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Issue 7, 2013
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Carbohydrate and lignin are simultaneously solubilized from unpretreated switchgrass by microbial action at high temperature

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Abstract

The three major components of plant biomass, cellulose, hemicellulose and lignin, are highly recalcitrant and deconstruction involves thermal and chemical pretreatment. Microbial conversion is a possible solution, but few anaerobic microbes utilize both cellulose and hemicellulose and none are known to solubilize lignin. Herein, we show that the majority (85%) of insoluble switchgrass biomass that had not been previously chemically treated was degraded at 78 °C by the anaerobic bacterium Caldicellulosiruptor bescii. Remarkably, the glucose/xylose/lignin ratio and physical and spectroscopic properties of the remaining insoluble switchgrass were not significantly different than those of the untreated plant material. C. bescii is therefore able to solubilize lignin as well as the carbohydrates and, accordingly, lignin-derived aromatics were detected in the culture supernatants. From mass balance analyses, the carbohydrate in the solubilized switchgrass quantitatively accounted for the growth of C. bescii and its fermentation products, indicating that the lignin was not assimilated by the microorganism. Immunoanalyses of biomass and transcriptional analyses of C. bescii showed that the microorganism when grown on switchgrass produces enzymes directed at key plant cell wall moieties such as pectin, xyloglucans and rhamnogalacturonans, and that these and as yet uncharacterized enzymes enable the degradation of cellulose, hemicellulose and lignin at comparable rates. This unexpected finding of simultaneous lignin and carbohydrate solubilization bodes well for industrial conversion by extremely thermophilic microbes of biomass that requires limited or, more importantly, no chemical pretreatment.

Graphical abstract: Carbohydrate and lignin are simultaneously solubilized from unpretreated switchgrass by microbial action at high temperature

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Publication details

The article was received on 18 Mar 2013, accepted on 14 May 2013 and first published on 17 May 2013


Article type: Paper
DOI: 10.1039/C3EE40932E
Citation: Energy Environ. Sci., 2013,6, 2186-2195
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    Carbohydrate and lignin are simultaneously solubilized from unpretreated switchgrass by microbial action at high temperature

    I. Kataeva, M. B. Foston, S. Yang, S. Pattathil, A. K. Biswal, F. L. Poole II, M. Basen, A. M. Rhaesa, T. P. Thomas, P. Azadi, V. Olman, T. D. Saffold, K. E. Mohler, D. L. Lewis, C. Doeppke, Y. Zeng, T. J. Tschaplinski, W. S. York, M. Davis, D. Mohnen, Y. Xu, A. J. Ragauskas, S. Ding, R. M. Kelly, M. G. Hahn and M. W. W. Adams, Energy Environ. Sci., 2013, 6, 2186
    DOI: 10.1039/C3EE40932E

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