Kinetics of chlorophenol degradation by benzoate-induced culture of Rhodococcus erythropolis M1

Abstract

A pure culture of Rhodococcus erythropolis was isolated with the ability to degrade 2-chlorophenol, 4-chlorophenol and 2,4-dichlorophenol. Degradation of 2-chlorophenol by the uninduced culture of Rhodococcus erythropolis began after a prolonged lag period and complete mineralization of the substrates took 45 days. With the aim of reducing the lag period and subsequently improving the rate of degradation, the cells of the isolate were induced with benzoate, phenol, toluene and catechol individually. Benzoate-induced cells showed the highest rate of degradation and were thus used for the study of the degradation kinetics of 2-chlorophenol, 4-chlorophenol and 2,4-dichlorophenol. Complete mineralization of these substrates was achieved up to a concentration of 300, 100 and 50 mg l−1 respectively. Degradation of the chlorophenols was initiated without any significant lag and took the remarkably short time periods of 84, 64 and 144 h for the highest concentrations of the substrate. Evaluation of kinetic parameters showed chlorophenol degradation to follow substrate inhibition kinetics. This is evident from the decrease in specific growth rate, growth yield and substrate uptake rate with increase in the initial substrate concentrations. Toxicity of the chlorophenols was observed to depend on the position of chlorine on the benzene ring and the degree of chlorination.