Comparing the physiochemical parameters of three celluloses reveals new insights into substrate suitability for fungal enzyme production

Abstract

BackgroundThe industrial applications of cellulases are mostly limited by the costs associated with their production. Optimized production pathways are therefore desirable. Based on their enzyme inducing capacity, celluloses are commonly used in fermentation media. However, the influence of their physiochemical characteristics on the production process is not well understood. In this study, we examined how physical, structural and chemical properties of celluloses influence cellulase and hemicellulase production in an industrially-optimized and a non-engineered filamentous fungus: Trichoderma reesei RUT-C30 and Neurospora crassa. The performance was evaluated by quantifying gene induction, protein secretion and enzymatic activities.ResultsAmong the three investigated substrates, the powdered cellulose was found to be the most impure, and the residual hemicellulosic content was efficiently perceived by the fungi. It was furthermore found to be the least crystalline substrate and consequently was the most readily digested cellulose in vitro. In vivo however, only RUT-C30 was able to take full advantage of these factors. When comparing carbon catabolite repressed and de-repressed strains of T. reesei and N. crassa, we found that cre1/cre-1 is at least partially responsible for this observation, but that the different wiring of the molecular signaling networks is also relevant.ConclusionsOur findings indicate that crystallinity and hemicellulose content are major determinants of performance. Moreover, the genetic background between WT and modified strains greatly affects the ability to utilize the cellulosic substrate. By highlighting key factors to consider when choosing the optimal cellulosic product for enzyme production, this study has relevance for the optimization of a critical step in the biotechnological (hemi-) cellulase production process.Electronic supplementary materialThe online version of this article (10.1186/s40694-017-0039-9) contains supplementary material, which is available to authorized users.

Crosstalk of Cellulose and Mannan Perception Pathways Leads to Inhibition of Cellulase Production in Several Filamentous Fungi

“…To further verify this result, we grew WT and Δ gh2-1 strains on mannan-free bacterial cellulose (Fig. S1F) (37) and added low concentrations (0.03% [wt/vol] corresponding to 3% [wt/wt] of the used bacterial cellulose) of commercially available mannans or mannobiose to roughly mimic the mannan content present in softwood (Fig. S1A).…”

“…To directly test which sugar molecules may cause the inhibition, both the WT and Δ gh2-1 mutant strain were grown on Avicel, a mannan-contaminated microcrystalline cellulose (Fig. S1F) (37–39). Afterwards, the heteronuclear single quantum coherence (HSQC) spectra for the anomeric region of the extracted intracellular sugars of both strains were observed by nuclear magnetic resonance (NMR).…”

“…For this, we grew the thermophilic fungus M. thermophila (43) on 1% hardwood-derived cellulose that is naturally poor in mannan (Emcocel [37]) with and without adding 0.05% glucomannan. Glucomannan addition clearly had an inhibitory effect on cellulase activity (Fig.…”

Growing a circular economy with fungal biotechnology: a white paper

“…• Climate change is slowly altering the tree composition, and it can be expected that hardwoods, such as beech and oak, will replace the more drought-and pathogen-sensitive softwoods, such as the currently predominating spruce, in the future. These types of wood differ in their composition, with clear implications for fungal degradation [67,68]. Directed or engineered fungal adaptation and the optimisation of fungal enzyme cocktails will be needed to address these differences in order to optimise utilisation.…”

Multifunctionality of Forests: A White Paper on Challenges and Opportunities in China and Germany

“…Fungi, as natural decomposers of plant biomass or their enzymes, are used more and more for the liberation of sugars from recalcitrant fibers [122]. However, the efficiency of deconstruction varies depending on the composition, including lignin content and cellulose crystallinity as key determinants [123,124]. Moreover, cellulase production in several fungi is inhibited by mannan, being the major hemicellulose in softwoods [125].…”