Prokaryotes growing at high temperatures have a high proportion of charged residues in their proteins to stabilize their 3D structure. By mining 175 disparate bacterial and archaeal proteomes we found that, against the general trend for charged residues, the frequency of aspartic acid residues decreases strongly as natural growth temperature increases. In search of the explanation, we hypothesized that the reason for such unusual correlation is the deleterious consequences of spontaneous chemical transformations of aspartate at high temperatures. Our subsequent statistical (...) analysis supported this hypothesis. This finding reveals that organisms have likely adapted to high temperatures by minimizing the harmful consequences of spontaneous chemical transformations. (shrink)

The mitochondrion is known as the “powerhouse” of eukaryotic cells since it is the main site of adenosine 5′‐triphosphate (ATP) production. Using a temperature‐sensitive fluorescent probe, it has recently been suggested that the stray free energy, not captured into ATP, is potentially sufficient to sustain mitochondrial temperatures higher than the cellular environment, possibly reaching up to 50 °C. By 50 °C, some DNA and mitochondrial proteins may reach their melting temperatures; how then do these biomolecules maintain their structure and function? (...) Further, the production of reactive oxygen species (ROS) accelerates with temperature, implying higher oxidative stresses in the mitochondrion than generally appreciated. Herein, it is proposed that mitochondrial heat shock proteins (particularly Hsp70), in addition to their roles in protein transport and folding, protect mitochondrial proteins and DNA from thermal and ROS damage. Other thermoprotectant mechanisms are also discussed. (shrink)

Two categories of life are currently recognized—chemosynthetic and photosynthetic—indicating their principal free energy resource as either chemicals or electromagnetic radiation. Building on recent developments in thermodynamics, we posit a third category of life—thermosynthetic life (TL)—which relies on environmental heat rather than traditional free energy sources. Since thermal energy is more abundant than chemicals or light in many settings, thermosynthesis offers compelling evolutionary possibilities for new life forms. Based on variants of standard cellular machinery, a physical model is proposed for the (...) conversion of thermal energy into biochemical work. Conditions favorable to thermosynthetic life and prospects for its discovery are assessed. Terrestrially, deep-subsurface unicellular anaerobic superthermophiles are deduced to be likely TL candidates. (shrink)