Isolation of Lignin-converting Microbes Contributing Towards Recalcitrant Carbon Degradation in Boreal Forest System

Abstract

Plant biomass, composed of cellulose, hemicellulose and lignin, are being explored as renewable carbon feedstock that could replace a significant amount of petroleum-derived chemicals and other products. Lignin, a component of wood, is the second most abundant natural organic polymer after cellulose. It provides strength and rigidity to plants and is highly recalcitrant to degradation due to its complex, three-dimensional structure. The valorization of lignin is essential for viable and sustainable uses of lignocellulosic biomass for the production of renewable fuels and chemicals. In order to achieve this, microbial degradation is extensively researched as microorganisms have evolved different enzymatic and/or non-enzymatic strategies to utilize biomass (Janusz et al., 2017). In boreal forest ecosystem, brown rot fungi are dominant players for decomposing and recycling carbon sources sequestered in tree biomass, but the carbohydrate-selective nutritional mode of these fungi does not allow them to consume all the forms of carbon in wood, with the undecayed lignin residues creating a recalcitrant carbon pool in the forest ecosystem. In this research, we investigated up to 200 functional microbes, including fungi and bacteria, involved in the breakdown of lignin components in this distinctive brown rot niche. Preliminary screening of the microbes was performed using indicator dyes, resulting in eight fungi and fourteen bacteria which were then screened to be further characterized. These isolates were identified using DNA extraction, PCR and sequencing and were further evaluated for their ability to degrade and metabolize lignin and aromatic lignin monomers. We anticipate understanding the lignin-degrading characteristics of microbes occurring naturally and its role in industrial lignin conversion or bioremediation of related recalcitrant aromatic hydrocarbons.