Photosynthesis provides energy for most life on Earth, but has an upper limit of ~70°C. Hydrogen-oxidizing bacteria live in geothermal hot springs where temperatures far exceed 70°C, and thus must use alternative methods to produce energy. By oxidizing readily available hydrogen, these organisms are able to produce energy without the need for photosynthesis.
These bacteria metabolize hydrogen using the enzyme hydrogenase and the electron-transport chain (ETC). The ETC uses a proton gradient to pump hydrogen through a complex known as ATP synthase, which generates ATP to use as energy. Oxygen is used as a “terminal electron acceptor”, which accepts the final electron at the end of the ETC and combines with hydrogen protons to form water. The difference between different types of hydrogen-oxidizing bacteria is which terminal electron acceptor they use. Many use oxygen, but other inorganic compounds, such as nitrate, sulfur, and sulfite, are also used.
This strategy was contributed by Richard Fisher and Laura Cuccaro.Edit Summary
“Most of Earth’s biomass is considered to be the product of photosynthesis. However, at temperatures higher than 70°C, photosynthesis is not known to occur, but thermophilic microbial communities develop well beyond that temperature. Consequently, high-temperature primary productivity must derive from chemosynthesis based on the oxidation of reduced inorganic or organic sources.” (Spear et al. 2004:2555).
Hydrogen and bioenergetics in the Yellowstone geothermal ecosystemPNAS. 102(7): 2555-2560
“The key enzymes involved in hydrogen metabolism are hydrogenases, which catalyse the reaction: H2 ←→ 2H+ + 2e–. Enzymes of the group 1 NiFe hydrogenases are membrane-bound respiratory enzymes that channel electrons from hydrogen into the quinone pool, providing the link between hydrogen oxidation and energy production.” (Petersen et al. 2011:176).