As bacterium goes, E. coli is a public health scourge, but a lab favorite. It’s one of the most thoroughly studied microbes out there, and so one of the most easily manipulated for genetic engineering. Scientists can tweak its metabolic pathways to produce insulin, antibiotics and anticancer drugs; they can increase its ability to make ethanol or even engineer it to manufacture hydrocarbons. But until now, they couldn’t push it to create something that didn’t exist naturally: long-chain alcohols.
By manipulating E. coli to produce alcohols with up to eight carbon atoms, James Liao and his colleagues at the University of California-Los Angeles recently introduced a new twist to the field of biofuels research. Long-chain alcohols overcome some of the traditional limitations of ethanol, which has only two carbon atoms. They have both high-energy density—on par with gasoline—and low water solubility, so they are compatible with existing infrastructure.
“Long-chain alcohols can be directly used in automobiles or aircraft,” Liao says. “Unlike E85, which requires retrofitted vehicles, [they] can be used without vehicle modification.”
The current research, published in the Proceedings of the National Academy of Sciences on Dec. 8, builds on work Liao published in the journal Nature last January. The Nature study demonstrated that E. coli can metabolize glucose into branched chain alcohols with four or five carbon atoms—and do so in higher yields (for isobutanol, 86 percent of the theoretical maximum) that will be necessary for large-scale biofuels production.
Alcohols with six to eight carbon atoms in each molecule could only be generated by pioneering a whole new metabolic pathway—a nonnatural one, created by chemically synthesizing amino acids that allow the microbe to manufacture alcohols longer than what would be naturally possible.