Antonov Elena, Wirth Steffen, Gerlach Tim, Schlembach Ivan, Rosenbaum Miriam A, Regestein Lars, Büchs Jochen
AVT‑Biochemical Engineering, RWTH Aachen University, Worringerweg 1, 52074, Aachen, Germany.
Institute of Applied Microbiology, RWTH Aachen University, Worringerweg 1, 52074, Aachen, Germany.
Microb Cell Fact. 2016 Sep 29;15(1):164. doi: 10.1186/s12934-016-0567-7.
Pretreated lignocellulosic biomass is considered as a suitable feedstock for the sustainable production of chemicals. However, the recalcitrant nature of cellulose often results in very cost-intensive overall production processes. A promising concept to reduce the costs is consolidated bioprocessing, which integrates in a single step cellulase production, cellulose hydrolysis, and fermentative conversion of produced sugars into a valuable product. This approach, however, requires assessing the digestibility of the applied celluloses and, thus, the released sugar amount during the fermentation. Since the released sugars are completely taken up by Trichoderma reesei Rut-C30 and the sugar consumption is stoichiometrically coupled to oxygen uptake, the respiration activity was measured to evaluate the digestibility of cellulose.
The method was successfully tested on commercial cellulosic substrates identifying a correlation between the respiration activity and the crystallinity of the substrate. Pulse experiments with cellulose and cellulases suggested that the respiration activity of T. reesei on cellulose can be divided into two distinct phases, one limited by enzyme activity and one by cellulose-binding-sites. The impact of known (cellobiose, sophorose, urea, tween 80, peptone) and new (miscanthus steepwater) compounds enhancing cellulase production was evaluated. Furthermore, the influence of two different pretreatment methods, the OrganoCat and OrganoSolv process, on the digestibility of beech wood saw dust was tested.
The introduced method allows an online evaluation of cellulose digestibility in complex and non-complex cultivation media. As the measurements are performed under fermentation conditions, it is a valuable tool to test different types of cellulose for consolidated bioprocessing applications. Furthermore, the method can be applied to identify new compounds, which influence cellulase production.
预处理的木质纤维素生物质被认为是可持续生产化学品的合适原料。然而，纤维素的顽固性质常常导致整个生产过程成本极高。一种有前景的降低成本的概念是整合生物加工，即将纤维素酶生产、纤维素水解以及将产生的糖发酵转化为有价值产品这三个步骤整合在一步中。然而，这种方法需要评估所用纤维素的消化率，进而评估发酵过程中释放的糖量。由于释放的糖被里氏木霉Rut-C30完全吸收，且糖的消耗与氧气吸收在化学计量上相关联，因此通过测量呼吸活性来评估纤维素的消化率。
该方法在商业纤维素底物上成功进行了测试，确定了呼吸活性与底物结晶度之间的相关性。用纤维素和纤维素酶进行的脉冲实验表明，里氏木霉在纤维素上的呼吸活性可分为两个不同阶段，一个受酶活性限制，另一个受纤维素结合位点限制。评估了已知（纤维二糖、槐糖、尿素、吐温80、蛋白胨）和新的（芒草浸出液）促进纤维素酶产生的化合物的影响。此外，还测试了两种不同预处理方法（有机催化法和有机溶剂法）对山毛榉木屑消化率的影响。
所介绍的方法能够在线评估复杂和非复杂培养基中纤维素的消化率。由于测量是在发酵条件下进行的，它是测试用于整合生物加工应用的不同类型纤维素的有价值工具。此外，该方法可用于鉴定影响纤维素酶产生的新化合物。
