Toxicity of copper oxide nanoparticles on agriculturally important soil rhizobacteria Bacillus megaterium

Abstract

Copper oxide nanoparticles are an integral part of modern agrochemical industries, such as pesticides and nano fertilizers. It has been extensively reviewed and reported that the interaction of nanoparticles with plant growth-promoting rhizobacteria (PGPRs) may be toxic due to their accumulation in the soil and may remain in contact for a long time which causes a negative impact on the soil microbial community. The study presented here, investigates the impact of the copper oxide nanoparticles on the isolated PGPR species Bacillius megaterium AGNTL MM7 in invitro conditions. We observed that the formation of Reactive Oxygen Species (ROS) at ¼ of Minimum Inhibitory Concentrations (MIC) of CuO nanoparticles resulted in a decrease in the Indole Acetic Acid (IAA) production (83.02 μg/ml) as the marker of the nanoparticles mediated stress on the Bacillus megaterium AGNTL MM7. The minimum inhibitory concentration (MIC) assay was observed at 4 mg/ml. The solubility of CuO nanoparticles was 0.014% and the Nanotracking analyzer estimated the mean average size 188 nm in a liquid medium such as water. Transmission Electron Microscopic (TEM) studies observed that the concentration of 1 mg/ml nanoparticles showed a strong affinity with cell envelope and caused a significant negative impact on the microorganism, resulting in 58% inhibition in IAA production was observed in comparison to the control i.e., 197.8 μg/ml. The flow cytometric analysis also significantly validated the toxicity at the same concentration.