The fatty acids can't be pumped directly into your gas tank – cars and trucks won't run on soap, after all – but they are an excellent precursor to biodiesel.

Biodiesel has so far lagged behind ethanol as a means of cutting fossil fuel use in vehicles because ethanol is easier and cheaper to make. But biodiesel has a higher energy density and lower water solubility than ethanol, which offer significant advantages.

"It is closer in chemical properties to a barrel of oil from Saudi Arabia than any other biologically derived fuel," Khosla said. Thus it could easily be blended into diesel and gasoline, or used alone as a bona fide transportation fuel.

If researchers can figure out how to manipulate the cellular means of production in E. coli, biodiesel could be made cheaply enough that the little engine of E. coli could end up powering a lot of larger engines at far less cost to the environment than with fossil fuels.

Xingye Yu, graduate student in chemical engineering, and Tiangang Liu, postdoctoral scholar in chemistry, contributed equally to the research and are coauthors of the paper.

The research was funded by a grant from LS9, a biofuels company.