A study on pesticide degradation by soil bacteria in tea and coffee plantations at Valparai estate region of western ghats

Abstract

In the current thesis, an effort is made to investigate the potential for local tea garden bacterial isolates to biodegrade a number of pesticides that are routinely used in agricultural fields. The composite sampling technique was used to gather soil samples from eight separate sampling locations. The soil samples' physiochemical characteristics were examined. the relationship between bacterial population and pesticide residues in sampling sites was also investigated. The bacterial population and pesticide fate in the environment are affected by physiochemical factors, particularly soil pH. Ten native bacterial isolates (DRNB1, EON2, SFN1, TXM1, F1T, Q1T, GLYB2, PTEB2, FXE1, and SFT1) were isolated and evaluated for degradation studies from pesticide-applied tea plantation areas. All the bacterial isolates are characterized by molecular analysis and the phylogenetic tree was also constructed using MEGA X. Through a disc diffusion assay, isolates were evaluated for their ability to tolerate up to 500 ppm concentrations of eight different pesticides (Deltamethrin, Spiromesifen, ethion, Thiamethoxam, Quinalphos, Fenpyroximate, Glyphosate, and Propargite). For tests on pesticide degradation, isolates that could withstand pesticide concentrations up to 500 ppm were used. The formation of biosurfactants, enzyme activity, and biofilm was also investigated in the bacterial isolates. The growth of bacterial isolates in carbon, nitrogen, and pesticide sources was examined. The optimization of parameters for pesticide degradation studies was done using the Taguchi optimization methodology. The metabolites formed through the pesticide degradation were analyzed by GC-MS analysis. A microbial consortium (PDMC1-Pesticide Degrading Microbial Consortium) was created for the pesticide deltamethrin's degradation, and about 91% of the pesticide's degradation in MSM was observed. DRNB1-Stenotrophomonas maltophilia, SFN1-Stenotrophomonas [Pseudomonas] geniculate, and FXE1-Pseudomonas aeruginosa are the three bacterial isolates that make up the consortium.