Yoav Shahar, Barak Yoav, Shamshoum Melina, Borovok Ilya, Lamed Raphael, Dassa Bareket, Hadar Yitzhak, Morag Ely, Bayer Edward A
Department of Plant Pathology and Microbiology, Robert H. Smith Faculty of Agriculture, Food and Environment, The Advanced School for Environmental Studies, The Hebrew University of Jerusalem, 76100 Rehovot, Israel.
Designer Energy Ltd, 2 Bergman Street, Rehovot, Israel.
Biotechnol Biofuels. 2017 Sep 18;10:222. doi: 10.1186/s13068-017-0909-7. eCollection 2017.
Bioethanol production processes involve enzymatic hydrolysis of pretreated lignocellulosic biomass into fermentable sugars. Due to the relatively high cost of enzyme production, the development of potent and cost-effective cellulolytic cocktails is critical for increasing the cost-effectiveness of bioethanol production. In this context, the multi-protein cellulolytic complex of () the cellulosome, was studied here. is known to assemble cellulosomes of various subunit (enzyme) compositions, in response to the available carbon source. In the current study, different carbon sources were used, and their influence on both cellulosomal composition and the resultant activity was investigated.
Glucose, cellobiose, microcrystalline cellulose, alkaline-pretreated switchgrass, alkaline-pretreated corn stover, and dilute acid-pretreated corn stover were used as sole carbon sources in the growth media of strain DSM 1313. The purified cellulosomes were compared for their activity on selected cellulosic substrates. Interestingly, cellulosomes derived from cells grown on lignocellulosic biomass showed no advantage in hydrolyzing the original carbon source used for their production. Instead, microcrystalline cellulose- and glucose-derived cellulosomes were equal or superior in their capacity to deconstruct lignocellulosic biomass. Mass spectrometry analysis revealed differential composition of catalytic and structural subunits (scaffoldins) in the different cellulosome samples. The most abundant catalytic subunits in all cellulosome types include Cel48S, Cel9K, Cel9Q, Cel9R, and Cel5G. Microcrystalline cellulose- and glucose-derived cellulosome samples showed higher endoglucanase-to-exoglucanase ratios and higher catalytic subunit-per-scaffoldin ratios compared to lignocellulose-derived cellulosome types.
The results reported here highlight the finding that cellulosomes derived from cells grown on glucose and microcrystalline cellulose are more efficient in their action on cellulosic substrates than other cellulosome preparations. These results should be considered in the future development of -based cellulolytic cocktails, designer cellulosomes, or engineering of improved strains for deconstruction of lignocellulosic biomass.
生物乙醇生产过程涉及将预处理的木质纤维素生物质酶水解为可发酵糖。由于酶生产成本相对较高，开发高效且具成本效益的纤维素分解酶混合物对于提高生物乙醇生产的成本效益至关重要。在此背景下，本文研究了（）纤维小体这种多蛋白纤维素分解复合体。已知其会根据可用碳源组装具有不同亚基（酶）组成的纤维小体。在当前研究中，使用了不同的碳源，并研究了它们对纤维小体组成和所得活性的影响。
葡萄糖、纤维二糖、微晶纤维素、碱预处理柳枝稷、碱预处理玉米秸秆和稀酸预处理玉米秸秆被用作菌株DSM 1313生长培养基中的唯一碳源。对纯化的纤维小体在选定纤维素底物上的活性进行了比较。有趣的是，源自以木质纤维素生物质为生长碳源的细胞的纤维小体在水解用于其生产的原始碳源方面并无优势。相反，源自微晶纤维素和葡萄糖的纤维小体在解构木质纤维素生物质的能力上相当或更优。质谱分析揭示了不同纤维小体样品中催化亚基和结构亚基（支架蛋白）的组成差异。所有纤维小体类型中最丰富的催化亚基包括Cel48S、Cel9K、Cel9Q、Cel9R和Cel5G。与源自木质纤维素的纤维小体类型相比，源自微晶纤维素和葡萄糖的纤维小体样品显示出更高的内切葡聚糖酶与外切葡聚糖酶比率以及更高的催化亚基与支架蛋白比率。
本文报道的结果突出了这一发现，即源自以葡萄糖和微晶纤维素为生长碳源的细胞的纤维小体在对纤维素底物的作用上比其他纤维小体制剂更高效。在未来基于（）的纤维素分解酶混合物、定制纤维小体或用于解构木质纤维素生物质的改良菌株工程开发中应考虑这些结果。
