glycerol vs glucose (side notes)

Monica Beadles beadles at mbi.org
Mon Dec 11 14:22:15 EST 1995


In article <4agfhu$ao9 at pith.uoregon.edu> Ted Michelini <tedm at darkwing.uoregon.edu> writes:
>From: Ted Michelini <tedm at darkwing.uoregon.edu>
>Subject: Re: glycerol vs glucose
>Date: 11 Dec 1995 05:28:30 GMT

My 0.02 cents...
What is your inoculation O.D.?  A good high number of healthy young troops at 
the start of your batch may make the difference.  Once you settled on the 
optimum inoculation O.D., stick with it. 

I also advise kicking up the oxygen. 
Buy stainless steel frits, like the one's used in gassing/filtering HPLC 
reagents.  These make the smallest bubbles.   The E. coli I've worked 
with will not go into the anaerobic (organic acid) cycling you describe given 
enough air.  Start sparging air at a batch volume/ minute and adjust downward.

You may also try pH correction with NaOH.  It probably will not create any 
carbonate buffering problems in the media, and you won't see too much CO2 
evolution.
Good luck and remember, your yield is probably better with glucose!

Monica Beadles


>        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






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