A culture of the Streptomyces bacteria
A group of biofuel experts led by Lawrence Berkeley National Laboratory (Berkeley Lab) takes inspiration from an antifungal molecule made by Streptomyces bacteria to develop a totally new type of fuel that reportedly has projected energy density greater than the most advanced heavy-duty fuels used today, including the rocket fuels used by NASA.
“This biosynthetic pathway provides a clean route to highly energy-dense fuels that, prior to this work, could only be produced from petroleum using a highly toxic synthesis process,” says project leader, Jay Keasling, a synthetic biology pioneer and CEO of the Department of Energy’s Joint BioEnergy Institute (JBEI), in a news release. “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.”
The energy potential of these fuel candidate molecules, called POP-FAMEs (for polycylcopropanated fatty acid methyl esters), comes from the fundamental chemistry of their structures. 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.
“The larger consortium behind this work, Co-Optima, was funded to think about not just recreating the same fuels from biobased feedstocks, but how we can make new fuels with better properties,” says Eric Sundstrom, an author on the paper describing POP fuel candidates published in the journal Joule, and a research scientist at Berkeley Lab’s Advanced Biofuels and Bioproducts Process Development Unit (ABPDU). “The question that led to this is: ‘What kinds of interesting structures can biology make that petrochemistry can’t make?’”
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,” says 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.”
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 the press release here.