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.
"Our goal has been to put as much chemistry as we can into microbes," Keasling says. "For advanced biofuels this requires a microbe with pathways for hydrocarbon production and the biomass-degrading capacity to secrete enzymes that efficiently hydrolyze cellulose and hemicellulose. We've now been able to engineer strains of Escherichia coli that can utilize both the cellulose and hemicellulose fractions of switchgrass that's been pre-treated with ionic liquids."
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
|Contact: Lynn Yarris|
DOE/Lawrence Berkeley National Laboratory