Bacteria Make Diesel from Biomass

Newly engineered E. coli streamline the conversion of cellulose into fuel.

Engineered bacteria have been rewired with the genetic machinery necessary to convert cellulose into a range of chemicals, including diesel fuel. The bacteria, developed by South San Francisco company LS9 in collaboration with researchers at the University of California, Berkeley, make the necessary enzymes for every step along the synthesis pathway and can convert biomass into fuel without the need for additional processing. LS9 has demonstrated the bacteria in pilot-scale reactors and plans to scale the process to a commercial level later this year.

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. Credit: Keasling lab

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.

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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.