Blue/White Screening and Overnight Cultures

1. Blue/White Screening and Overnight Cultures Bayonne High School

2. So what is a Blue/White Screening? Blue/White screening is a technique that utilizes the E. Coli lacZ gene to permit visual detection of colonies that contain plasmids with DNA inserts.

3. Colonies with insert will be white. Colonies without insert will be blue. The lacZ gene produces an enzyme- Beta galactosidase. Beta galactosidase cleaves the substrate X-gal, thus producing blue colonies. An insert ( a fragment of DNA) is purposely cloned into the lacZ gene. When a DNA fragment is cloned into the lacZ gene, the coding region is disrupted and Beta galactosidase is not produced. However, if the lacZ gene is disrupted, X-gal will not be cleaved, which results in colonies that remain white.

4. So how is an overnight setup? First of all, an overnight is a procedure done to grow up a bacterial colony.

5. With a sterile wooden stick, pick up a white colony from a library plate. Inoculate the colony into 3 milliliters of LB/Amp. Incubate at 37*C Overnight, which shakes the cultures for aeration. Remove from the incubator. The culture should be cloudy, indicating growth!