Bacteria Use Hydrogen as Energy

photograph of cracked dirt ground next to hot spring in front of green trees and cloudy sky

Biological Strategy

Hydrogenobacter thermophilus

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Regulate Reproduction or Growth

Reproduction and growth are two physiological processes that occur in all living systems. There are situations when conditions are right for both, and other situations when continuing either harms the living system because both have a very high energy cost. Reproduction and growth are unique in that both can stop until conditions improve, although stopping either for an extended time can cause problems. An example of regulating reproduction is a process called delayed implantation or embryonic diapause found in some mammals, such as otters. An otter’s embryos sometimes temporarily cease developing and won’t develop further until the female senses that conditions are suitable.

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Transform Chemical Energy

Life’s chemistry runs on the transformation of energy stored in chemical bonds. For example, glucose is a major energy storage molecule in living systems because the oxidative breakdown of glucose into carbon dioxide and water releases energy. Animals, fungi, and bacteria store up to 30,000 units of glucose in a single unit of glycogen, a 3-D structured molecule with branching chains of glucose molecules emanating from a protein core. When energy is needed for metabolic processes, glucose molecules are detached and oxidized.

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Bacteria

Domain Bacteria (“small staff”): L. acidophilus, Staphylococcus

From inside of our own bodies to the deepest parts of the ocean, bacteria have adapted to almost every possible environment. All bacteria are unicellular, microscopic, and lack a membrane-bound nucleus and organelles, and come in three basic shapes: spherical (cocci), rod (bacilli), and spiral (spirilla). Some strains can be deadly, like Staphylococcus aureus (MRSA) while others, like Lactobacillus acidophilus, found in our intestinal microbiome, keep us healthy. Cyanobacteria, also known as blue green algae, caused the Great Oxidation Event 2.4 billion years ago, producing Earth’s first oxygenated atmosphere.

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Hydrogen-oxidizing bacteria metabolize hydrogen from their environment to use as energy

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 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.

Last Updated August 7, 2017

References

“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).

Journal article

Hydrogen and bioenergetics in the Yellowstone geothermal ecosystem

PNAS. 102(7): 2555-2560 | Spear JR, Walker JJ, McCollom TM, Pace NR.

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Reference

“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).

Journal article

Hydrogen is an energy source for hydrothermal vent symbioses

Nature. 476(7359):176–180. | Petersen JM, Zielinski FU., Pape T, Seifert R, Moraru C, Amann R, Hourdez S, Girguis PR, Wankel SD, Barbe V

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