Holwerda Evert K, Worthen Robert S, Kothari Ninad, Lasky Ronald C, Davison Brian H, Fu Chunxiang, Wang Zeng-Yu, Dixon Richard A, Biswal Ajaya K, Mohnen Debra, Nelson Richard S, Baxter Holly L, Mazarei Mitra, Stewart C Neal, Muchero Wellington, Tuskan Gerald A, Cai Charles M, Gjersing Erica E, Davis Mark F, Himmel Michael E, Wyman Charles E, Gilna Paul, Lynd Lee R
1Thayer School of Engineering, Dartmouth College, 14 Engineering drive, Hanover, NH 03755 USA.
2BioEnergy Science Center, Oak Ridge National Laboratory, Oak Ridge, TN 37831 USA.
Biotechnol Biofuels. 2019 Jan 17;12:15. doi: 10.1186/s13068-019-1353-7. eCollection 2019.
The recalcitrance of cellulosic biomass is widely recognized as a key barrier to cost-effective biological processing to fuels and chemicals, but the relative impacts of physical, chemical and genetic interventions to improve biomass processing singly and in combination have yet to be evaluated systematically. Solubilization of plant cell walls can be enhanced by non-biological augmentation including physical cotreatment and thermochemical pretreatment, the choice of biocatalyst, the choice of plant feedstock, genetic engineering of plants, and choosing feedstocks that are less recalcitrant natural variants. A two-tiered combinatoric investigation of lignocellulosic biomass deconstruction was undertaken with three biocatalysts (, Novozymes Cellic Ctec2 and Htec2), three transgenic switchgrass plant lines (COMT, MYB4, GAUT4) and their respective nontransgenic controls, two natural variants, and augmentation of biological attack using either mechanical cotreatment or cosolvent-enhanced lignocellulosic fractionation (CELF) pretreatment.
In the absence of augmentation and under the conditions tested, increased total carbohydrate solubilization (TCS) was observed for 8 of the 9 combinations of switchgrass modifications and biocatalysts tested, and statistically significant for five of the combinations. Our results indicate that recalcitrance is not a trait determined by the feedstock only, but instead is coequally determined by the choice of biocatalyst. TCS with was significantly higher than with the other two biocatalysts. Both CELF pretreatment and cotreatment via continuous ball milling enabled TCS in excess of 90%.
Based on our results as well as literature studies, it appears that some form of non-biological augmentation will likely be necessary for the foreseeable future to achieve high TCS for most cellulosic feedstocks. However, our results show that this need not necessarily involve thermochemical processing, and need not necessarily occur prior to biological conversion. Under the conditions tested, the relative magnitude of TCS increase was augmentation > biocatalyst choice > plant choice > plant modification > plant natural variants. In the presence of augmentation, plant modification, plant natural variation, and plant choice exhibited a small, statistically non-significant impact on TCS.
纤维素生物质的顽固性被广泛认为是实现经济高效地生物转化为燃料和化学品的关键障碍，但物理、化学和基因干预单独及联合作用对改善生物质加工的相对影响尚未得到系统评估。植物细胞壁的溶解可通过非生物强化来增强，包括物理共处理和热化学预处理、生物催化剂的选择、植物原料的选择、植物基因工程以及选择顽固性较低的天然变异体作为原料。我们对木质纤维素生物质解构进行了两层组合研究，采用了三种生物催化剂（诺维信公司的纤维素酶Ctec2和Htec2）、三种转基因柳枝稷品系（COMT、MYB4、GAUT4）及其各自的非转基因对照、两种天然变异体，并使用机械共处理或助溶剂强化木质纤维素分级分离（CELF）预处理来增强生物攻击。
在未进行强化且在所测试的条件下，在所测试的9种柳枝稷修饰与生物催化剂组合中，有8种组合的总碳水化合物溶解量（TCS）增加，其中5种组合具有统计学显著性。我们的结果表明，顽固性并非仅由原料决定，而是同样由生物催化剂的选择决定。使用[具体生物催化剂名称未给出]时的TCS显著高于使用其他两种生物催化剂时的TCS。CELF预处理和连续球磨共处理均能使TCS超过90%。
基于我们的研究结果以及文献研究，在可预见的未来，对于大多数纤维素原料而言，似乎某种形式的非生物强化对于实现高TCS可能是必要的。然而，我们的结果表明，这不一定涉及热化学处理，也不一定在生物转化之前进行。在所测试的条件下，TCS增加的相对幅度为强化＞生物催化剂选择＞植物选择＞植物修饰＞植物天然变异体。在存在强化的情况下，植物修饰、植物天然变异和植物选择对TCS的影响较小，且无统计学显著性。
