Symbiont Solutions

Purdue research investigates digestive enzymes
By Bryan Sims | August 15, 2011

Delving into termite guts to find the best cellulases or lignocellulases to efficiently convert cellulose and hemicelluloses, even lignin, into advanced biofuels isn’t a new concept within the biorefining community, but researchers at Purdue University say they have discovered a cocktail of enzymes in termite guts that may be better at getting around the barriers that inhibit cellulosic biofuel production derived from woody biomass.

The results, published online in the journal Public Library of Science One, are the first to measure the sugar output from enzymes created by the termites themselves and the output from symbionts, which are protozoa that reside in termite guts and aid in digestion of wood, according to Mike Scharf, O. Wayne Rollins/Orkin Chair in Molecular Physiology and Urban Entomology and lead on the research.

To find the best enzymes, Scharf and his research partners separated the termite guts, testing portions that did and did not contain symbionts on sawdust to measure the sugars created. Once the enzymes were identified, Scharf worked with Chesapeake Perl, a protein production company based in Maryland, to create synthetic versions. The genes responsible for creating the enzymes were inserted into a virus and fed to caterpillars, which produced large amounts of the enzymes.

Scharf and his team identified three synthetic enzymes that are able to function on different parts of the biomass. Two enzymes are responsible for the release of C5 (pentose) and C6 (glucose) sugars. The third is able to break down lignin, the rigid exterior found in plant cell walls. Scharf’s team determined about one-third of the activity came from the host and two-thirds came from the symbiont enzymes.

Before considering any type of scale-up effort, Scharf says he wants to find the best symbionts that work best with the cellulases to more effectively remove the lignin. “Cellulases can degrade cellulosic and hemicellulosic sugars, including lignin, but nobody has a handle exactly how the termites do it,” Scharf explains. “You have to break that lignin somehow to get the sugars away so that you can depolymerize them. We’re trying now to find the symbiont cellulases that we can combine with host ones we already have, and lignases, to really boost that sugar output.”

Scharf hopes that one day his work will lead to the discovery of a lignase enzyme that could work at ambient temperatures to replace heat pretreatment. “That would be kind of our dream, but more work needs to be done before we get that far,” he says. 

—Bryan Sims, associate editor, Biorefining Magazine