A strategy for bacterial degradation of lignin: alkaline sterilization and glucose as co-substrate

Efficient lignin conversion remains a significant challenge in the bioconversion of biomass. The difficulty in solubilization and degradation of lignin becomes a bottleneck in this regard. To address this issue, alkaline sterilization and glucose as co-substrate were employed to optimize conditions for lignin degradation and conversion. Lignin-degrading bacteria, specifically Pseudomonas putida L77, Stutzerimonas chloritidismutans L78 and Bacillus stercoris L90 were isolated from cow dung. First, alkaline sterilization was applied to the lignin medium, which enhanced the ionization of acidic groups. This process led to a more stable lignin dissolution and significantly reduced the precipitation rate from 21.17 % to 3.80 %. The addition of glucose as co-substrate further promoted the activity of key enzymes, laccase and peroxidase. Consequently, the degradation rates achieved by the three bacterial strains reached 28.71 %, 44.71 %, and 37.6 %, respectively. Further analysis showed significant changes in the particle size and molecular weight of the degraded lignin samples, and a significant decrease in the concentration of lignin-related components after bacterial treatment, as well as the appearance of degradation products such as glycol, glycerol, guaiacol and ethyl gallate. These findings demonstrate the feasibility of employing alkaline sterilization and co-substrate strategies to enhance lignin degradation by the selected bacterial strains.