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Hydrogen is the cleanest and most abundant fuel there is, but extracting it from water or organic material is currently not a very efficient process. Scientists are therefore studying certain bacteria that exhale hydrogen as part of their normal metabolism.
"The production of hydrogen by microorganisms is intimately linked to their cellular processes, which must be understood to optimize bioenergy yields," said Amy VanFossen of North Carolina State University.
Of particular interest are microbes that thrive in hot temperatures, near the boiling point of water. VanFossen and her colleagues carried out a detailed DNA study of one of these thermophilic (heat-loving) bacteria called Caldicellulosiruptor saccharolyticus, which was first found in a hot spring in New Zealand.
The results, presented last week at the American Chemical Society meeting in Philadelphia, indicate which genes allow C. saccharolyticus to eat plant material, referred to as biomass, and expel hydrogen in the process.
Hydrogen economy
Fuel cell vehicles are starting to be available for lease in California and the New York area. They run off of hydrogen gas and emit only water vapor out the tail pipe.
Hydrogen can be found everywhere: it's the "H" in H2O and a major element in biological processes. The problem is that it takes quite a bit of energy to separate the hydrogen from the molecules it is found in.
However, certain organisms, such as the bacteria in cow stomachs, get energy from food through a chemical reaction that releases hydrogen gas. Often this hydrogen is immediately taken up by other bacteria, called methanogens, that convert it to methane.
One of the challenges, therefore, of producing hydrogen from bacteria is to prevent the methanogens from gobbling up the gas. The advantage of thermophiles is that they operate at temperatures that are typically too hot for methanogens. C. saccharolyticus, for example, prefers a toasty 160 degrees Fahrenheit (70 degrees Celsius).
Furthermore, the chemistry of hydrogen formation is easier at these higher temperatures, said Servé Kengen from Wageningen University in the Netherlands.
"In general, thermophiles have a simpler fermentation pattern compared to [lower temperature] mesophiles, resulting in fewer byproducts," he said.
Bionic microbe
Kengen is part of a European Union project called Hyvolution, which is developing decentralized hydrogen production that can be performed near where biomass is grown.
"Biological hydrogen production is well suited for decentralized energy production," Kengen said. "The process is performed at almost ambient temperature and pressure, and therefore it is expected to be less energy intensive than thermochemical or electrochemical production methods [which are alternative ways to get hydrogen]."
Kengen said that C. saccharolyticus, or what he calls "Caldi," is very attractive for this application. It is unique in that it eats a wide range of plant materials, including cellulose, and can digest different sugars (technically carbohydrates) at the same time.
"The wide range of carbohydrates it grows on suggests that C. saccharolyticus will yield a plethora of industrially relevant carbohydrate degrading enzymes," VanFossen told LiveScience.
These enzymes — now isolated through VanFossen's genetic analysis — could help get more hydrogen from a given quantity of biomass.
"Once we are able to engineer Caldi (not yet possible) we want to further improve its hydrogen producing capacity," Kengen said.
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