DEGRADATION OF METHOXYLATED AROMATIC-ACIDS BY PSEUDOMONAS-PUTIDA

A newly-isolated strain of Pseudomonas putida (HVA-1) utilized homovan illic acid as sole carbon and energy source. Homovanillate-grown bacte ria oxidized homovanillate and homoprotocatechuate but monohydroxylate d and other methoxylated phenylacetic acids were oxidized poorly; meth oxy-substituted benzoates were not oxidized. Extracts of homovanillate -grown cells contained homoprotocatechuate 2,3-dioxygenase but the pri mary homovanillate-degrading enzyme could not be detected. No other me thoxylated phenylacetic acid supported growth of the organism but vani llate was utilized as a carbon and energy source. When homovanillate-g rown cells were used to inoculate media containing vanillate a 26 h la g period occurred before growth commenced. Vanillate-grown bacteria ox idized vanillate and protocatechuate but no significant oxygen uptake was obtained with homovanillate and other phenylacetic acid derivative s. Analysis of pathway intermediates revealed that homovanillate-grown bacteria produced homoprotocatechuate, formaldehyde and the ring-clea vage product 5-carboxymethyl 2-hydroxymuconic semialdehyde (CHMS) when incubated with homovanillate but monohydroxylated or monomethoxylated phenylacetic acids were not detected. These results suggest that homo vanillate is degraded directly to the ring-cleavage substrate homoprot ocatechuate by an unstable but highly specific demethylase and then un dergoes extradiol cleavage to CHMS. It would also appear that the upta ke/degradatory pathways for homovanillate and vanillate in this organi sm are entirely separate and independently controlled. If stabilizatio n of the homovanillate demethylase can be achieved, there is potential for exploiting the substrate specificity of this enzyme in both medic al diagnosis and in the paper industry.