Life at High Temperatures

by Thomas D. Brock

Up the Temperature Gradient

© 1994 Yellowstone Association for Natural Science, History & Education, Inc. Yellowstone National Park, Wyoming 82190.

Temperature is one of the most important environmental factors and organisms differ strikingly in their ability to adapt to high temperatures. Biologists recognize three major categories of living organisms, called Eucarya, Archaea, and Bacteria. Higher organisms (plants and animals) are all Eucarya, so called because their cells have true nuclei and undergo cell division by mitosis. We call these organisms with true nuclei eucaryotic. Archaea and Bacteria are both much simpler organisms, seldom occurring as multicellular forms, and lacking true nuclei and mitosis. They are called procaryotic.

The table below shows the upper temperature limits for growth of various types of living organisms. Note that the eucaryotes are unable to adapt to high temperatures, their upper limit being about 60-62 degrees C (140-144 degrees F). The upper temperature limit for plants and animals is even lower, less than 50 degrees C (120 degrees F). It is important to note that only a very few eucaryotes are able to adapt to these upper limits, the majority being restricted to much lower temperatures.

At temperatures above 60-62 degrees C (140-144 degrees F) the only organisms present are procaryotes. The photosynthetic bacteria have upper temperature limits lower than those of nonphotosynthetic bacteria. The upper limit of photosynthetic bacteria, defined by the "V" shown in the photo below and on the previous page, is about 70-73 degrees C (158-163 degrees F). At higher temperatures, only nonphotosynthetic bacteria are able to grow. At the highest temperatures, over 100 degrees C (212 degrees F), the only bacteria found are a few unusually heat-adapted Archaea called hyperthermophiles. Water boils in Yellowstone at about 92 degrees C (198 degrees F). These bacteria are not just surviving, they are thriving in the boiling water!

The "V" shaped pattern is defined by photosynthetic bacteria growing near their upper temperature limit of 70-73 degrees C (158-163 degrees F) in the run-off channel.

This bacterium, shown under the electron microscope, lives well in boiling water.

Upper Temperature Limits for Growth of Various Organisms

Group Upper temperature limits (degrees C) Upper temperature limits (degrees F)
Fish 38 100
Insects 45-50 113-122
Ostracods (crustaceans) 49-50 120-122
Vascular plants 45 113
Mosses 50 122
Eucaryotic microorganisms
Protozoa 56 133
Algae 55-60 131-140
Fungi 60-62 140-144
Cyanobacteria (oxygen-producing photosynthetic bacteria) 70-73 158-163
Other photosynthetic bacteria (do not produce oxygen) 70-73 158-163
Heterotrophic bacteria (use organic nutrients) 90 194
Methane-producing bacteria 110 230
Sulfur-dependent bacteria 115 239

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