Bacterial degradation of m-nitrobenzoic acid

Pseudomonas sp. strain JS51 grows on m-nitrobenzoate (m-NBA) with stoichiometric release of nitrite. m-NBA-grown cells oxidized m-NBA and protocatechuate but not 3-hydroxybenzoate, 4-hydroxy-3-nitrobenzoate, 4-nitrocatechol, and 1,2,4-benzenetriol. Protocatechuate accumulated transiently when succinate-grown cells were transferred to media containing m-NBA. Respirometric experiments indicated that the conversion of m-NBA to protocatechuate required 1 mol of oxygen per mol of substrate. Conversions conducted in the presence of 18O2 showed the incorporation of both atoms of molecular oxygen into protocatechuate. Extracts of m-NBA-grown cells cleaved protocatechuate to 2-hydroxy-4-carboxymuconic semialdehyde. These results provide rigorous proof that m-NBA is initially oxidized by a dioxygenase to produce protocatechuate which is further degraded by a 4,5-dioxygenase.