Bacteria for Blastoff: Using Microbes to Make Supercharged New Rocket Fuel
by Aliyah Kovner (Lawrence Berkeley National Laboratory) … Well aware of the advantages biology has to offer, a group of biofuel experts led by Lawrence Berkeley National Laboratory (Berkeley Lab) took inspiration from an extraordinary antifungal molecule made by Streptomyces bacteria to develop a totally new type of fuel that has projected energy density greater than the most advanced heavy-duty fuels used today, including the rocket fuels used by NASA.
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(Project leader Jay Keasling, a synthetic biology pioneer and CEO of the Department of Energy’s Joint BioEnergy Institute (JBEI)) “As these fuels would be produced from bacteria fed with plant matter – which is made from carbon dioxide pulled from the atmosphere – burning them in engines will significantly reduce the amount of added greenhouse gas relative to any fuel generated from petroleum.”
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Polycylcopropanated molecules contain multiple triangle-shaped three-carbon rings that force each carbon-carbon bond into a sharp 60-degree angle. The potential energy in this strained bond translates into more energy for combustion than can be achieved with the larger ring structures or carbon-carbon chains typically found in fuels. In addition, these structures enable fuel molecules to pack tightly together in a small volume, increasing the mass – and therefore the total energy – of fuel that fits in any given tank.
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Keasling’s team, comprised of JBEI and ABPDU scientists, studied the genes from the original strain (S. roseoverticillatus) that encode the jawsamycin-building enzymes and took a deep dive into the genomes of related Streptomyces, looking for a combination of enzymes that could make a molecule with jawsamycin’s toothy rings while skipping the other parts of the structure.
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First author Pablo Cruz-Morales was able to assemble all the necessary ingredients to make POP-FAMEs after discovering new cyclopropane-making enzymes in a strain called S. albireticuli. “We searched in thousands of genomes for pathways that naturally make what we needed. That way we avoided the engineering that may or may not work and used nature’s best solution,” said Cruz-Morales, a senior researcher at the Novo Nordisk Foundation Center for Biosustainability, Technical University of Denmark and the co-principal investigator of the yeast natural products lab with Keasling.
Unfortunately, the bacteria weren’t as cooperative when it came to productivity.
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” When two different engineered Streptomyces failed to make POP-FAMEs in sufficient quantities, he and his colleagues had to copy their newly arranged gene cluster into a more “tame” relative.
The resulting fatty acids contain up to seven cyclopropane rings chained on a carbon backbone, earning them the name fuelimycins. In a process similar to biodiesel production, these molecules require only one additional chemical processing step before they can serve as a fuel.
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The simulation data suggest that POP fuel candidates are safe and stable at room temperature and will have energy density values of more than 50 megajoules per liter after chemical processing. Regular gasoline has a value of 32 megajoules per liter, JetA, the most common jet fuel, and RP-1, a popular kerosene-based rocket fuel, have around 35.
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One of the team’s next goals to create a process to remove the two oxygen atoms on each molecule, which add dead weight. “When blended into a jet fuel, properly deoxygenated versions of POP-FAMEs may provide a similar benefit,” (Alexander) Landera added.
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Since publishing their proof-of-concept paper, the scientists have begun work to increase the bacteria’s production efficiency even further to generate enough for combustion testing. They are also investigating how the multi-enzyme production pathway could be modified to create polycyclopropanated molecules of different lengths. “We’re working on tuning the chain length to target specific applications,” said Sundstrom. “Longer chain fuels would be solids, well-suited to certain rocket fuel applications, shorter chains might be better for jet fuel, and in the middle might be a diesel-alternative molecule.”
Author Corinne Scown, JBEI’s Director of Technoeconomic Analysis, added: “Energy density is everything when it comes to aviation and rocketry and this is where biology can really shine. The team can make fuel molecules tailored to the applications we need in those rapidly evolving sectors.”
Eventually, the scientists hope to engineer the process into a workhorse bacteria strain that could produce large quantities of POP molecules from plant waste food sources (like inedible agricultural residue and brush cleared for wildfire prevention), potentially making the ultimate carbon-neutral fuel. READ MORE
Biosynthesis of polycyclopropanated high energy biofuels (Joule)
Badass POP missile fuel arrives from Berkeley’s labs: Will America keep a hold of them? (Biofuels Digest)
