Revealing an environmentally friendly process for degradation of walnut green husk by Klebsiella variicola M6 and β-xylosidase: Characterization and application

The walnut green husk is a by-product generated during walnut processing, the waste of walnut green husk posed a potential threat to agricultural ecosystem. We aimed to developed a biodegradation technique to promote the lignocellulose degradation of walnut green husk. The results suggested that the activity of cellulose-degrading enzyme secreted by Klebsiella variicola M6 reached the peak on the 3 rd day of degradation. Moreover, the degradation rate treated with K. variicola M6 was significantly higher ( p <0.05), and FTIR and SEM also characterized the structure alterations of walnut green husk. Additionally, the β-xylosidase (KvXyl43) from K. variicola M6 was expressed, showing optimal activity at 35°C and pH 6.0. Combining K. variicola M6 (4% inoculation) with KvXyl43 (5 U/g supplementation), the degradation rate of walnut green husk reached 78.6±2.9% after 10 days, demonstrating the efficacy of strain-enzyme synergy in lignocellulose degradation. This research was pivotal for the degradation of walnut by-products. • Structure and morphology of walnut green husk were analyzed by FTIR and SEM. • β-xylosidase (KvXyl43) was heterologously expressed in E. coli BL21. • The enzymatic properties of β-xylosidase (KvXyl43) were characterized. • K. variicola M6 and KvXyl43 enhanced the degradation rate of walnut green husk.