Other innovators are taking similar approaches. Two California-based companies—Amyris Biotechnologies, which Keasling co-founded in Emeryville in 2003, and LS9 in San Carlos—have engineered bacteria to eat plants and secrete biodiesel. Biodiesel is best known as the fuel made from recycled vegetable oil, the kind used by superenvironmentalists such as singer Willie Nelson, who calls it “BioWillie.” But we simply don’t eat enough french fries to make large volumes of fuel this way. Qteros, a company based in Hadley, Mass., is using a proprietary bacterium it calls the “Q microbe” to break down cellulosic plants and convert them to ethanol. Gevo, a biotech firm in Englewood, Colo., is engineering bacteria to make isobutanol from sugarcane and cellulosic plant waste. “This is not a dream,” says Frances Arnold, a chemical engineer at the California Institute of Technology and one of Gevo’s founders. “The technology works great.”
Indeed, biofuels aren’t really a stretch—humans have been using microorganisms to ferment plants into ethanol ever since Stone Age people began making beer around 10,000 B.C. Today’s work hinges on engineering a perfect microbe that will eat the entirety of a plant, retain only a little of this food for itself and spew out the rest as a high-energy fuel. “We’re at a point in biology,” Keasling says, “where we don’t have to accept what nature has given us.”
Pond Scum Revisited
Other scientists argue that fermentation is not the best way to make fuel. Venter believes his more forward-thinking approach will prevail. The “most exciting” biofuel, he says, will be made from microbes that, when exposed to sunlight, consume carbon dioxide and turn it into energy directly—the equivalent of upgrading to a direct airline flight from one that had a long stopover. The idea might sound too good to be true, but Venter, who is known for his restless ambition, says it is possible.
The earth’s energy comes from the sun. An hour’s worth of sunlight holds enough power to meet a year’s worth of human energy needs. But less than a tenth of 1 percent of that energy is captured by plants. Venter and other scientists are experimenting with photosynthetic microbes such as algae and cyanobacteria (sometimes referred to as blue-green algae). Not only do these microbes remove carbon dioxide from the air, they also grow quickly—some forms double in just 12 hours, whereas grasses and other large plants can take weeks or months to do so. Photosynthetic microbes also store plenty of fat, which forms the basis for fuel. Biologist Willem Vermaas of Arizona State University recently engineered cyanobacteria to accumulate up to half their dry weight in fat; just by opening up the cells, he can harvest the stored fats and convert them, in a few simple steps, into biofuel. Some plants, such as soybeans, also store fats and can be used as fuel sources, but Bruce Rittmann, Vermaas’s colleague at Arizona State, argues that photosynthetic microbes produce nearly 250 times more fat per acre.
The concept of algae-based fuel is not exactly new, and it’s fraught with problems. In 1978 the DOE began trying to make biodiesel from algae, but the program ended 18 years later after the government concluded the concept wasn’t economically feasible. Algae and cyanobacteria are complicated critters: although they can grow in open ponds, unwanted microbial strains can easily contaminate the water and interfere with the growth of the fuel-making strains. Venter’s alternative is to grow algae in transparent, outdoor vessels called photobioreactors, but these containers are expensive to build and maintain. They must also be constructed so that the right amount of sunlight hits them—too much or too little slows growth. What is more, harvesting the microbes and sucking out the stored fats requires environmentally unfriendly solvents, and new organisms have to be grown to replace the harvested ones.