Geiser Elena, Reindl Michèle, Blank Lars M, Feldbrügge Michael, Wierckx Nick, Schipper Kerstin
Institute of Applied Microbiology (iAMB), Aachen Biology and Biotechnology (ABBt), RWTH Aachen University, Aachen, Germany Bioeconomy Science Center (BioSC), Forschungszentrum Jülich, Jülich, Germany.
Heinrich Heine University Düsseldorf, Cluster of Excellence on Plant Sciences, Institute for Microbiology, Düsseldorf, Germany Bioeconomy Science Center (BioSC), Forschungszentrum Jülich, Jülich, Germany.
Appl Environ Microbiol. 2016 Aug 15;82(17):5174-85. doi: 10.1128/AEM.00713-16. Print 2016 Sep 1.
The microbial conversion of plant biomass to valuable products in a consolidated bioprocess could greatly increase the ecologic and economic impact of a biorefinery. Current strategies for hydrolyzing plant material mostly rely on the external application of carbohydrate-active enzymes (CAZymes). Alternatively, production organisms can be engineered to secrete CAZymes to reduce the reliance on externally added enzymes. Plant-pathogenic fungi have a vast repertoire of hydrolytic enzymes to sustain their lifestyle, but expression of the corresponding genes is usually highly regulated and restricted to the pathogenic phase. Here, we present a new strategy in using the biotrophic smut fungus Ustilago maydis for the degradation of plant cell wall components by activating its intrinsic enzyme potential during axenic growth. This fungal model organism is fully equipped with hydrolytic enzymes, and moreover, it naturally produces value-added substances, such as organic acids and biosurfactants. To achieve the deregulated expression of hydrolytic enzymes during the industrially relevant yeast-like growth in axenic culture, the native promoters of the respective genes were replaced by constitutively active synthetic promoters. This led to an enhanced conversion of xylan, cellobiose, and carboxymethyl cellulose to fermentable sugars. Moreover, a combination of strains with activated endoglucanase and β-glucanase increased the release of glucose from carboxymethyl cellulose and regenerated amorphous cellulose, suggesting that mixed cultivations could be a means for degrading more complex substrates in the future. In summary, this proof of principle demonstrates the potential applicability of activating the expression of native CAZymes from phytopathogens in a biocatalytic process.
This study describes basic experiments that aim at the degradation of plant cell wall components by the smut fungus Ustilago maydis As a plant pathogen, this fungus contains a set of lignocellulose-degrading enzymes that may be suited for biomass degradation. However, its hydrolytic enzymes are specifically expressed only during plant infection. Here, we provide the proof of principle that these intrinsic enzymes can be synthetically activated during the industrially relevant yeast-like growth. The fungus is known to naturally synthesize valuable compounds, such as itaconate or glycolipids. Therefore, it could be suited for use in a consolidated bioprocess in which more complex and natural substrates are simultaneously converted to fermentable sugars and to value-added compounds in the future.
在整合生物过程中将植物生物质微生物转化为有价值的产品，可以极大地提高生物精炼厂的生态和经济影响。目前水解植物材料的策略大多依赖于外部应用碳水化合物活性酶（CAZymes）。另外，可以对生产生物进行工程改造以分泌CAZymes，从而减少对外部添加酶的依赖。植物病原真菌拥有大量水解酶以维持其生活方式，但相应基因的表达通常受到高度调控，并且仅限于致病阶段。在这里，我们提出了一种新策略，即利用活体营养型黑粉菌玉米黑粉菌在无菌生长过程中激活其内在酶潜力来降解植物细胞壁成分。这种真菌模式生物完全配备了水解酶，此外，它还天然产生增值物质，如有机酸和生物表面活性剂。为了在无菌培养中与工业相关的酵母样生长过程中实现水解酶的失控表达，将各个基因的天然启动子替换为组成型活性合成启动子。这导致木聚糖、纤维二糖和羧甲基纤维素向可发酵糖的转化率提高。此外，具有激活的内切葡聚糖酶和β-葡聚糖酶的菌株组合增加了羧甲基纤维素和再生无定形纤维素中葡萄糖的释放，这表明混合培养可能是未来降解更复杂底物的一种手段。总之，这一原理证明表明了在生物催化过程中激活植物病原体天然CAZymes表达的潜在适用性。
本研究描述了旨在通过黑粉菌玉米黑粉菌降解植物细胞壁成分的基础实验。作为一种植物病原体，这种真菌含有一组可能适合生物质降解的木质纤维素降解酶。然而，其水解酶仅在植物感染期间特异性表达。在这里，我们提供了原理证明，即在与工业相关的酵母样生长过程中可以合成激活这些内在酶。已知该真菌天然合成有价值的化合物，如衣康酸或糖脂。因此，它可能适用于未来将更复杂的天然底物同时转化为可发酵糖和增值化合物的整合生物过程。
