Surviving deadly radiation: Lessons from tardigrades.

Life on Earth is viable within a narrow window of physical parameters such as temperature, atmospheric pressure, oxygen concentration, etc. Fortunately, all these parameters are within that life-permissive window in most parts of our planet. Although most organisms cannot live beyond a limited range of these parameters, some fascinating lifeforms can survive, and some of them can even thrive, in extreme physical conditions beyond the optimal range. For example, Methanopyrus kandleri, a methanogenic archaeon, thrives at 122 °C (Takai et al. 2008). Archaea belonging to the genus Picrophilus can withstand pH values below 0.5 (Schleper et al. 1995). While just 5-10 Gy of radiation is fatal to humans, the bacterium Deinococcus radiodurans can tolerate 5000 Gy of radiation (Battista 1997; Krisko and Radman 2013).