What is true about blue-white screening technology?
Blue-white screening is a rapid and efficient technique for the identification of recombinant bacteria. It relies on the activity of β-galactosidase, an enzyme occurring in E. coli, which cleaves lactose into glucose and galactose.
How could you have a white colony but no insert?
It is also possible (but again unlikely) to get a white colony with no insert (false positive). This could result from nuclease degradation of the linearised vector disrupting the α-peptide before re-ligation. Therefore, it is always a good idea check your insert by sequencing too.
What does a white colony indicate during blue white screening?
Blue colonies therefore show that they may contain a vector with an uninterrupted lacZα (therefore no insert), while white colonies, where X-gal is not hydrolyzed, indicate the presence of an insert in lacZα which disrupts the formation of an active β-galactosidase.
What happen if the medium used to culture bacterial cell does not contain ampicillin?
The bacterium cannot grow in the presence of the antibiotic ampicillin unless it contains the plasmid, and so there will be no growth on the LB/Amp plate of the bacteria without the plasmid.
Can you do blue-white screening without Iptg?
In some blue/white screening systems, an additional reagent must be used: IPTG (isopropylthiogalactoside). IPTG is an inducer that de-represses lacZ expression (it turns the gene on). In some cases, without IPTG, not enough β-galactosidase is produced to turn the colony blue even if the lacZ gene is intact.
Can you do blue white screening without Iptg?
What is true plasmid?
A plasmid is a small, often circular DNA molecule found in bacteria and other cells. Plasmids are separate from the bacterial chromosome and replicate independently of it. They generally carry only a small number of genes, notably some associated with antibiotic resistance.
