|MadSci Network: Microbiology|
Life is now considered by most scientists to have arisen as thermophilic organism, (The word thermophile means to love heat). When most people first hear this statement view as weird. But we are looking at life from our perspective, because we are a mesophile (warm loving) we think everything should be that way. However all organisms, including you, have an optimum temperature for growth. Outside of that optimum they die, or cease to grow. So what causes this to occur? Well, the nature of the cell. Organisms have to have the ability to adapt to worldly changes but all abilities have limits. Too cold: Fluidity of the membrane is reduced to such as state that the membrane no longer allows the transport of molecules. Another reason is that enzymes are adapted to operate at certain temperatures. At too low of a temperature their effectiveness as a catalyst is reduced. Too hot and again lipid and protein function is impaired. As the temperature rises the membrane becomes too liquid while proteins start to denature. So who can grow the hottest. Pyrolobus: The Pyrolobus group is said to hold the world record for growth temperature, growing at 113 oC (Pyrolobus fumarii). It will not grow below 90 oC because it is too cold. These organisms are found in the walls of black smokers on the ocean's floor. I suspect that one of these organisms also holds the record for pressure but pressure is not such a problem to cells and I have no data here. Although we mainly consider proteins and membranes when we mention stability and therefore the extreme temperatures of life, as we are all aware that proteins denature etc., perhaps the biggest limit to the extremes of life is monomers. The two biggest are ATP and NADH, which are highly unstable at temperature above 120 oC. This is thought to be the biggest hurdle to life at high temperatures and although we suspect there may be organisms out there that can grow up to 150 oC, tests of black smokers at 250 oC have shown them to be sterile, so far.
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