MICROBIAL-METABOLISM OF THE PLANT PHENOLIC-COMPOUNDS FERULIC AND SYRINGIC ACIDS UNDER 3 ANAEROBIC CONDITIONS

Ferulic and syringic acids are methoxylated aromatic compounds that of ten serve as models of the subunits of lignin. Although these compound s have important implications for global carbon cycles, there is limit ed information on their fate in anoxic environments. Enrichment cultur es were established on these two model compounds under methanogenic, s ulfidogenic, and denitrifying conditions, using a Raritan River (New J ersey) marsh sediment as the inoculum. All cultures completely degrade d similar to 1.5 mM of both substrates. Methane production in the meth anogenic cultures corresponded to the stoichiometric values expected f or complete mineralization to CO2 and CH4. Sulfate and nitrate reducti on in their respective cultures were both greater than 60% of the amou nts predicted for complete mineralization. Aromatic intermediates of f erulic and syringic acid metabolism were identified, and pathways of d egradation under sulfidogenic and denitrifying conditions are proposed . Syringic acid is sequentially O-demethylated to gallic acid under bo th sulfate and nitrate-reducing conditions before ring cleavage occurs . Ferulic acid undergoes propenoate side chain reduction, O-demethylat ion, removal of an acetate moiety from the side chain, and decarboxyla tion to form catechol. Catechol is further degraded under sulfidogenic conditions. Under denitrifying conditions, ferulic acid undergoes los s of an acetate moiety, prior to O-demethylation, to form protocatechu ic acid, the last product detected before ring cleavage.