Metabolism of Lignin Model Compounds of the Arylglycerol-β-Aryl Ether Type by Pseudomonas acidovorans D3

A natural bacterial isolate that we have classified as Pseudomonas acidovorans grows on the lignin model compounds 1-(3,4-dimethoxyphenyl)-2-(2-methoxyphenoxy)propane-1,3-diol (compound 1) and 1-(4-hydroxy-3-methoxyphenyl)-2-(2-methoxyphenoxy)propane-1,3-diol (compound 1′), as well as on the corresponding 1-oxo compounds (2 and 2′) as sole sources of carbon and energy. Metabolic intermediates present in cultures growing on compound 1 included compound 2, 2-methoxyphenol (guaiacol [compound 3]), β-hydroxypro-pioveratrone (compound 4), acetoveratrone (compound 5), and veratric acid (compound 6). Also identified were compounds 1′, 2′, β-hydroxypropiovanillone (compound 4′), and acetovanillone (compound 5′), indicating that 4-O demethylation also occurs. The phenolic intermediates were the same as those found in cultures growing on compound 1′. Compounds 2 and 2′ were in part also reduced to compounds 1 and 1′, respectively. Compound 3 was shown to be derived from the 2-methoxyphenoxy moiety. A suggested degradation scheme is as follows: compound 1→2→(3 + 4)→5→6 (and similarly for 1′). In this scheme, the key reaction is cleavage of the ether linkage between C-2 (Cβ) of the phenylpropane moiety and the 2-methoxyphenoxy moiety in compounds 2 and 2′ (i.e., β-aryl ether cleavage). On the basis of compounds identified, viz., 3 and 4 (4′), cleavage appears formally to be reductive. Because this is unlikely, the initial cleavage products probably were not detected. The implications of these results for the enzyme(s) responsible are discussed.