NASA researchers develop cellulosic technology

By Erin Voegele
Posted August 20, 2009, at 2:33 p.m. CST

Scientists at NASA Ames Research Center in California are working to develop an enzymatic hydrolysis process that could be used to convert waste biomass material into food and fuel, using what is called bionanotechnology. The research team is assembling enzyme structures with multiple functions, modeled after a natural enzyme complex that breaks down inedible plant material into usable sugars.

Ames Research Scientist Chad Paavola said that NASA's interest in cellulosic technologies stems from the potential for long-term missions in space. "For long-term missions involving either long transit times or for long-term missions on Mars, the moon or other extraterrestrial environments, it becomes worthwhile to cultivate plants for food," he said. "Depending on what crop you are cultivating, a varying amount of the plant will be edible, and a significant fraction of the plant is not edible … We believe that cellulosic technology could be used to convert that [cellulosic material] back into fermentable sugars, which could then be used to create food, fuels or chemicals for the mission."

It is difficult to access the sugar contained in cellulose because it is arranged in polymers that are hard to break down. In nature, enzyme complexes, known as cellulosomes, are among the most effective ways to convert cellulose into usable sugars.

"Cellulosomes are natural structures that have been observed in a lot of anaerobic bacteria that break down cellulosic material," Paavola said. "They are naturally assembled complexes of enzymes that occur on the surface of these anaerobic bacteria that feed on cellulosic biomass." The research conducted by Paavola and his team focuses on taking those enzymes from this very complicated natural complex, and trying to understand how they interact with each other in an engineered complex. "We can then learn what the principles are at work in this very complicated complex, and use that understanding of the basic principles to create very efficient complexes of enzymes for breaking down very specific sources of cellulosic biomass," Paavola continued.

In other words, to better understand how cellulosomes work and mimic their function, the researchers have built enzyme complexes modeled after natural cellulosomes using protein parts from different microbes. By placing the microbes' DNA sequences for these component parts into a common laboratory bacterium, the scientists were able to create a protein structure to act as a scaffold to attach enzymes with different functions, allowing the enzymes to work together more efficiently. This allows the enzymes to produce significantly more sugar from cellulose than the same enzymes are able to produce when they are not attached to the scaffold.

"What we did was take a self-assembling double ring structure and engineer that to accommodate up to 18 enzymes," Paavola said. "We've engineering it to accommodate 18 interchangeable sites, so this is something that is a mimic of the kind of organization that happens in the natural celluosome."

While the Ames researchers are working primarily to develop technologies applicable for use in space, this research may also be applicable for fuel and chemical projects on Earth. "One of the things that NASA really encourages us to do is to find partners to work with, and to do our best to transfer this technology to commercial operations," Paavola said. "We have patented this technology, but the purpose of the patent is really to provide the kind of intellectual property protection that a company needs … to actually take it to market. As researchers, we really want to see this technology get into the market and benefit people."

According to Paavola, the unique constraints of developing a technology for use in space may also be beneficial for small-scale biomass conversion facilities. "The space application has some unique constraints," he said. "We have to really minimize the kind of consumable chemicals that are used in the process, and we have to really minimize the hazardous chemicals used in the process, and we also have to minimize energy required for the process and the weight of the equipment."

"Those constraints might allow us to create systems that are uniquely adapted for smaller-scale, more distributed kinds of cellulosic biomass processing, which could be something that benefits rural economies," Paavola said.