pH Optimum study of Trichoderma reesei Cel7A at different temperatures

Christine Dilling-Hansen, Sofie Block Schultz, Mille Sejberg Batz, Emilie Nellemose Christensen, Matilde Lee Horsbøll Petersen & Natacha Marie Skotte Hansen

Student thesis: Subject Module Project


The production of bioethanol from lignocellulosic material is a promising field of research as a sustainable energy source to replace fossil fuels. The current challenge is that the production is extensive and expensive, which has to be optimized in order for it to be competitive as an energy source. One way of doing so is by optimizing the important production step where cellulose, a component of lignocellulosic material, is enzymatically hydrolyzed. A wide range of cellulases is used in this process, one of the most common being the cellobiohydrolase Cel7A that is derived from the fungus Trichoderma reesei (TrCel7A). The scientific literature has multiple examples of the use of cellulose analogue substrates, such as the soluble substrate para-Nitrophenyl β-ᴅ-Lactopyranoside (pNPL), as a determinant for the optimal conditions for cellulases as TrCel7A. The aim of this study was to investigate the pH optimum of this enzyme at different temperatures. This was done by experiments involving two very different substrates; the artificial cellulose analogue pNPL and the insoluble microcrystalline cellulose Avicel. With pNPL as a substrate, our experiment indicated that TrCel7A has a narrow pH optimum around 4-5, independent of the temperature, and that the specific rate of the enzyme is highest at 60C. With Avicel as a substrate, the enzyme is pH independent at pH 2-7 at the temperatures 20-50C which is inconsistent with the theory. Furthermore, the enzyme shows a broader pH range at 60C in the Avicel experiment compared to pNPL. When comparing the results of each experiment, it suggests that TrCel7A has a higher specific rate with pNPL as a substrate but is more pH tolerant with Avicel as a substrate. This study thus indicates that the soluble substrate is not sufficient for determination of the conditions for cellulases as TrCel7A, because the activity of the enzyme is highly dependent on the type of substrate.

EducationsMolecular Biology, (Bachelor/Graduate Programme) Bachelor
Publication date15 Dec 2017
Number of pages32
SupervisorsNanna Sandager Røjel