Wood-eating clams fuel energy research

As fuel prices and global temperatures steadily increase, researchers are intensifying their search for renewable energy alternatives. One promising avenue of research (bioconversion) seeks to convert cellulose, a major component of domestic and agricultural wastes, into ethanol, a fuel that can supplement or replace fossil fuels used in cars and trucks. A critical part of this research is the search for new and better cellulases, the enzymes that convert cellulose into sugar which in turn is fermented to ethanol. Researchers at Ocean Genome Legacy are turning to an unlikely source for such enzymes: marine clams that eat wood!

The shipworm, Lyrodus pedicellatus and Bankia setacea, are ideal candidates to study bioconversion of cellulose. Although it looks like a worm, it is actually a worm-like marine clam, closely related to New England’s beloved “steamer clam”, Mya arenaria. Unlike its steamer clam cousin, however, shipworms can live on a diet solely composed of wood! This unusual diet is made possible by bacterial symbionts that live inside cells of a specialized organ within its gills. The bacteria make enzymes that convert cellulose, which is indigestible to most animals, into glucose, a sugar that is easily used by all animals and also, easily fermented to ethanol.

In order to better understand how these bacteria help the shipworm consume wood, we are sequencing their DNA.  One of these symbionts, Teredinibacter turnerae, strain T7901 contains over 100 putative genes involved in complex polysaccharide degradation.  To date we have found evidence of over 800 genes involved in wood degradation in the shipworm symbionts.  With the Joint Genome Institute, we are sequencing the DNA of these special bacteria to find the genes that help the shipworms degrade wood and understand the community’s metabolic capacity.  From the sequence data we hope to discover novel enzymes involved in woody material and cellulose degradation.

The shipworm project demonstrates that marine organisms can contain many unexpected treasures and that such treasures are often found in the most unpredictable species. Who would guess that a clam that eats wood might hold keys to energy production?  This work underscores the fact that we must make every effort to protect, preserve, study and share the valuable, but highly threatened, genomic diversity of the oceans, and that no species may be too insignificant to warrant our interest and concern.

Some of the shipworm research done at OGL is part of a large, international collaboration including U.S. and Filipino scientists called the Philippine Mollusk Symbiont- International Collaborative Biodiversity Group (PMS-ICBG). Link to the project website for more information.

Current Funding and Support

National Science Foundation (NSF) – IOS:
Lignocellulose degradation by shipworms and their bacterial endosymbionts
Award 0920540

National Institutes of Health (NIH), Fogarty International Center, ICBG:
Diverse drug lead compounds from bacterial symbionts of tropical marine mollusks.
Subaward GEBSN0062ST-OGLF