Saturday, June 18, 2011

Cellulosic Ethanol, One Step Closer to Practical

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The fermentation of the natural sugars (and starches) in grains and grapes yields beer and wine, and this has remained essentially unchanged for almost 10,000 years.  Distilling these products yields pure ethanol.
An E-85 (85% Ethanol Fuel Pump)
By Mariordo Mario Roberto Duran Ortiz (Own work) [CC BY-SA 3.0], via Wikimedia Commons
Recently, there's been much ado about Ethanol subsidies in Congress. Corn producers are very keen on keeping these subsidies intact, of course. However, utilizing a good portion of our food grain for fuel production probably isn't a long term solution as it will serve to increase food prices.

In the production of our food crops, we have several tons of secondary material - such as corn stalks, which essentially go to waste. This material, is indigestible by yeast because it mostly consists of lignin. Furthermore, plants like switchgrass cannot be used for large scale ethanol production because most of the carbohydrate it contains is in lignin. (Switchgrass can grow on land unfit for food production making it an ideal biofuel crop.)

For many years, scientists have been trying to develop methods of breaking down lignin to produce fermentable sugars. Fungi which can break down lignins have been known for a quarter century, but scientists have been unable to develop that into an industrial technology. Recently, however, a potentially revolutionary discovery was made. The soil bacterium Rhodococcus jostii was discovered to contain a gene (dypB) which has lignin peroxidase activity. Bacterial genes are inherently easier to manipulate than fungal genes 

In their discussion, the authors state that they suspect that they have identified just one of a host of enzymes which make lignin digestion possible. In the future, scientists may be able to engineer a bacteria which overexpresses these genes and that might lead to industrial scale production of cellulosic ethanol.

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