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Q: growing bacteria in a synchronised fashion

Thomas J. Dougherty, Ph.D. Thomas_J._Dougherty at ccMail.bms.com
Thu Jan 22 15:03:29 EST 1998

Guy Tremblay wrote:
> Hi,
> I am growing a certain number of tubes of bacteria. I have to induce a
> plasmid in those cells at a certain OD and collect them at an other one.
> Since I induce very early (0.15 OD600), it is very difficult to induce
> at the right time. In order to improve my method, I try to have my
> bacteria at about the same OD so that I have less OD readings to do.
> In order to synchronise my cultures, I measure the OD of a dilution of
> an o/n culture and strongly centrifuge my o/n bacteria to break
> bacterial
> clusters. This ensures that I will start my culture with
> about the same quantity of bacteria in each tube.
> Problem: Even taking these precautions, the bacteria have relatively
> different ODs after about 2hrs culture and it reduces the quality of my
> results.
> Question: Is there a simple way I could synchronize my cultures so that
> I can induce all of them at the same OD/time?
> Hope someone has the solution because I am quite angry against my
> undisciplined bacteria! Thanks in advance.
> ----*-----*-----*-----*-----*-----*-----*-----*----*-----*-----*----
> Guy  Tremblay
> tremblgu at magellan.umontreal.ca

This can be tricky, as you are using low numbers to begin with, and
there is an inherent variability.  One thing that may help, is to
prewarm your media before inoculation.  Also, assuming that you use E.
coli (if not, it's important to know what organism you are using), you
should grow up your overnight in tryptone broth, a relatively poor
growth media, at 30C.  Lag phase upon reinoculation into fresh,
prewarmed rich media will be minimised by this procedure.  Good luck!

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