Lignocellulolytic enzymes by aspergillus sp. A1 and bacillus sp. B1 isolated from gut of bulbitemes sp. in solid state fermentation using sawdust as substrate

Abstract

Sawdust is one of the common lignocellulosic waste biomass produced during the process of planning mills, moulding plants and furniture manufacturing. In practice, the sawdust is discarded in landfill areas, causing dust and dirt pollution in nearby localities. Therefore, the need to find an efficient and practical approach to revalorize sawdust as a starting raw material in the production of lignocellulolytic enzymes is essential as a way to manage and turn the residues into value added products. Prospecting for efficient degrading lignocellulose microorganisms is crucial to facilitate the process of lignocellulolytic enzymes production from the lignocellulosic biomass. This study aimed to exploit microorganisms isolated from gut of termite Bulbitermes sp. in producing lignocellulolytic enzymes under solid-state fermentation (SSF) system by using untreated sawdust as substrate. Seventeen bacterial and five fungal with positive lignocellulolytic enzymes activities were successfully isolated from the gut of two hundred termites. Four isolates identified as Aspergillus sp. A1, Bacillus sp. B1, Bacillus sp. B2 and Brevibacillus sp. Br3 were selected for further characterization. Among the isolates, Aspergillus sp. A1 showed highest activities of lignin peroxidase (LiP) (729.12 U/g) and ß-glucosidase (22.97 U/g). The highest activities of endoglucanase (138.77 U/g) and manganese peroxidase (MnP) (47.73 U/g) were recorded in Bacillus sp. B1. The Bacillus sp. B2 produced the highest activities of exoglucanase (32.16 U/g) and laccase (71.18 U/g). The highest xylanase activity (104.96 U/g) was observed in Brevibacillus sp. Br3. The production of endoglucanase, ß-glucosidase, xylanase, LiP and laccase were approximated 17?93% higher in co-culture compared to individual culture. Compared to other di-, tri- and quad-mixed culture, Aspergillus sp. A1 (A1) and Bacillus sp. B1 (B1) co-culture produced the highest lignocellulolytic enzymes activities (endoglucanase, 190.1; exoglucanase, 13.5; ß- glucosidase, 33.7; xylanase, 202.5; LiP, 713.5; MnP, 23.3 and laccase, 52.1 U/g). The interaction between A1 and B1 is not antagonistic. Study on the effect of SSF operational variables showed that the use of unsieved sawdust produced significantly higher activities of exoglucanase, xylanase, LiP and laccase compared to that of sieved sawdust. In addition, temperature, pH and moisture content significantly impacted lignocellulolytic enzymes production. In comparing to control, moistening the unsieved sawdust with Mandel basal medium (pH 8) to 1:2.5 (solid:moisture) ratio, and incubation at 35 °C for 9 days produced 1.2?49.4 fold higher lignocellulolytic enzymes activities. Endoglucanase, ß-glucosidase and xylanase could be classified as moderately thermostable enzymes with better stability in acidic pH range. Meanwhile, ligninases possessed thermophilic and alkaliphilic characteristics. The co-culture produced 1.9?11.8 fold higher reducing sugars than those yielded by single cultures in the enzymatic degradation of sawdust. The use of co-culture enzymes also produced 3.6?85.4% higher reducing sugars as well as 1.3?2.3 times higher raffinose, cellobiose, maltose, glucose and xylose concentrations compared to that of commercial cellulase (Celluclast) solution. As conclusion, this work has generated a microbial co-culture that could be used for improved lignocellulolytic enzymes and reducing sugars production using untreated sawdust as substrate.