How to tell if competent cells or SOC are contaminated? - (Jan/17/2006 )
if you do a transformation and plate out some reasonable dilutions, at a 'short overnight' say 15 or 16 hrs, you'll get some small colonies. put the plate back in for the rest of the day, or until the next morning, and you will get e coli...but probably without your plasmid
thank you again ...about the incubation time i have incubated for 18 hours....i dont know is it too long? today im doing new batch of BL21 electrocompitant and ill check again if there are any colonies from just the e coli i think i would suspect that the BL21 either grew ampiccilin resistance (long time in minus 70) or had some insert in it???
18 hrs can be pretty long. I've had a problem with satellite colonies once, and I just doubled met Amp concentration and the problem didn't occur anymore. What concentration of Amp are you using?
im using 100ug/ml.....ok todays results: no contamination.... 
....yesterday i have prepared new stock of electrocompitant e coli and incubated them as well as medium on the plate....and no colonies!!! so i guess the stock that i have prepared last time was contaminated ....i didnt work near the fire and another thing i begun harvesting the bacteria when OD was 1.2.... 
..was told in the lab that it is ok....so i guess somewhere ampiccilin resistant bacteria grew over....thanx a lot anyway...
Good you have no contamination now BUT
Don´t forget to check the competency of the cells you have made before starting cloning with them.
just to avoid more delays.
Don´t forget to check the competency of the cells you have made before starting cloning with them.
just to avoid more delays.
thanx yes i thought of testing them.....ill test them before i clone....