Purdue research investigates digestive enzymes in termites
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 from the guts of termites that may be better at getting around the barriers that inhibit cellulosic biofuel production derived from woody biomass.
The results, published in the online version of 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.
Scharf explained to Biorefining Magazine that the project has taken on different shapes from its beginnings 10 years ago from initially sequencing genes obtained from the termite gut to now characterizing those genes and finding out how the symbionts work and interact with the enzymes that break down wood.
“In doing that, we found all these digestive enzymes,” Scharf said. “For a lot of years we didn’t have a good way to quantify or measure their contributions to digestion until now.”
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 said he 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 other, he said, 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 said 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 explained. “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.”
In the future, Scharf admits one day his work will go so far as to discover 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 said.