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blue/white colony screening - (Jun/27/2006 )

I see so many kits stuffing around with blue white colony screening usingg IPTG and Xgal to screen for inserts into the B-galactosidase gene of vectors, but I can't see why you wouldn't just plate out on MacConkey agar and look for pink or orange colonies.

It is much cheaper, works just as well and most labs would have MacConkey agar freely available.

What is the advantage of the blue /white method over good old MacConkey agar?


MacConkey agar will not indicate that a colony harbors a plasmid that contains your insert..... it is useful in seeing acid end-products of lactose fermentation by enterics....


"it is useful in seeing acid end-products of lactose fermentation"

Precisely. If b-galactosidase is functional (no insert) you see red colonies. If an insert is present, it will disrupt the b-gal gene and you see white colonies. I use MacConkey agar instead of blue-white screening and it seems to work fine. I'm pretty much a noob though so someone correct me if this is wrong.

The only difference that I can think of between the two methods is cost. I think X-gal is more expensive than MacConkey, but I haven't checked very carefully.