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MARGINALIA

Thermophiles in Kamchatka

Roald Hoffmann

Eat What's on Your Plate

I've never seen salmon prepared in as many tasty ways as at the rural hostel where we stayed. Thermophiles have to eat too. The building blocks of the remarkably varied archaeal diet in the hydrothermal fields (or submarine volcanic vents) are CO2, CO, H2, H2S, N2, S and several oxidized sulfur species. That more than suffices, in the presence or absence of oxygen. Some typical reactions are

S + 3/2O2 + H2O —> H2SO4
H2S + 2O2 —> H2SO4
CO2 + 4H2 —> CH4 + 2H2O

Normal green-plant photosynthesis is endothermic, by 481 kilojoules (change in free energy per mole CO2). The energy to get it done comes from light. Who needs light when you can have the H2S reaction above? It releases 706 kilojoules per mole! That's enough energy to reduce lots and lots of CO2 to sugar.

Most remarkable are biological systems that use as their source of energy inorganic ions such as Fe++ and Mn++. Thiobacillus ferroxidan's name tells it all. The oxidation of such metal ions is exothermic, and of course it is used. It is conceivable that much magnetite is of biological origin.

Figure 2. Microscopic thermophilesClick to Enlarge Image



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