Process development of fungus-assisted one-pot valorization of lignin to phenols

Lignocellulosic (LC) biomass is a significant source of biopolymers such as cellulose and hemicellulose which are also being used as a product or are converted into renewable and high-value chemicals. However, lignin, a complex and heterogeneous biopolymer that provides the structural support to plants, is underutilized despite being the second most abundant renewable polymer after cellulose. To extract value added products from lignin, researchers face challenge of breaking it down into useful components as its structure is resistant to depolymerization. Fungi, particularly white rot fungi, are one promising approach for lignin depolymerization, as they excrete lignin modifying enzymes, which selectively attack lignin superstructure and release oligomers and monomers which can be used as precursors in various other industries. Deep eutectic solvents (DES) have been used for delignification of LC biomass, as an alternative green solvent, in contrast to conventional solvents, derived from fossil resources. DES have been used to extract lignin from LC biomass. They have also been studied to enhance the solubility of lignin, which is otherwise not soluble in water. Moreover, it has been shown, that when certain DES have been used as solvents for bio-transformations, enzymes such as laccase and manganese peroxidase presented higher activity than in buffered control solution. Combining the enhanced solubility of lignin in DES, which also enhances the activity of enzymes, secreted by the fungi, presents an interesting option to perform the fungal fermentation of lignin in DES. This project’s aim is, therefore, the development of a novel production system to extract bio-based aromatic monomers or oligomers derived from lignin. The project involves 5 consecutive objectives, including the optimization of Pleurotus ostreatus strain, to secrete lignin peroxidases, manganese peroxidases, versatile peroxidases, and laccases. The fungal spores will be incorporated into 3D printed spherical particles and tested in submersed fermentation mode. Near-neutral DES with a pH 4.5-5 will be prepared, and the combination of lignin-DES will be selected for the development of a “one-pot” system. The latter step will be crucial to confirm industrial viability of “one-pot” process for the production of monomers and oligomers, or at least provide information on the bottlenecks of such operating mode. The last objectives are to develop downstream processes for the separation of the monomers and oligomers and kinetic modeling of the whole process to improve the understanding of the process and to discover as much bottlenecks as possible. The research has the potential to create significant environmental and economic benefits as lignin is abundant, inexpensive and underutilized. It can be used for the production of aromatic carbohydrates, which can be used in various industries or also as end products with added value. The proposed method of using fungi and DES to depolymerize lignin into monomers and oligomers can create a sustainable and cost-effective process that can increase the value of lignin as a bio-based feedstock.