Question

A) Explain how auxotrophic bacteria are isolated. B) Briefly explain the differences between F+, F, Hfr, and F' cells. What types of matings are possible between F+, F-, Hfr, and F' cells? C) D)What outcomes do these matings produce? E) What is the role of the F factor in conjugation?

Answer 1

A) The cells are irradiated with visible light50 for 30 minutes to kill prototrophic cells, which have incorporated BUdR, and are then transferred to complete medium. Colonies which appear after 1 to 2 weeks of incubation are isolated by standard cloning methods and tested for their specific nutritional requirements.

B) F+ Cells: -These are the plasmid-containing bacterial cells. They are literally called F+ since they have plasmid F. It's named plasmid F because it has element F which is component Fertility. This factor in fertility contains the genes required for the transmission or conjugation.

  F – Cells: -F- cells are plasmid-free cells. These cells act as recipient cells because they don't have plasmid F and therefore they can't donate the genetic material. They are known as F – simply because they don't have plasmid F.

Hfr Cells = Derivatives of F+ cells where F plasmid has integrated into host chromosomal DNA

F 'Cells = Hfr cell derivatives in which F plasmid has disintegrated from the host chromosome and collects certain host genes next to F plasmid integration sites

E) The F-factor allows the donor to make a thin, tube-like structure called a pilus that is used by the donor to contact the recipient. The pilus then brings together the two bacteria, at which stage the sender bacterium passes genetic material to the receiving bacterium.