Temperatures above 90 degrees Fahrenheit often send people reaching for the dial on the air conditioning. A newly discovered single-celled microbe puts our heat tolerance to shame. Researchers writing in the current issue of the journal Science report that the organism, dubbed Strain 121, can survive at temperatures of 121 degrees Celsius or 250 degrees F. The finding may help scientists better understand where and when life could have evolved on the very hot early earth.

Kazem Kashefi and Derek R. Lovley of the University of Massachusetts recovered the microorganism from water collected in a hydrothermal vent 2.4 kilometers below the surface of the northeast Pacific Ocean. They first cultured a sample at 100 degrees C to mimic the environment of the vent. But when they observed that some of the bugs continued to thrive and grow, they increased the heat. At 121 degrees C, Strain 121 doubled its cell numbers in a 24-hour period. Even at 130 degrees C, Strain 121 survived, although its growth was curtailed and only resumed once it was returned to lower temperatures. "Growth at 121 [degrees] C is remarkable," the authors write, "because sterilization at 121 C, typically in pressurized autoclaves to maintain water in a liquid state, is a standard procedure shown to kill all previously described microorganisms and heat-resistant spores."

The previous record holder for hot living was Pyrolobus fumarii, which can grow at 113 degrees C, but only 1 percent of P. fumarii cells survived the autoclaving that failed to kill Strain 121. The scientists do not yet know what factors allow Strain 121 to grow at such high temperatures, but they hope further research will elucidate which molecules are most important in defining the upper temperature limit for life.