Ethanol from Reusable Solar-Powered Microbes


This article was published by Newsletter, issue #43, 2008-05-01.

With global supplies of fossil-based fuels declining, energy companies and governments alike are anxious to find economically and technologically viable alternatives to the hydrocarbon fuel sources upon which our societies run. Of all the biofuels, ethanol is currently a popular choice — particularly in the Americas — and can be derived from glucose (e.g., corn), sucrose (e.g., sugarcane), and cellulose (e.g., switchgrass and wood). However, these sources of ethanol have at least two significant disadvantages: they are destroyed in the process of ethanol extraction, and they require large amounts of water relative to the amount of ethanol that can be derived from them.

Fortunately, researchers at the University of Texas at Austin have created a microbe that can produce cellulose that can be converted into ethanol and other biofuels. Professor R. Malcolm Brown Jr. and Dr. David Nobles Jr. developed the cyanobacteria (a.k.a. blue-green algae) through genetic modification — specifically by adding a set of cellulose-making genes from Acetobacter xylinum, a non-photosynthetic "vinegar" bacterium that produces large quantities of cellulose.

Both of the aforementioned problems with conventional ethanol sources, are largely overcome by this promising new alternative. The cyanobacteria secrete cellulose, glucose, and sucrose, which allows those substances to be harvested without killing or even damaging the cyanobacteria. Also, the cyanobacteria can be grown in production facilities on non-agricultural lands, even using salty water that, if untreated, is useless for human consumption or growing crops.

There are two additional advantages: Like all forms of algae, the cyanobacteria derive their energy directly from sunlight. This is critical, because in the long run, solar power will likely far outlast the Earth's supplies of oil, natural gas, coal, and materials suitable for atomic energy. But with present technologies, liquid fuels are necessary for all forms of air transportation, including the rockets that boost into orbit large and heavy payloads, such as satellites. Electricity derived from natural gas-burning plants and hydroelectric dams, cannot be used for such vehicles, because of the prohibitive weight of the batteries that would be needed. Only liquid fuels contain the concentration of energy necessary for such uses.

Another major advantage that the cyanobacteria have over ethanol produced from feed crops, is that they can be grown without requiring conventional fertilizer, which is made from petroleum. This will reduce the demand for — and thus our dependency upon — the natural gas that we are currently using for creating fertilizers, as well as burning to produce heat in homes and other buildings, and burning to produce electricity.

Moreover, the previously mentioned sources of cellulose can require a nontrivial amount of machine processing to extract the actual cellulose, primarily because the plant-based material is highly crystalline and impure, being mixed with lignins and other structural compounds. In contrast, these newly-created cyanobacteria produce a gel-like cellulose that is easily processed. This further reduces the amount of energy needed to produce the resultant energy, and is quite unlike corn-based ethanol, which is estimated to consume almost as much energy as it produces — in the form of natural gas-based fertilizer to grow the crops, and diesel fuels to power all of the heavy equipment utilized to harvest and process those crops.

The two researchers have patented their discovery, and are now exploring ways to scale up production of the cyanobacteria.

Copyright © 2008 Michael J. Ross. All rights reserved.

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