Plasmid loss?

Paul Wary paul_wary at yahoo.com
Fri Jun 7 14:09:33 EST 2002

Can bacteria that were streaked out on agar plates containing
ampicilline lose their transformed plasmid (containing AmpR) if they
have been incubated at 37 °C for several days (instead of being
incubated for 1-2 days only and then being stored at 4 °C)?

Is there any chance that bacteria which have lost the plasmid
(containing AmpR) can still grow to some degree in LB broth media
containing ampicilline?

I ask these question because in an experiment of mine I did just what
I described above and after growing up cultures from the
"over-incubated" streaks (Note: The cultures were growing unusually
slowly.), I tried to isolate plasmid DNA and the yield was extremely
low. I checked all possible errors regarding the plasmid isolation
procedure but couldn't find anything. So, I figured my bacteria might
have lost the plasmid.

I'm thankful for any comments.

Paul W.

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