Dissecting cellobiose metabolic pathway and its application in biorefinery through consolidated bioprocessing in Myceliophthora thermophila
Dissecting cellobiose metabolic pathway and its application in biorefinery through consolidated bioprocessing in Myceliophthora thermophila
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通过整合生物加工剖析嗜热毁丝霉的纤维二糖代谢途径及其在生物精炼中的应用
DOI：
10.1186/s40694-019-0083-8
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发表时间：
2019-11-13
影响因子：
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通讯作者：
Tian, Chaoguang
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作者：
Li, Jingen;Gu, Shuying;Tian, Chaoguang
木质纤维素生物质长期以来一直被认为是工业应用的潜在可持续资源。将植物生物质转化为可发酵糖的相关成本是生产具有成本竞争力的生物化学品的一个重大障碍。综合生物处理（CBP）被认为是实现生物质燃料和商品化学品成本效益生产的潜在突破。在纤维素降解过程中，纤维素二糖（纤维素酶活性的主要最终产物）在纤维素降解生物体内通过水解和磷酸化途径进行分解代谢。然而，纤维素分解真菌的两种细胞内纤维素糖代谢途径的细节仍未被揭示。结果以产苹果酸的工程真菌JG207为实验材料，证实了嗜热丝霉菌胞内纤维二糖代谢均通过β-葡萄糖苷酶水解途径和磷酸化酶磷酸化途径进行，且苹果酸的产率受益于磷酸化裂解的能量优势。两种纤维素糖分解代谢途径的调控存在明显差异。嗜热ajg207生长在纤维素糖或Avicel上。在纤维素糖条件下，mtcppin菌株JG207的破坏导致苹果酸产量下降，而细胞内所有三个β-葡萄糖苷酶基因的表达水平显著上调，以挽救Avicel条件下磷酸化途径的损伤。当水解途径通量降低时，我们发现由bgl1编码的β-葡萄糖苷酶是水解途径中的优势酶，bgl1的缺失导致蛋白质分泌显著增加，但苹果酸盐的产生减少。综合调控纤维素二糖利用途径和通过过表达纤维素二糖转运体增强纤维素二糖摄取，最终菌株JG412Δbgl2Δbgl3produced从纤维素二糖和Avicel中分别获得101.2 g/L和77.4 g/L苹果酸，产量分别为1.35 g/g和1.03 g/g，比起始菌株JG207有显著提高。结论本文首次对纤维素分解真菌细胞内纤维素糖分解代谢进行了详细的研究。thermophila。这些结果提供了可以应用于工业真菌从纤维素和纤维素中生产生物燃料和生化物质的见解。
BackgroundLignocellulosic biomass has long been recognized as a potential sustainable source for industrial applications. The costs associated with conversion of plant biomass to fermentable sugar represent a significant barrier to the production of cost-competitive biochemicals. Consolidated bioprocessing (CBP) is considered a potential breakthrough for achieving cost-efficient production of biomass-based fuels and commodity chemicals. During the degradation of cellulose, cellobiose (major end-product of cellulase activity) is catabolized by hydrolytic and phosphorolytic pathways in cellulolytic organisms. However, the details of the two intracellular cellobiose metabolism pathways in cellulolytic fungi remain to be uncovered.ResultsUsing the engineered malic acid production fungal strain JG207, we demonstrated that the hydrolytic pathway by β-glucosidase and the phosphorolytic pathway by phosphorylase are both used for intracellular cellobiose metabolism inMyceliophthora thermophila, and the yield of malic acid can benefit from the energy advantages of phosphorolytic cleavage. There were obvious differences in regulation of the two cellobiose catabolic pathways depending on whetherM. thermophilaJG207 was grown on cellobiose or Avicel. Disruption ofMtcppin strain JG207 led to decreased production of malic acid under cellobiose conditions, while expression levels of all three intracellular β-glucosidase genes were significantly up-regulated to rescue the impairment of the phosphorolytic pathway under Avicel conditions. When the flux of the hydrolytic pathway was reduced, we found that β-glucosidase encoded bybgl1was the dominant enzyme in the hydrolytic pathway and deletion ofbgl1resulted in significant enhancement of protein secretion but reduction of malate production. Combining comprehensive manipulation of both cellobiose utilization pathways and enhancement of cellobiose uptake by overexpression of a cellobiose transporter, the final strain JG412Δbgl2Δbgl3produced up to 101.2 g/L and 77.4 g/L malic acid from cellobiose and Avicel, respectively, which corresponded to respective yields of 1.35 g/g and 1.03 g/g, representing significant improvement over the starting strain JG207.ConclusionsThis is the first report of detailed investigation of intracellular cellobiose catabolism in cellulolytic fungusM. thermophila. These results provide insights that can be applied to industrial fungi for production of biofuels and biochemicals from cellobiose and cellulose.