Degradation of Imidacloprid from Polluted Soil by Rhizosphere Microflora, <i>Bacillus safensis</i> Isolated from Sunflower (<i>Helianthus annuus</i>)

Abstract

Imidacloprid is a systemic pesticide which is used on many plants to kill pests. Due to its excessive use, it is known to be a soil contaminant which can reach other non-target areas in a short period of time. Hence, it becomes important to remove this pesticide from soil. The ability of microflora isolated from the Sunflower rhizosphere to degrade imidacloprid was studied in the liquid growth medium. Subsequently, the isolated organism was used as a ‘bio-remediator’ to degrade excessive imidacloprid from contaminated soils. The microbial culture present in Sunflower rhizosphere spiked with imidacloprid was isolated and enriched in Mineral Salt Medium containing imidacloprid as a sole source of carbon and maintained at 35±2°C. Organism was selected based on its ability to grow in highest imidacloprid concentration and was identified as Bacillus safensis. The soil was further amended with the isolated culture at a concentration of 36 X 108 cells in two set ups, autoclaved soil and unautoclaved soil. The imidacloprid removal efficiency of the culture was studied using High Performance Liquid Chromatography. Soil samples were taken out at different time intervals of 5, 10, 20, 40 and 80 days. In soil amended with B. safensis, along with imidacloprid residue, one metabolite of the imidacloprid degradation pathway, 6-Chloronicotinic Acid was detected in both the set ups. The imidacloprid residues followed Pseudo first-order kinetics in both the soils. The isolated culture showed good imidacloprid degradation (53-60%) from broth and soils suggesting the role of the organism as a bio-remediator. This is the first-time study of the potential role of Bacillus safensis in remediation of soils contaminated with excessive amounts of pesticides containing imidacloprid.