By Deborah Zabarenko, Environment Correspondent
Ethanol from cellulose, the kind of sugar in the likes of cornstalks and sawdust, is being promoted as an environmentally friendly alternative to fossil fuels, with the advantage that it does not use food crops such as corn as raw materials.
The genetically engineered bacteria ferment cellulose to produce ethanol more efficiently, the scientists wrote in the Proceedings of the National Academy of Science.
Naturally occurring bacteria can also ferment cellulose but they do it at lower temperatures that require the use of an expensive enzyme called cellulase, said Lee Lynd of Dartmouth College, an author of the study.
The newly engineered bacterium, known as ALK2, can ferment all the sugars present in biomass and can do it at 122 degrees F (50 degrees C), compared with conventional microbes that cannot function above 98.6 degrees F (37 degrees C).
At higher temperatures, the fermentation process required two and a half times less cellulase in one controlled experiment, Lynd said in a telephone interview.
Doing it the natural way produces organic acids in addition to the ethanol, while ethanol is the only organic product of fermentation with the new bacteria, Lynd said.
ALK2 is more efficient than the microorganisms now in use in breaking down all five sugars present in cellulosic biomass simultaneously, he said.
"This bug will ferment them all and it will ferment them at the same time," Lynd said.
Cellulosic ethanol has almost no net emissions of climate-warming greenhouse gases because the carbon dioxide captured in growing the plants that go into it roughly equals what is emitted while running an engine, Dartmouth said in a statement.
In addition to being a professor at Dartmouth, Lynd is chief scientific officer and co-founder of Mascoma Corp, a company working to develop processes to make cellulosic ethanol.
(Editing by John O'Callaghan)