Dissection of a symbiosis:  Understanding carbon flow through wood-eating fishes.

Dr. J.A. Nelson and Dr. J. E. M. Watts

Cellulose is the most abundant carbon polymer in the biosphere, yet, few degradation pathways have been characterized.  As cellulose is an important compound in the global carbon cycle and a potential source for biomass fuel generation, it is critical that we better understand its degradation in the environment.  One approach for identifying and defining cellulose-degradation pathways includes the discovery and characterization of microorganisms capable of using this carbon polymer in symbiotic relationships with animals.  This project focuses on a group of armored catfish, from the genus Panaque, which include members that are capable of surviving and obtaining energy from a wood diet.  Wood eating, or xylophagy, is a rare vertebrate dietary strategy and often involves a complex intestinal tract microbial community.  A major goal of this project is to identify the microbial communities present in the gastrointestinal (GI) tract of the wood eating Panaque nigrolineatus and examine the mechanisms used for cellulose decomposition and nitrogen fixation that enable this xylophagous lifestyle.  A long-term dietary experiment will be performed, to compare the microbial communities in fish fed an herbaceous diet to those fed a wood-only diet.  To bypass issues with culturability, microbial community DNA will be extracted from the fish GI tract and subjected to a number of molecular approaches.  These molecular methods will allow the description of microbial communities in fish subjected to different dietary regimes and furthermore, compare microbial communities in different regions of the fish GI tract, pinpointing key areas involved in cellulose breakdown.  Nitrogen fixation will also be examined by isolating genes involved in this vital global process, as well as growing nitrogen fixing microorganisms associated with the Panaque GI tract.  Broader scientific implications of this project include enhancing our knowledge of cellulolytic and nitrogen fixation gene diversity and the importance of the microbial communities within xylophagous vertebrates.  Examining microbes involved in xylophagy will result in a better understanding of carbon and nitrogen cycles in the Amazonian ecosystem.  Furthermore, any discovery of novel pathways may have critical implications for biofuel production.