Many plants, insects and microbes naturally produce small quantities of alkanes and alkenes, the long-chain carbon and hydrogen molecules that are major components of diesel, petrol (gasoline) and jet fuel.
The biotechnology company LS9, based in South San Francisco, California, has now pinpointed the biochemical pathway bacteria use to do this – after receiving patents for the genes responsible, of course.
In a paper published today in Science (Science, 329, 559; 2010 doi:10.1126/science.1187936), they report that they expressed these genes in the bacterium Escherichia coli, fed it glucose, and showed that it directly secreted diesel-like fuel – a mixture of alkanes and alkenes with chain lengths from 13 to 17 carbon atoms. This is about what you need for diesel, though the company would have to do some more tweaking to generate the hydrocarbons used in petrol and jet fuel.
The pathway involves two cyanobacteria genes which code for enzymes that convert metabolites of fatty acids (which would normally be used to build cell membranes) into alkanes and alkenes.
The only other known pathway that allows engineered microbes to make pure hydrocarbons, works via a different biochemical route: the conversion of isoprenoid compounds, which are used to fine-tune cell membranes, into hydrocarbons with multiple double bonds. This pathway – favoured by other synthetic biofuels companies, such as Amyris – requires further chemical conversion outside the fermenter, whereas LS9’s process involves direct, one-step conversion of feedstock to fuel.
It’s LS9’s second biofuel tour de force this year: in January, the team showed (Nature, 468, 559-562; 2010 and Nature news article) that they could engineer E. coli to convert sugars or hemicellulose into biodiesel, which is clean and road-ready. The biodiesel consists of a non-hydrocarbon molecule: methyl esters. That project is further advanced, industrially, than the alkane/alkenes pathway that LS9 announce today.
Have LS9 found the only direct E.coli-to-alkane pathway that exists? “There are most likely other pathways in other organisms,” says the company’s Andreas Schirmer. Insects, for example, can use P450 enzymes to make alkanes, though no-one has yet published the genes involved in this pathway. Moreover, it will be hard to find pathways that can be transferred to an industrial organism like E. coli, Schirmer notes. So LS9 may have sown up the intellectual property rights on this one.
The big question for all of these microbial fuel efforts (whose competition is summarised by GreentechMedia) is whether the processes can be scaled up to produce large amounts of fuel, cheaply enough to compete with oil. So far, nobody knows.
“From a purely business perspective, LS9 is doing reasonably well,” says Mark Bünger, research director at business consultancy Lux Research in San Francisco. “They claim their costs [for biodiesel] are under $100 per barrel of oil equivalent today (still a bit high – crude sells for about $79); but they are hoping to produce at $50 per barrel by 2012,” he says. The company has won $25 million in new funding from various sources, including a strategic partnership with oil giant Chevron last September. They also purchased a bankrupt plant in Florida for $2 million in 2009, which they are now retrofitting in order to produce up to 100,000 gallons of biodiesel capacity in 2010.