Microbial Conversion of Switchgrass to Multiple Drop-In Biofuels

The Science

The low efficiency and high cost of enzymes used to break down plant material into sugars remains a major barrier to economically competitive production of cellulosic biofuels. Consolidated biomass processing, in which a single microorganism both produces cellulose-degrading enzymes and converts the resulting sugars to a desired biofuel, presents a promising alternative to improve efficiency and reduce costs, but few organisms naturally possess both capabilities. Researchers at the Joint Bioenergy Institute (JBEI) have now engineered a modified strain of the workhorse industrial microbe E. coli that expresses a tailored set of cellulases, allowing it to degrade both the cellulose and hemicellulose chains released from switchgrass pretreated with ionic liquid. This was accomplished by cloning cellulase genes from Cellvibrio japonicus, a soil microbe with similar protein secretion systems to E. coli, and modifying the genes to allow proper timing and level of cellulase expression in the host. The team then added metabolic pathways that allowed E. coli to convert resulting sugars to either of two drop-in automotive biofuels (biodiesel and butanol) or a jet fuel precursor terpene compound. This presents a promising new advance in consolidated biomass processing, and, given the relative ease of genetic modification in E. coli, offers tremendous potential for subsequent engineering to increase conversion efficiency or synthesize a broader range of fuels.


One approach to reducing the costs of advanced biofuel production from cellulosic biomass is to engineer a single microorganism to both digest plant biomass and produce hydrocarbons that have the properties of petrochemical fuels. Such an organism would require pathways for hydrocarbon production and the capacity to secrete sufficient enzymes to efficiently hydrolyze cellulose and hemicellulose. To demonstrate how one might engineer and coordinate all of the necessary components for a biomass-degrading, hydrocarbon-producing microorganism, we engineered a microorganism naïve to both processes, Escherichia coli, to grow using both the cellulose and hemicellulose fractions of several types of plant biomass pretreated with ionic liquids. Both cellulolytic and hemicellulolytic strains were further engineered with three biofuel synthesis pathways to demonstrate the production of fuel substitutes or precursors suitable for gasoline, diesel, and jet engines directly from ionic liquid-treated switchgrass without externally supplied hydrolase enzymes. This demonstration represents a major advance toward realizing a consolidated bioprocess. With improvements in both biofuel synthesis pathways and biomass digestion capabilities, our approach could provide an economical route to production of advanced biofuels.

Principal Investigator

Jay D. Keasling
Lawrence Berkeley National Laboratory
[email protected]

BER Program Manager

Dawn Adin

U.S. Department of Energy, Biological and Environmental Research (SC-33)
Biological Systems Science Division
[email protected]


Bokinsky, G., P. P. Peralta-Yahyn, A. George, B. M. Holmes, E. J. Steen, J. Dietrich, T. S. Lee, D. Tullman-Ercek, C. A. Voigt, B. A. Simmons, and J. D. Keasling. 2011. “Synthesis of Three Advanced Biofuels from Ionic Liquid-Pretreated Switchgrass Using Engineered Escherichia coli,” Proceedings of the National Academy of Sciences of the United States 108(50), 19949-54. DOI:10.1073/pnas.1106958108.