Researchers at the Thayer School of Engineering and Mascoma Corporation have announced the creation of a new type of bacteria tailored to manufacture cellulosic ethanol, a potential breakthrough in ethanol production. The results of the team's study were published online by the Proceedings of the National Academy of Science earlier this month, and have garnered international attention for their implications on the development of alternative fuels.
By genetically modifying an existing species of bacteria to limit its ability to produce by-products during ethanol fermentation, the research team was able to create a strain, T. saccharolyticum, that produced exclusively ethanol, according to the group's study.
"It became clear to us that practical ethanol production requires that ethanol be produced at high yield," Lee Lynd, a Thayer professor and co-author of the study, said in an e-mail to The Dartmouth. "We knocked out -- that is, rendered non-functional -- genes associated with formation of undesirable products other than ethanol."
The new strain is an improvement over previous attempts to engineer ethanol-forming bacteria, like yeast, as these bacteria are thermophilic, meaning they can operate in hotter environments, the team reported.
"[T. sac.] is an organism that grows at a high temperature, and the enzymes that degrade woody material work better at high temperatures. They're actually one of the most expensive steps in this whole conversion process," Joe Shaw, co-author of the team's paper, said.
With the new bacteria, the fermentation process requires the addition of fewer enzymes to break down plant materials into the sugars used for fermentation, reducing costs of ethanol production.
Cellulosic ethanol, "a leading candidate among alternatives to petroleum-derived transportation fuels," according to the team's paper, is generally considered more environmentally sound than ethanol produced from corn, because it is made from inedible plant materials and releases less carbon during production and use. Cellulosic ethanol, however, has also been more costly to produce, precluding its widespread adoption as an alternative fuel.
"It's been something that a lot of people weren't sure would work," Shaw said. "It was a project that Lee's been involved with for many years, I'd say probably the last 15 to 20. It took a lot of careful work to get the framework in place to do the experiment and show it would be successful."
Shaw said that although the new strain represents a significant breakthrough, it is only a proof of concept and will require further research before it becomes commercially viable. T. saccharolyticum produce ethanol yields equal to conventional methods using yeast, but remain more susceptible to environmental fluctuations.
"The major challenge compared to yeast is process robustness, how well it can survive things that happen in real life," Shaw said. "We've used yeast for thousands of years, we know how it behaves. The real question is can we learn how this organism behaves?"
Mascoma will continue to work with T. saccharolyticum to make it suitable for commercial use, Shaw said, but added that the timeline of its is difficult to predict. Shaw said he hopes the bacteria will be further developed and marketable within the next five years. The success of the study also heightens expectations for future research into ethanol-producing bacteria that could be used with T. saccharolyticum to make the process more efficient, he said.
Scientists hope to engineer another organism, C. thermocellum, to process glucose, which T. saccharolyticum is unable to process. Successful engineering of C. thermocellum could result in the production of ethanol without the use of additional enzymes.
"If we could engineer that organism in conjunction with T. sac., that would be basically opening the door up for cellulosic ethanol," he said. "It would be one of the biggest game-changers for this industry."
