Agar Plates for Selection of Clones in Bacteria 


Cloning of PCR products


LB Agar: Luria Broth after Lennox:

per Liter

10 g
Yeast Extract

5 g

Sodium Chloride
5 g
Bact.  Agar
15 g

 pH 7.0

Autoclave and store sterile at room temperature 

Stock solutions:
Store all frozen in aliquots at -20C (can be stored in dark at 4C but -20 is usually as simple!)

X-Gal: 20 mg/ml in Dimethylformamide (DMF)
IPTG: 100 mM
Ampicillin: 100 ug/ml (micrograms)

(see also page on BAC isolation with BACs including chloramphenicol resistance.)

Filter sterilize

X-Gal is 5-bromo-4-chloro-3-indolyl-beta-D-galactoside. It is hydolysed by. beta galactosidase to form an indigo-type blue-green precipitate. Bacteria with the B-galactosidase gene give blue colonies.
IPTC is isopropylthio-beta-D-galactoside. It is a false substrate (not cleaved) and inducer of  beta-galactosidase
Ampicillin is an antibiotic which requires the resistance plasmid in the bacteria

Final concentrations on plates

X-gal of 80ug/ml (1:250 dilution of the stock solution, can use half this)
IPTG 0.05 mM /L (1:200 dilution of stock, can use twice this)

so to 100 ml LB agar (molten but < 50C, ie you can hold the bottle in your hand without burning), add 100 ul Ampicillin stock, 400 ul X-Gal stock and 500 ul IPTG stock

Use 20 ml per Petri dish (cover bottom then move once side-to-side to distribute).