why do some colonies keep growing in the chiller? - (Sep/25/2012 )

On some of my plates the colonies keep growing even in the chiller. Usually after 2-3 days the whole plate is full. The plates smell really bad. First I thought it is because of degraded ampicilin, but then I noticed this is only happening to the plates that have colonies of transformed chemically competent cells. The plates that have colonies of transformed electroporation competent cells don't have this problem. Why is that? Is this because of bacilli contamination?

How your colonies look like? are they normal morphology? if not they may be contamination. are your bacteria motile? motile bacteria may be moving on plate. Did you check whether they are transformed or not by growing on LB+amp?

yes I tried, all of'em are transformed. They look normal after 16 hrs of incubation at 37C, but when I put them in the chiller they still keep growing.

For bacteria optimal temperature for growth is 37 C. But normally is range of temperature they grow, even at cold also. Abt electroporated and transformed growth differences, hard to tell.

I'd suggest your competent cells stock is contaminated with some other species, likely a mold, or a tap water bacterium. Many are resistant to amp. Are these homemade competent cells?

Yes, my student makes them in the lab.

Related old thread:
http://www.protocol-online.org/biology-forums-2/posts/17044.html

yes I have read this before. I'm really puzzled what's going on.