Blue White screening of bacterial cell:-

*Principle:-
The blue–white screen is a screening technique that allows for the rapid and convenient detection of recombinant bacteria in vector-based molecular cloning experiments. DNA of interest is ligated into a vector. The vector is then inserted into a competent host cell viable for transformation, which are then grown in the presence of X-gal. Cells transformed with vectors containing recombinant DNA will produce white colonies; cells transformed with non-recombinant plasmids (i.e. only the vector) grow into blue colonies. This method of screening is usually performed using a suitable bacterial strains

The blue-white screen is a screening technique that allows for the detection of successful ligations in vector-based gene cloning. DNA of interest is ligated into a vector. The vector is then transformed into competent bacterial cells

Blue-White selection is the technique used to determine whether the host (Bacteria) which is transformed has the plasmid (vector) with the gene of interest or not, i.e., to distinguish between the transformants having a recombinant and non-recombinant vector.
The complete protocol of blue-white screening includes 3 important steps: 
*Ligation: ligation of foreign DNA into MCS of the plasmid vector. *Transformation: introduction of plasmid vector with foreign DNA insert into competent E. ... *Screening: blue-white screening to identify recombinant bacterial colonies.

*Protocol:-
Ligation
Component                      Volume (µL)                  Final concentration
T4 DNA ligase buffer 2 1X
Vector x 1-10 ng/µL
Insert x 1-10 ng/µL
T4 DNA ligase 1 6U/µL
Sterile water x NA
Total volume 20  
                  ⬇️

Add all the above components into a clean reaction tube.
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Incubate for 30 minutes at 25°C (can be performed in a thermo cycler).
                      ⬇️

Purify DNA using PCR clean-up column and elute in approximately 50 µL.
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Transform 0.1-10 ng of the ligation product into chemical or electrocompetent cells that are compatible with the vector.
                       ⬇️

Transformation
High quality plasmid is essential for the transformation procedure. 
                    ⬇️

The following kits isolate and purify high quality plasmid suitable for transformation.
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Spread 40 µL or appropriate amount of stock solution of chromogenic substrate and 10 µL of IPTG solution on LB agar plates using a sterile spreader.
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The plates should include those with appropriate antibiotic and without antibiotic as controls.
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Leave the plates to dry in laminar flow chamber with lids slightly open.
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Spread 10-100 µL of transformed E. coli cells onto the LB agar plates using sterile spreader.
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Incubate the plates at 37°C for 24-48 hours.
                 ⬇️

Blue and white colonies appear on the agar surface. Select the recombinant cells in the white colonies to culture.
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