AbstractA 4‐nitrophenol degrading strain PNP1 isolated from the El‐Harrach River near Algiers (Algeria) was studied with respect to its growth behaviour. According to the morphological and biochemical characteristics this strain was assigned to Pseudomonas putida. Besides 4‐nitrophenol, the strain also used 1,2‐ and 1,4‐dihydroxybenzene, benzoate, 4‐hydroxybenzoate and 3,4‐dihydroxybenzoate as sources of carbon and energy, degrading them exclusively via the ortho pathway. Pseudomonas putida PNP1 degrades 4‐nitrophenol through a purely oxidative pathway with release of the nitro group as nitrite. During cultivation with 4‐nitrophenol in ammonium‐containing mineral medium, the strain PNP1 grew optimally at pH 7 and at a temperature between 30 and 35°C and showed stoichiometric nitrite release (at pH 7 and 30°C MONOD model parameters μmax = 0.615 h−1 and KS = 0.145 mg/l). A phenomenological model for the description of growth inhibition at high 4‐nitrophenol concentrations was derived (below 400 mg/l only weak inhibition and at 600 mg/l acute toxicity). In ammonium‐free medium, the maximum specific growth rate was reduced to 0.318 h−1 and part of the 4‐nitrophenol‐N was used as the nitrogen source (32% N in biomass and 68% N in nitrite). The yield coefficients of strain PNP1 were smaller in ammonium‐free than in ammonium‐containing medium (e.g. with 4‐nitrophenol YX/S = 0.305 g/g compared to 0.350 g/g), which can be explained by the energy expense for the assimilatory nitrite reduction in the biosynthesis of N‐containing cellular compounds. But the oxygen consumption was only slightly influenced by the ammonium content of the cultivation medium (e.g. with 4‐nitrophenol YO/S = 1.005 g/g compared to 0.954 g/g).