Depolimerizzazione della lignina mediante biocatalisi multi-step

Lignin is, beside cellulose and hemicellulose, one of the three components of the lignocellulosic biomass. Since its peculiar phenyl-propanoic structure, it represents the first renewable source of aromatics on Earth: the valorisation of this biopolymer represents a primary target of the bioeconomy and circular economy. The present work highlights different biochemical strategies for lignin valorisation, focusing on the use of different enzymes as high-selective biocatalysts. Firstly, the dye-decolorizing Rh_DypB and the superoxide dismutase MnSOD-1 from Rhodococcus jostii RHA1 and Sphingobium sp. T2, respectively, were overexpressed in a recombinant form and characterized. Here, for the first time, Rh_DypB was fully produced as folded holoenzyme (>100 mg/L, >90% purity). Rh_DypB is a versatile biocatalyst active on lignin model compounds, dyes and Aflatoxin B1. Beside different bacterial laccases, MnSOD-1 was used in the enzymatic depolymerisation of unfractionated and solvent-fractionated technical lignins. The obtained degradation products were quantitatively analysed by GC-MS: vanillin was obtained up to 0.35 mg/g lignin. Finally, a synthetic multi-enzymatic pathway for the bioconversion of vanillin (the only commercialised aromatic compound obtained from lignin) into the value-added cis,cis-muconic acid (a precursor of plastic materials) was set up. The one pot reaction allowed the formation of 1 g of ccMA at the 70% of its commercial cost (>96% yield, 15 h).