--- title: "Bacteriophages as Predators and as Laboratory Tools" description: "Bacteriophages infect bacteria. Their host ranges shape which bacterial populations they affect and allow phage typing. Plaque assays measure infectious units, and phages also provide tools for studyi" canonical: https://lightmysky.com/learn/science/bacteriophages-as-predators-and-as-laboratory-tools-mt_vOnjSpXjrj source: https://lightmysky.com/learn/science/bacteriophages-as-predators-and-as-laboratory-tools-mt_vOnjSpXjrj.md retrieved: 2026-11-12 --- > **Agent view.** This is the Markdown twin of the page, for tools and assistants. > When to use this site, and the call that answers each job: https://lightmysky.com/agent-instructions.md > API description (OpenAPI 3.1): https://lightmysky.com/openapi.json · Authentication: https://lightmysky.com/auth.md > Pricing: https://lightmysky.com/pricing.md · Catalog: https://lightmysky.com/llms.txt · Full catalog: https://lightmysky.com/llms-full.txt > Every machine-readable file on this domain: https://lightmysky.com/.well-known/ai-catalog.json > Ask for Markdown with `Accept: text/markdown`, a `.md` address, or `?mode=agent`. # Bacteriophages as Predators and as Laboratory Tools Bacteriophages infect bacteria. Their host ranges shape which bacterial populations they affect and allow phage typing. Plaque assays measure infectious units, and phages also provide tools for studying and transferring genes. Subject: Science · Area: Microbiology · Ages 19 to 21 Page: https://lightmysky.com/learn/science/bacteriophages-as-predators-and-as-laboratory-tools-mt_vOnjSpXjrj ## Ready when they can - Explains host range and why receptor binding alone does not guarantee productive infection. - Interprets separated plaques as plaque-forming units in the plated portion under stated assay conditions. - Explains how phages support bacterial typing, tests of genetic material and transfer of bacterial genes. ## Lesson: Phages: host range, plaques and laboratory uses You have studied lysis. A bacteriophage, or phage, infects bacteria. Its host range is the strains in which it can reproduce under given conditions. Many tailed phages use binding proteins, including tail fibres, to recognize bacterial surface receptors. Compatible receptors permit attachment, but later steps may be blocked by host defences. Host range can include one strain or several. **Example.** A plaque is a patch of reduced growth in a bacterial lawn caused by phage infection. New phages spread to nearby cells, so one plaque involves many infections. Count well-separated plaques as plaque-forming units (PFU): 46 plaques represent 46 PFU in the portion plated. PFU measures infectivity on the chosen host under the assay conditions, not every physical particle. An aggregate of particles may form one plaque; some particles form none. *(drawing: A plaque involves local spread through many cells. It is not the mark of just one dead bacterial cell.)* Phage typing compares a bacterial isolate's responses to a standard panel of phages with reference lysis patterns. An isolate is a bacterial culture obtained from a sample. Different host ranges give different patterns of lysis. A matching pattern supports a phage type, but one positive spot does not uniquely identify a strain. Use standard conditions and controls when comparing patterns. Hershey and Chase labelled T2 phage DNA and protein in separate preparations. After infection, they removed the attached phage coats and separated bacterial cells from the fluid. Most DNA label was with the cells; most protein label was in the fluid. This supported DNA as T2 phage's genetic material. It did not show that all viruses have DNA genomes. Phages can transfer bacterial genes by transduction. In generalized transduction, a particle can package a fragment of the donor bacterium's DNA during phage production. It can deliver that fragment to another bacterium, the recipient. If the DNA is retained and expressed, the recipient may gain a trait. The DNA carrying the transferred bacterial gene comes from the donor, rather than being only the usual phage genome. *(drawing: A possible transduction outcome: bacterial DNA reaches a recipient and may supply a trait if it is retained and expressed.)* Lytic phages reproduce inside susceptible bacteria and release new particles when infected cells lyse. This can reduce susceptible strains and change competition among bacteria. A common strain is not necessarily susceptible. Host range, encounter rates and resistance affect the outcome, so phages do not always remove the most abundant strain. Resistance can prevent attachment or block a later step. Losing or altering a receptor can stop a phage that needs it from attaching. If attachment remains normal but no new phages are produced, the block can be after attachment. Compare with a susceptible control under the same conditions. These results locate a stage, not the exact defence mechanism. **Recap.** Host range requires successful reproduction. Plaques measure PFU under assay conditions. Phages can type bacteria, investigate genetic material and transfer bacterial DNA. *Lesson, questions, worked solutions and flashcards written for this dataset.* ## Practice 8 questions on this page, each with its working shown. ## Needs first - [Viral Life Cycles: Lysis, Lysogeny and Latency](https://lightmysky.com/learn/science/viral-life-cycles-lysis-lysogeny-and-latency-mt_OI8-dySb5A) ## Opens up - [Horizontal Gene Transfer: Uptake, Contact and Delivery](https://lightmysky.com/learn/science/horizontal-gene-transfer-uptake-contact-and-delivery-mt_mrmn0_nQf7)