Degradation kinetics and mechanistic study on herbicide bioremediation using hyper butachlor-tolerant Pseudomonas putida G3

Abstract

The present study reports a new bacterial isolate identified as Pseudomonas putida strain G3 that can be used for the efficient biodegradation of butachlor, a systemic selective herbicide. Reports suggests butachlor to be a persistent pollutant, a suspected carcinogen and mutagen which poses threat to the environment. Batch biodegradation of the herbicides over a concentration ranging from 100 to 1000 mg/L by the bacterial strain has been studied after process parameter optimization. The bacterial strain is able to degrade up to 700 mg/L of butachlor completely within 360 h. However, increasing the concentration of the herbicide resulted in substrate inhibition in the efficiency of the microbial strain G3. Thus, to determine the bio-kinetic parameters, various inhibition models were fitted to the results obtained during batch biodegradation study. The maximum estimated specific degradation rate was found to be 2.74 mg/L/h. To enhance the bioremediation efficiency of the bacterial strain in presence of higher concentration of the herbicide, the microbial cells were immobilized on Ca-alginate beads and the efficiencies of free and immobilized bacterial cultures were evaluated. The ESI-MS analysis indicated that butachlor biodegradation took place with 2-chloro-N-(2,6-diethylphenyl)-N-hydroxymethylacetamide, 2-chloro-N-(2,6-diethylphenyl) acetamide and 2,6-diethylaniline as intermediate metabolites and a degradation pathway has been proposed. The bacterial strain is able to degrade up to 500 mg/L and 1000 mg/L of other herbicides such as Alachlor and Glyphosate efficiently proposing its wide substrate specificity. The study serves as an important basis that should help to design future bioremediation technology that would be expedient for the treatment of various herbicides.