DdvK, a Novel Major Facilitator Superfamily Transporter Essential for 5,5'-Dehydrodivanillate Uptake by Sphingobium sp. Strain SYK-6

The microbial conversion of lignin-derived aromatics is a promising strategy for the industrial utilization of this large biomass resource. However, efficient application requires an elucidation of the relevant transport and catabolic pathways. In sp. strain SYK-6, most of the enzyme genes involved in 5,5'-dehydrodivanillate (DDVA) catabolism have been characterized, but the transporter has not yet been identified. Here, we identified SLG_07710 ( ) and SLG_07780 ( ), genes encoding a putative major facilitator superfamily (MFS) transporter and MarR-type transcriptional regulator, respectively. A mutant of SYK-6 completely lost the capacity to grow on and convert DDVA. DdvR repressed the expression of the DDVA -demethylase oxygenase component gene ( ), while DDVA acted as the gene inducer. A DDVA uptake assay was developed by employing this DdvR-controlled transcriptional regulatory system. A UT26S transformant expressing acquired DDVA uptake capacity, indicating that encodes the DDVA transporter. DdvK, probably requiring the proton motive force, was suggested to be a novel MFS transporter on the basis of the amino acid sequence similarity. Subsequently, we evaluated the effects of overexpression on the production of the DDVA metabolite 2-pyrone-4,6-dicarboxylate (PDC), a building block of functional polymers. A SYK-6 mutant of the PDC hydrolase gene ( ) cultured in DDVA accumulated PDC via 5-carboxyvanillate and grew by utilizing 4-carboxy-2-hydroxypenta-2,4-dienoate. The introduction of a -expression plasmid into a mutant increased the growth rate in DDVA and the amounts of DDVA converted and PDC produced after 48 h by 1.35- and 1.34-fold, respectively. These results indicate that enhanced transporter gene expression can improve metabolite production from lignin derivatives. The bioengineering of bacteria to selectively transport and metabolize natural substrates into specific metabolites is a valuable strategy for industrial-scale chemical production. The uptake of many substrates into cells requires specific transport systems, and so the identification and characterization of transporter genes are essential for industrial applications. A number of bacterial major facilitator superfamily transporters of aromatic acids have been identified and characterized, but many transporters of lignin-derived aromatic acids remain unidentified. The efficient conversion of lignin, an abundant but unutilized aromatic biomass resource, to value-added metabolites using m