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E. Coli Bacteria Engineered to Eat Switchgrass and Make Transportation Fuels
Joint BioEnergy Institute (JBEI) Researchers Reach Milestone on the Road to Biofuels
November 29, 2011
Lynn Yarris (510) 486-5375
[email protected]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.
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E. coli bacteria normally cannot grow on switchgrass, but JBEI researchers engineered strains of the bacteria to express several enzymes that enable them to digest cellulose and hemicellulose and use one or the other for growth. These cellulolytic and hemicellulolytic strains of
E. coli, which can be combined as co-cultures on a sample of switchgrass, were further engineered with three metabolic pathways that enabled the
E. coli to produce fuel substitute or precursor molecules suitable for gasoline, diesel and jet engines. While this is not the first demonstration of
E. coli producing gasoline and diesel from sugars, it is the first demonstration of
E. coli producing all three forms of transportation fuels. Furthermore, it was done using switchgrass, which is among the most highly touted of the potential feedstocks for advanced biofuels.
…
“We already have hydrocarbon fuel production pathways that give far better yields than what we obtained with this demonstration,” says Bokinsky. “And these other pathways are very likely to be compatible with the biomass-consumption pathways we’ve engineered into our
E. coli. However, we need to find enzymes that can both digest more of the ionic liquid pre-treated biomass and be secreted by
E. coli. We also need to work on optimizing the ionic liquid pre-treatment steps to yield biomass that is even easier for the microbes to digest.”
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