Hydroquinone as the Ring-fission Substrate in the Catabolism of 4-Ethylphenol and 4-Hydroxyacetophenone by Pseudomonas putida JD1

SUMMARY: A bacterium capable of growth on 4-ethylphenol was isolated from soil and identified as Pseudomonas putida. Intact cells grown on 4-ethylphenol rapidly oxidized 4-hydroxyaceto-phenone as well as growth substrate and the bacterium was also capable of growth on 4-hydroxyacetophenone. The initial enzymes for 4-ethylphenol catabolism were still present, although at lower activities, in succinate-grown cells which oxidized 4-ethylphenol to 4-hydroxyacetophenone. Extracts of 4-ethylphenol-grown cells oxidized 4-hydroxyacetophenone when provided with NADPH. When this activity was partially purified a stoichiometry of 1 μmol O2 consumed per μmol of substrate was observed with the production of hydroquinone as required for a monooxygenase producing 4-hydroxyphernyl acetate followed by hydrolysis by an esterase. Cell extracts contained esterase activity and hydrolysed 4-hydroxyphenyl acetate to yield hydroquinone. Intact cells converted the analogue, acetophenone, into phenol. Hydroquinone served as the ring-fission substrate and was cleaved by an O2-requiring reaction. The enzymes of the proposed pathway were induced by growth on 4-ethylphenol or 4-hydroxyacetophenone.