Kinetic characteristics of bacterial azo-dye decolorization by Pseudomonasluteola

A Pseudomonas luteola strain expressing azoreductase activity was utilized to remove the color of an azo dye (reactive red 22) from contaminated solut ions. The effects of substrate concentrations, medium compositions, and ope ration parameters (e.g., pH, temperature, dissolved oxygen, etc.) on decolo rization of the azo dye by a P. luteola strain were systematically investig ated to reveal the key factors that dominate the performance of ate-dye dec olorization. The metabolites resulting from bacterial decolorization were a nalyzed by high-performance liquid chromatography (HPLC) and mass spectrome tery (MS). The results show that the dissolved oxygen and glucose concentra tion retarded decolorization of reactive red 22 by P. luteola. The optimal ate-dye decolorization occurred at 37 degreesC, while more rapid decoloriza tion took place over pH 7-9. Yeast extract and tryptone strongly enhanced t he decolorization. The Michaelis-Menten model can satisfactorily describe t he dependence of specific decolorization rate on the concentration of subst rate (reactive red 22 or yeast extract). Decolorization of the azo dye by i ntact cells of P. luteola was essentially independent of the growth phase, whereas the azoreductase activity of the cell-free extract decreased in the order of late-stationary phase > early-stationary phase > mid-log phase. T his suggests that mass transfer of the azo dye across the cell membrane may be the rate-limiting step. The HPLC and MS analyses suggest that both part ial reduction and complete cleavage of the ate bond could contribute to dec olorization of reactive red 22 by P. luteola. (C) 2001 Elsevier Science Ltd . All rights reserved.