A milestone has been reached on the road to developing advanced biofuels that can replace gasoline, diesel and jet fuels with a domestically-produced clean, green, renewable alternative.

Researchers with the U.S. Department of Energy (DOE)’s Joint BioEnergy Institute (JBEI) have engineered the first strains of Escherichia coli bacteria that can digest switchgrass biomass and synthesize its sugars into all three of those transportation fuels. What’s more, the microbes are able to do this without any help from enzyme additives.

“This work shows that we can reduce one of the most expensive parts of the biofuel production process, the addition of enzymes to depolymerize cellulose and hemicellulose into fermentable sugars,” says Jay Keasling, CEO of JBEI and leader of this research. “This will enable us to reduce fuel production costs by consolidating two steps – depolymerizing cellulose and hemicellulose into sugars, and fermenting the sugars into fuels – into a single step or one pot operation.”

Keasling, who also holds appointments with the Lawrence Berkeley National Laboratory (Berkeley Lab) and the University of California (UC) Berkley, is the corresponding author of a paper in the Proceedings of the National Academy of Sciences (PNAS) that describes this work. The paper is titled “Synthesis of three advanced biofuels from ionic liquid-pretreated switchgrass using engineered Escherichia coli.”

Advanced biofuels made from the lignocellulosic biomass of non-food crops and agricultural waste are widely believed to represent the best source of renewable liquid transportation fuels. Unlike ethanol, which in this country is produced from corn starch, these advanced biofuels can replace gasoline on a gallon-for-gallon basis, and they can be used in today’s engines and infrastructures. The biggest roadblock to an advanced biofuels highway is bringing the cost of producing these fuels down so that they are economically competitive.

Unlike the simple sugars in corn grain, the cellulose and hemicellulose in plant biomass are difficult to extract in part because they are embedded in a tough woody material called lignin. Once extracted, these complex sugars must first be converted or hydrolyzed into simple sugars and then synthesized into fuels. At JBEI, a DOE Bioenergy Research Center led by Berkeley Lab, one approach has been to pre-treat the biomass with an ionic liquid (molten salt) to dissolve it, then engineer a single microorganism that can both digest the dissolved  biomass and produce hydrocarbons that have the properties of petrochemical fuels.