Researchers create cellulose-producing microbe

By Dave Nilles | June 02, 2008
While the ethanol industry's quest to convert agricultural residues to fuel continues, researchers at the University of Texas at Austin may have found another avenue for cellulosic ethanol production. A newly created microbea strain of cyanobacteria, commonly called blue-green algaeis capable of producing cellulose, sucrose and glucose, all of which have potential for ethanol production.

University of Texas Professors R. Malcolm Brown and David Nobles Jr. created the cyanobacteria by giving them a set of cellulose-making genes from a non-photosynthetic bacterium called Acetobacter xylinum, which is commonly used for producing vinegar. The new cyanobacteria produce a relatively pure, gel-like form of cellulose that can be easily broken down into readily fermentable sugars. They also secrete sucrose and glucose, which are already prominent sources of ethanol, most commonly in the form of sugarcane and corn, respectively.

Brown told EPM that Acetobacter bacterium is the most prolific cellulose producer in the world. Its cells divide every three to four hours, compared with up to once per day for many plants. Scientists are struggling with converting plant-based cellulose into ethanol due to the enzymatic and mechanical costs associated with existing processes. Plant-based cellulose contains crystalline-like lignin and hemicellulose structures that must be degraded with acids or cellulase enzymes.

Brown said his "eureka moment" came when he realized the low molecular weight and noncrystalline form of cellulose produced by the cyanobacteria was well-suited for enzymatic breakdown.

The easily fermentable cellulose and sugars produced by the new cyanobacteria may also be applied to existing technology found at conventional corn-based ethanol facilities. The fermentation process releases carbon dioxide, which in turn can be used to feed the cyanobacteria. The cyanobacteria require a few micronutrients and fixed nitrogen to thrive, as well as sunlight for an energy source. Therefore, the cyanobacteria could be grown in open-pond production facilities on nonagricultural land, or in closed-loop photobioreactors. In fact, both are possible, depending on the strain of cyanobacteria, according to Brown. The open-pond system would allow the cyanobacteria to be grown in briny water and/or areas not typically suited for agricultural production.

Another potential benefit is that cyanobacteria fix nitrogen from the atmosphere, eliminating the need for nitrogen-based fertilizers that are used to raise corn.
Brown, who has devoted much of his personal career to this and similar projects, said he and Nobles continue to collect laboratory data. Two of their patent applications were recently published in the U.S. Patent and Trade Office. However, the next step is scaling up the process in a demonstration facility. Brown cautioned that despite its potential, commercializing the cyanobacteria-to-ethanol process carries plenty of risks. "Scaling up is the hard thing, [along with] figuring out capital costs with new technologies," he said.