Biological delignification of rice straw using laccase from Bacillus ligniniphilus L1 for bioethanol production: A clean approach for agro-biomass utilization

Abstract

The recalcitrance of lignocellulosic biomass due to severe lignification and complex cross-linking between lignin and cellulose fibers is a major hindrance in its clean and economical conversion to bioethanol . In the present study, the ligninolytic activity of purified bacterial laccase (BLac) from Bacillus ligniniphilus L1 was evaluated for delignification of rice straw for environment-friendly bioethanol production . BLac showed significant delignification activity at varying pH (3, 4, 7, and 9), and decreased the lignin (8.93%) and phenolic (44.8%) contents of rice straw. The chemical and structural changes in rice straw caused by BLac pretreatment determined via scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), and Fourier transform infrared (FTIR) spectroscopy confirmed the successful delignification of rice straw. BLac improved the cellulase (CL) hydrolysis of rice straw by releasing 15.8 mg/mL glucose and 21.8 mg/mL reducing sugar, and produced 22.3 mg/mL bioethanol. These findings indicate that BLac has the potential to efficiently utilize the rice straw resources for economical and environmentally feasible bioethanol production. • BLac reduced lignin (8.93%) and phenolic contents (44.8%) of rice straw. • BLac enhanced the release of glucose (15.8 mg/mL) and reducing sugar (21.8 mg/mL). • BLac caused significant physicochemical changes in rice straw biomass. • High ethanol production (22.3 mg/mL) from rice straw via BLac pretreatment.