Image: Pablo Morales-Cruz
Fossil fuel burning is leading to climate change, and scientists across the globe are working hard to come up with renewable alternatives, like electric vehicles and solar energy, to reduce the environmental impact. However, certain industries, like aviation, do not have feasible renewable jet fuel yet.
However, researchers at Lawrence Berkeley National Laboratory in partnership with DTU Biosustain have come up with an alternative jet fuel using commonly found soil bacteria. For the new biofuel, scientists harvested the carbon molecules generated from the metabolic process of common soil bacteria. The study has been published in the journal Joules.
According to Pablo Cruz-Morales, a microbiologist at DTU Biosustain, the researchers were motivated by the urgency for alternative fuels in the aviation industry. With a renewable alternative to petroleum-derived fuels, it would be easier to slow down the process of climate change.
The synthetic biologists genetically tweaked common soil bacteria to create compounds including chains of three-membered rings. These cyclic molecules with strained bond angles are energy-rich and can store more energy compared to the non-cyclic molecules. The scientists also noted that they can store the highest amount of energy in cyclopropanes, which are hard to generate via organic synthesis.
The research team at Berkley was looking for a way to create a renewable fuel. At that time, Jay Keasling, a professor of chemical engineering at the University of California, collaborated with and connected with researcher Pablo Cruz Morales. Together, they successfully produced a molecule called Jawsamycin.
Image: Pablo Morales-Cruz
Cruz-Morales had earlier worked with streptomyces bacteria. So, he knew that Jawsamycin is a naturally produced molecule due to the metabolic reactions in the streptomyces bacteria. This bacterial antifungal compound has five cyclopropane rings that resemble a jaw filled with teeth.
Keasling’s team further studied the original bacterial strain (Streptomyces roseoverticillatus). They also studied another unusual enzyme that forms an olefin in every catalytic cycle that’s further modified into a cyclopropane ring.
To create renewable jet fuel compounds, the researchers further modified jawsamycin’s biosynthesis process. They interrupted this process at a step where a nitrogen-containing ring is included in the cyclopropane chain. After that, they created a route to fatty acids that involved a bizarre thioesterase enzyme found in a similar bacterium.
The resulting compounds now include six or seven cyclopropane rings and a carbon backbone called fuelimycins. Just one addition to the processing step – creating methyl esters – has turned the fatty acids into fuel. The methyl esters have a total heating value of 40MJ/l. This makes it comparable to the value of 32MJ/l for petrol and 35MJ/l for the kerosene-based rocket fuel.
Image: SpaceX/Unsplash
However, there are still some challenges to overcome. For instance, Keasling’s team made only 10mg/l of fuelimycins. Ideally, they need to produce grams per liter, per hour. So, there are still some changes to make. Nevertheless, the overall study is quite impressive. With the right funding, it is possible to create sufficient renewable fuel to help power airplanes and rockets. Hence, it’s a piece of great news for the aviation industry.
Although Streptomyces are currently used to make antibiotics commercially, Cruz-Morales says other bacteria such as Clostridium or Pseudomonas could also be genetically engineered to generate fuel from waste.