Identifying the key organisms, pathways and locations of lignocellulosic biomass transformation and hydrogen production in wood-feeding Passalid beetles
EMSL Project ID
48434
Abstract
Passalid beetles, such as Odontotaenius disjunctus, are subsocial insects that process large amounts of woody biomass by feeding on triturated wood. These beetles have co-evolved with their digestive tract microorganisms, enriching their metabolic capabilities by providing digestive enzymes that degrade complex plant polysaccharides and lignin in addition to fixing atmospheric nitrogen, enabling their subsistence on a low-nutrient diet. Through the study of this co-evolved system we seek to determine how these processes are organized in space and time in the beetle's digestive tract, and ultimately aspire to reconstruct microbial assemblages of reduced complexity in an artificial system. In our ongoing research, we are integrating microarray-based stable isotope probing (ChipSIP) and isotopic imaging (NanoSIMS), with measurement of micron-scale physiological gradients, metagenomics and functional metagenomics to determine where specific process may occur and by whom and through which pathways. We have shown that cellulose and hemi-cellulose (xylose) are degraded during transit through the beetle gut and that lignin undergoes side-chain oxidation. When analyzed at the micrometer scale, what appear to be bulk anaerobic conditions are in fact steep radial oxygen gradients that vary in extent by gut region -- suggesting that oxidative reactions such as lignin side-chain oxidation can occur in close proximity to anaerobic processes necessary for H2 production (i.e. fermentation). Preliminary metagenomic and proteomic data analyses have shown that stratification of genetic potential and protein expression occurs in different regions of the beetle gut. While our previous analyses have provided valuable insights into the composition of the microbial community in the Passalid gut and the extent of plant polymer degradation as woody material passes through (cellulose > xylose > lignin) -- significant questions persist (who does what, where, by what mechanism, in what order?). With this proposal we are requesting proteomics including Protein Stable-Isotope Probing (Pro-SIP), in addition to metabolomics to test hypotheses regarding the key organisms and the spatial localization of processes related to plant polymer decomposition and subsequent hydrogen fermentation processes. The use of Pro-SIP will allow us to quantify isotopic enrichment in detected peptides after incubation with 13C or 15N labeled substrates, and the high mass accuracy of instruments like the Thermo LTQ-Orbitrap Velos at EMSL will allow detection of near-background levels of isotopic enrichment in individual populations even when relatively short incubation times and environmentally relevant substrate concentrations are used. Samples for EMSL analyses will be collected following series of controlled lab feeding experiments where we systematically vary the isotopically labeled components of an artificial diet which mimics the Passalids' natural substrates.Combined with our physiological, metagenomic and functional metagenomic information, the protein expression, stable-isotope incorporation and metabolite analyses gained in this EMSL project will allow us to add significant detail to our empirical and conceptual model of this complex natural system and will provide new insights on the importance of spatial organization in plant polymer decomposition.
Project Details
Project type
Large-Scale EMSL Research
Start Date
2014-10-01
End Date
2016-09-30
Status
Closed
Released Data Link
Team
Principal Investigator
Co-Investigator(s)
Team Members