Abstract
BackgroundThe efficiency of cellulolytic enzymes is important in industrial biorefinery processes, including biofuel production. Chemical methods, such as alkali pretreatment, have been extensively studied and demonstrated as effective for breaking recalcitrant lignocellulose structures. However, these methods have a detrimental effect on the environment. In addition, utilization of these chemicals requires alkali- or acid-resistant equipment and a neutralization step.ResultsHere, a radical generator based on non-thermal atmospheric pressure plasma technology was developed and tested to determine whether oxygen-radical pretreatment enhances cellulolytic activity. Our results showed that the viscosity of carboxymethyl cellulose (CMC) solutions was reduced in a time-dependent manner by oxygen-radical pretreatment using the radical generator. Compared with non-pretreated CMC, oxygen-radical pretreatment of CMC significantly increased the production of reducing sugars in culture supernatant containing various cellulases from Phanerochaete chrysosporium. The production of reducing sugar from oxygen-radical-pretreated CMC by commercially available cellobiohydrolases I and II was 1.7- and 1.6-fold higher, respectively, than those from non-pretreated and oxygen-gas-pretreated CMC. Moreover, the amount of reducing sugar from oxygen-radical-pretreated wheat straw was 1.8-fold larger than those from non-pretreated and oxygen-gas-pretreated wheat straw.ConclusionsOxygen-radical pretreatment of CMC and wheat straw enhanced the degradation of cellulose by reducing- and non-reducing-end cellulases in the supernatant of a culture of the white-rot fungus P. chrysosporium. These findings indicated that oxygen-radical pretreatment of plant biomass offers great promise for improvements in lignocellulose-deconstruction processes.
Highlights
The efficiency of cellulolytic enzymes is important in industrial biorefinery processes, including biofuel production
Proteins identified in the microcrystalline cellulose (MCC) medium were categorized into three classes: (1) enzymes involved in cellulose degradation, (2) enzymes involved in xylan degradation, and (3) other proteins (Table 1)
The major cellulolytic enzymes were CBHI belonging to the GH7 family (Fig. 2b; spots 5, 6, and 11) and CBHII belonging to the GH6 family (Fig. 2b; spot 12)
Summary
The efficiency of cellulolytic enzymes is important in industrial biorefinery processes, including biofuel production. Chemical methods, such as alkali pretreatment, have been extensively studied and demonstrated as effective for breaking recalcitrant lignocellulose structures. White-rot basidiomycetes are responsible for the complete degradation of lignocelluloses and produce several cellulolytic enzymes, including endo-glucanases (EC 3.2.1.4), cellobiohydrolases (CBHs; EC 3.2.1.91 and EC 3.2.1.176), and β-glucosidases (EC 3.2.1.74) [4, 5]. Endo-glucanases randomly hydrolyze the internal β-1,4linkage of the glucose backbone, whereas CBHs release cellobiose from both the reducing and non-reducing ends of cellulose polymers [5,6,7,8]. Beta-glucosidase alleviates the inhibitory effect of cellobiose on endo-glucanase activity by hydrolyzing the substrate to glucose [7]. LPMOs combined with cellulolytic enzymes offer an opportunity to improve lignocellulose-deconstruction processes [13, 14]
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