A colorimetric screening system, based on the expression of the lac operon’s ?-galactosidase coding gene lacZ, is widely used in the selection of bacterial transformants.

A colorimetric screening system, based on the expression of the lac operon’s β-galactosidase coding gene lacZ, is widely used in the selection of bacterial transformants. Colonies which harbor recombinant plasmids appear white due to the disruption of the lacZ gene. Blue colonies arise from transformants harboring the original plasmid so that a functional lacZ gene is expressed. VWR offers the lac operon inducer IPTG as a dioxane-free powder or as a 20 mg/ml solution. X-gal, offered as a powder, forms an intense blue precipitate in the presence of β-galactosidase. Additionally, VWR offers a ready-to-use IPTG/X-Gal solution in a convenient dropper bottle.