Bacteriophages, commonly known as phages, are viruses that infect and replicate within bacteria. First discovered independently by Frederick Twort and Félix d'Hérelle in the early 20th century, these viral entities are the most abundant biological organisms on Earth. In the modern era of biotechnology, mastering phage terminology is essential for researchers navigating the complex landscape of molecular biology, genetic engineering, and therapeutic development.
Fig.1
Bacteriophage structure.1
Creative Biolabs is a global leader in phage technology, providing cutting-edge Phage Services ranging from library construction to clinical-grade production. This glossary serves as an authoritative resource to clarify essential concepts such as phage definition biology, the distinction between the lytic and lysogenic cycle, and advanced applications like phage display.
Understanding the fundamental structure and classification of phages is the first step in virology research. Below are key terms related to what is phage and its components.
Bacteriophage meaning: A virus that infects and replicates within bacteria and archaea. Derived from the Greek "bacteria" and "phagein" (to eat). Phages are highly specific, targeting only specific bacterial strains, making them precision tools in microbial control.
The protein shell of a virus that encloses its genetic material. In tailed phages (Caudovirales), the capsid (or head) protects the double-stranded DNA or RNA genome.
The spectrum of bacterial strains or species that a specific phage can infect. This is determined by the interaction between phage tail fibers and bacterial surface receptors. We also offer services for Phages with Wild Host Range Production to target specific pathogens.
The first step of the phage infection process, where the phage attaches to specific receptors on the bacterial cell surface. This interaction is highly specific and often irreversible.
A classic model organism in molecular biology, the T4 phage is a large, tailed virus that infects Escherichia coli bacteria. It belongs to the Myoviridae family and relies exclusively on the lytic cycle for replication.
A temperate bacteriophage that infects E. coli. Unlike T4, the lambda phage can choose between the lytic and lysogenic pathways, making it a critical model for studying gene regulation and genetic recombination.
A filamentous bacteriophage of the Ff family that infects E. coli via the F pilus. Its non-lytic lifecycle allows infected cells to continually secrete new virions. The M13 phage is a cornerstone of phage display technology due to its ability to display foreign peptides on its coat proteins.
A member of the Microviridae family, closely related to PhiX174. It is a small, isometric, single-stranded DNA virus. Phage S13 Production is utilized in studies of viral evolution and DNA replication mechanisms.
A wild-type or modified phage (e.g., M13KO7, VCSM13) used to provide necessary viral components for the packaging of phagemids, which lack the genes required for replication and assembly. Helper Phage Production is essential for successful phage display library screening.
The replication strategy of a phage determines its application in therapy and research. The distinction between the lytic and lysogenic cycle is fundamental.
The lytic cycle is a viral reproductive cycle that results in the destruction of the infected cell and its membrane. Virulent phages (like T4) exclusively use this cycle, hijacking the host's machinery to produce new virions before lysing the cell to release them. This cycle is the basis for phage therapy.
The lysogenic cycle involves the integration of the viral genome into the host bacterial chromosome, becoming a prophage. The virus replicates passively with the host DNA without destroying the cell. Stressors can trigger induction, switching the phage back to the lytic cycle.
The genetic material of a bacteriophage, incorporated into the genome of a bacterium and able to produce phages if specifically activated. Prophages are a key feature of the lysogenic cycle.
The process by which a prophage excises itself from the bacterial chromosome and enters the lytic cycle. This is often triggered by DNA damage or environmental stress (e.g., UV light, chemicals).
Bacteriophages (such as Lambda phage) that can undergo both lytic and lysogenic life cycles. In contrast, virulent phages can only undergo the lytic cycle.
The average number of phage particles released from a single infected bacterial cell upon lysis. A higher burst size indicates a more productive infection, which is desirable for Phage Production.
The time interval between the adsorption of the phage to the host cell and the release of new phage progeny (lysis). This period includes the eclipse phase where no infectious particles are yet assembled.
The ability of a lysogen (bacterium containing a prophage) to resist infection by the same or a closely related phage. This is mediated by repressors produced by the resident prophage.
From quantification to protein engineering, these methods utilize phages definition in practical laboratory settings. Creative Biolabs offers specialized services for each technique.
The process of identifying novel bacteriophages from environmental samples (e.g., soil, water, sewage) that target a specific bacterial host. Our Phage Discovery service uses high-throughput screening to find potent phages for therapy or research.
The procedure of separating a single phage strain from a mixed population. Techniques like the plaque assay are used to pick single clones. We offer comprehensive Phage Isolation services to ensure pure, monoclonal phage stocks.
A technique used to increase the concentration of specific phages in a sample by incubating it with the target host bacteria, allowing the relevant phages to replicate. Learn more about our Phage Enrichment protocols.
The removal of bacterial debris, endotoxins, and contaminants from a phage lysate. Methods include PEG precipitation, CsCl gradient centrifugation, and chromatography. High-purity Phage Purification is critical for clinical and sensitive analytical applications.
The analysis of phage properties, including morphology (TEM), genomic sequence, host range, and stability. Phage Characterization is essential for regulatory approval and understanding phage biology.
Phage display is a laboratory technique for the study of protein–protein, protein–peptide, and protein–DNA interactions that uses bacteriophages to connect proteins with the genetic information that encodes them. By inserting a gene fragment into a phage coat protein gene, the polypeptide is displayed on the surface of the phage. Visit our Phage Display page for more details.
An affinity selection technique used in phage display to isolate peptides or antibodies that bind to a specific target. It involves multiple rounds of binding, washing, elution, and amplification. We offer expert Phage Display Library Screening and Biopanning services.
The plaque assay is the gold standard method for quantifying viral titer. It involves infecting a bacterial lawn with a phage sample. Lytic activity creates clear zones (plaques) on the agar plate, where each plaque represents a single infectious unit (Plaque Forming Unit, PFU).
A suite of analytical methods used to assess phage quality, titer, and stability. This includes biophysical, biochemical, genetic, and immunological analyses. Explore our full range of Phage Analytics.
Modern biotechnology has expanded the phages definition beyond simple viruses to versatile tools for medicine and industry.
High-quality, pre-made libraries allow for the rapid selection of high-affinity binders against a wide range of targets without the need for immunization.
Comprehensive kits designed to streamline the construction of diverse antibody libraries, ensuring high transformation efficiency and library quality.
High-titer helper phages, such as M13KO7, essential for the packaging of phagemid DNA into infectious viral particles for display applications.
Specialized electrocompetent and chemically competent bacterial strains optimized for high-efficiency transformation and phage propagation.
Q: What is the main difference between lytic and lysogenic cycles?
Q: How is phage display used in drug discovery?
A: Phage display is used to screen billions of peptide or antibody variants to find those that bind with high affinity to a specific target (antigen). This technique is crucial for antibody development, epitope mapping, and identifying novel therapeutic ligands.
Q: Are phages safe for use in research and potential therapy?
A: Phages are highly specific to bacteria and do not infect human cells, making them generally safe. However, for therapeutic applications, phages must be purified to remove bacterial endotoxins. All our services are currently For Research Use Only.
Q: What is a plaque assay used for?
A: A plaque assay is a quantitative method used to determine the concentration of viral particles (titer) in a sample. It relies on counting the number of plaques (clear zones) formed on a bacterial lawn.
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