Image courtesy of Benson Kua under a Creative Commons license.
Researchers are genetically engineering microorganisms to produce high-energy biofuels that can directly replace petroleum in existing engines.
Researchers have engineered the yeast Saccharomyces cerevisiae to produce from simple sugars the highest ever reported yields of drop-in fuel precursors derived from energy-rich fatty acids. Having also engineered strains to generate drop-in fuels directly, the team envisions that their approach will offer a scalable, controllable, and economic route to fatty acid–based chemicals for bioenergy.
The development of renewable substitutes for fuels and chemicals supplied by petroleum is an important aspect of achieving energy security and decreasing the environmental impacts of energy use. As an alternative to traditional production of transportation fuels, Department of Energy (DOE) researchers are re-engineering microbes to produce not just ethanol, but “drop-in” advanced biofuels having the same properties as gasoline, diesel, or jet fuel. These fuels have a higher energy density than ethanol and are far more compatible with existing engines and fuel infrastructures.
Diesel fuels are composed mainly of long-chain hydrocarbon esters similar to the fatty acids produced by yeast and other microorganisms for construction of their cell membranes. Engineering yeast to overproduce fatty acids is no easy task because elaborate regulatory and feedback systems prevent excessive accumulation of these building blocks. To overcome this hurdle, researchers at the DOE Joint BioEnergy Institute replaced the highly-regulated native promoters for fatty acid production machinery with new high-intensity promoters. These promoters are effectively always “on,” directing the cell to make more machinery for fatty acid assembly. The researchers also engineered cellular machinery to reroute fatty acids from cell membrane manufacture to free fatty acids that can be transformed through industrial processes to drop-in biofuels. These engineering changes led to a more than 500-fold increase in production of free fatty acids when compared to the native strain. Strains also were engineered to produce drop-in biofuels directly, rerouting fatty acids into fatty alcohols and fatty acid ethyl esters that can be used in diesel engines. With these increased yields of fatty alcohols and fatty acid ethyl esters, this work represents a major advance toward production of next-generation drop-in biofuels.
Joint BioEnergy Institute, Emeryville, CA 94608
Conducted by the Joint BioEnergy Institute, this work was supported by the Office of Biological and Environmental Research within the U.S. Department of Energy Office of Science under Contract no. DE-AC02-05CH11231.
Runguphan, W., and J. D. Keasling. “Metabolic engineering of Saccharomyces cerevisiae for production of fatty acid-derived biofuels and chemicals,” Metabol. Eng. 21, 103–113 (2013). [DOI: 10.1016/jymben.2013.07.003].
University, DOE Laboratory