Biodegradation of Organophosphorus Insecticides by <i>Bacillus</i> Species Isolated From Soil

This study investigates the biodegradation of methyl parathion, an organophosphate pesticide used in paddy fields. Microbial degradation transforms toxic pesticides into less harmful compounds, influenced by the microbial community in the soil. To isolate different microbial colonies, soil samples from an organophosphorus-treated groundnut field were plated on nutrient agar and MSM with 1% glucose and 0.25 mM methyl parathion. Biodegradation efficiency was determined by estimating the OP hydrolase enzyme activity spectrophotometrically. HPLC was used to quantify residual methyl parathion concentrations in the culture medium. The identified isolate effectively degraded methyl parathion in MSM with 0.25 mM methyl parathion which showed peak hydrolase activity (2.02 µmol/min/mg) after 96 h of incubation and the residual methyl parathion level was determined as 6.2 µmol by HPLC quantification. The efficient isolate was identified as Bacillus cereus by using a 16S rRNA molecular marker and the sequence was subjected to MEGA11 phylogenetic tree construction. The results show that the SM6 clade shared with B. cereus 16S rRNA sequence. B. cereus (SM6) showed substantial enzyme activity and the specific reported opdA gene-coded protein is involved in ATP hydrolysis. This OP hydrolase makes it a strong candidate for bioremediation of methyl parathion. Molecular analysis suggested that the opdA gene, likely chromosomally located, plays a key role in degradation, with potential involvement of the "Cell division protein FtsK" gene responsible for hydrolase activity. Organophosphorus compounds, widely used in agriculture, pose environmental concerns due to their persistence. This study focuses on isolating pesticide-degrading bacteria to expedite bioremediation, aiming for efficient degradation. This study highlights the cross-adaptation phenomenon, where B. cereus strains degrade similar compounds, improving bioremediation strategies.