The non-oxidative decarboxylation of p-hydroxybenzoic acid, gentisic acid, protocatechuic acid and gallic acid by Klebsiella aerogenes (Aerobacter aerogenes).

Abstract

Klebsiella aerogenes adapted to a chemically-defined mineral salts medium with glucose orp-hydroxybenzoate as sole source of carbon and energy possessed constitutive decarboxylases for gentisate (2,5-dihydroxybenzoate), protocatechuate (3,4-dihydroxybenzoate) and gallate (3,4,5-trihydroxybenzoate) whose pH optima were respectively 5.9, 5.6 and 5.8. A decarboxylase for PHB was induced by PHB in both growing and resting cells; the induction was delayed or inhibited by chloramphenicol and by ultrasonic disruption of the bacteria. Crude ultrasonic preparations of PHB decarboxylase had an optimum pH of 6.0, a Michaelis constant of 4mm and an activation energy of 25,500 cal mole−1 at 28 – 38 C. All four decarboxylations proceeded without O2 and for every mole of phenolic acid decomposed one mole of CO2 and one mole of the corresponding phenol were produced. The effects of ultrasonic disruption of the bacteria suggested that permeability barriers limited the rate of decarboxylation of PHB and 2,5-DHB but not of 3,4-DHB or 3,4,5-THB. During ultrasonic disintegration PHB and 3,4-DHB decarboxylases were retained solely by insoluble centrifugeable particles, whereas 2,5-DHB and 3,4,5-THB decarboxylases were gradually released into solution. The decarboxylation of protocatechuic acid is an essential stage in the assimilation ofp-hydroxybenzoic acid byK. aerogenes, whereas the decarboxylation ofp-hydroxybenzoate itself is an injurious side reaction.