<FATIMA at AIMP.UNA.AC.AT writes,
>> Dear tpillay at ucsd.edu et al.,
>> The reason why we grow yeast at 30 degrees is that yeast is used
> to lower temperatures, since it originally comes from such environments
> as e.g. the surface of grapes - unlike E. coli, which, after all, came
> from our gut.
>> Fatima
>This is partially true, and raises a question that has intrigued me for
a while, which I'll throw out for discussion.
Perhaps there actually IS a semi-tropical climate in wine-country, or
grape country, or whereever the heck the ancestor of lab S. cerevisiae
is at home, where the temperature is 30C day and night all year round
(plus or minus 1C, a la the incubator). More likely, yeast is accustomed
to variable temperatures, and I'd guess on the average substantially lower
than 30C. Well, anyone who has done heat- or cold-sensitive genetics
knows that it takes the critters seemingly forever to grow to a decent
colony size at 24C, and longer-than-forever at a nice CS temp like 16C.
So a large part of the reason we use 30 is to have growth fast enough to
finish a dissertation in less than a lifetime. Now, that's pretty
ridiculously arbitrary, really, so we're getting a pretty arbitrary view
of how yeast would behave in a proper habitat. (Yeah, OK, so maybe X2180
has now gone through so many generations in the lab at 30C that that's
the only proper habitat for it, and in YEPD to boot). Anyway, one of these
days someone should stick some yeast in a thermal cycler to see what
happens, say, to heat shock systems, under a 42C 60 sec/20C 60 sec 600 cycle
protocol. Maybe the generation time under cycling conditions would be
twice as short as at 30C constant???? You could finish your experiments
in half the time?
Rob Preston
rapr at med.pitt.edu
