Identification and characterization of lignin depolymerization enzymes in Bacillus subtilis strain S11Y isolated from a tropical environment in Malaysia

Biological pretreatment using microbial enzymes appears to be the most promising pre-treatment technology for the breakdown of recalcitrant lignin structure. This research focuses on the identification and characterization of lignin-depolymerizing enzymes in Bacillus subtilis strain S11Y, previously isolated from palm oil wastes in Malaysia. The draft genome sequences of this highly lignindepolymerizing strain revealed that the genome lacked any of the well-known dye-decolorizing peroxidase or catalase-peroxidase that are commonly reported to be involved in lignin depolymerization by bacteria, indicating that strain S11Y has distinct sets of potential lignin depolymerization genes. The oxidative stress -related enzymes Cu/Zn typesuperoxide dismutase (Sod2) and a heme-containing monofunctional catalase (Kat2) were identified in the genome sequences that are of interest. Their lignin-depolymerizing ability were evaluated by treating Alkali lignin (AL) with each enzyme and their degradation ability were evaluated using gel -permeation chromatography (GPC), ultrahigh -pressure liquid chromatography-mass spectrometry (UHPLC/MS), and gas chromatography- mass spectrometry (GC/MS), which successfully proved lignin depolymerizing ability. Successful evaluation of lignin depolymerizing enzymes can be applicable for lignin pre-treatment process in green energy production and generation of valuable chemicals in bio-refinery.