If recombinant lambda phage vector is transferred to ecoli cells it will generate clear or turbid plaques?
Answers
Answer:
here are a variety of viral life cycle strategies, and not all of them involve certain death for the cell. We discussed one such example in a previous lecture, when we looked at the filamentous bacteriophages such as M13, fd and f1.
Temperate bacteriophage may enter a cell and produce no progeny virus whatever! They lie silently, allowing the DNA replication machinery of the cell to copy their genomes during the course of the normal cell cycle, and having little discernable effect on the health of the host. At some point, in response to an environmental trigger, the virus leaves its cryptic state and enters a lytic cycle that leads to host cell death and virus release .
Cryptic infection by temperate bacteriophage
The most thoroughly studied temperate bacteriophage is lambda, which was pulled out of a Paris sewer 50 years ago by Lwoff, Jacob and Monod. They found that certain strains of E. coli, when exposed to ultraviolet light, generated viral plaques on a plate - that is, small areas of bacterial lysis. The word "lysogeny" was coined to describe this type of cryptic infection. Plaques generated by lambda are typically "turbid" rather than "clear" because after an initial round of lytic growth on rapidly dividing E. coli, there follows an overgrowth of bacteria carrying lambda lysogenically. These lysogenic bacteria are "immune" to lytic lambda infection, because they already harbor the virus!
Lambda can be engineered to carry DNA into cells.
Do you recall the definition of bacterial transformation? That's when bacteria take up free DNA from their surroundings. If a virus injects its genome into a cell, that's clearly a different type of "uptake" of DNA (or RNA, as the case may be) - we would call that "infection" of course. What term do we use when the infecting virus is carrying DNA that is not normally its own? We call it "transduction" and with integrating viruses like lambda we distinguish between the transfer of genomic DNA adjacent to the normal integration site (specialized transduction) and tranfer of essentially random fragments from the E. coli genome (generalized transduction).