glycerol vs glucose

Ted Michelini tedm at darkwing.uoregon.edu
Mon Dec 11 00:28:30 EST 1995

	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.

Ted Michelini
Institute of Molecular Biology
University of Oregon
tedm at darkwing.uoregon.edu

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