Deconstruction of Wheat Straw Lignin by Streptomyces Viridosporus As Insight Into Biological Degradation Mechanism

Lignins are secondary natural organic compositions of plant cell wall besides cellulose and hemicelluse. Structurally lignins are linked with hemicelluloses and cellulose to form recalcitrant complex that resist the environmental stress. Biological systems created by nature over millions of years of evolution can be capitalized for targeted deconstruction of plant cell walls through selective cleavage and structural modification of lignin. Such modification causes changes in cell wall structure for facilitating enzymatic attack to cellulose for sugar release. The study of biological degradation mechanism on lignocellulosic materials could provide the new knowledge to convert plant biomass to biofuel and high value co-products. In this study, we have investigated the effect of wheat straw lignin structural changes by Streptomyces viridosporus on downstream enzymatic hydrolysis. ¹³C CPMAS NMR revealed that the rising of carbonhydrate/lignin ratio accompany with enhanced intensity of methoxyl group in bio-treated wheat straw. The degraded lignin were isolated and analyzed by Fourier Transmission Infrared (FTIR), Pyrolysis Gas Chromatography/Mass Spectrometry (Py-GC/MS) and two dimenssional heteronuclear multiple quantum coherence nuclear magnatic resonance (2D HMQC NMR) to elucidate their structural change. The results indicate that the biological pretreated lignin were associated with critical change and/or modification on their structure implying selective removal of  guaiacyl (G) lignin unit which is more condense than syringyl (S) unit. Moreover, the treated lignin also dramatically reduced the inhibition of cellulose hydrolysis. This information provides new insights for understanding the biological degradation mechanism on lignin for cellulose utilization and exploring a possible route to convert lignin derived co-products.