Why does Yeast reach a Stationary Phase?

Hi everybody,

I've got a very geeky question:

Why does Yeast reach a Stationary Phase?

( Some explanation about stationary phase can be found here:
http://www.wyeastlab.com/he-yeast-fundamentals.cfm )

You might think that yeast want to propagate as much as possible. But apparently it doesn't work that way.

Even more interesting, even in increasing high sugar concentration, yeast reach a maximum population.

See that chart: http://www.rpi.edu/dept/chem-eng/Biotech-Environ/Contin/overload.html

Sugar dilution rate is increased, but yeast doesn't propagate any further.

This chart comes along with some studies about the crabtree effect, which appears to be wrong; but this is a different debate.

I'd like to focus on why does Yeast reach a maximum density (population) ?

I've got some theories:

- Maybe Yeast reaches his maximum metabolism capabilities.
i.e. his enzymes cannot work faster (transferring the energy to all the cells, strengthening the cell walls, ...) although there is heaps of energy around.

I guess at some point, yeast is limited to the maximum speed of the different "actors" of the respiratory system (like the speed the positively charged elements are transported within the system, then the speed they're processed in the electron transport chain, and so forth )

So, I guess if you could pitch Yeast in a constant glucose concentration and in an unlimited space, at some point yeast would reach a maximum population.


- Another theory would be a "survival" behaviour.
Yeast actually stores sugar and stops propagating, to prepare for a possible change of environment. Maybe it's been coded that way in his genes because we don't live in a world with unlimited energy supply.


Apparently, Wyeastlab haven't come up with an answer to that question. But maybe there is a future Nobel Prize winner around


Anyone willing to contribute to this topic is welcome.

Cheers!

Its like when a tornado is predicted and people stop playing around go to the store to stock up on water and batteries. Survival instinct. Yeast haven't been around for thousands of years because they are lucky.


Please if you cite my research just give me credit.

I'll quote you in my research : "Yeast haven't been around for thousands of years because they are lucky. "

Lots of scientists when they cannot find "why", they just say "it's just the way nature works."

As far as I know nobody has been able to answer the question "why positively charged elements and negatively charged elements attract each other" (which is probably the fundamental of chemistry and quantum physics) ---> It's just nature's way.

Similarly, "this survival instinct" might be just nature's way.
I'll just stick to it

This might be what your looking for

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC372915/