Bacterial catabolic system of acetovanillone and acetosyringone useful for upgrading aromatic compounds obtained through chemical lignin depolymerization
Acetovanillone is a major aromatic monomer produced in oxidative/base-catalyzed lignin depolymerization. However, the production of chemical products from acetovanillone has not been explored due to the lack of information on the microbial acetovanillone catabolic system. Here acvABCDEF was identified as specifically induced genes during the growth of Sphingobium sp. strain SYK-6 cells with acetovanillone and these genes were essential for SYK-6 growth on acetovanillone and acetosyringone (a syringyl-type acetophenone derivative). AcvAB and AcvF produced in Escherichia coli phosphorylated acetovanillone/acetosyringone and dephosphorylated the phosphorylated acetovanillone/acetosyringone, respectively. AcvCDE produced in Sphingobium japonicum UT26S converted the dephosphorylated phosphorylated acetovanillone/acetosyringone intermediate into vanilloyl acetic acid/3- (4-hydroxy-3,5-dimethoxyphenyl)-3-oxopropanoic acid through carboxylation. To demonstrate the feasibility of producing cis,cis-muconic acid from acetovanillone, a metabolic modification on a mutant of Pseudomonas sp. strain NGC7 that accumulates cis,cis-muconic acid from catechol was performed. The resulting strain expressing vceA and vceB required for converting vanilloyl acetic acid to vanillic acid and aroY encoding protocatechuic acid decarboxylase in addition to acvABCDEF successfully converted 1.2 mM acetovanillone to approximate equimolar cis,cis-muconic acid. Our results are expected to help improve the yield and purity of value-added chemical production from lignin through biological funneling. IMPORTANCEIn the alkaline oxidation of lignin, aromatic aldehydes (vanillin, syringaldehyde, and p-hydroxybenzaldehyde), aromatic acids (vanillic acid, syringic acid, and p- hydroxybenzoic acid), and acetophenone-related compounds (acetovanillone, acetosyringone, and 4-hydroxyacetophenone) are produced as major aromatic monomers. Also, base-catalyzed depolymerization of guaiacyl lignin resulted in vanillin, vanillic acid, guaiacol, and acetovanillone as primary aromatic monomers. To date, microbial catabolic systems of vanillin, vanillic acid, and guaiacol have been well characterized, and the production of value-added chemicals from them has also been explored. However, due to the lack of information on the microbial acetovanillone and acetosyringone catabolic system, chemical production from acetovanillone and acetosyringone has not been achieved. This is the first study to elucidate the acetovanillone/acetosyringone catabolic system, and to demonstrate the potential of using these genes for value-added chemicals production from these compounds.