The Diversity of Soil Microbes Holds the Key to Advancing Bioenergy Production

Biomass is generally recognized as the only source of liquid transportation fuels that may replace the world's finite supply of oil. Cellulosic ethanol derived from non-food biomass, such as woodchips, switchgrass, and agricultural waste, is one of the most promising such fuels with major environmental and economic benefits in the form of reduced greenhouse gas emissions and decreased dependence on imported oil. Rural economies also would benefit with higher incomes and employment due to the increased value of agricultural crops and crop residues and through the introduction of new energy crops. Cellulosic ethanol is a viable alternative to current U.S. corn ethanol production. Its positive energy return on investment derives from the fact that cellulosic ethanol production makes use of the whole plant. However, the recalcitrance of cellulosic biomass to breakdown and the lack of appropriate microbial catalysts capable of fermenting the wide range of carbohydrates found in biomass pose significant obstacles to the development of cellulosic ethanol technologies. An approach to overcome these hurdles involves tapping the natural diversity that exists in biomass-decomposing soil microbial communities. For example, a microbial bioprocessing strategy was developed at the University of Massachusetts Amherst, and is being commercialized by SunEthanol, Inc. that employs Clostridium phytofermentans, a novel microbe first isolated from forest soil. This bacterium actively and efficiently decomposes cellulose and produces ethanol as its primary fermentation product. C. phytofermentans possesses exceptional nutritional versatility and is capable of decomposing all fermentable components of biomass, including the hemicellulosic portion. The properties of C. phytofermentans indicate that it is an ideal organism for use in the direct conversion of cellulosic biomass to ethanol, a biomass-processing scheme referred to as "consolidated bioprocessing" because production of the cellulase enzymes, cellulose decomposition, and fermentation are consolidated in a single step, yielding significant economic advantages.