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|Bacteria Make Diesel from Biomass|
Bacteria Make Diesel from Biomass
By Katherine Bourzac
Bacteria power: The E. coli bacteria in this microscopic image are excreting droplets of diesel fuel. The bacteria are the small dark rods clustered in the top corners and at the bottom of the image.
Jay Keasling, professor of chemical engineering and bioengineering at UC Berkeley and one of LS9's founders, and scientists at LS9 report engineering E. coli bacteria to synthesize and excrete the enzyme hemicellulase, which breaks down cellulose into sugars. The bacteria can then convert those sugars into a variety of chemicals--diesel fuel among them. The final products are excreted by the bacteria and then float to the top of the fermentation vat before being siphoned off.
Using these methods, it's possible to create a range of fuels from biomass, but LS9 is focusing on diesel rather than fuels similar to gasoline for the time being, says Stephen del Cardayre, the company's vice president of research and development. Diesel specifications are easier to meet and the market for diesel is growing by 2 to 4 percent a year, while that for gasoline is flat. Last May, LS9 partnered with Procter & Gamble to develop fuels as well as commodity chemicals.
The effort by LS9 is part of an increasing push by bioengineers to bring down the cost of biofuels by developing microbes that can turn biomass, such as switchgrass and agricultural waste, into fuels without any additional processing that would require expensive catalysts and high temperatures. Microbes can typically complete only part of the conversion, requiring post-processing to convert the chemical precursors made by the microbes. The newly engineered E. coli "are a singular vehicle that can accomplish all this at once, providing a very efficient process to make products already on the market," says David Berry, a partner at Flagship Ventures, which cofounded LS9.
Fatty acids are a large class of molecules that can form the basis of many commodity chemicals and fuels that are conventionally derived from petroleum. These metabolic pathways are complex networks, and taking advantage of them required changing several of the bacterium's existing genes as well as adding new ones. After years of engineering, says Keasling, "we can get the molecule we want specifically."
Del Cardayre says LS9 has tested the diesel-production process at its 1,000-liter pilot-scale plant in South San Francisco using sugarcane as a feedstock. The company will scale the process to a commercial level at a 75,000-liter plant this year.
LS9 isn't the only company turning sugarcane into diesel: last year, another synthetic biology company founded by Keasling, Amyris Biotechnologies of Emeryville, CA, opened a demonstration plant in Campinis, Brazil. Amyris's process is based around yeast engineered to convert sugars into hydrocarbon-fuel precursors. Del Cardayre says LS9 may open a plant in Brazil as well, but because the new bacteria can convert cellulose, not just sugar, the company isn't tied to sugarcane or any other feedstock.
Jim Collins, professor of biomedical engineering at Boston University, says the question now is whether LS9's process will be cost-effective on a large scale. "As you go from 10 gallons to thousands of gallons, the biology changes, and analyses that worked well in the lab no longer work," notes Collins, because the microbes' environment changes. "The interesting question in the next few years is, which company can get their yields high enough, and get their processes up to scale to keep costs down," says Collins.
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