1. DOE Joint Genome Institute, 2800 Mitchell Drive, Walnut Creek, California 94598, USA
2. Verenium Corporation (formerly Diversa), 4955 Directors Place, San Diego, California 92121, USA
3. IBM Thomas J. Watson Research Center, PO Box 218, Yorktown Heights, New York 10598, USA
4. Oak Ridge National Laboratory, Biosciences Division, Oak Ridge, Tennessee 37831-6026, USA
5. Department of Environmental Science and Engineering,
6. Division of Biology, Mailcode 138-78, California Institute of Technology, Pasadena, California 91125, USA
7. INBio, Instituto Nacional de Biodiversidad, Apdo. Postal 22-3100 Santo Domingo de Heredia, Costa Rica
8. These authors contributed equally to this work.
9. Present addresses: Synthetic Genomics, Inc., 11149 North Torrey Pines Road, Suite 100, La Jolla, California 92037, USA (T.H.R., E.J.M.); Max Planck Institute for Computer Science, Stuhlsatzenhausweg 85, 66123 Saarbrücken, Germany (A.C.M.).

Correspondence to: Jared R. Leadbetter^5,8 Correspondence and requests for materials should be addressed to J.R.L. (Email: jleadbetter@caltech.edu).

From the standpoints of both basic research and biotechnology, there is considerable interest in reaching a clearer understanding of the diversity of biological mechanisms employed during lignocellulose degradation. Globally, termites are an extremely successful group of wood-degrading organisms¹ and are therefore important both for their roles in carbon turnover in the environment and as potential sources of biochemical catalysts for efforts aimed at converting wood into biofuels. Only recently have data supported any direct role for the symbiotic bacteria in the gut of the termite in cellulose and xylan hydrolysis². Here we use a metagenomic analysis of the bacterial community resident in the hindgut paunch of a wood-feeding 'higher' Nasutitermes species (which do not contain cellulose-fermenting protozoa) to show the presence of a large, diverse set of bacterial genes for cellulose and xylan hydrolysis. Many of these genes were expressed in vivo or had cellulase activity in vitro, and further analyses implicate spirochete and fibrobacter species in gut lignocellulose degradation. New insights into other important symbiotic functions including H₂ metabolism, CO₂-reductive acetogenesis and N₂ fixation are also provided by this first system-wide gene analysis of a microbial community specialized towards plant lignocellulose degradation. Our results underscore how complex even a 1-l environment can be.

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