Sulfate vs. sulfate-free mediums.

Steve J. Quest Squest at
Mon Dec 22 14:20:10 EST 1997

On Mon, 22 Dec 1997, Munn Alan Leslie wrote:

> Dear Steve, You're right, yeast need sulphate for growth.  We don't grow
> the yeast in sulphate-free medium.  We grow them in medium with sulphate
> and then incubate them in low sulphate medium or sulphate-free medium to
> starve them for a couple of hours before adding radio-labelled sulphate to
> label them.  We do a lot of protein radio-labelling experiments.  You can
> just ignore the low sulphate and sulphate-free media recipes since they are
> no use for what you are doing.

	Ah, I see.  :)  That makes sense now.  I've ordered some books on
yeast mycology which should arrive sometime around the first of the year.
I should understand more at that time.  I also found some books published
for enologists that deal with yeasts, do you think they might be of value?
That is the primary commercial use for yeasts, the production of alcohols.

>         Regarding your conversion of sucrose to glucose and fructose, why
> not just grow the yeast with sucrose as sole carbon and energy source.

	I'm trying to reduce my costs.  Inverting commercial sugar is MUCH
cheaper than buying pure sucrose.  This is not a company venture, but a
personal venture, I have interest in fungus and yeasts, and got hooked as
I watched S. Cerevisiae budding under the microscope.  :)  Someone such as
yourself can probably understand my zeal, while most people look at me
like I need help or something.  :-/  "What's the big deal" is what my
girlfriend said.  :)  I guess it takes a special breed to study yeasts. 
Soon I hope to be doing what you're doing, radiolabeling and sequencing
nucleic acids.  :)  I'm already certified with the NRC and CDRH to handle
radioisotopes, something I did professionally years ago.  I'll have to get
storage and waste disposal issues taken care of, but I'm a LONG way from
that point.  Right now I'm learning how to propagate, and select various
slants.  Later I'll jump into sequencing nucleic acid using
electrophoresis.  I would probably guess I'm the first amateur you've run
across in this field, correct?  If not, I'd like to meet others.  :)

> Yeast secrete large amounts of invertase enzyme activity which converts the
> sucrose in the medium to glucose and fructose anyway.  Instead of glucose,
> just add 2% sucrose to the synthetic medium.  It should work great.

	Actually, they grow much faster, something like 10 times faster in
glucose/fructose than they do in sucrose.  Plus, when grown anaerobically
they fail to thrive after a certain point, I believe by the buildup of
EtOH which I think interferes with the invertase enzyme.  The yeasts die
or go dormant long before the carbon base is depleted.  The yeasts seem to
convert _all_ of the glucose/fructose in an equal (18 Brix) solution.
Temperature also seems to effect the invertase enzyme.  If I elevate the
temperature, inversion seems to stop, until the temperature drops, while
in a glucose/fructose solution, temperature is not that critical.


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