Biodegradation of diazinon by the Stenotrophomonas maltophilia PS: pesticide dissipation kinetics and breakdown characterization using FTIR

Abstract

A diazinon-degrading bacterium was isolated from paddy soils under flooded conditions. Biochemical characterization and 16S rRNA sequencing showed the isolate was an oxidase-positive Stenotrophomonas maltophilia. The isolate could grow on a mineral salt medium (MSM) supplemented with diazinon as the main carbon source (50 µg ml−1) and dissipate the pesticide in a simple first-order manner with DT50 and DT90 of 4.54 and 15.09 days, respectively. The addition of glucose favored the bacterial growth and reduced the pesticide’s DT50 and DT90 to 3.39 and 11.27 days, respectively. The dissipation of diazinon in MSM was accompanied by a slight reduction of the pH which was more significant in the glucose-treated media. FTIR analysis proved the separation of the heterocyclic leaving group by hydrolyzing the ester bond and aerobic cleavage of the aromatic ring as the main pathways of diazinon degradation in the MSM. The dissipation of diazinon (150 µg g−1) in the inoculated sterilized flooded paddy soils was biphasic, and based on this, only 31.55 µg g−1 of the initial concentration declined with a faster rate while the rest of the residue dissipated slowly as the adsorbed phase. In the non-inoculated non-sterilized soils, diazinon dissipated more slowly with an initial lag phase.