DOE Oak Ridge Scientists Find Ethanol Gene

A team of researchers at the Department of Energy’s BioEnergy Science Center (BESC) have pinpointed the exact, single gene that controls ethanol production capacity in the bacterium Clostridium thermocellum. The organism has long been studied for its ability to digest cellulose into ethanol. One limiting factor is that C. thermocellum also makes the waste byproducts acetate, formate and lactate. Another is that it can’t live when its own ethanol production pollutes its environmental soup.

Now a multidisciplinary team has created a strain of C. thermocellum with a mutated bifunctional acetaldehyde-CoA/alcohol dehydrogenase gene (adhE). This gene has been shown to confer ethanol tolerance, and it opens the door to using the bacterium as an efficient converter of high-cellulose feedstocks, such as switchgrass and corn stover, for ethanol production. It may also be possible to insert the gene into more voracious bugs. These tailor-made bacteria could break down lignin walls to get at a plant’s sugars, and ferment them, in a single step, without the use of expensive enzymes to “pre-digest” the feedstock.

BESC is a multidisciplinary coalition led by Oak Ridge national Laboratory (ORnL). The team’s results were published in the Proceedings of the National Academy of Sciences, in a paper titled “Mutant alcohol dehydrogenase leads to improved ethanol tolerance in Clostridium thermocellum,” by Steven D. Brown, Adam M. Guss, Tatiana V. Karpinets, Jerry M. Parks, Nikolai Smolin, Shihui Yang, Miriam L. Land, Dawn M. Klingeman, Miguel Rodriguez Jr., Babu Raman, Jonathan R. Mielenz, Jeremy C. Smith and Martin Keller of ORNL, and Ashwini Bhandiwad, Xiongjun Shao and Lee R. Lynd of Dartmouth College.

—SETH MASIA

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