An archaeon known as Thermococcus gammatolerans has been identified as one of the most radiation-resistant organisms, capable of withstanding a radiation dose of 30,000 grays. This dose is 6,000 times higher than the amount lethal to humans.
Discovery and Extreme Habitat
The microbe was discovered in the Guaymas Basin, located approximately 2,600 meters (8,530 feet) beneath the ocean's surface in the Gulf of California. This environment is characterized by hydrothermal vents that release superheated, mineral-rich fluids.
The Guaymas hydrothermal field is a region where the ocean floor is fractured, allowing volcanic heat and chemistry to enter the water. These conditions, including extreme pressure and heat, are highly challenging for most life forms.
Lab Confirmation of Extreme Resistance
T. gammatolerans was initially collected decades ago by scientists using a submersible. In laboratory experiments, a team led by microbiologist Edmond Jolivet of the French National Center for Scientific Research exposed cultures to 30,000 grays of gamma radiation from a cesium-137 source.
One species, later identified as the previously undescribed T. gammatolerans, continued to grow following this irradiation.
Despite its resistance, radiation was not considered a necessary survival factor in the microbe's natural habitat.
T. gammatolerans thrives at temperatures around 88 degrees Celsius (190 degrees Fahrenheit) and metabolizes sulfur compounds.
Unraveling the Mechanisms
Further research in 2009, led by microbiologist Fabrice Confalonieri of the University of Paris-Saclay, examined the genome of T. gammatolerans. Researchers anticipated finding an elevated proportion of DNA dedicated to protection and repair mechanisms, but its DNA repair machinery was found to be normal.
A 2016 study by a team led by chemical biologist Jean Breton of Grenoble Alpes University investigated the effects of ionizing radiation on T. gammatolerans. Their experiments showed that gamma rays do cause damage to the microbe's DNA. However, the oxidative damage from free radicals released by radiation was notably lower than expected, and much of the damage was repaired within an hour.
The Habitat-Resistance Hypothesis
Scientists hypothesize that the microbe's extreme habitat plays a role in its radiation resistance. Life at hydrothermal vents involves constant exposure to intense heat, chemical stress, and reactive molecules, all of which can damage DNA.
The systems developed by T. gammatolerans to survive these harsh, oxygen-free conditions may also provide protection against ionizing radiation. Evolutionary pressures for survival in hydrothermal vents may have incidentally resulted in its ability to resist radiation doses that would prove lethal to larger organisms. This suggests that the adaptations sufficient for its primary environment were also effective against an unforeseen challenge like high radiation.