Impact of Copper oxide nanoparticles on soil isolated Bacillus megaterium

Bacillus megaterium is a plant growth-promoting bacteria that performs various activities like producing hydrolytic enzymes in the soil such as protease and xylanase, releasing various growth hormones and other bioactive compounds that inhibit the plant pathogenic microbes in the soil. These microorganisms are not only part of the rhizosphere but instrumental in activities such as soil conditioning and nutrient cycling. But as the modernization of agriculture practices comes up with new age agrochemicals, called nano-agrochemicals, the concerns of toxicity also increased. These nano agrochemicals (such as CuO nanoparticles) have several advantages over the traditional chemicals, however, several properties like small size, lower dissolution, and potential to alter soil properties such as pH, raise serious threats to the soil beneficial microbes. It is also estimated that the accumulation of nanoparticles in the soil may become available for microbial ecosystems and cause toxicity with unique mechanisms, eg contact mode toxicity. Copper oxide nanoparticles are integral to new-era agrochemicals like nano-pesticides, nano-fertilizers, etc. There are mixed reviews on the toxicity of CuO nanoparticles on soil owing to diverse microbiota. Our in vitro studies were focused on the analysis of the size and dose-dependent impact of nanoparticles on the plant growth-promoting species  Bacillus megaterium at cellular, morphological as well as Indole acetic acid (IAA) production potential. Our study reveals that the small dose (0.05mg/ml) of copper oxide is not harmful to the microbes because copper is one of the essential elements However at upper concentration around 0.5mg to 1 mg/ml was significantly toxic for the Bacillus megaterium. The size-dependent toxicity on IAA production was also tested with the two different sizes of the CuO nanoparticles and the results were not significantly different.