New Biofuel Could Replace Today’s Standard Fuel for Diesel Engines

From Lawrence Berkeley National Laboratory comes the announcement that researchers with the U.S Department of Energy (DOE)’s Joint BioEnergy Institute (JBEI) have identified a potential new advanced biofuel that could replace today’s standard fuel for diesel engines.  It would be clean, green, renewable and produced in the U.S. The full announcement can be found here.

JBEI research team used synthetic biology tools to engineer strains of two microbes, a bacteria and yeast, to produce a precursor to bisabolane, a member of the terpene class of chemical compounds that are found in plants and used in fragrances and flavorings. Preliminary tests by the team showed that bisabolane’s properties make it a promising biosynthetic alternative to No. 2 diesel fuel.

Researchers at JBEI are pursuing the fundamental science needed to make production of advanced biofuels cost-effective on a national scale. One of the avenues being explored is sesquiterpenes, terpene compounds that contain 15 carbon atoms (diesel fuel typically contains 10 to 24 carbon atoms).

Taek Soon Lee, who directs JBEI’s metabolic engineering program and is a project scientist with Lawrence Berkeley National Laboratory (Berkeley Lab)’s Physical Biosciences Division said, “This is the first report of bisabolane as a biosynthetic alternative to D2 diesel, and the first microbial overproduction of bisabolene in Escherichia coli and Saccharomyces cerevisiae. This work is also a proof-of-principle for advanced biofuels research in that we’ve shown that we can design a biofuel target, evaluate this fuel target, and produce the fuel with microbes that we’ve engineered.”

Path to Make Bisabolane as Diesel Altenative.

The team’s paper about the research has been published in the journal Nature Communications entitled  “Identification and microbial production of a terpene-based advanced biofuel.”  Lee the corresponding author is joined with Pamela Peralta-Yahya, the lead author of the paper and Mario Ouellet, Rossana Chan, Aindrila Mukhopadhyay and Jay Keasling.

The hunt is very much on for alternatives to fossil based fuels.  Advanced biofuels for liquid transportation fuels derived from the cellulosic biomass of perennial grasses and other non-food plants, as well as from agricultural waste are highly touted for their potential to replace gasoline, diesel and jet fuels.

Keasling, the CEO of JBEI and a leading authority on advanced biofuels points out, “We desperately need drop-in, renewable biofuels that can directly replace petroleum-derived fuels, particularly for vehicles that cannot be electrified. The technology we describe in our Nature Communications paper is a significant advance in that direction.”

Lee explains the hunt in the sesquiterpenes zone, “Sesquiterpenes have a high-energy content and physicochemical properties similar to diesel and jet fuels. Although plants are the natural source of terpene compounds, engineered microbial platforms would be the most convenient and cost-effective approach for large-scale production of advanced biofuels.”

In earlier work Lee and the team engineered a new metabolic reaction critical to biosynthesis (also called mevalonate pathway) in both E. coli and S. cerevisiae that resulted in these two microorganisms over-producing a chemical compound called farnesyl diphosphate (FPP), which can be treated with enzymes to synthesize a desired terpene. In the latest work, Lee’s team used that mevalonate pathway to create bisabolene, which is a precursor to bisabolane.

When they began the work, the team did not know whether bisabolane could be used as a biofuel, but they targeted it on the basis of its chemical structure. Their first step was to perform fuel property tests on commercially available bisabolene, which comes as part of a mixture of compounds. Convinced they were onto something, the researchers then used biosynthesis to extract pure biosynthetic bisabolene from microbial cultures for hydrogenation into bisabolane. Subsequent fuel property tests on the bisabolane were again promising.

Lee tells the story, “Bisabolane has properties almost identical to D2 diesel but its branched and cyclic chemical structure gives it much lower freezing and cloud points, which should be advantageous for use as a fuel. Once we confirmed that bisabolane could be a good fuel, we designed a mevalonate pathway to produce the precursor, bisabolene. This was basically the same platform used to produce the anti-malarial drug artemisinin except that we introduced a terpene synthase and further engineered the pathway to improve the bisabolene yield both in E. coli and yeast.”

“Once the complete fuel properties of hydrogenated biosynthetic bisabolene can be obtained, we’ll be able to do an economic analysis that takes into consideration production variables such as the cost and type of feedstock, biomass depolymerization method, and the microbial yield of biofuel. We will also be able to estimate the impact of byproducts present in the hydrogenated commercial bisabolene, such as farnesane and aromatized bisabolene. Lee said.

Lee and his colleagues would like to replace the chemical processing step of bisabolene hydrogenation with an alkene reductase enzyme engineered into the E.coli and yeast so that all of the chemistry is performed within the microbes.

Looking down the road Lee said, “Enzymatic hydrogenation of this type of molecule is a very challenging project and will be a long term goal. Our near-term goal is to develop strains of E.coli and yeast for use in commercial-scale fermenters. Also, we will be investigating the use of sugars from biomass as a source of carbon for producing bisabolene.”

The JBEI project looks good, even as a two step process.  It looks like the raw material would be sugar – a product of intense interest as noted yesterday.  If the cheap sugar matter is resolved with a bit of competition, projects like this have a good shot at getting to market.

By. Brian Westenhaus

Source: A New Synthetic Diesel Fuel