Table 2_Novel insecticide-removal activity against deltamethrin and malathion in a lithic-derived Modestobacter strain.docx

A large fraction of agricultural pesticides, including insecticides, fails to reach target organisms and instead persists in soil, where residues may accumulate and generate transformation products with unpredictable or enhanced toxicity. Therefore, sustainable mitigation strategies require not only efficient pesticide removal but also effective detoxification. Soil-dwelling bacteria, particularly actinobacteria, possess diverse enzymatic capabilities that can contribute to the transformation of these chemical compounds, thereby influencing their environmental fate. In this study, we evaluated the insecticide-removal potential of 70 actinobacterial strains isolated from oligotrophic environments (dust and stone surfaces) in Tunisia using deltamethrin (a pyrethroid) and malathion (an organophosphate) as model insecticides. Thirty-two strains grew in minimal medium containing 3.2 mg/L of at least one insecticide, with 14 strains growing on both compounds. Among them, the actinobacterium Modestobacter marinus strain G96 (order Geodermatophilales) exhibited the highest apparent insecticide removal, as quantified by high-performance liquid chromatography. The concomitant increase in bacterial growth, together with the absence of growth in insecticide-free minimal medium, indicates that the apparent removal of parent insecticides is attributable to bacterial proliferation rather than to passive adsorption alone. Incubation of insecticide with G96 also resulted in reduced toxicity, with malathion-treated supernatants becoming completely non-toxic to Artemia salina by day 14. Malathion apparent removal was further assessed in a complex edaphic substrate (i.e., soil-slurry microcosms), where the concentration of the parent compound decreased by 90% over the 21-day incubation. Overall, our findings identify M. marinus G96 as a promising candidate for the biological removal and detoxification of insecticides and highlight the biotechnological potential of extremotolerant actinobacteria for the sustainable remediation of pesticide-contaminated soils, particularly in arid and dryland ecosystems.