by Merry Youle
There is something both endearing and enduring about E. coli. Just when you think that all kinds of other fascinating bugs are about to give it a shove into history, news emerges of its renewed importance. This time, it's biofuels.
Ethanol for use as fuel currently comes from the fermentation of glucose by yeast. The glucose comes from corn. The more corn we feed our vehicles, the less corn for us. Looking for another source of sugar, eyes have turned to lignocellulosic biomass, a significant source of pentose sugars. Unfortunately, yeasts are reluctant to ferment pentoses. Better fermentation was obtained with E. coli, but by a method that employed genetic engineering to introduce the required foreign genes. In contrast, a recent paper reports development of an ethanolgenic E. coli K-12 mutant (SE2378) which converts pentoses to ethanol ─ and it does it at high efficiency using only the genes present on the E. coli chromosome. No plasmids needed. No foreign genes.
Unlike the parent strain, this ethanol-producing mutant grows anaerobically on either glucose or xylose (a pentose often called wood sugar). Either way, ethanol accounts for a hefty 88% of the fermentation product. Production of ethanol by this mutant from xylose is actually higher than from glucose, and notably it is even higher than that reported for S. cerevisiae growing on glucose. Not bad for something that eats wood sugars. What's the trick here? The mutation blocks the native pathway for ethanol production in E. coli and the resultant metabolic shift activates another pathway which is normally inhibited during anaerobic growth.
Looking to the future, the authors expect to "optimize this pathway towards the development of a nonrecombinant ethanologen that can ferment all of the sugars in lignocellulosic biomass." Pretty cool!