Uptake system of lignin-derived aromatic acids in promising Sphingomonadaceae strains for lignin valorization through biological funneling.

The production of value-added chemicals from lignin-derived aromatic compounds through bacterial catabolism has attracted attention. Sphingobium lignivorans SYK-6 can catabolize various lignin-derived aromatic compounds that can be used for this purpose. PcaK (Sl-PcaK), a member of the major facilitator superfamily (MFS) transporters in SYK-6, is known to be involved in the uptake of protocatechuic acid (PCA) and vanillic acid (VA) in the inner membrane. Here, we demonstrated that Sl-PcaK also mediates the uptake of 4-hydroxybenzoic acid (HBA), syringic acid (SA), and ferulic acid (FA). Saro_0804 (Na-pcaK), with 58% amino acid sequence identity to Sl-PcaK, is present in Novosphingobium aromaticivorans DSM 12444. Na-pcaK plays a role in the uptake of PCA, HBA, VA, and SA. The increased expression of Sl-pcaK or Na-pcaK in SYK-6 cells improved the conversion rates of VA, SA, and FA 1.12-1.33-fold compared with the control strain, suggesting that these genes could serve as tools to improve the production efficiency of target metabolites.