Prospects of Plant Growth Promoting Bacterium, Bacillus megaterium, for the Biodegradation of Selected Novel Pesticides

Abstract

Bacillus megaterium, a phosphorus-solubilizing bacterium, has been exploited as a biofertilizer to increase crop yield. Thiamethoxam and chlorantraniliprole are novel insecticides that are applied as granular and foliar formulations for insect pest control. The present study evaluated the potential of B. megaterium for the bioremediation of these novel pesticides in natural and amended soils. The survivability of B. megaterium was studied in a liquid half-strength nutrient broth supplemented with thiamethoxam or chlorantraniliprole (5-100 mg.L-1). In addition, soil microcosm studies were conducted (21 days) to explore the bio-stimulating effect on the degradability of B. megaterium in pesticide-treated soils (@ 10 mg.kg-1) using organic amendments, vermicompost and Vesicular Arbuscular Mycorrhiza (VAM). The impact of pesticides was evaluated by calculating the enzymatic activities of dehydrogenase, phosphatase, and β-D-glucosidase. The experimental results revealed that B. megaterium could survive in pesticide-supplemented conditions, with maximum optical densities of 0.734 AU and 0.965 AU at 100 mg.kg-1 for thiamethoxam and chlorantraniliprole, respectively. Furthermore, these B. megaterium cultures also exhibited colony-forming units when plated on nutrient agar supplemented with thiamethoxam (21 × 105) and chlorantraniliprole (43 × 105) at the end of 21 days, indicating their adaptability. The soil application of B. megaterium combined with vermicompost or VAM exhibited higher degradation efficiency for thiamethoxam (2.61 and 2.16 mg.kg-1) and chlorantraniliprole (2.58 and 3.92 mg.kg-1), resulting in rapid degradation. The observed half-life values in these combined treatments were 11-12 days (thiamethoxam) and 11 and 15 days (chlorantraniliprole), which were on par with each other and significantly differed (two-factor ANOVA, p<0.05) when compared to natural attenuation (29–35 days). The enzymatic activity was negatively impacted for all enzymes under study. However, vermicompost amendments can recover enzymatic activity over time. Thus, B. megaterium has the potential to bioremediate thiamethoxam and chlorantraniliprole, and the application of soil amendments can reduce the sublethal effects of these pesticides.