Effect of cellulase family and structure on modification of wood fibres at high consistency

Abstract

Enzymatic modification of bleached softwood kraft fibres for improved fibre reactivity was studied at high (20% w/w) and low (1% w/w) dry matter content. The role of enzyme family and structure in fibre modification was assessed using endoglucanases from three structurally different glycoside hydrolase (GH) families (5, 7 and 45) with and without a carbohydrate binding module (CBM). Based on the amount of dissolved sugars, enzyme action at high consistency was about sixfold higher compared to a fibre treatment at low consistency. The GH45 endoglucanase was found to be most specific in acting on pulp cellulose whereas the family 5 and 7 endoglucanases had activity also on pulp hemicelluloses. The GH45 endoglucanase was found to be most efficient in reducing molecular weight and viscosity of the pulp. In addition, treatment with the GH45 endoglucanase resulted in the highest micropore volume in fibres and thus an increase in cellulose accessibility. The increased accessibility could be seen as decreased dissolution time in cupriethylenediamine using recently developed analytical techniques: viscometric analysis and microscopic video analysis. At high consistency, CBM was not promoting enzyme action, although CBMs are known to be beneficial at low dry matter conditions.

Carbohydrate Binding Modules: Diversity of Domain Architecture in Amylases and Cellulases From Filamentous Microorganisms

“…Only in the GH6 of Aspergillus, the CBM1 is positioned at the N-terminus ( Figure 3A). Similar domain structures are also present in other fungi such as Trichoderma (Rahikainen et al, 2019). In a few special cases multiple CBM1 domains are present in a single protein.…”

Engineering Robust Cellulases for Tailored Lignocellulosic Degradation Cocktails

“…This synergy can be expressed as synergy degree (SD), which is the ratio between the mixture activity and the sum of the individual cellulase activities [27,28]. The synergy can be explained by a model where endo-β-1,4-glucanases hydrolyze the interior of the cellulose polymer, generating new reducing ends for the action of the cellobiohydrolase (Figure 2) [29]. Although, this might be an oversimplification of cellulase synergy because there are other factors that influence cellulase synergy [27].…”

High consistency mechano-enzymatic pretreatment for kraft fibres: effect of treatment consistency on fibre properties

“…The smallest endoglucanases that have been applied in fibre modification are ca. 3 9 5 nm in diameter (Rahikainen et al 2019). A recent study by Imai et al (2019) showed with a fluorescent labelled cellulase mix that complete enzyme penetration to a never dried softwood kraft fibre takes 4-25 h (Imai et al 2019).…”

“…However, recent studies show that combined mechanical and enzymatic treatments at high consistency act synergistically resulting in a more pronounced effect than if the mechanical and enzymatic treatments follow each other (Grönqvist et al 2015;Wang et al 2015). At high consistency the low water content causes fibre-fibre friction which disrupts the fibre structure and enhances enzyme accessibility to the fibre walls (Rahikainen et al 2019). High dry matter content has also a positive effect on how enzymes find, recognise and adsorb onto cellulose surfaces (Várnai et al 2013;Wang et al 2015).…”