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ABSTRACT

The study aims to explore potential xylanase-producing indigenous fungi isolated from soil and vegetable wastes containing plant degraded matter, reporting multilocus phylogenetic analysis and xylanase enzyme activity from selective strains. Four potential xylanolytic fungi were identified through distinct primary and secondary screening of 294 isolates obtained from the samples. Morphological characterization and multigene analysis (ITS rDNA, 18S rDNA, LSU rDNA, β-tubulin, and actin gene) confirmed them as Aspergillus sp. AUMS56, Aspergillus tubingensis AUMS60 and AUMS64, and Aspergillus fumigatus AUKEMS24; achieving crude xylanase activities (through submerged fermentation using corn cobs) of 18.9, 32.29, 30.68, and 15.82 U ml −1 , respectively. AUMS60 and AUMS64 (forming lineage with A. tubingensis and Aspergillus niger in the same phylogroup with 100% Bayesian posterior probability support) secreted single xylanase (Xyn60; 36 kDa) and multiple xylanases (Xyn64A and Xyn64B; 33.4 and 19.8 kDa) respectively, having pH optima of 6.0 and exhibiting maximal activity at 60°C. These enzymes were highly stable at 40°C (120 h) and retained more than 70% activity at 50°C and at pH 5-6 (upon 72 h incubation). Our analysis suggested these enzymes to be endoxylanases demonstrating substrate hydrolysis within 15 min of reaction and maximum efficiency of xylanases from AUMS60 and AUMS64 achieving 51.1% (13 h) and 52.2% (24 h) saccharification, respectively. They also showed enhanced catalytic activity with various cations.Based on our investigation on xylan hydrolysis, we believe that these xylanases may find significant industrial applications as they have a real potential of working as a bio-catalytic cocktail (patent file number: IN E1/38213/2020-DEL) for the enhanced saccharification of lignocelluloses.

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The conversion of plant‐based lignocellulosic materials into alternative fuels entails various pretreatment strategies (chemical, physico‐chemical or enzymatic) to boost the release of sugar constituents from biomass. This investigation reports the influence of different pretreatment techniques such as acid, alkali and steam treatment followed by enzymatic hydrolysis in single and (or) consolidated system, for releasing fermentable reducing sugars from sugarcane bagasse (SB) and corn cobs (CC) (major agricultural residues). Alkaline pretreatment facilitated maximal lignin removal, 83.2 and 69.4% from CC and SB, respectively, thereby expediting enzymatic hydrolysis by in‐house xylanases produced from indigenously isolated Aspergillus tubingensis strains, AUMS60 (Xyn60) and AUMS64 (Xyn64A, B). The major operating conditions for enzymatic treatment of raw and pretreated residues were set at a substrate loading of 2% (w/v), an enzyme loading of 100–500 U g−1 substrate and incubation at 40°C, 140 rpm for 72 h. Treatment with Xyn60 and Xyn64A, B resulted in 81.4% (72 h) and 75.9% (24 h) saccharification of delignified SB and CC, respectively. Scanning electron micrographs and Fourier transform infrared spectra corroborated structural deformations induced by physico‐chemical pretreatment processes, thereby validating the maximal enzymatic hydrolysis of delignified substrates. The analysis of enzyme hydrolysis products suggested higher saccharification of hemicellulosic fraction as compared with cellulose. The observations of the present study signify that the thermotolerant in‐house enzymes show great potential in the saccharification of lignocelluloses within a short span of time and may open a new vista for biomass valorization in the bioenergy sector. © 2022 Society of Chemical Industry and John Wiley & Sons, Ltd.