Monday, April 30, 2012
Napoleon Ballroom C-D, 3rd fl (Sheraton New Orleans)
Conversion of plant biomass into biofuels is a major challenge because of the recalcitrance of the plant material. Caldicellulosiruptor bescii is a strictly anaerobic bacterium that grows up to 90*C on untreated plant biomass such as switchgrass (SG). It also utilizes spent SG, which is the residual material remaining after microbial growth. After three successive cultivations at 78°C on spent biomass, 85% of the SG was solubilized, compared with 17% conversion in the absence of the organism. The relative amounts of and the spectroscopic and physical properties of the cellulose, hemicellulose and lignin in all residual biomass samples were similar to those of the initial SG material. C. bescii is therefore able to solubilize lignin as well as the C5 and C6 sugars. Immunoanalyses of SG using monoclonal antibodies against various cell wall epitopes demonstrated that virtually the same set of glycan epitopes was extracted regardless of how many treatments with C. bescii the biomass has undergone. These data suggest an onion-peeling mechanism for microbial biomass degradation. Microarray analyses of C. bescii revealed that 94 genes were significantly up-regulated during growth on SG, including several that encode extracellular CAZy-type enzymes. Some of their potential substrates correlate with epitopes identified by immunoanalysis. Taken together these results indicate that extremely thermophilic microbes take advantage of both abiotic and biotic contributions for the efficient conversion of untreated plant biomass.
This work was supported by the Bioenergy Science Center of the Office of Biological and Environmental Research, DOE Office of Science.