the same is true, to a point, of the chemical reactions of life. they are usually enzymatically catalyzed which changes reaction rates, but with constant catalytic action, the rule of thumb is still mostly applicable. in the particular case of bacteria and fungi, the reactions needed to feed and reproduce increase at higher temperatures, up to the point that the proteins and other compounds in their cells themselves begin to breakdown, or denature, so quickly that they cannot be replaced. this is the reason high temperatures kill bacteria and other micro organisms; 'tissue' breakdown reactions reach such rates that they cannot be compensated for and the cell dies. on the other hand, 'elevated' temperatures short of these result in increased growth and reproduction; if the organism is harmful, perhaps to dangerous levels.