Chemical Pretreatment-Independent Saccharifications of Xylan and Cellulose of Rice Straw by Bacterial Weak Lignin-Binding Xylanolytic and Cellulolytic Enzymes

Abstract

Complete utilization of carbohydrate fractions is one of the prerequisites for obtaining economically favorable lignocellulosic biomass conversion. This study shows that xylan in untreated rice straw was saccharified to xylose in one step without chemical pretreatment, yielding 58.2% of the theoretically maximum value by B-6 PcAxy43A, a weak lignin-binding trifunctional xylanolytic enzyme, endoxylanase/β-xylosidase/arabinoxylan arabinofuranohydrolase. Moreover, xylose yield from untreated rice straw was enhanced to 78.9% by adding endoxylanases PcXyn10C and PcXyn11A from the same bacterium, resulting in improvement of cellulose accessibility to cellulolytic enzyme. After autoclaving the xylanolytic enzyme-treated rice straw, it was subjected to subsequent saccharification by a combination of the endoglucanase CtCel9R and β-glucosidase TbCglT, yielding 88.5% of the maximum glucose yield, which was higher than the glucose yield obtained from ammonia-treated rice straw saccharification (59.6%). Moreover, this work presents a new environment-friendly xylanolytic enzyme pretreatment for beneficial hydrolysis of xylan in various agricultural residues, such as rice straw and corn hull. It not only could improve cellulose saccharification but also produced xylose, leading to an improvement of the overall fermentable sugar yields without chemical pretreatment. Ongoing research is focused on improving "green" pretreatment technologies in order to reduce energy demands and environmental impact and to develop an economically feasible biorefinery. The present study showed that PcAxy43A, a weak lignin-binding trifunctional xylanolytic enzyme, endoxylanase/β-xylosidase/arabinoxylan arabinofuranohydrolase from B-6, was capable of conversion of xylan in lignocellulosic biomass such as untreated rice straw to xylose in one step without chemical pretreatment. It demonstrates efficient synergism with endoxylanases PcXyn10C and PcXyn11A to depolymerize xylan in untreated rice straw and enhanced the xylose production and improved cellulose hydrolysis. Therefore, it can be considered an enzymatic pretreatment. Furthermore, the studies here show that glucose yield released from steam- and xylanolytic enzyme-treated rice straw by the combination of CtCel9R and TbCglT was higher than the glucose yield obtained from ammonia-treated rice straw saccharification. This work presents a novel environment-friendly xylanolytic enzyme pretreatment not only as a green pretreatment but also as an economically feasible biorefinery method.

Relationship between sugarcane culm and leaf biomass composition and saccharification efficiency

“…While lignin is the most universally recognized cause of recalcitrance, the importance of other biomass components has been increasingly reported [32–36]. For instance, several studies have shown that removing xylan increases the porosity of the biomass and results in higher conversion of cellulose during saccharification [37–41]. Hydroxycinnamic acids, ferulic acid (FA) and p -coumaric acid (CA) [23, 42, 43] and lignin composition (S/G ratio) [31, 44, 45] are other factors that have been implicated in influencing recalcitrance because they affect the strength and abundance of the cross-links between lignin and xylan [10, 46].…”

Clostridium manihotivorumsp. nov., a novel mesophilic anaerobic bacterium that produces cassava pulp-degrading enzymes

“…Moreover, the cassava pulp degrading enzyme of C. manihotivorum CT4 T may be active and low binding to lignin in cassava pulp. Teeravivattanakit et al (Teeravivattanakit et al, 2017) reported that because the bacterial multifunctional enzyme PcAxy43A from Paenibacillus curdlanolyticus B-6 was a weak lignin-binding enzyme, this enzyme was capable of converting xylan contained in agricultural residues to xylose in one step without chemical pretreatment to remove lignin. Therefore, a weak lignin-binding enzyme is a potential factor for obtaining enzymes suitable for the hydrolysis of lignocellulosic materials (Berlin et al, 2006).…”

Bioconversion of Untreated Corn Hull into L-Malic Acid by Trifunctional Xylanolytic Enzyme from Paenibacillus curdlanolyticus B-6 and Acetobacter tropicalis H-1

“…PcAxy43A produced mainly xylose, but it did not produce arabinose, in which arabinose is one component of arabinoxylan of corn hull. This may be because the arabinose in arabinoxylan of corn hull is linked to lignin and/or cellulose [7]. Teeravivattanakit et al [13] also found that the trifunctional xylanolytic enzyme, PxAxy43A, has the ability to hydrolyze xylan in rice straw to xylose in one step.…”