PhcK mediates transport of a β-5-type lignin-derived dimer in Sphingobium lignivorans SYK-6

Lignin is a major component of plant cell walls; however, its heterogeneous and complex structure has hindered its efficient utilization. Recently, strategies that combine chemical pretreatment with microbial conversion to produce valuable chemicals have attracted attention. To develop an ideal microbial platform for this purpose, it is essential to elucidate the complete bacterial catabolic system for lignin-derived aromatic compounds. Here, we identified an inner membrane transporter gene involved in the uptake of a metabolite of dehydrodiconiferyl alcohol (DCA), a lignin-derived β-5 dimer, in Sphingobium lignivorans SYK-6. SLG_12820 (phcK) was found to encode a major facilitator superfamily transporter belonging to the endosomal spinster family and is regulated by PhcR, a transcriptional regulator of DCA catabolism genes. Through mutant analysis and a specific uptake assay based on PhcR effector recognition, we demonstrated that PhcK functions as an inner membrane transporter that specifically imports the DCA metabolite, 3-(2-(4-hydroxy-3-methoxyphenyl)-3-(hydroxymethyl)-7-methoxy-2,3-dihydrobenzofuran-5-yl)acrylic acid.