METABOLISM OF LIGNIN MODEL COMPOUNDS OF THE ARYLGLYCEROL-BETA-ARYL ETHER TYPE BY PSEUDOMONAS-ACIDOVORANS D3
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1987
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Abstract
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]), .beta.-hydroxypropioveratrone (compound 4), acetoveratrone (compound 5), and veratric acid (compound 6). Also identified were compounds 1'', 2'', .beta.-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 .fwdarw. 2 .fwdarw. (3 + 4) .fwdarw. 5 .fwdarw. 6 (and similarly for 1''). In this scheme, the key reaction is cleavage of the ether linkage between C-2 (C.beta.) of the phenylpropane moiety and the 2-methoxyphenoxy moiety in compounds 2 and 2'' (i.e., .beta.-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.