Doubly Engineered Microbes For Biofuels

A multi-institutional research team has succeeded in genetically engineering both biomass-degrading and biofuel-producing capabilities into a single microorganism. This so-called consolidated bioprocess eliminates the need for a separate enzymatic process to hydrolyze cellulose and hemicellulose, which has been a cost barrier to commercial production of fully renewable transportation fuels. Led by Gregory Bokinsky and Jay D. Keasling of the Department of Energy’s Joint BioEnergy Institute, the researchers first engineered Escherichia coli to produce a suite of enzymes that convert switchgrass into fermentable sugars. They pretreat the switchgrass with an ionic liquid to loosen the plant fibers and reduce lignin content. The team also endowed the bacterium with the genes needed to convert the sugars into different fuel feedstocks: One version produces butanol for gasoline, a second version produces fatty acid ethyl esters for diesel fuel, and a third version produces pinene for jet fuel (Proc. Natl. Acad. Sci. USA, DOI: 10.1073/pnas.1106958108). Bruce E. Dale, a biofuels expert at Michigan State University, gives the research team “full marks” for demonstrating an important proof of concept. But to achieve a commercial process, Dale adds, the digestion and fermentation capabilities of the E. coli strains require significant improvements.