Common soil microbes are capable of synthesising a unique organic compound 'with teeth' that could become the highly efficient fuel of the future.
Fossil fuels - oil, gas and coal - enable cars to drive, planes to fly and ships to cross oceans. But extracting, refining and using them does a lot of harm to the environment. One way to reduce that damage is to make the fuel more efficient, so that more energy comes from burning the same amount. Such fuel has been found in common soil bacteria - as have the enzymes with which it can be produced. This is revealed in an article published in the journal Joule.
"In chemistry, anything that requires energy to produce releases energy when it decays," says Pablo Cruz-Morales, one of the authors of the new work. This is why biologists have turned their attention to unusual molecules that certain bacteria synthesise. I am talking about organic compounds that carry additional "addition" in the form of several triangular structures of cyclopropane - polycyclopropanated fatty acids. In contrast to cycles containing five or six carbon atoms (as in benzene), these three-membered cycles are tense and require a lot of effort to produce. Because of this, they carry an exceptionally large amount of energy.
Such triangular cyclopropane structures are very rare. Having studied the known genomes of bacteria that produce such molecules, scientists have identified proteins that synthesise cyclopropane structures - enzymes from the polyketide synthase (PKS) family. Of particular interest has been streptomycetes, which produce jawsamycin to fight fungi. Jawsamycin is named after the cult film thriller Jaws because it involves several triangular cycles, resembling shark teeth and all together making a jaw.
The authors succeeded in modifying the PCC protein, increasing its productivity by more than 20-fold and turning the microbes into "living factories" of josamycin. They estimate that such fuel could be orders of magnitude more efficient than existing fuels: its energy density is up to 50 megajoules per litre - more than any fuel in use today, including rocket fuel. But for now, scientists are busy scaling up the process, trying to set up at least experimental production.