Question

Explain how colony color can be used as evidence of the state of the lacZgene in the bacteria

Answer 1

The well characterised bacterial lac operon contains a gene called lacZ. The lacZ gene encodes an enzyme called beta-galactosidase an intracellular enzyme, which is responsible for splitting lactose into readly usable glucose and galactose. The bacterial enzyme beta galactosidase (gene LacZ) is used as reporter gene. It can be easily located with a LacZ stain using the artificial substrate X-gal which turns blue when it is cleaved by beta galactosidase. This protocol describes the staining of cultured cells containing active lacZ genes.

Colony color can be used in the lacZgene. Blue white screening of bacterial colonies using X- gal. It is a screening technique that allows for the detection of successful ligations in vector based gene cloning. If the ligation was successful, the bacterial colony will be white, if not, the colony will be blue. Any color containing the plasmid will turn blue with the presence of beta-galactosidase activity. This called alpha-complementation. The insert disrupted the beta-galactosidase gene, and therefore these colonies remains white. White colonies cannot metabolise X-Gal to produce the blue color, because they donot produce functional beta-galactosidase after taking up plasmid carrying the inserted DNA and disrupting the lacZ alpha gene. These white colonies contains recombinant bacteria and should be selected.