Combined Enzyme Systems Degrade Cellulose More Efficiently

Researchers at the National Renewable Energy Laboratory (US Department of Energy) and Weizmann Institute (Israel) have found a dramatic increase in the enzymatic breakdown of plant biomass with a combination of two microbial enzyme systems.

Enzymes produced by some microbes naturally degrade the cellulose in plant biomass, so that the sugars release from this breakdown can be fermented into ethanol. However, plants possess natural barriers that make it harder for the enzymes to target the cellulose in their cell walls, and overcoming this barrier increases the cost of producing biofuels. Researchers have been exploring various pre-treatment methods and combinations of enzymes that can hasten the breakdown of cellulose.

The present study, published in the journal Energy & Environmental Science, looked into the biomass-degrading mechanisms of two prominent enzyme systems. One is known as the free enzyme system, produced by a fungus, which is a cocktail of enzymes with one or several catalytic domains per enzyme. The other is termed cellulosomes, multi-enzyme complexes produced by a bacterium with multiple catalytic units per complex. When the two enzyme systems were combined, deconstruction of the cell walls occurred more efficiently.

Evidence from transmission electron microscopy revealed the different mechanisms of cellulose breakdown by both enzyme systems. Insight into these mechanisms may lead to new strategies for enzyme engineering for more optimal enzyme formulations in cellulosic biofuel production.