I am trying to grow E coli to high cell densities in order to enhance the yield of my recombinant protein. I understand that auto-induction media with appropriate aeration give good results here. My question concerns how to determine the exact concentration of lactose and glucose in the medium, so that the glucose is depleted at the right time and the lactose then kicks in (between them, a "buffer" of glycerol as interim carbon source, of course).
How are these concentrations determined? Are they connected to the doubling time or growth rate in any way? Is there a rule of thumb or anything does it have to be determined empirically?
then another question would be ...what is the "right" time? :)
when you know the yield coefficient of your carbon source (for glucose and E. coli something around 0.3 g/g) then you can calculate how much biomass you can produce with a certain amount of C-source.
I would determine it emperically ...use medium to grow your cells that do contain a certain amount of glucose, follow the OD ...then use medium with glucose and glycerol ...follow the OD ...then glucose, glycerol, lactose ....and so on.
This should give you a good feeling for what is going on. You can estimate the final biomass for glucose and glycerol (using the yield coefficient) but it becomes complicated when you add complex components like yeast extract or NZamine.
You can use the recipies from Bill Studiers publications ...he has developed different autoinduction media and is more or less a guru for those things:
http://www.bnl.gov/tcp/uploads/files/BSA02-29j.pdf
Good luck!
All the best,
Jürgen
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