Thursday, August 31, 2006

Selection for adaptation   posted by Fly @ 8/31/2006 12:46:00 PM

Human bodies maintain an optimal environment for cellular function. Cold-blooded animals function sluggishly when cold. I've wondered how bacteria manage to function at different temperatures. I'd assumed that bacteria are highly adapted to either high or low temperatures and that homeostatic feedback maintains biological systems in a viable range over modest daily temperature changes. But what happens when their environment rapidly changes? Does that bacterial line die out? Perhaps not.

Bacteria beat the heat

"A general rule for enzyme reactions states that as the heat rises, so does the reaction rate. Contrary to this rule, and the scientist's expectations, both reaction rates peaked at a certain point, and remained steady thereafter. For each enzyme, the peak occurred in the bacteria's 'comfort zone.' Further comparisons of the enzymes, which were nearly identical, turned up differences in just two of the hundreds of amino acids making up the enzyme sequence. When the scientists replaced these two amino acids in the enzyme adapted to the moderate temperatures with those of the heat-loving enzyme, they observed an increase of about 10 degrees in the average temperature at which the reaction rate peaked. Scherz: 'This study shows that enzyme efficiency is tuned to the average temperature of the bacterial habitat, rather than the immediate conditions. This may protect the cells from harmful swings in enzyme activity' "

In this experiment, changing two amino acids in an enzyme changed the temperature of peak reaction rate. The bacteria colony could adapt to new temperatures with just a few mutations. Life has evolved to adapt rapidly to changing environments. Lifeforms that couldn't adapt went extinct.