Selective vanillate production from sugarcane bagasse-derived aromatic compounds using an engineered Pseudomonas sp....

In this study, Pseudomonas sp. NGC7 was engineered to selectively produce vanillate (VA) from aromatic compounds in the sugarcane bagasse alkaline extract. A VA O-demethylase gene (vanA4B4)-disrupted strain derived from NGC7 grew and produced VA from the extract containing no saccharides. The organic acids in the extract promoted the strain to grow. The aromatics in the extract were further concentrated by the solid phase extraction with DIAION HP20 resin, and the organic acids were fractionated into the flow-through fraction. A fed-batch culture of NGC7ΔvanA4B4 strain using this concentrated alkaline extract exhibited increased VA production; however, the accumulation of syringate (SA) and 4-hydroxybenzoate (HBA) was also observed along with VA production, despite the strain possessing the genes responsible for SA and HBA degradation. Analysis of the mutants capable of degrading SA while producing VA revealed that mutations in vanR2, a transcriptional repressor of the genes responsible for SA degradation, enabled SA degradation during VA production. In addition, the expression of praI, an HBA hydroxylase derived from Paenibacillus sp. JJ-1b, was suitable for efficient HBA degradation. Thus, the mutation in vanR2 and the expression of praI represented the key engineering strategies for achieving the selective VA production. As the growth of the engineered strains was promoted by the organic acids present in the extract, VA production from the concentrated extract was evaluated in a flow-through-based medium supplemented with mineral salts and metals. Finally, the engineered VA-producing strain produced 4.30 mM VA selectively at a yield of 77 mol% in the practical medium.