Production of Ligninolytic Enzymes from Thermophilic Bacterial Strains Isolated from Palm Oil Wastes

The conversion of lignocellulosic biomass into bioethanol or biochemical products requires a crucial pre-treatment process to break down the recalcitrant lignin structure. Biological depolymerization of lignin using microbial enzyme appeared to be a promising pre-treatment alternative as it offers environmentally friendly treatment with lower energy requirements. In this study, three (3) thermophilic bacterial strains (S2, S11Y, S23) with lignin-degrading potential were previously isolated from palm oil wastes and identified as Stenotrophomonas sp., Bacillus subtilis, and Aeribacillus sp., respectively. These isolates demonstrated the capability to grow in a medium containing AL as the sole carbon source. Most isolates also demonstrated enzymatic activities toward lignin peroxidase (LiP), manganese peroxidase (MnP), and laccase (Lac) enzymes within a short period of 72 h. The highest LiP was secreted by strain S2 (70.97 ± 0.059 U/L), followed by S11Y (63.570 ± 0.021 U/L) and S23 (60.880 ± 0.042 U/L). MnP was generated with low activities of approximately 1.313 ± 0.037 U/L by S11Y, 0.364 ± 0.004 U/L by S2, and 0.215 ± 0.021 U/L by S23. For the Lac enzyme, low activities were detected only in S2 and S11Y, with 2.075 ± 0.612 U/L and 1.463 ± 0.116 U/L, respectively. This preliminary study appeared to show that the isolated thermophilic bacteria have the potential to be applied for lignin degradation application.