Fermentation of pentose sugars to ethanol and other neutral products by microorganisms

The current and projected shortage of petroleum and natural gas has led to renewed interest in processes for the microbial conversion of renewable biomass resources to liquid and gaseous fuels. Pentose sugars represent a significant fraction of the total fermentable carbohydrate content of biomass. A number of biochemical pathways are known for the conversion of pentose to ethanol and other neutral products. Beside ethanol, potential neutral fermentation products include 2,3-butanediol, acetone, isopropanol, butanol and hydrogen. Other products include carbon dioxide and organic acids. Specific ethanol-producing fermentations are reviewed, and future directions for research and development are suggested.