Lignin depolymerization by fungal secretomes and a microbial sink
Lignin depolymerization by fungal secretomes and a microbial sink
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DOI：
10.1039/c6gc01531j
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发表时间：
2016-01-01
期刊：
影响因子：
9.8
通讯作者：
Beckham, Gregg T.
中科院分区：
文献类型：
--
作者：
Salvachua, Davinia;Katahira, Rui;Beckham, Gregg T.
在自然界中，白腐菌和一些细菌分泌的强大的氧化酶催化木质素解聚，一些微生物能够分解生成的芳香族化合物作为碳源和能源。综上所述，这两个过程为木质素的微生物价化提供了一条潜在的途径。然而，在实现这一概念方面仍然存在许多挑战，包括负责木质素解聚的氧化酶也催化低分子量木质素的聚合。在这里，在玉米秸秆生物精炼厂残留的木质素固体流存在下，对多个担子菌分泌体进行了木质素分解酶活性的筛选，该木质素被称为DMR-EH(脱乙酰化、机械精炼和酶解)木质素。选择了两个含有高水平漆酶和过氧化物酶的真菌分泌体，用于DMR-EH木质素解聚测定。杏鲍菇分泌体具有最高的漆酶活性，在pH值为7的条件下，与相同条件下处理的对照和初始DMR-EH木质素相比，木质素的平均相对分子质量(M-w)分别降低了63%和75%，并随时间的变化用于进一步的解聚分析。当培养3天后观察到再聚合时，一株芳香分解代谢微生物(恶臭假单胞菌KT2440)与真菌分泌体和DMR-EH木质素一起培养。这些实验表明，细菌的存在促进了木质素的解聚，这可能是由于细菌对低分子木质素的分解代谢，这可能部分阻止了木质素的再聚合。此外，还将蛋白质组学应用于杏仁假单胞菌分泌组，以鉴定用于解聚分析的真菌鸡尾酒中存在的酶，其中突出了大量的葡萄糖/甲醇/胆碱(GMC)氧化还原酶和漆酶。总体而言，这项研究表明，木质素分解酶可用于部分解聚固体、高木质素含量的生物精炼流程，并且芳香分解代谢细菌作为“微生物汇”的存在改善了酶促木质素解聚的程度。
In Nature, powerful oxidative enzymes secreted by white rot fungi and some bacteria catalyze lignin depolymerization and some microbes are able to catabolize the resulting aromatic compounds as carbon and energy sources. Taken together, these two processes offer a potential route for microbial valorization of lignin. However, many challenges remain in realizing this concept, including that oxidative enzymes responsible for lignin depolymerization also catalyze polymerization of low molecular weight (LMW) lignin. Here, multiple basidiomycete secretomes were screened for ligninolytic enzyme activities in the presence of a residual lignin solid stream from a corn stover biorefinery, dubbed DMR-EH (Deacetylation, Mechanical Refining, and Enzymatic Hydrolysis) lignin. Two selected fungal secretomes, with high levels of laccases and peroxidases, were utilized for DMR-EH lignin depolymerization assays. The secretome from Pleurotus eryngii, which exhibited the highest laccase activity, reduced the lignin average molecular weight (M-w) by 63% and 75% at pH 7 compared to the Mw of the control treated at the same conditions and the initial DMR-EH lignin, respectively, and was applied in further depolymerization assays as a function of time. As repolymerization was observed after 3 days of incubation, an aromatic-catabolic microbe (Pseudomonas putida KT2440) was incubated with the fungal secretome and DMR-EH lignin. These experiments demonstrated that the presence of the bacterium enhances lignin depolymerization, likely due to bacterial catabolism of LMW lignin, which may partially prevent repolymerization. In addition, proteomics was also applied to the P. eryngii secretome to identify the enzymes present in the fungal cocktail utilized for the depolymerization assays, which highlighted a significant number of glucose/methanol/choline (GMC) oxidoreductases and laccases. Overall, this study demonstrates that ligninolytic enzymes can be used to partially depolymerize a solid, high lignin content biorefinery stream and that the presence of an aromatic-catabolic bacterium as a "microbial sink" improves the extent of enzymatic lignin depolymerization.