Glycosyl hydrolases of Bacillus spp. from the vermicasts of epigeicEudrilus eugeniaefor biomass valorization

Biomass conversion mediated by microbes associated with earthworm casts has significant implications for developing bio-based high-value products in biorefineries. The present study reports two cellulose and hemicellulose deconstructing microbes from earthworm casts. Of the eleven bacterial isolates, DLC4 recorded maximum activities of endo-beta-1,4-glucanase [0.93 IU mL(-1)], exo-beta-1,4-glucanase [0.50 IU mL(-1)], and beta-1,4 -glucosidase [0.43 IU mL(-1)], followed by the type strain Cellulomonas fimi MTCC 24. The isolate PSX1 produced maximum xylanase activity of 11.55 IU mL(-1), followed by the type strains Bacillus pumilus MTCC 9861 and Arthrobacter sp. MTCC 6915 exhibited 11.27 IU mL(-1) and 10.49 IU mL(-1), respectively. Based on morphological, biochemical, and molecular [16S rRNA] identification, the potential isolates DLC4, SDX3, and PSX1 were identified as Bacillus subtilis DLC4, Bacillus subtilis SDX3, and Bacillus flexus PSX1, respectively. The Bacillus spp displayed maximum cellulase and xylanase activities at the pH range between 5.5 and 6.5 and a temperature of 37 degrees C. Organic nitrogen [N] amendment involving the combination of yeast extract and tryptone enhanced the xylanase activity, while CMC and xylan at 1% level increased the cellulase and xylanase activities, respectively. Hence, vermicasts are a potential source for bioprospecting unique multifunctional carbohydrate-modifying enzymes for lignocellulosic valorization toward sustainable production of biofuel and green chemicals.

Automated summary

Microbes associated with earthworm casts in biomass conversion have implications for biorefineries. This study identified two cellulose and hemicellulose deconstructing microbes from earthworm casts. The isolates Bacillus subtilis DLC4, Bacillus subtilis SDX3, and Bacillus flexus PSX1 showed high cellulase and xylanase activities, making vermicasts a potential source for carbohydrate-modifying enzymes in biofuel and green chemical production.