GROWTH-KINETICS OF THE 4-NITROPHENOL DEGRADING STRAIN PSEUDOMONAS-PUTIDA PNP1

A 4-nitrophenol degrading strain PNP1 isolated from the El-Harrach Riv er near Algiers (Algeria) was studied with respect to its growth behav iour. According to the morphological and biochemical characteristics t his strain was assigned to Pseudomonas putida. Besides 4-nitrophenol, the strain also used 1,2-and 1,4-dihydroxybenzene, benzoate, 4-hydroxy benzoate and 3,4-dihydroxybenzoate as sources of carbon and energy, de grading them exclusively via the ortho pathway. Pseudomonas putida PNP 1 degrades 4-nitrophenol through a purely oxidative pathway with relea se of the nitro group as nitrite. During cultivation with 4-nitropheno l in ammonium-containing mineral medium, the strain PNP1 grew optimall y at pH 7 and at a temperature between 30 and 35 degrees C and showed stoichiometric nitrite release (at pH 7 and 30 degrees C MONOD model p arameters mu(max) = 0.615 h(-1) and K-S = 0.145 mg/l). A phenomenologi cal model for the description of growth inhibition at high 4-nitrophen ol concentrations was derived (below 400 mg/l only weak inhibition and at 600 mg/l acute toxicity). In ammonium-free medium, the maximum spe cific growth rate was reduced to 0.318 h(-1) and part of the 4-nitroph enol-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 ammoni um-free than in ammonium-containing medium (e.g. with 4-nitrophenol Y- X/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 biosynthe sis of N-containing cellular compounds. But the oxygen consumption was only slightly influenced by the ammonium content of the cultivation m edium (e.g. with 4-nitrophenol Y-O/S = 1.005 g/g compared to 0.954 g/g ).