Zhu Daochen, Si Haibing, Zhang Peipei, Geng Alei, Zhang Weimin, Yang Bin, Qian Wei-Jun, Gabriel Murillo, Sun Jianzhong
1Biofuels Institute, School of the Environment and Safety Engineering, Jiangsu University, Zhenjiang, Jiangsu China.
2State Key Laboratory of Applied Microbiology Southern China, Guangdong Provincial Key Laboratory of Microbial Culture Collection and Application, Guangdong Open Laboratory of Applied Microbiology, Guangdong Institute of Microbiology, Guangzhou, China.
Biotechnol Biofuels. 2018 Dec 27;11:338. doi: 10.1186/s13068-018-1341-3. eCollection 2018.
The efficient depolymerization and utilization of lignin are one of the most important goals for the renewable use of lignocelluloses. The degradation and complete mineralization of lignin by bacteria represent a key step for carbon recycling in land ecosystems as well. However, many aspects of this process remain unclear, for example, the complex network of metabolic pathways involved in the degradation of lignin and the catabolic pathway of intermediate aromatic metabolites. To address these subjects, we characterized the deconstruction and mineralization of lignin with milled wood lignin (MWL, the most representative molecule of lignin in its native state) and alkali lignin (AL), and elucidated metabolic pathways of their intermediate metabolites by a bacterium named SP-35.
The degradation rate of MWL reached 30.9%, and its particle size range was decreased from 6 to 30 µm to 2-4 µm-when cultured with C. serinivorans SP35 over 7 days. FTIR analysis showed that the C-C and C-O-C bonds between the phenyl propane structures of lignin were oxidized and cleaved and the side chain structure was modified. More than twenty intermediate aromatic metabolites were identified in the MWL and AL cultures based on GC-MS analysis. Through genome sequencing and annotation, and from GC-MS analysis, 93 genes encoding 33 enzymes and 5 regulatory factors that may be involved in lignin degradation were identified and more than nine metabolic pathways of lignin and its intermediates were predicted. Of particular note is that the metabolic pathway to form the powerful antioxidant 3,4-dihydroxyphenylglycol is described for the first time in bacteria.
Elucidation of the β-aryl ether cleavage pathway in the strain SP-35 indicates that the β-aryl ether catabolic system is not only present in the family of Sphingomonadaceae, but also other species of bacteria kingdom. These newly elucidated catabolic pathways of lignin in strain SP-35 and the enzymes responsible for them provide exciting biotechnological opportunities for lignin valorization in future.
木质素的高效解聚与利用是木质纤维素可再生利用的重要目标之一。细菌对木质素的降解和完全矿化也是陆地生态系统中碳循环的关键步骤。然而，这一过程的许多方面仍不清楚，例如，参与木质素降解的复杂代谢途径网络以及中间芳香族代谢物的分解代谢途径。为了解决这些问题，我们用磨木木素（MWL，木质素在天然状态下最具代表性的分子）和碱木质素（AL）对木质素的解构和矿化进行了表征，并通过一种名为SP - 35的细菌阐明了其中间代谢物的代谢途径。
与丝氨酸食纤维菌SP35一起培养7天后，MWL的降解率达到30.9%，其粒径范围从6至30微米减小到2至4微米。傅里叶变换红外光谱（FTIR）分析表明，木质素苯丙烷结构之间的C - C键和C - O - C键被氧化并断裂，侧链结构发生了改变。基于气相色谱 - 质谱（GC - MS）分析，在MWL和AL培养物中鉴定出二十多种中间芳香族代谢物。通过基因组测序和注释，并结合GC - MS分析，鉴定出93个编码33种酶和5种可能参与木质素降解的调控因子的基因，并预测了木质素及其中间体的九条以上代谢途径。特别值得注意的是，首次在细菌中描述了形成强大抗氧化剂3,4 - 二羟基苯乙二醇的代谢途径。
菌株SP - 35中β - 芳基醚裂解途径的阐明表明，β - 芳基醚分解代谢系统不仅存在于鞘脂单胞菌科，也存在于细菌界的其他物种中。菌株SP - 35中新阐明的这些木质素分解代谢途径及其相关酶为未来木质素的增值提供了令人兴奋的生物技术机会。
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