Tuesday, May 3, 2011
Conversion of plant biomass into biofuels is a great challenge because the plant material is highly recalcitrant to microorganisms and their enzymes. Caldicellulosiruptor bescii DSM 6725 is a strictly anaerobic bacterium and is the most thermophilic cellulose-degrading organism known (Tmax 90oC). It degrades untreated plant biomass including plants with high lignin content like switchgrass and grows efficiently on hot water-washed, one- and two-times spent switchgrass (where the spent material is that remaining after cell growth). After three cultivations, total amount of switchgrass solubilized after 18 hr at 78°C was 17%, compared to 85% in the presence of C. bescii. After such treatments, the ratio glucose:xylose:lignin was not significantly changed from that of the original biomass. Similarly, the properties of cellulose, hemicellulose and lignin in both treated and untreated biomass were similar. Glycome profiling using monoclonal antibodies raised against 150 plant biomass epitopes (but excluding cellulose and lignin) indicated that hot water-washed switchgrass become less rigid and less recalcitrant. The data imply that thermal and microbial factors work in a concert to solubilize switchgrass, and that both treatments have a similar mechanism which we term the “onion peeling model”.