Ethanol is not the most energy-dense of fuels nor the cheapest. Consequently, Amyris Biotechnologies in Emeryville, Calif., has come up with a potentially better solution. It did so by starting with a long roster of organic compounds from which it chose potential replacements for gasoline, diesel and jet fuel that could be burned in modern engines and would be compatible with the existing petroleum infrastructure. Then the company used custom-designed microbes to produce the new fuels by fermentation from a conventional ethanol feedstock.

To create the novel strains was no small genetic feat. The task required substantial alterations to the yeast genome. Genes from the original plant source and two other organisms were inserted, and a preexisting biochemical pathway was carefully adjusted. The engineered yeast boasted a millionfold increase in yield.

A leader in the emerging field of synthetic biology, Amyris is well known for developing a strain of yeast for large-scale manufacture of a precursor to the antimalarial drug artemisinin, for which the Asian plant source is in short supply. The company, chosen in 2006 by the World Economic Forum as a Technology Pioneer, is now close to its goal of supplying cheap industrial quantities of artemisinin to developing countries.

Amyris decided that its expertise could prove equally profitable when applied to biofuels. It initiated a search for fuels that could be produced in the lab and that met criteria on energy content, volatility and water solubility.

The difference between engineering microbes to produce drugs versus fuel is that, ounce for ounce, drugs are much more valuable: a fuel end product has to be cheap enough to burn. Amyris will have to optimize each microbial strain so that it cranks out fuel without poisoning itself and produces enough fuel molecules so that it is economically worthwhile to grow. In the history of the large-scale chemical industry, the subtlety of technical expertise involved in this project is without precedent. Yet Amyris, which last June added several oil industry veterans to its management, has shown that it means business.