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Wednesday, January 16, 2008 Better Bugs for Making ButanolEngineered E. coli proves efficient at churning out the biofuel. By Alexandra M. Goho
In a push to find better biofuels to reduce gasoline consumption and lower greenhouse-gas emissions, scientists have genetically engineered E. coli that is highly efficient in producing butanol, a promising new type of biofuel. The new technology could speed up the development of butanol biofuels into a cost-effective alternative to ethanol. While ethanol is the main biofuel on the market today, energy firms are increasingly looking to alternatives such as butanol. "It has many attractive properties," says Jim McMillan, manager of biorefining process R&D at the National Renewable Energy Laboratory's National Bioenergy Center, in Golden, CO. Because butanol packs more energy per gallon than ethanol does, cars running on butanol get better mileage. And, unlike ethanol, it doesn't mix with water, so it can be shipped in existing petroleum pipelines without causing problems. A number of research groups are engineering microbes that can convert sugar from various feedstocks into butanol. Most of these groups rely on the bacterium Clostridium acetobutylicum, which naturally makes a form of butanol called 1-butanol. "But Clostridium is not easy to deal with," says James Liao, a chemical engineer at the University of California, Los Angeles. "It grows slowly, it's very fastidious, and it's not easy to genetically manipulate." Despite decades of tinkering by scientists, the microbe still can't produce enough butanol to make it economically viable as a transportation fuel, Liao says. Instead, he and his colleagues turned to E. coli. Although the bacterium does not produce butanol naturally, it is easy to modify and grows fast. Instead of tweaking the pathway that the microbes employ for fermenting sugar into alcohol, Liao reasoned that he could program E. coli to produce butanol by diverting some of the microorganism's metabolites into alcohol production. These metabolites, called keto acids, are involved in the synthesis of amino acids, the building blocks of proteins. To make butanol from keto acids, the researchers inserted two different nonnative genes into E. coli. The first gene came from a microbe commonly used in the production of cheese. The gene codes for an enzyme that converts keto acids into aldehydes. The second gene, derived from yeast, codes for an enzyme that converts aldehydes into butanol. Initially, when linked together in E. coli, the two genes allowed the microbe to produce small amounts of butanol. With further genetic modifications, Liao was able to dramatically increase the efficiency of the process. For instance, deleting certain genes and boosting the activity of others increased the amount of keto acids available for conversion into butanol. With all the combined manipulations, the engineered microbes achieved an efficiency high enough for industrial use, says Liao. |
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Cheap Ethanol from Tires and Trash
01/14/2008
Comments
rhansing on 01/16/2008 at 12:26 PM
11
But a great use would be to use the tons of "fuel" trash, that we dump in the dumpyards.
Biofuelsimon on 01/17/2008 at 9:10 AM
1
killian on 01/18/2008 at 4:48 PM
54
DJTal on 01/20/2008 at 5:54 AM
108
killian on 01/21/2008 at 11:16 AM
54
420M people in 2050, 9300 VMT per person gives 3.9 trillion miles. 35 MPG for gasoline gives 112 billion gallons gasoline, or 154 billion gallons of E85 (adjusting for the energy content), requiring 131 billion gallons of ethanol. Schmer et. al in PNAS recently reported switchgrass yields of 7100kg/ha and cellulosic ethanol at 0.38 L/kg which gives 2700 L/ha, or 185,000 gallons/mi^2. That gives 710,000 mi^2, or 19% of the U.S. Scale.
Oh, and then there's freight...
DJTal on 01/25/2008 at 10:39 AM
108
killian on 01/30/2008 at 4:29 AM
54
DJTal on 01/30/2008 at 11:16 AM
108
killian on 02/09/2008 at 2:14 PM
54
However, more importantly, two articles in Science just did calculations for greenhouse gas emissions from biofuels due to land use change, and the data really looks bad for most biofuels, unless they are made from waste. For example, Fargione's paper said, "Our results show that converting native ecosystems to biofuel production results in large carbon debts. ... The carbon debts attributed to biofuels would not be repaid by the annual carbon repayments from biofuel production for decades or centuries."
As a specific example, Searchinger's paper said, "This analysis has implications for other biofuels. Cellulosic ethanol could use wastes that do not trigger land use change. But if American corn fields of average yield were converted to switchgrass for ethanol, replacing that corn would still trigger emissions from land use change that would take 52 years to pay back and increase emissions over 30 years by 50%."
This suggests that we had better restrict our ethanol feedstocks to waste products rather than growing crops specifically to make into ethanol.
quickerest on 05/12/2008 at 2:28 PM
1
I do agree that there has to be a very big barrier between our food and fuel production or we will end up being reliant on others again for one of our two greatest needs; food or power.