Over the years, significant progress has been made in reducing cellulose enzyme costs, and very impressive cost reductions have been reported recently (37, 38). Although this progress is a major step toward the economic competitiveness of the overall biochemical process, further cost reductions in cellulose enzymes are still needed. Essentially there are two ways to reduce cellulose enzyme costs, which are typically expressed on a normalized cost of gallon-of-ethanol-produced basis: increase enzyme-specific activity or decrease enzyme production costs. Although both enzyme cost reduction approaches are useful and necessary to accomplish the cellulase enzyme cost reduction goal, increasing the enzyme-specific activity has the added benefit of reducing saccharification time, which also increases the effective utilization of capital. Specific research needed to accomplish these objectives is as follows:

• Understand cellulase interactions at the plant cell wall ultrastructural level to optimize hydrolysis processes, enzyme kinetics, and, ultimately, cellulase use and cost

• Determine how cellulase enzymes move along the cellulose chain and the roles of enzyme substructures

• Conduct targeted substitutions of enzyme components to increase specific activity guided by molecular modeling of cellulase/substrate interactions

• Identify enzyme production processes and logistics to minimize processing and trans­portation costs of enzyme products.