The efficiency of biological systems as an option for pretreating lignocellulosic biomass has to be improved to make the process practical. Fungal treatment with manganese (Mn) addition for improving lignocellulosic biomass fractionation and enzyme accessibility were investigated in this study. The broad-spectrum effect was tested on two different types of feedstocks with three fungal species. Since the physicochemical and structural properties of biomass were the main changes caused by fungal degradation, detailed characterization of biomass structural features was conducted to understand the mechanism of Mn-enhanced biomass saccharification. The glucose yields of fungal-treated poplar and wheat straw increased by 2.97- and 5.71-fold, respectively, after Mn addition. Particularly, over 90% of glucose yield was achieved in Mn-assisted Pleurotus ostreatus-treated wheat straw. A comparison study using pyrolysis gas chromatography mass spectrometry (Py-GC/MS) and two-dimensional 1H–13C heteronuclear single quantum coherence (2D HSQC) nuclear magnetic resonance (NMR) spectroscopy was conducted to elucidate the role of Mn addition on fungal disruption of the cross-linked structure of whole plant cell wall. The increased Cα-oxidized products was consistent with the enhanced cleavage of the major β-O-4 ether linkages in poplar and wheat straw lignin or in the wheat straw lignin–carbohydrate complexes (LCCs), which led to the reduced condensation degree in lignin and decreased lignin content in Mn-assisted fungal-treated biomass. The correlation analysis and principal component analysis (PCA) further demonstrated that Mn addition to fungal treatment enhanced bond cleavage in lignin, especially the β-O-4 ether linkage cleavage played the dominant role in removing the biomass recalcitrance and contributing to the glucose yield enhancement. Meanwhile, enhanced deconstruction of LCCs was important in reducing wheat straw recalcitrance. The findings provided not only mechanistic insights into the Mn-enhanced biomass digestibility by fungus, but also a strategy for improving biological pretreatment efficiency of lignocellulose. The mechanism of enhanced saccharification of biomass by Mn-assisted fungal treatment mainly through Cα-oxidative cleavage of β-O-4 ether linkages further led to the decreased condensation degree in lignin, as a result, biomass recalcitrance was significantly reduced by Mn addition.

中文翻译：

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锰对白腐真菌处理木本草木质纤维素酶解促进作用的综合研究


生物系统作为木质纤维素生物质预处理的一种选择，其效率必须得到提高，才能使该工艺实用。本研究研究了通过添加锰 (Mn) 进行真菌处理以改善木质纤维素生物质分馏和酶可及性。在两种不同类型的原料和三种真菌物种上测试了广谱效应。由于生物质的理化和结构特性是真菌降解引起的主要变化，因此对生物质结构特征进行了详细表征，以了解锰增强生物质糖化的机制。添加Mn后，经过真菌处理的杨树和麦秆的葡萄糖产量分别增加了2.97倍和5.71倍。特别是，在锰辅助平菇处理的麦秆中，葡萄糖产量达到了90%以上。使用热解气相色谱质谱 (Py-GC/MS) 和二维 1H–13C 异核单量子相干 (2D HSQC) 核磁共振 (NMR) 光谱进行比较研究，以阐明添加 Mn 对破坏真菌的作用整个植物细胞壁的交联结构。 Cα-氧化产物的增加与杨树和麦秆木质素或麦秆木质素-碳水化合物复合物（LCC）中主要β-O-4醚键的增强裂解一致，这导致木质素缩合度降低并降低了锰辅助真菌处理的生物质中的木质素含量。 相关分析和主成分分析（PCA）进一步表明，真菌处理中添加Mn增强了木质素中的键断裂，尤其是β-O-4醚键断裂，在消除生物质不顺性和提高葡萄糖产量方面发挥了主导作用。同时，加强对LCCs的解构对于减少麦秆的抗逆性具有重要意义。这些发现不仅提供了对真菌增强锰生物质消化率的机制见解，而且还提供了提高木质纤维素生物预处理效率的策略。 Mn辅助真菌处理增强生物质糖化的机制主要是通过Cα氧化裂解β-O-4醚键，进一步导致木质素缩合度降低，因此，Mn的添加显着降低了生物质的不顺应性。