America’s gluttonous demand for energy shows no signs of abating anytime soon. We burn through 20 million barrels of oil per day and are projected to use 28.3 million barrels per day by 2025. In order to meet that demand, Department of Energy analysts estimate that we’ll need to double the amount of oil we import. And that is just the appetizer. Spencer Abraham, who served as Secretary of Energy during President George W. Bush’s first term, has blithely predicted that America’s growing electric power needs can be met only if we build between 1,300 and 1,900 new power plants by 2025.
For solutions, scientists are going back to basics—to the sun, but not to photovoltaics, the direct conversion of sunlight into electricity. After decades of failed promise, photovoltaics remain expensive and inefficient and account for less than .03 percent of the electricity supply nationwide. The smart money is on innovative efforts by biologists to genetically hijack photosynthesis, the processes that plants and other organisms use to turn solar rays into molecular energy.
Photosynthesis, of course, is the original source of fossil fuels. In past ages, the remains of plants and organisms that consumed sunlight ended up in deposits in the Earth’s crust, where they were converted over millions of years into coal, oil, and gas. We’ve depleted much of that photosynthetic treasure trove in less than two centuries, so some scientists are looking to genetic engineering as a means to turn various living organisms into more efficient energy producers.
In organisms that run the gamut from microbes to magnolias, photosynthesis creates biomass. Water (H2O) plus carbon dioxide (CO2) plus light energy (solar radiation) produces carbohydrates plus oxygen. Normally, no hydrogenase (a natural enzyme that promotes the formation of gaseous hydrogen) is involved in the process. But with microbes, it is possible to intervene genetically in ways that encourage the activation of hydrogenase enzymes. The end result is an altered photosynthetic process that produces less oxygen and more hydrogen.
Researchers at the National Renewable Energy Laboratory in Golden, Colorado, have already succeeded in converting solar energy directly and continuously into hydrogen by manipulating photosynthesis in Chlamydomonas reinhardtii, a common species of green algae. Biologist Michael Seibert and his colleagues found they could activate hydrogenase during photosynthesis by withholding sulfate. “This is a neat little system that shows that you can get an alga to produce hydrogen for days. In fact, we’ve now done it for about six months, continuously,” says Seibert.
Ramping up the efficiency and scale of the photosynthesis-to-hydrogen process to industrial production will be a challenge. But strange as it may seem, visions of pond scum may soon be dancing in energy analysts’ heads. Seibert offers this scenario: “Imagine if 200 million passenger vehicles in this country were fuel-cell driven—and that may be something that happens—and we could get this process working at a 10 percent conversion efficiency. Then it would take an area of bioreactors—hydrogen-impermeable covered ponds, essentially—equivalent to a square plot about 100 miles on each side in, say, New Mexico or Arizona to produce all the hydrogen needed to run those 200 million vehicles.”
J. Craig Venter, the innovative scientist who spearheaded the sequencing of the human genome in 2000, is exploring ways of using genomics to engineer microbes with enhanced capabilities for converting solar radiation to usable forms of fuel. He and his colleagues at the J. Craig Venter Institute in Rockville, Maryland, recently completed a microbial sampling of the near surface of the Sargasso Sea that turned up 1,800 new species and 1.2 million new genes, including 782 new photoreceptors that utilize solar radiation.
What are the energy implications of photoreceptor genes?
V: A lot of biology that was not known before, including the biology of the upper oceans, seems to be driven by capturing energy directly from the sun. And we’ve speculated, along with others, that maybe you could make an array of photoreceptors. The research also has a lot of implications in terms of understanding carbon sequestration issues. But those are huge leaps.
What else have you found that could alter our energy picture?
V: We’ve found hundreds of new cellulases just randomly in the ocean environment. Plants are one way to capture the energy from the sun, and if you can break down the complex sugars—which is what cellulases do—into simple sugars, then the simple sugars can drive the metabolism and things like fermentation to produce ethanol. It’s a big leap from finding new cellulases in the environment to producing ethanol, but the potential for biological sources of energy is very high.
What is the Venter Institute’s approach?
V: We’ve been pushing for more fundamental research to see if biology can play a role in producing clean energy. You know, people have been looking, at a modest level, for biological sources of energy for a long time. People have been looking for organisms that produce hydrogen, but I think it would be surprising to find an organism in the environment—naturally occurring—that produced enough hydrogen for commercial production. So what we’ve proposed is applying the new tools of genomics to see if we could alter or enhance existing pathways to change the production levels. If the cost of ethanol production goes down because people incorporate cellulases to use most of the plant that now gets thrown away or burned, that has a chance of changing the energy equation.
How can biology help?
V: Right now, ethanol production is not very efficient because people are using just the sugar from sugarcane or the simple sugars from corn. The complex sugars that make up most of the plant are not readily accessible. These are areas where biology could potentially play a big role. A large number of groups and companies are working on making better cellulases, or finding better ones from the environment, to make these processes become more efficient. If that happens, it’ll probably be from something that’s engineered, not something that’s found.
Are you working on that kind of engineering?
V: Yes, we are engineering an organism to break down the complex sugars and do the fermentation steps—simultaneously.
What obstacles are involved?
V: These are enzyme complexes. It’s not like just making a single enzyme and throwing it at a plant, and all of a sudden the plant dissolves. And doing anything on an industrial scale obviously requires a lot of energy and a lot of chemical input. So just having an enzyme system that works better won’t solve the whole thing instantaneously.
How much energy from biology do we need?
V: If biology were able to contribute just 10 percent of the solution, that is still a huge impact. If we can engineer cells to produce hydrogen or butane or butanol—something that is a clean fuel—you could do that locally in conjunction with fuel cells. That’s different from having to do a whole manufacturing plant and distribution and storage systems. Even though people have been looking for a long time to biology for alternative energy sources, we’re talking about a substantial effort to truly modify biology to increase energy production. And we’ve been told that it’s the first new thing on the block in decades.