High-Tech Microbes Could Bolster Production of Natural Sweetener

Genetically engineered bacteria that eat hemicellulose in corn fiber and other sources could set the stage for a new, biobased method of making xylitol, a mint-flavored sweetener used in chewing gum, toothpaste, mouthwash and other products.

Agricultural Research Service (ARS) chemist Badal Saha and collaborators developed the modified bacteria—patent-pending strains of Escherichia coli—through a cooperative agreement with zuChem, Inc., of Chicago, and the Biotechnology Research and Development Corporation in Peoria, Ill.

Xylitol is produced naturally by many fruits and vegetables, and even to some degree by the human body. It is used as a sugar substitute because it has one-third fewer calories, imparts a cool mint flavor, helps fight cavity-causing bacteria, and can pass through the human gut without involving insulin.

Commercial-scale quantities are derived primarily from birch-wood fibers that have been subjected to a combination of acids, high pressure and temperature, chemical catalysts, and a series of separation and purification steps. But the process is expensive, and the resulting xylitol must be imported, primarily from Finland and China, notes Saha, who works at the ARS National Center for Agricultural Utilization Research in Peoria.

In studies at the center's Fermentation Biotechnology Research Unit, Saha and colleagues used an approach called metabolic pathway engineering to retool the enzyme-making machinery of E. coli bacteria so that they could convert two hemicellulose sugars—xylose and arabinose—into xylitol. At the laboratory scale, the bacteria were kept inside special biofermentors and fed a "broth" of corn fibers or other hemicellulose sources. The xylitol they excreted was later purified from the broth as a white, crystalline powder.

Under the cooperative agreement, Saha is helping zuChem develop a commercial-scale process that could cut xylitol's production costs and open the door to its manufacture in the Unites States from corn and other homegrown crops.

ARS is the U.S. Department of Agriculture's chief scientific research agency.