Co-upgrading of ethanol-assisted depolymerized lignin: A new biological lignin valorization approach for the production of protocatechuic acid and polyhydroxyalkanoic acid

This study presents a promising biological co-upgrading of ethanol-assisted depolymerized lignin (EDL) into protocatechuic acid (PCA) and polyhydroxyalkanoic acid (PHA) without any separation process. A depolymerized alkali lignin containing various G-lignin-type monomers at a concentration of 77 mg/mL was used for co-upgrading. An engineered Pseudomonas putida KT2440 strain was constructed by knocking out the protocatechuate 3, 4-dioxygenase, expression of the formaldehyde utilization pathway, and the expression of aldehyde dehydrogenase to enhance the efficiency of the ethanol utilization pathway. The growth and production of valueadded bioproducts have been promoted by the utilization of formaldehyde, resulted in 6.73 +/- 0.26 mg/L of PCA with a 17.5% (w/w) yield of total lignin monomers, and 303.66 +/- 26.75 mg/L of PHA with 21.26% (w/w) of dry cell weight from 0.5 mL EDL. Moreover, the ethanol solvent used for lignin depolymerization was also utilized along with depolymerized lignin for co-upgrading to value-added products.

Automated summary

This study demonstrates a promising biological co-upgrading of ethanol-assisted depolymerized lignin into protocatechuic acid and polyhydroxyalkanoic acid without the need for separation processes. By engineering a Pseudomonas putida KT2440 strain, the efficiency of ethanol utilization pathway was enhanced, resulting in the production of value-added bioproducts. The utilization of formaldehyde promoted the growth and production of PCA and PHA from depolymerized lignin, with ethanol solvent also being used for co-upgrading.