Project description:Aromatic compounds are an important renewable source of commodity chemicals traditionally produced from fossil fuels. Aromatics derived from plant lignin can potentially be converted into commodity chemicals through depolymerization followed by microbial funneling of monomers and low molecular weight oligomers. This study investigates the catabolism of the b-5 linked aromatic dimer dehydrodiconiferyl alcohol (DC-A) by the bacterium Novosphingobium aromaticivorans. We used genome wide screens to identify candidate genes involved in DC-A catabolism. Subsequent in vivo and in vitro analyses of these candidates elucidated a catabolic pathway composed of four required gene products and several partially redundant dehydrogenases that convert DC-A to aromatic monomers that can be funneled into the central aromatic metabolic pathway of N. aromaticivorans. Specifically, a newly identified γ-formaldehyde lyase, PcfL, opens the phenylcoumaran ring to form a stilbene and formaldehyde. A lignostilbene dioxygenase, LsdD, then cleaves the stilbene to generate the aromatic monomers, vanillin and 5-formylferulate (5-FF). We also show that an aldehyde dehydrogenase FerD oxidizes 5-FF before it is decarboxylated by LigW, yielding ferulic acid. We found that some enzymes involved in b-5 catabolism pathway can act on multiple substrates and that some steps in the pathway can be mediated by multiple enzymes, providing new insights into the robust flexibility of aromatic catabolism in N. aromaticivorans. We performed a comparative genomic analysis to predict that key enzymes in the newly discovered b-5 aromatic catabolic pathway are common among Sphingomonads.
Project description:Aromatic diketones are a major product of formic acid lignin depolymerization. Novosphingobium aromaticivorans can degrade these diketones, but the enzymes used in this process were unknown. We used RNA-Seq to identify aromatic dimer dehydrogenases as potential candidates for the initial reduction of the aromatic G-diketone, then verified this using in vitro enzyme assays.
