Study of pesticide-decomposing bacteria Bacillus megaterium immobilised on Gliricidia sepium (Wetamara) biochar

Abstract

The application of pesticides has played an indispensable role in agriculture for centuries. Profenofos is an organophosphorus pesticide, extensively applied for insect control in agriculture. It poses health risks and disrupts beneficial microorganisms and insects, causing ecological imbalance. Consequently, environment-friendly and sustainable remediation techniques should be developed for pesticide detoxification. This study examines the use of Gliricidia sepium biochar (GSB) as a carrier material to immobilise a Profenofos-degrading bacterium, Bacillus megaterium, for the remediation of Profenofos-contaminated soil. Uncontaminated soils from a 0-20 cm depth were collected from a hillside dense forest in Samanalawewa reservoir area, Imbulpe, Sabaragamuwa Province. Three experimental setups were conducted to evaluate the growth, shelf life, and pesticide degradation potential of the B. megaterium immobilized Gliricidia sepium biochar (BM-GSB). Bacterial cultures were grown to an Optical Density (OD) of 1.0 at a wavelength of 600 nm, harvested, and immobilised onto biochar (1% w/v). The growth of B. megaterium was evaluated by colony counting on agar plates and OD measurements of solutions containing BM-GSB powder over successive days. The contaminated soil was prepared by spiking 1.0 kg of sterilised soil with 200 ppm Profenofos pesticide solution. A batch incubation experiment with four treatments was conducted, containing 50.00 g of soil samples. They are unamended soil (control), Profenofos-contaminated soil, Profenofos-contaminated soil amended with GSB, and Profenofos-contaminated soil amended with BM-GSB. Residual Profenofos content was extracted and analysed via GC-MS. SEM imaging was performed to observe bacterial adherence to the biochar surface. The shelf-life of B. megaterium on GSB was 37 days, with high initial colony growth followed by a noticeable decline over time. The pesticide degradation was evaluated using GC-MS. In the presence of GSB biochar, 70.97% Profenofos reduction was achieved. A 37.83% reduction was observed when introducing the BM-GSB. The SEM analysis confirmed the successful immobilisation of B. on GSB was 37 days, with high initial colony growth followed by a noticeable decline over time. The pesticide degradation was evaluated using GC-MS. In the presence of GSB biochar, 70.97% Profenofos reduction was achieved. A 37.83% reduction was observed when introducing the BM-GSB. The SEM analysis confirmed the successful immobilisation of B.megaterium on GSB. The findings suggest that BM-GSB was an effective, eco-friendly material for reducing Profenofos residues in agricultural soils, offering a sustainable approach to soil detoxification.