Tracking toxicity of copper oxide nanoparticles (CuO NPs) on PGPR Bacillus megaterium in the presence of melatonin

Abstract

The application and accumulation of CuO NPs in the soil may adversely affect the soil microbial community and limit its functional properties. Thus, researchers have tried to mitigate the toxicity of CuO NPs by investigating their underlying mechanisms. However, a detailed mechanism has not been adequately reported to date. Elevated levels of reactive oxygen species (ROS) and contact-mode toxicity are possible reasons for the toxicity of CuO NPs. Herein, we propose the use of melatonin as a mitigating agent for CuO-mediated toxicity due to its ROS neutralization potential. The present study showed that melatonin can reduce the toxicity of CuO NPs on isolated PGPR B. megaterium. Disc diffusion results demonstrated a decrease in the zone of clearance after adding melatonin at a particular concentration, which was significantly observed with CuO NPs (0.1 mg mL⁻¹ and 1 mg mL⁻¹). Changes in the morphology and the cell envelope during the mid-log phase were observed via TEM analysis. Furthermore, the application of melatonin in the IAA production medium inhibited the reduction in IAA production, which was observed earlier due to the presence of CuO NPs in the medium. Additionally, the DCFH staining and live-dead analysis confirmed the potential of melatonin in reducing the toxicity of CuO NPs at specific concentrations (20 and 50 μM).