Pyrococcus furiosus, or "rushing fireball."
The Microbe Hunters Are Back
February / March 2008
Volume 6 Number 1
Storing hydrogen on a vehicle poses several challenges. Although hydrogen fuel is environmentally friendly, especially when used to power a virtually emission-free fuel cell, it is not dense and is also quite volatile. This poses space and safety concerns, not to mention the additional wait to recharge a hydrogen storage tank, compared to the relative speed of pumping gas.
One concept to circumvent the challenges of fueling up with hydrogen would be to harness the ability of naturally existing microbes to create the gas in the vehicle's powertrain. When combined with a fuel cell power supply, the concept is known as a hybrid microbial fuel cell.
It's being approached on several fronts, including research into exotic microbes that might fit the bill as hydrogen generators.
One potential candidate that has been explored for its suitability has been subject to research at Lawrence Livermore National Laboratory.
These primordial microbes from Porto Levante in Italy aren't picky eaters.
They'll consume extracts of hot sulfur or snack on starchy plant matter, digesting the carbohydrate in a way that not only provides energy but also releases hydrogen gas.
It was their ability to manufacture hydrogen that particularly intrigued Livermore researcher Paul Henderson, when he read a paper by one of the foremost experts on their metabolism about a year ago. The microbes belong to a branch of life called Achaea that evolved early, when the Earth had a hot, volcanic climate with ample sulfur but little oxygen. Discovered in marine sediment at a volcanic vent in Italy, these organisms function at boiling-hot conditions that would scramble and inactivate most cellular machinery. They are named Pyrococcus furiosus, which stands for "rushing fireball."
Such extremophiles are of interest because they can survive without oxygen, withstand extremely acidic conditions or radioactive environments, and operate at high temperature. Indeed, enzymes from P. furiosus are used in thermocycling preparations for genome and protein research due to their high heat resistance.
Henderson had been analyzing cancer drugs with super-sensitive accelerator mass spectrometry at the lab. He became interested in looking into new avenues of energy research and was aware of a new capability devised by his colleague Paul Hoeprich, who is leading a Laboratory Directed Research and Development (LDRD) project aimed at developing a new capability for studying membrane-bound proteins.
Called nanolipoprotein particles, or NLPs, the capability consists of nanometer-sized complexes that enable the study of proteins that are particularly challenging to capture in the native form, due to being associated with cell membranes. Cell membranes are essentially bubbles of fatty material.
Proteins associated with cell membranes often lose their native state in solutions used to isolate and purify soluble proteins, just as oil and water do not mix. Hoeprich's particles have a protein ring around a lipid bilayer, which is similar to a cell membrane, and can reconstitute insoluble proteins.
Henderson envisioned taking the hydrogen-producing enzyme system described in the research paper and putting it inside the donut-shaped nanolipoprotein particles. His ultimate vision is to create a bio-based power supply for a hybrid microbial fuel cell by immobilizing enzymes on porous silicon, where they would manufacture hydrogen to run the device.
Since oxygen can stop the enzyme's function by clogging its active site, Henderson's team modified a glove box to carry out enzyme-particle assembly in an oxygen-free atmosphere. The hood was vacuum-pumped and filled with inert argon. The small space holds compact versions of normal bench-top lab equipment so all the work can be carried out in the confined conditions.
The work started after Henderson corresponded with the microbe expert, Mike W. Adams of the University of Georgia, to collaborate. Adams sent Henderson the enzyme complex to combine with the particles. Henderson recently sent back the completed disks for testing to verify that the assemblies produce hydrogen.
In fuel cells, hydrogen converts chemical energy into electrical energy by combining with oxygen to produce water. For a renewable source, hydrogen gas might be generated from agricultural waste, such as corn husks, using microbial action or enzymes. Currently, commercially available hydrogen is primarily created from natural gas, or by hydrolysis. Neither of those processes saves energy overall, although hydrogen-powered fuel cells are still attractive for environmental reasons.
Much of the project was completed with the help of summer intern Cheryl Cox, a student in integrative biology at the University of California, Berkeley, who has interned for three summers with Henderson.
"She made a nice contribution and learned a lot," he remarked, adding that, due to prior research activities, "We were poised to do this, thanks to her previous experience and the availability of some new funding."
The work was supported by a $125,000 LDRD supplement, which was stretched by modifying existing hardware and using student labor. The support was available through Hoeprich's successful Strategic Initiative in NLP research, funded by LDRD. "It's an example of how LDRD funding can help students learn while advancing cutting-edge energy research," Henderson said.
Nancy Garcia is a Lawrence Livermore National Laboratory public information officer.
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