Production of xylanase by Aspergillus niger GIO and Bacillus megaterium through solid-state fermentation

Xylanase breaks xylan down to xylose, which is used in industries such as pulp and paper, food and feed, among others. The utilization of wastes for xylanase production is economical, hence this work aimed at producing xylanase through solid-state fermentation and characterizing the enzyme. Xylanase-producing strains of Bacillus megaterium and Aspergillus niger GIO were inoculated separately in a 5 and 10 day solid fermentation study on maize straw, rice straw, sawdust, corn cob, sugarcane bagasse, conifer litters, alkaline-pretreated maize straw (APM) and combined alkaline and biological-pretreated maize straw, respectively. The best substrate was selected for xylanase production. The crude enzyme was extracted from the fermentation medium and xylanase activity was characterized using parameters such as temperature, cations, pH and surfactants. Among different substrates, the highest xylanase activity of 3.18 U ml^-1 was recorded when A. niger GIO was grown on APM. The xylanase produced by A. niger GIO and B. megaterium had the highest activities (3.67 U ml^-1 and 3.36 U ml^-1) at 40 °C after 30 and 45 min of incubation, respectively. Optimal xylanase activities (4.58 and 3.58 U ml^-1) of A. niger GIO and B. megaterium , respectively, were observed at pH 5.0 and 6.2. All cations used enhanced xylanase activities except magnesium ion. Sodium dodecyl sulfate supported the highest xylanase activity of 6.13 and 6.90 U ml^-1 for A. niger GIO and B. megaterium , respectively. High yields of xylanase were obtained from A. niger GIO and B. megaterium cultivated on APM. The xylanase activities were affected by pH, temperature, surfactants and cations.

Recent progress in key lignocellulosic enzymes: Enzyme discovery, molecular modifications, production, and enzymatic biomass saccharification

Lignocellulose, the most prevalent biomass on earth, can be enzymatically converted into carbohydrates for bioethanol production and other uses. Among lignocellulosic enzymes, endoglucanase, xylanase, and laccase are the key enzymes, owing to their ability to disrupt the main structure of lignocellulose. Recently, new discovery methods have been established to obtain key lignocellulosic enzymes with excellent enzymatic properties. Molecular modification of enzymes to modulate their thermostability, catalytic activity, and substrate specificity has been performed with protein engineering technology. In addition, the enzyme expression has been effectively improved through expression element screening and host modification, as well as fermentation optimization. Immobilization of enzymes, use of surfactants, synergistic degradation, and optimization of reaction conditions have addressed the inefficiency of enzymatic saccharification. In this review, recent advances in key lignocellulosic enzymes are summarized, along with future prospects for the development of super-engineered strains and integrative technologies for enzymatic biomass saccharification.

Characteristics of recombinant xylanase from camel rumen metagenome and its effects on wheat bran hydrolysis

In the present study, we explored the effects of a novel xylanase from camel rumen metagenome (CrXyn) on wheat bran hydrolysis. CrXyn was heterologously expressed in Escherichia coli and showed maximum activity at 40 °C and pH 7.0. Furthermore, CrXyn exhibited preferential hydrolysis of xylan, but no obvious activity toward other substrates, including carboxymethylcellulose and Avicel. Using wheat straw xylan as a substrate, the Km and Vmax values for CrXyn were 5.98 g/L and 179.9 μmol xylose/min/mg protein, respectively. Mn²⁺ was a strong accelerator and significantly enhanced CrXyn activity. However, CrXyn activity was inhibited (~50 %) by 1 mM and 5 mM ethylenediaminetetraacetic acid (EDTA) and completely inactivated by 5 mM Cu²⁺. CrXyn tolerated 5 mM sodium dodecyl sulphate (SDS) and 15 % methanol, ethanol, and dimethyl sulfoxide (DMSO), with >50 % residual activity. CrXyn effectively hydrolyzed wheat bran, with xylobiose and xylotetraose accounting for 79.1 % of total sugars produced. A remarkable synergistic effect was found between CrXyn and protease, leading to an obvious increase in amino acids released from wheat bran compared with the control. CrXyn also enhanced the in vitro hydrolysis of wheat bran. Thus, CrXyn exhibits great potential as a feed additive to improve the utilization of wheat bran in monogastric animal production.

Safe production of Aspergillus terreus xylanase from Ricinus communis: gene identification, molecular docking, characterization, production of xylooligosaccharides, and its biological activities

BACKGROUND

The production of industrial enzymes such as xylanase using sufficient cost-effective substrates from potent microorganisms is considered economically feasible. Studies have reported castor cake (Ricinus communis) as the most potent and inexpensive alternative carbon source for production of xylanase C by using Aspergillus terreus (A. terreus).

RESULTS

A. terreus strain RGS Eg-NRC, a local isolate from agro-wastes, was first identified by sequencing the internal transcribed spacer region of a nuclear DNA encoding gene cluster deposited in GenBank (accession number MW282328). Before optimization of xylanase production, A. terreus produced 20.23 U/g of xylanase after 7 days using castor cake as a substrate in a solid-state fermentation (SSF) system that was employed to achieve ricin detoxification and stimulate xylanase production. Physicochemical parameters for the production of xylanase were optimized by using a one-variable-at-a-time approach and two statistical methods (two-level Plackett-Burman design and central composite design, CCD). The maximum xylanase yield after optimization was increased by 12.1-fold (245 U/g). A 60-70% saturation of ammonium sulfate resulted in partially purified xylanase with a specific activity of 3.9 IU/mg protein. At 60 °C and pH 6, the partially purified xylanase had the highest activity, and the activation energy (Ea) was 23.919 kJmol. Subsequently, antioxidant capacity and cytotoxicity tests in normal Ehrlich ascites carcinoma human cells demonstrated xylooligosaccharides produced by the xylanase degradation of xylan as a potent antioxidant and moderate antitumor agent. Further investigations with sodium dodecyl sulfate polyacrylamide gel electrophoresis then determined the molecular weight of partially purified xylanase C to be 36 kDa. Based on the conserved regions, observations revealed that xylanase C belonged to the glycosyl hydrolase family 10. Next, the xylanase-encoding gene (xynC), which has an open reading frame of 981 bp and encodes a protein with 326 amino acids, was isolated, sequenced, and submitted to the NCBI GenBank database (accession number LC595779.1). Molecular docking analysis finally revealed that Glu156, Glu262, and Lys75 residues were involved in the substrate-binding and protein-ligand interaction site of modeled xylanase, with a binding affinity of -8.7 kcal. mol^-1. CONCLUSION: The high production of safe and efficient xylanase could be achieved using economical materials such as Ricinus communis.