Rich batch E. coli cultures often include glycerol, but the use of
glucose is preferable in most fed batch media. This is due in part to
the higher specific growth rates with glucose. The downside with glucose
comes from the so called "bacterial crabtree effect": having too much
glucose around causes the formation of large amounts of organic acids,
usually acetate and lactate, when the bug cannot support a high enough
level of aerobic metabolism to utilize what is present. The pH of the
media goes down, acetate goes up and a lot of usable carbon goes up the
flue as CO2. The key to using glucose to grow E. coli seems to be adding
it at a rate which supports the high growth rate while avoiding an
oversupply, this has led to fancy exponential feed schemes and control
algorithims which gauge feed rate to dissolved O2,pH etc.
Glycerol doesn't do this and thus enough to support a good cell density
can be included in the begining of the culture with no real negative
effect, save a slower growth rate. This can actually be a plus in
typical batch cultures (ie shake flasks) so glycerol is usually the way
to go.My $0.02.
regards,
Ted Michelini
Institute of Molecular Biology
University of Oregon
tedm at darkwing.uoregon.edu
