Kinetics study of nicosulfuron degradation by a Pseudomonas nitroreducens strain NSA02

A bacterial strain NSA02, isolated from contaminated soil and identified as Pseudomonas nitroreducens based on partial 16S rDNA gene sequence analysis and BIOLOG microbiology analysis, was used to study biodegradation of nicosulfuron in the culture medium. The optimal degradation conditions were determined to be 30 °C and pH 7.0. Batch tests were performed for seven different initial substrate concentrations to observe substrate degradation and associated cell growth. The biodegradation kinetics was found to follow a first-order model with regression values greater than 0.98. Specific degradation rate and specific growth rate of bacterial cells were observed to follow substrate inhibition kinetics, and the maximum values of both rates were observed at 100 mg L^-1 of nicosulfuron concentration. Kinetic parameters of three substrate inhibition models (Haldane, Aiba-Edwards and Teissier-Edwards) were fitted to the relationship between those rates and substrate concentrations. With the date obtained, Haldane and Teissier-Edwards models provide better representation when compared to Aiba-Edwards model. Inoculating nicosulfuron-treated soil samples with strain NSA02 resulted in a 5-6 times higher rate of nicosulfuron removal than that in non-inoculated soil. Five metabolites of nicosulfuron degradation were detected and identified by liquid chromatography mass spectrometry, and three possible biotransformation pathways were proposed. These results highlight the potential of the isolated bacterium to be used in the bioremediation of nicosulfuron-contaminated soils.