A new microbe engineering trick could potentially make butanol, a promising biofuel, so cheaply that it could compete with ethanol. By tapping into a highly efficient metabolic pathway, scientists at Rice University engineered E. coli to convert sugars to butanol 10 times more efficiently than any other organism.
Butanol, which is typically made by fermenting sugar, packs more energy per gallon than ethanol and can be shipped via existing oil pipelines.
Several companies are now trying to commercialize biobutanol, including some seeking to retrofit existing ethanol facilities. However, the bugs normally used to produce butanol don’t tolerate it well and so produce only small quantities. “You can get over 10 percent ethanol in the fermentation process from corn,” says Jonathan Mielenz, a biofuels researcher at Oak Ridge National Laboratory. “Butanol is nothing near that level. It’s typically not much more than 1 or 2 percent.”
The new E. coli work faster than other fuel-producing microbes. They also produce five to 10 times more fuel from the same amount of sugar. That means they require less sugar feedstock and can be grown in smaller vessels, cutting capital and operational costs. Ramon Gonzalez, a chemical and biomolecular engineering professor who led the work, says that several companies have shown interest in the technology, and he expects to see it on the market within the next three years.
Cobalt Biofuels, a biobutanol startup based in Mountainview, California, uses Clostridium bacteria to break down plant matter and convert the resulting sugars into a mix of butanol, acetone, and ethanol. Gevo, a company based in Englewood, Colorado is working with E. coli that are altered to divert some of their metabolites, which would otherwise be involved in synthesizing amino acids, toward alcohol production. And Butamax, a joint venture between Dupont and BP, is using genetically modified yeast.