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 (Populus trichocarpa) utilizing a lignocellulose-degrading, metabolically engineered bacterium, Caldicellulosiruptor bescii. The poplar lines were assessed by incubation with an engineered C. bescii 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 C. bescii, 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 (R2 = 0.8) between conversion efficiency and lignin content was observed with lower lignin samples more easily converted and solubilized by C. bescii. 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 C. bescii 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 C. bescii. 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.

中文翻译：

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使用木质纤维素降解细菌 Caldicellulosiruptor bescii 评估野生型和转基因杨树的顽抗性和转化

木质纤维素生物质的生物转化受到原料顽抗性的显着阻碍，原料顽抗性通常通过酶消化测定进行评估，通常先进行热和/或化学预处理。在这里，我们利用木质纤维素降解、代谢工程细菌 Caldicellulosiruptor bescii 检测了 17 个未经预处理的转基因黑杨 (Populus trichocarpa) 品系。通过与工程改造的贝斯库氏菌菌株一起孵育来评估杨树品系，该菌株溶解己糖和戊糖碳水化合物并将其转化为乙醇和乙酸盐。然后利用所得的发酵滴度和生物量溶解作为生物量顽抗性的量度，并与先前报道的转基因杨树样品的数据进行比较。在用 C. bescii 检测的 17 个转基因杨树品系中，观察到溶解度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不顺应性，总溶解度仅为 20%，发酵滴度为 7.3 mM，而转基因品系则导致溶解度为 15% 至 79%，发酵滴度为 6.8 至 29.6 mM。此外，观察到转化效率和木质素含量之间存在很强的负相关性（R2 = 0.8），木质素含量较低的样品更容易被 C. bescii 转化和溶解。转基因植物可以显着减少原料的不顺从，但找到正确的修饰可能需要大量样本集来识别对原料最有利的基因修饰。利用贝氏梭菌作为顽抗性的筛选测定，香豆酸 3-羟化酶 3 (C3H3) 下调的杨树品系导致贝氏梭菌的最高程度的溶解和转化。其中一个品系的生长表型与野生型相似，产生的发酵产物是野生型杨树对照的三倍多，这表明可以在不影响树的适应性的情况下实现优异的消化率。