Straub Christopher T, Bing Ryan G, Wang Jack P, Chiang Vincent L, Adams Michael W W, Kelly Robert M
1Department of Chemical and Biomolecular Engineering, North Carolina State University, EB-1, 911 Partners Way, Raleigh, NC 27695-7905 USA.
2Department of Forestry and Environmental Resources, North Carolina State University, Raleigh, NC 27695 USA.
Biotechnol Biofuels. 2020 Mar 11;13:43. doi: 10.1186/s13068-020-01675-2. eCollection 2020.
Biological conversion of lignocellulosic biomass is significantly hindered by feedstock recalcitrance, which is typically assessed through an enzymatic digestion assay, often preceded by a thermal and/or chemical pretreatment. Here, we assay 17 lines of unpretreated transgenic black cottonwood () utilizing a lignocellulose-degrading, metabolically engineered bacterium, . The poplar lines were assessed by incubation with an engineered strain that solubilized and converted the hexose and pentose carbohydrates to ethanol and acetate. The resulting fermentation titer and biomass solubilization were then utilized as a measure of biomass recalcitrance and compared to data previously reported on the transgenic poplar samples.
Of the 17 transgenic poplar lines examined with , a wide variation in solubilization and fermentation titer was observed. While the wild type poplar control demonstrated relatively high recalcitrance with a total solubilization of only 20% and a fermentation titer of 7.3 mM, the transgenic lines resulted in solubilization ranging from 15 to 79% and fermentation titers from 6.8 to 29.6 mM. Additionally, a strong inverse correlation ( = 0.8) between conversion efficiency and lignin content was observed with lower lignin samples more easily converted and solubilized by .
Feedstock recalcitrance can be significantly reduced with transgenic plants, but finding the correct modification may require a large sample set to identify the most advantageous genetic modifications for the feedstock. Utilizing as a screening assay for recalcitrance, poplar lines with down-regulation of coumarate 3-hydroxylase 3 (C3H3) resulted in the highest degrees of solubilization and conversion by . One such line, with a growth phenotype similar to the wild-type, generated more than three times the fermentation products of the wild-type poplar control, suggesting that excellent digestibility can be achieved without compromising fitness of the tree.
木质纤维素生物质的生物转化受到原料顽固性的显著阻碍，通常通过酶消化试验进行评估，该试验通常在热和/或化学预处理之前进行。在此，我们利用一种木质纤维素降解代谢工程细菌对17株未经预处理的转基因黑杨（）品系进行了检测。通过与一种工程化的菌株孵育来评估杨树品系，该菌株可将己糖和戊糖碳水化合物溶解并转化为乙醇和乙酸盐。然后将所得的发酵滴度和生物质溶解率用作生物质顽固性的衡量指标，并与先前报道的转基因杨树样品的数据进行比较。
在用检测的17个转基因杨树品系中，观察到溶解率和发酵滴度存在很大差异。野生型杨树对照表现出相对较高的顽固性，总溶解率仅为20%，发酵滴度为7.3 mM，而转基因品系的溶解率在15%至79%之间，发酵滴度在6.8至29.6 mM之间。此外，观察到转化效率与木质素含量之间存在很强的负相关（= 0.8），木质素含量较低的样品更容易被转化和溶解。
转基因植物可显著降低原料顽固性，但要找到正确的修饰可能需要大量样本集，以确定对原料最有利的基因修饰。利用作为顽固性的筛选试验，香豆酸3 - 羟化酶3（C3H3）下调的杨树品系在溶解和转化方面表现出最高程度。其中一个生长表型与野生型相似的品系产生的发酵产物是野生型杨树对照的三倍多，这表明在不影响树木适应性的情况下可以实现优异的消化率。
