally without lysis. This study reveals its broad host range and potential for dual lifestyles, explaining its abundance in gut microbiomes.

Keywords:
BacteroidotaCarjivirus communisPhocaeicolabacteriophagecrAssphagemicrobial genomicsmicrobiomephage culturingphage-plasmidplasmid

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Area of Science:

  • Microbiology
  • Virology
  • Human Gut Microbiome Research

Background:

  • The crAssphage (Caudovirales), a ubiquitous human gut virus, is poorly understood due to its uncultured nature.
  • Its non-lytic behavior suggests an atypical lifestyle, distinct from typical bacteriophages.

Purpose of the Study:

  • To characterize the lifestyle and host interactions of the prototypic crAssphage (Caudovirales).
  • To investigate the replication and persistence mechanisms of crAssphage within prevalent gut bacteria.

Main Methods:

  • Utilized a plaque-free culturing technique to study crAssphage replication.
  • Analyzed phage-plasmid gene transcription and potential replication origins.
  • Determined host range on key gut bacteria, including Phocaeicola and Bacteroides species.

Main Results:

  • Demonstrated that crAssphage exists as a linear phage-plasmid, maintaining extrachromosomal persistence.
  • Identified transcription of phage and plasmid genes, indicating active replication.
  • Revealed a broad host range, with successful replication in Phocaeicola vulgatus, P. dorei, and Bacteroides stercoris without significant lysis.

Conclusions:

  • CrAssphage exhibits a unique dual lifestyle, functioning as both a phage and a plasmid.
  • Its ability to replicate extrachromosomally and persist across diverse hosts contributes to its prevalence in the human gut microbiome.