It Takes "Guts" to Explore the Next Proteomics Frontier
Looking at bacterial communities in termite gut helps reconstruct metabolic pathways
Image from “The Termite Gut: Nature’s Microbial Bioreactor for Digesting Wood and Making Biofuels,” U.S. DOE Genomic Science Program, (accessed June 21, 2010). Enlarge Image
Molecular snapshot of enzymes (illustrated as Enzyme Commission numbers) identified in the termite hindgut microbial community and their main processes. (PFOR EC:1.2.7.-) Enlarge Image
In the quest to find new sources of biofuel, researchers are studying one of the most efficient bioreactors on earth: the termite. The same insect that causes distress to homeowners with its wood-consuming abilities also provides scientists with a fascinating area of study: the symbiotic microbial community that enables the termite to digest wood cellulose.
Researchers at Pacific Northwest National Laboratory analyzed the metaproteome—all proteins—of the bacterial community that lives in the hindgut paunch segment of the wood-feeding "higher" termite (Nasutitermes). Their goal: to define the contribution and sources of enzymes from the community to the insect.
Initially, they hoped this information would lead to identifying new and novel cellulases, which in turn could provide raw materials for the synthesis of ethanol. However, while such insights remain elusive, they still gained biological insights into the necessary associations of this symbiotic system from their analyses, thus advancing understanding of the microbial community function in the termite gut and eventually pointing to important interactions in the degradation of wood products.
Why it's important. This work represents an important advancement of community proteomics efforts that can impact studies of any microbial community. Community proteomics is emerging as the next proteomics frontier—where the precise genome of the organisms being studied is unknown. Microbial communities play important roles across the biosphere from carbon and nutrient cycling in the atmosphere to impacting and protecting human health.
Methods. Using mass spectrometry-based global proteomics strategies available through EMSL, the PNNL team identified 886 proteins, 197 of which are known to be enzymes. Using these enzymes, the researchers reconstructed complete metabolic pathways. These pathways revealed such important functions as carbohydrate transport and metabolism, nitrogen fixation and assimilation, energy production, and amino acid synthesis. Perhaps of greatest significance was determining the high level of redundancy of a protein important to nitrogen fixation and the breakdown of glucose: pyruvate ferredoxin/flavodoxin oxidoreductase (PFOR EC: 1.2.7.-). It has been reported that Nasutitermes lacks measurable pyruvate dehydrogenase activity in its tissues; therefore, bacterial PFOR may be critical to making nitrogen and acetate available to the termite.
"Our observations could not have been developed without reconstructing known bacterial metabolic pathways, and placing these pathways in context to what is currently known about metabolic pathways in the termite host," said Dr. Kristin Burnum, a PNNL biochemist and first author of a manuscript that appears in The ISME Journal.
What's Next. Understanding the symbiotic relationship between the community and the termite is only the first step in the elucidation of cellulose degradation in the system. While this work suggests that the activity associated with these enzymes in the community may play more of a role in the symbiotic relationship between the hindgut microbial community and its termite host than activities related to cellulose degradation, these results create a framework for future studies on all insect-microbial community studies to explore new cellulose-degrading activities.
Acknowledgments. This work was funded by the Genomic Science Program of the U.S. Department of Energy's Office of Biological and Environmental Research (BER) and performed in EMSL, the Environmental Molecular Sciences Laboratory, a DOE national scientific user facility located at PNNL. Researchers at the DOE Joint Genome Institute (JGI) sequenced the termite gut. The research team includes Kristin Burnum, Mary Lipton, Stephen Callister, Carrie Nicora, Sam Purvine, and Dick Smith, all PNNL; and Philip Hugenholtz, Falk Warnecke, and Rudolf Scheffrahn, JGI.
Reference. Burnum KE, SJ Callister, CD Nicora, SO Purvine P Hugenholtz, F Warnecke, RH Scheffrahn, RD Smith, and MS Lipton. 2010. "Proteome Insights into the Symbiotic Relationship between a Captive Colony of Nasustitermes corniger and its Hindgut Microbiome." The ISME Journal, advance online publication July 8, 2010, doi:10.1038/ismej.2010.97.