Missiles And Rockets Might Soon Smell Like Pine TreesIn an effort to launch  things skyward in a more sustainable way researchers have coaxed bacteria to produce a highly combustible compound called pinene.  Conifers naturally excrete the stuff in their resin lending  the plants part of their distinctive scent. Pinene* also happens to rival the properties  of JP-10--a  liquid rocket fuel that's widely used for commercial and military launches.So  pretty soon  a rocket or missile flying overhead might spew exhaust that smells like pine trees.JP-10 and other energy-dense rocket fuels are derived from oil  and don't come cheap. (The cost of JP-10  is about $25 per gallon and rising as oil demand  grows.)  Meanwhile no biofuels today can compete with traditional rocket fuels on the market. Although ethanol derived from corn for example can more or less replace gasoline  even the latter and more energetic  fuel packs about 20 percent less punch per gallon than JP-10.A breakthrough in rocket-compatible biofuel came in 2011. That's when the Navy discovered chemicals that link together or dimerize two molecules of pinene  into a fuel with properties similar to JP-10. Because leveling pine forests to extract a little pinene isn't practical however researchers have since sought alternative production methods.The new research effort--a joint venture by Georgia Tech and the Department of Energy's Joint BioEnergy Institute--builds on the work of the Navy by offloading pinene synthesis to bacteria. The group genetically engineered E. coli bacteria to produce conifer-derived proteins that assemble pinene.Stephen Sarria and Pamela Peralta-Yahya two Georgia Tech researchers who collaborated on the new work published in  ACS Synthetic Biology broke down the process for Popular Science in four steps:  First the researchers picked two groups of enzymes--pinene synthases and geranyl diphosphate synthases--to produce molecules of pinene. Second they inserted genes that code for the enzymes into the DNA of E. coli (chosen because it's one of the easiest bacteria to genetically engineer). Third the team grew up the bacteria in large fermenters  very similar to how you'd make beer Peralta-Yahya said. With the brewing of pinene complete they used the Navy-discovered chemicals to dimerize pinene molecules into rocket-ready fuel.*This new bacteria-driven method to make pinene is six times better than any other biological process but the yield is still quite low.  Right now we re seeing about 1 percent of theoretical yield Peralta-Yahya said. To be commercially competitive we need to reach  about 26 percent of  theoretical yield.The biggest hurdle for the team right now is pinene synthase itself. Both the enzyme's product pinene and its partner enzymes the geranyl diphosphate syntheses inhibit pinene-creating activity. Peralta-Yahya says there are two ways to solve the problem: either engineer a new kind of pinene synthase or lower the concentration of geranyl diphosphate synthase.For now the team is trying both methods in hopes of making a  drop-in biofuel that's cheaper and more sustainable option for launching rockets or missiles without changing engines or existing infrastructure.*Correction: Pinene dimers have a similar high energy density as the JP-10 not pinene.  *Correction: .  The Navy research introduced  the technique for dimerizing pinene  but the  research team did not proceed to dimerize pinene in their experiments.