Isolation and characterization of lignin monomer- degrading bacteria under acidic condition from tropical peatland in Malaysia

Abstract

Tropical peatlands account for one of the largest carbon storages in the form of organic matter as a result of the accumulation of plant litter and waterlogged conditions. Recent anthropogenic disturbances such as forest fire, agricultural conversion, and draining of natural tropical peatlands have caused a vast amount of carbon released into the atmosphere, whereby these changes broadly impact microbial activities. A recent study states that many phenol-degrading and lignin-degrading bacteria prefer alkaline and neutral pH conditions. The acidic environment in tropical peatlands does not prevent microorganisms from utilizing lignin and phenolic derivative from the peat. This study aims to isolate and characterize lignin monomerdegrading bacteria from tropical peatlands under acidic conditions using phenolic aldehyde as the substrate for carbon input. Evaluation of greenhouse gas (GHG) emission and analysis of the chemical composition of tropical peat soil are essential to relate the peat utilization by the isolated bacteria. The GHG emission in pristine forests, secondary forests, and oil palm plantations was monitored using the closed chamber method. Peat water chemical composition were also identified using ultrahigh performance liquid chromatography quadrupole time of flights (UPLC-QTOF). Two isolates showed the capability to utilize phenolic aldehyde based on building blocks of lignin abundant in tropical peatlands, including hydroxyphenyl, guaiacyl, and syringyl branches. Identification of these isolates by 16S rRNA gene showed that strain S38 is similar to Stenotrophomonas sp. while strain S46 is similar to Burkholderia sp. Further characterization of these isolate showed their ability to degrade 4- hydroxybenzaldehyde and vanillin into phenolic acids within 24 hours of incubation and 7 days for syringaldehyde respectively. The findings indicated an increase in GHG emissions during the dry season due to the peat being exposed to oxidation. This is due to the peat soil composition containing a vast amount of lignin and phenolic derivative. In conclusion, the isolated strains show the ability to degrade lignin monomers into phenolic acid and withstand the acidic environment of tropical peatland, which is useful in the lignin industry.