DEGRADATION OF WHEAT STRAW CELL WALL BY WHITE ROT FUNGI PHANEROCHAETE CHRYSOSPORIUM

Jijiao Zeng

The main aim of this dissertation research was to understand the natural microbial degradation process of lignocellulosic materials in order to develop a new, green and more effective pretreatment technology for bio-fuel production. The biodegradation of wheat straw by white rot fungi Phanerochaete chrysosporium was investigated. The addition of nutrients significantly improved the performance of P.chrysosporium on wheat straw degradation. The proteomic analysis indicated that this fungus produced various pepetides related to cellulose and lignin degradation while grown on the biomass. The structural analysis of lignin further showed that P.chrysosporium preferentially degraded hydroxycinnamtes in order to access cellulose. In details, the effects of carbon resource and metabolic pathway regulating compounds on manganeses peroxidase (MnP) were studied. The results indicated that MnP activity of 4.7 ± 0.31 U mL-1 was obtained using mannose as a carbon source. The enzyme productivity further reached 7.36 ± 0.05 U mL-1 and 8.77 ± 0.23 U mL-1 when the mannose medium was supplemented with cyclic adenosine monophosphate (cAMP) and S-adenosylmethionine (SAM) respectively, revealing highest MnP productivity obtained by optimizing the carbon sources and supplementation with small molecules. In addition, the effects of nutrient additives for improving biological pretreatment of lignocellulosic biomass were studied. The pretreatment of wheat straw supplemented with inorganic salts (salts group) and tween 80 was examined. The extra nutrient significantly improved the ligninase expression leading to improve digestibility of lignocellulosic biomass. Among the solid state fermentation groups, salts group resulted in a substantial degradation of wheat straw within one week, along with the highest lignin loss (25 %) and ~ 250% higher efficiency for the total sugar release through enzymatic hydrolysis. The results were correlated with pyrolysis GC-MS (Py-GC-MS), thermogravimetric (TG) /differential thermogravimetric (DTG) and X-ray diffraction (XRD). Finally, the fungal secretomes and composition, functional groups, and structural changes of the fungal spent wheat straw lignin were determined.Milled wood lignin (MWL) was extracted from biological treated and untreaed wheat straw. Detailed structural analysis through two dimentional heteronuclear multiple quantum coherence nuclear magnetic resonances (2D HMQC NMR) of the pretreated lignin (acetylated) revealed low abundances of the substructures dibenzodioxacin and cinnamyl alcohol. Further analysis of lignin by Fourier transmission infrared (FTIR) and pyrolysis gas chromatography/ mass spectrometry (Py-GC/MS) demonstrated the significant decrease of guaiacyl units. The results support previous findings on the biodegradation of wheat straw as analyzed by 13C cross polarization magic angle spinning (CPMAS). Revealing the characteristic behavior of P. chrysosporium-mediated biomass degradation, the information presented in this paper offers new insight into the understanding of biological lignin degradation of wheat straw by P. chrysosporium.

DEGRADATION OF WHEAT STRAW CELL WALL BY WHITE ROT FUNGI PHANEROCHAETE CHRYSOSPORIUM

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