背景:在其处理过程中从木质纤维素生物质中释放的抑制剂代表了阻碍其在化学品的生物技术生产中的大量利用的主要瓶颈之一。这项研究表明,抑制剂的负面影响可以通过适当的喂养策略来减轻。两者,使用贝氏梭菌NRRLB-598作为生产菌株,在丙酮-丁醇-乙醇(ABE)发酵中测试了未脱毒的木质纤维素水解产物和补充有相应抑制剂的复合培养基。
结果:首先,研究发现,不同生长阶段,贝依林克对抑制剂的敏感性不同,在早期产酸阶段最重要,在晚期产酸和早期溶剂发生时不太明显。因此,测试了具有三种补料方案的补料分批方案的毒性水解产物(在分批模式下没有观察到生长)。当在接近代谢开关处开始饲喂其他有毒的水解产物时,可获得最佳结果。导致稳定和高ABE生产。完全利用葡萄糖,和高达88%的木糖,已获得。碱性小麦秸秆水解物中存在的最丰富的抑制剂是阿魏酸和香豆酸;在培养的早期阶段以及在饲喂期间,两种酚酸都被梭菌的固有代谢活性有效地解毒。从而防止其积累。最后,使用补充了两种抑制剂的TYA培养基验证了最佳补料策略,导致丁醇滴度相对于其中在接种前添加抑制剂的对照分批培养增加500%。
结论:正确定时的顺序喂食可有效防止酸崩溃,并能够利用其他有毒底物。这项研究明确表明,适当的生物技术过程控制策略可以完全消除木质纤维素衍生抑制剂的负面影响。
BACKGROUND: Inhibitors that are released from lignocellulose biomass during its treatment represent one of the major bottlenecks hindering its massive utilization in the biotechnological production of chemicals. This study demonstrates that negative effect of inhibitors can be mitigated by proper feeding strategy. Both, crude undetoxified lignocellulose hydrolysate and complex medium supplemented with corresponding inhibitors were tested in acetone-butanol-ethanol (ABE) fermentation using Clostridium beijerinckii NRRL B-598 as the producer strain.
RESULTS: First, it was found that the sensitivity of C. beijerinckii to inhibitors varied with different growth stages, being the most significant during the early acidogenic phase and less pronounced during late acidogenesis and early solventogenesis. Thus, a fed-batch regime with three feeding schemes was tested for toxic hydrolysate (no growth in batch mode was observed). The best results were obtained when the feeding of an otherwise toxic hydrolysate was initiated close to the metabolic switch, resulting in stable and high ABE production. Complete utilization of glucose, and up to 88% of xylose, were obtained. The most abundant inhibitors present in the alkaline wheat straw hydrolysate were ferulic and coumaric acids; both phenolic acids were efficiently detoxified by the intrinsic metabolic activity of clostridia during the early stages of cultivation as well as during the feeding period, thus preventing their accumulation. Finally, the best feeding strategy was verified using a TYA culture medium supplemented with both inhibitors, resulting in 500% increase in butanol titer over control batch cultivation in which inhibitors were added prior to inoculation.
CONCLUSIONS: Properly timed sequential feeding effectively prevented acid-crash and enabled utilization of otherwise toxic substrate. This study unequivocally demonstrates that an appropriate biotechnological process control strategy can fully eliminate the negative effects of lignocellulose-derived inhibitors.