Temperature:

Procedure

The rates of chemical reactions in a cell are determined by the activities of its enzymes.  Enzymes are proteins that act as catalysts, substances that increase the rate of a chemical reaction without being permanently altered or consumed.  The temperature range over which a microorganism grows reflects the temperatures at which its enzymes function.  Within this range, three cardinal temperatures can be identified: minimum, optimum and maximum growth temperatures. 

Temperatures higher than the maximum growth temperature cause irreversible denaturation of enzymes and therefore cell death.  At temperatures below the minimum, molecular motion and enzymatic activities effectively cease.  In addition to the effects of temperature on enzymes, other cell structures, such as the cytoplasmic membrane, are temperature sensitive.  At temperatures below the minimum or above the maximum, they will cease to function because of changes in the fluidity of lipid bilayers and membrane transport proteins.  According to their growth temperature range, bacteria are classified as:

• psycrophiles: cold-loving organisms, optimum growth temperature is 15°C or lower.  These extremophiles are found in the Arctic, Antarctic and lakes fed by glaciers.
• Psychrotrophs: these species have an optimum growth temperature between 20 and 30ºC but can grow at 0 to 7º C.  These play a major role in spoilage of refrigerated foods
• mesophiles: include most bacteria, optimum growth temperature is 20 - 45°C.  Many pathogens are mesophiles as their preferred temperature is body temperature (37ºC).
• thermophiles: heat-loving organisms, optimum growth temperature is 55-65°C.  Thermophiles can be found in hot springs, compost heaps, and hot water heaters.
• hyperthermophiles: love extreme heat, optimum growth temperature is 70-110°C.  Members of this group are generally Archaea.

Rachel Watson, M.S.
AG 5010
766-3524
Cell: 307-760-2942
rwatson@uwyo.edu