Among the most pressing issues facing society today is the need to transition from dependence on fossil fuels to alternative renewable fuel sources. Alcohol derived from a plant material called cellulose is considered to be one such alternative. Cellulose, a major component of woody and leafy plants, is one of the most abundant biomaterials on earth and constitutes a major potential source of renewable energy. However, to take advantage of this energy, efficient enzyme systems must be identified that can convert cellulose to its component sugars and then to alcohol. Shipworms are wormlike wood boring marine clams that contain such enzyme systems. Shipworms are the only marine animals that are known to grow and reproduce normally with wood as their sole food source. This unusual ability may be due, at least in part, to their association with a consortium of intracellular symbiotic bacteria. These symbionts are thought to provide shipworms with enzymes that aid in wood digestion. The purpose of this research project is to use advanced methods of genomics, proteomics and imaging to 1) uncover the physiological and enzymatic systems that allow shipworms to thrive on this unusual diet, 2) reproduce these enzymes in the laboratory, and 3) evaluate qualities of these enzymes that may be useful for development of commercial cellulosic alcohol production. The research will also help to broaden scientific understanding of beneficial interactions between bacteria and animals. The project will result in the training of one postdoctoral research scientist, as well as several high school and college level interns through the Ocean Genome Legacy's active educational outreach programs.
Cellulose is the major structural component of green plants, including all woody and leafy plant material. This makes cellulose by far the most abundant biological material on earth. Not surprisingly, this material is also a major component of domestic, industrial, and agricultural waste as it is found in paper waste and in crop residues like corn, soy and wheat stalks. As such, there is great potential value in recycling this cellulosic waste to produce renewable fuels (e.g. ethanol) and fine chemicals. However, the lack of enzymes that can cheaply and effectively break down paper and raw plant materials into their soluble components is a major bottleneck for these recycling efforts. In this investigation, we studied cellulose digestion in a group of wood-eating clams called shipworms. Shipworms, sometimes called the termites of the sea, are among the few animals on earth capable of digesting wood. We showed that these animals use enzymes made by beneficial bacteria (symbionts) that live in a specialized organ within their gills that serves as a factory for enzyme production. Using modern techniques of high throughput DNA sequencing (genomics) and protein identification (proteomics), we identified over 700 enzymes encoded in the symbiont genomes that are predicted to degrade cellulose and other plant cell wall materials. We then showed that about 40 of these enzymes are selectively transported to the shipworm gut where they help to digest wood. As a result of this work we have identified and demonstrated the activities of the most abundant symbiotic proteins in the gut and a provisional patent has been filed to protect these enzymes as we continue to explore their qualities and applications. This work has also contributed to the education of over a dozen high school, undergraduate and graduate students and two postdoctoral researchers and components have been incorporated into lesson plans and educational and outreach materials developed by the Center for Coastal Margin Observation & Prediction Geoscience Class for the Hyda tribal school system, Hydaburg, AK.
