Molecular cloning and characterization of a GH11 endoxylanase from Chaetomium globosum, and its use in enzymatic pretreatment of biomass

Abstract

An endo-1,4-β-xylanase gene, xylcg, was cloned from Chaetomium globosum and successfully expressed in Escherichia coli. The complete gene of 675 bp was amplified, cloned into the pET 28(a) vector, and expressed. The optimal conditions for the highest activity of the purified recombinant XylCg were observed at a temperature of 40 °C and pH of 5.5. Using oat-spelt xylan, the determined K m, V max, and k cat/K m values were 0.243 mg ml⁻¹, 4,530 U mg⁻¹ protein, and 7,640 ml s⁻¹ mg⁻¹, respectively. A homology model and sequence analysis of XylCg, along with the biochemical properties, confirmed that XylCg belongs to the GH11 family. Rice straw pretreated with XylCg showed 30 % higher conversion yield than the rice straw pretreated with a commercial xylanase. Although xylanases have been characterized from fungal and bacterial sources, C. globosum XylCg is distinguished from other xylanases by its high catalytic efficiency and its effectiveness in the pretreatment of lignocellulosic biomass.

Enhanced Saccharification of Steam-Pretreated Rice Straw by Commercial Cellulases Supplemented with Xylanase

“…Hemicelluloses may add to the recalcitrance of cellulose and enzymes such as xylanase are common in industrial enzyme cocktails for lignocellulose processing [31]. Rice straw pretreated with a GH11 endoxylanase from Chaetomium globosum showed a decrease in hemicellulose content from 25.8 to 11.4% and an increased saccharification rate [9]. This was due to the hydrolysis of hemicelluloses, thereby exposing a more accessible surface area of cellulose to cellulase.…”

“…Therefore, supplementation of enzyme cocktails with xylanases can alleviate the problem of inhibition of cellulase enzyme action caused by xylan oligosaccharides. Xylanase supplementation in combination with other pretreatments and cellulase improves sugar yields [8,9]. The reactivity of component enzymes differs with the enzymatic activity and biomass, and for higher saccharification ability, cellulases need high hemicellulase activity as well as high β-glucosidase activity [10].…”

Xylanase production from a new strain of Aspergillus terreus S9 and its application for saccharification of rice straw using combinatorial approach

“…CFR 303 xylanase showed more prominent saccharification of wheat straw than rice straw [16]. Xylanase from Chaetomium globosum exhibited better performance for saccharification of rice straw than the commercial xylanase [6]. A pilot level dilute acid pretreatment of rice straw, followed by enzymatic saccharification at high solid loadings resulted in high sugar recovery [9].…”

“…While pretreatment with dilute sulfuric acid causes the swelling of biomass and decrease the complexity/polymerization, and substantially enhances the enzymatic hydrolysis [29]. Xylanase from Chaetomium globosum exhibited better performance for saccharification of rice straw than the commercial xylanase [6]. CFR 303 xylanase showed more prominent saccharification of wheat straw than rice straw [16].…”

“…Xylan constitutes one of the major hemicellulosic component of LB, and consists primarily of a backbone of b-1,4-linked-Dxylopyranosyl residues and side chains with varying substituent groups [4,5]. Being an heteropolysaccharide xylan requires several enzymes for its complete breakdown but endo b-(1,4)-xylanase or simply xylanase (EC 3.2.1.8), is the main enzyme which cleaves the internal b-(1,4)-linked Dxylosyl glycosidic bonds in heteroxylan [6,7]. Xylanases may have application potential for several biotechnological processes such as pulp and paper industries for biobleaching, nutrition-rich animal feed production, bioconversion of LB into simple sugars that can be fermented to produce bioethanol/butanol (biofuel), xylitol, and a variety of other platform chemicals/materials of commercial importance [3,8,9].…”