How bacteria may help make sustainable, super-efficient rocket fuel

New York: Scientists have used a molecule made by bacteria to develop a new class of sustainable biofuels powerful enough to launch rockets.

A team of biofuel experts, led by Lawrence Berkeley National Laboratory (Berkeley Lab) in the US, 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.

“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,” said 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,” Keasling added.

Researchers said that their fuel candidate is also extremely energetic, potentially boosting rockets beyond their current capabilities. The key molecules used are called POP-FAMEs, short for “polycylcopropanated fatty acid methyl esters”.

The team’s work focuses on two known examples of organic compounds, both made by Streptomyces bacteria and impossible to grow in a lab. Genes from another species called S. roseoverticillatus was genetically analysed, and, in 1990, scientists announced the discovery of a natural product called jawsamycin.

This “toothy” molecule inspired Keasling’s team to examine the genomes of related Streptomyces species for potential rocket fuel applications. They subsequently uncovered the “necessary ingredients” for POP-FAMEs in another strain, S. albireticuli.

Unfortunately, the bacteria weren’t as cooperative when it came to productivity. When two different engineered Streptomyces failed to make POP-FAMEs in sufficient quantities, the team copied their newly-arranged gene cluster into a more “tame” relative, the researchers said.

The next stage in rocket fuel development would be to produce enough molecules for field tests, which generally require at least 10 kgs. The researchers are not nearly there yet, which is why the research remains tentative at this time.

But, 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 litre after chemical processing. Regular gasoline has a value of 32 megajoules per litre, JetA, the most common jet fuel, and RP1, a popular kerosene-based rocket fuel, have around 35.

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.

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