Researchers at Los Alamos National Laboratory and Great Lakes Bioenergy Research Center have found a potential key for unlocking the energy potential from non-edible biomass materials such as corn leaves and stalks, or switch grass.
Los Alamos researchers S. Gnanakaran, Giovanni Bellesia, and Paul Langan joined Shishir Chundawat and Bruce Dale of Michigan State University, along with collaborators from the Great Lakes Bioenergy Research Center, on a potential pretreatment method that can make plant cellulose five times more digestible by enzymes that convert it into ethanol, a useful biofuel.
Biomass is a desirable renewable energy source because fermentable sugars within the cellulose network of plant cells can be extracted with enzymes and then converted into ethanol. Yet a key difficulty in creating biofuels from plant matter is that the cellulose tends to orient itself into a sheet-like network of highly ordered, densely packed molecules. These sheets stack upon themselves and bond together tightly due to interactions between hydrogen atoms. This stacking and bonding arrangement prevents enzymes from directly attacking most of the individual cellulose molecules and isolating the sugar chains within them.
Currently, ethanol can only be extracted in usable quantities if the biomass is pretreated with costly, potentially toxic chemicals in an energy-intensive process. The research team has discovered a way to develop potentially cost-effective pretreatment methods that could make biomass an economically viable contender in the biofuels arena.
Using recent experimental data provided by their collaborators, Gnanakaran and his Los Alamos colleagues used state-of-the-art computational methods and molecular modeling to examine how cellulose changes structurally into an intermediate form that can be enzymatically attacked when pretreated with ammonia.
“Our modeling showed, and the experimental evidence confirmed, that the pretreatment reduced the strength of hydrogen bonds in the cellulosic network,” said Gnanakaran. This, in turn, significantly reduced the tightness of the cellulose network and left it more vulnerable to conversion into sugar by fungi-derived cellulolytic enzymes.
The end result is a potentially less costly and less energy intensive pretreatment regimen that makes the cellulose five times easier to attack.
“This work helps address some of the potential cost barriers related to using biomass for biofuels,” Gnanakaran said.