A new batch of genetically engineered bacteria may be able to slash the cost of producing ethanol from tough materials like wood chips and switchgrass, pushing the young ethanol industry closer to its goal of creating commercially competitive alternative fuel from the waste products of farming and forestry. 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 [Reuters].
Ethanol from corn and sugarcane is relatively easy to produce, because yeast convert the readily accessible sugars and starches into ethanol. Cellulose presents a stiffer challenge. Cellulose fibers contain longer polysaccharide chains than those found in starches and surround them with lignin and hemicelluose, which hold the fibers together and provide strength. This makes them tough—tough enough to hold up a tree—but it also makes the sugars within very hard to access [Ars Technica].
Turning cellulose into ethanol involves two steps: using enzymes to break complex cellulose into simple sugars such as glucose, and then using yeast to ferment the sugar into ethanol. Both steps add to the price of ethanol [Technology Review]. In the new study, published in the Proceedings of the National Academy of Science [subscription required], researchers created a genetically engineered bacterium, known as ALK2, which both requires the use of fewer enzymes and converts sugar more efficiently.
Researchers say the new bacteria can function at temperatures up to 122 degrees Fahrenheit, a large improvement over the microbes that have previously been used in ethanol production, which cease functioning at 98.6 degrees Fahrenheit. At that higher temperature, the process requires two and a half times less of the expensive enzyme, according to lead researcher Lee Lynd. The new bacteria also converts all five sugars present in cellulose at once: “This bug will ferment them all and it will ferment them at the same time,” Lynd says [New Scientist].