Clues To Biofuel Production In A Gribble’s Gut?

Courtesy of Dr Simon Cragg and Graham Malyon, University of Portsmouth

Monday, March 15th, 2010--

As scientists search for more efficient ways to convert woody biomass, such as woodchips and corn stalks, into liquid fuel, one group of researchers is looking for clues in an unusual place: inside the gut of the gribble.

This marine crustacean is a notorious wood-eater. It’s the size of a small ant and pale white, with black button eyes and an appetite for piers and fishing boats. But unlike other organisms that eat woody material, including termites, bark beetles and giant pandas, gribble (Limnoriidae sp.) don’t rely on bacteria living in their gut to digest the plants for them. Instead, a gribble manufactures its own set of enzymes to do the job, according to a report published in the journal Proceedings of the National Academy of Sciences (PNAS).

Woody plants are full of energy-rich compounds, primarily cellulose, but the structure of cellulose makes it difficult to digest. “It’s physically robust stuff,” said Simon McQueen-Mason, a plant biologist at University of York in the U.K. and an author of the PNAS report. Breaking these compounds down into simple sugars, which can sustain an organism or be fermented and turned into fuel for cars, McQueen-Mason explained, requires specialized enzymes.

The majority of organisms known to manufacture these wood-destroying enzymes are bacteria and fungi. Commercial biotechnology companies, such as Novozymes and Genencor in Denmark, are already using some of these fungi- and bacteria-derived enzymes to make biofuel on an industrial scale. But the process is “very inefficient,” said McQueen-Mason. “You need an awful lot of enzymes to process a small amount of plant material.”

So as McQueen-Mason considered where to look for better enzymes, he thought of gribble. Before he was a plant biologist, he was a professional fisherman in southern England, where gribble, he remembered, “were quite a pest.” He called up colleagues at University of Portsmouth who study gribble and learned that they have no gut microbes.

“I thought, ‘My God! That’s so unusual,” McQueen-Mason said, “because I don’t know of any other animal with a sterile digestive tract.” Gribble, he realized, must make their own wood-digesting enzymes.

McQueen-Mason and his colleagues examined the DNA of one species of gribble (Limnoria quadripunctata). The researchers looked at genes that are expressed only in its gut—more than 400,000 total—and found that about a quarter of them coded for enzymes that break down cellulose and similarly tough compounds.

The researchers are just beginning to compare these enzymes to those made by bacteria and fungi and determine how useful they may be for fuel production. If some prove promising, McQueen-Mason said, the next step would be to insert the gribble genes into simpler organisms, such fungi or bacteria, which could churn out gribble enzymes in large quantities.