JBEI researchers discover bisabolane-to-diesel pathway
Bisabolane is part of the terpene class of chemical compounds found in plants, and although traditionally used in fragrances and flavorings, a team of researchers at the U.S. DOE’s Joint BioEnergy Institute has discovered how to utilize bisabolane as an alternative to No. 2 diesel.
The research team, led in part by Taek Soon Lee, director of JBEI’s metabolic engineering program, genetically engineered two different microbes, E. coli and Saccharomyces cerevisiae, creating a new mevalonate pathway to overproduce a chemical compound called farnesyl diphosphate (FFP), which, when treated with enzymes can then be synthesized into terpene. Using the same microbes and the same pathway, the team created bisabolane as well, based on the mevalonate pathway that increased the biosynthesis ability in the microbes.
Lee said that through multiple rounds of large-scale preparation in shake flasks, the team was able to prepare roughly 20 milliliters of biosynthetic bisabolane using the over-producing microbes. But, Lee also said that his team wasn’t sure if the work to create bisabolane would translate into useful biofuels research. Using commercially available bisabolane, the team performed fuel property tests and found that the work was promising.
“Bisabolane has properties almost identical to D2 diesel but its branched and cyclic chemical structure gives it much lower freezing and cloud points,” Lee said. Using the mevalonate pathway, the same basic pathway used to produce the anti-malarial drugs artemisinin made famous by research at JBEI that led to the formation of Amyris, the team tweaked the pathway to improve the bisabolane yields.
The team is now working to create gallons of hydrogenated bisabolane for fuel property tests and Lee said, “economic analysis that takes into consideration production variables such as the cost and type of feedstock, biomass depolymerization method, and the microbial yield of the biofuels,” as well as the estimated impact or presence of byproducts like farnesane or aromatized bisabolane.
Eventually, Lee said the team hopes to replace the hydrogenation step required to create the commercial bisabolane by implanting an alkene reductase enzyme into the E.Coli or yeast that would be compatible with commercial-grade fermenters.
Lee coauthored a paper on the work in the journal of Nature Communications titled “Identification and microbial production of a terpene-based advanced biofuels.” Joining Lee on the paper were JBEI researchers Pamela-Yahya, Mario Ouellet and others.
The terpene-based compounds that include the bisabolane the team is working with contain 15 carbon atoms. Diesel fuel typically contains 10 to 24 carbons, according to Lee. “Although plants are the natural source of terpene compounds,” he added, “engineered microbial platforms would be the most convenient and cost-effective approach for large-scale production of advanced biofuels.”