Ethanol from cellulose, the kind of sugar in 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. Genetically engineered bacteria could make cellulosic ethanol cheaper to manufacture, researchers report. The finding could unlock more energy from the waste products of farming and forestry.
The genetically engineered bacteria are able to ferment cellulose to produce ethanol more efficiently than current methods, says Lee Lynd of Dartmouth College, New Hampshire, an author of the study. Naturally occurring bacteria can also ferment cellulose, but they do it at lower temperatures that require the use of an expensive enzyme called cellulase.
The newly engineered bacterium, known as ALK2, can ferment all the sugars present in biomass at 50 °C, compared with conventional microbes that cannot function above 37 °C.
At these higher temperatures, the fermentation process required two and a half times less cellulase in one controlled experiment, Lynd says. Doing it the natural way produces contaminating organic acids in addition to the ethanol, while ethanol is the only organic product of fermentation with the new bacteria.
ALK2 is also more efficient than the microorganisms currently used to break down all five sugars present in cellulosic biomass simultaneously: “This bug will ferment them all and it will ferment them at the same time,” Lynd says.
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 the emissions produced while running an engine.
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, which has a financial interest in the bacterium described here.
NewScientist.com , 2008-09-09.