**1. Introduction**

The insecticides have been used over the past 40 years for protection of crops against insects. Most insecticides cause pollution of air, soil and water due to application by spraying in large

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quantities. The use of pesticides has become an integral part of the modern agricultural system. It is estimated that 4 million tons of pesticides have been applied to world crops annually for pest control [1]. The residual pesticides may become the contamination sources and pose a serious threat to the soil and groundwater environment through the rainfall infiltration process. Some pesticides act on biochemical processes that are common to many animals, plants and microorganisms, and thus are a greater hazard to non-target organisms. Imidaclo‐ prid is a systemic chloronicotinyl insecticide and is used for soils, seeds and foliar applications for the control of sucking insects, including rice hoppers, aphids, thrips, whiteflies, termites, turf insects, soil insects and some beetles [2]. The active chemical works by interfering with the transmission of stimuli in the insect's nervous system [3]. Imidacloprid is a Category II acute toxicant, and thus, is classified as a General Use Pesticide. Imidacloprid is hazardous to the insects, especially honeybees, and also to fish, birds and algae.

In humans it is linked to reproductive and mutagenic effects and is considered neurotoxic. Reproductive toxicity testing also showed that imidacloprid is an agonist to the acetylcholine receptors that regulates the endocrine system in the brain [4]. The over accumulation of this pesticide in environment requires higher awareness about this pesticide. Imidacloprid is reported to have different impacts on soil bacterial community and also cluster analyzing clearly showed that imidacloprid has significant negative impact on soil bacterial diversity in highly polluted farms and soil microbial balance has been gradually upset by the application of more pesticide.

Oxidative stress is a misbalance between reactive oxygen species (ROS) generation and detoxification, resulting in increased levels of enzyme activity. ROS are of increasing interest in environmental toxicity as they may provide insights to toxicity mechanisms and may identify novel biomarkers. ROS can modify and inactivate proteins in a variety of ways. It is commonly recognized that *Escherichia coli* is the most suitable model system for the investiga‐ tion of the cell response to oxidative stress. When organisms or cells are exposed to low levels of certain harmful physical or chemical agents, the organisms acquire an induced tolerance against the adverse effects. The effect of hydrogen peroxide on the activity of Sox RS and Oxy R regulon enzymes in different strains of *Escherichia coli* has been studied. Exposure to acetamiprid in *Escherichia coli*, *Pseudomonas* and *Bacillus subtilis* resulted in synthesis of stress enzymes [5].

The term "genomics" was first used by Winkler to describe the haploid set of chromosomes and the genes associated with them. Genomics includes many scientific disciplines [6]. Toxicogenomics is the subdiscipline combining the fields of genomics and toxicology [7]. It has also been described as the study of genes and their products important in adaptive responses to chemical-derived exposures. The toxicogenomic approach provides opportuni‐ ties to improve understanding of the molecular mechanisms underlying toxic responses to environmental contaminants [8]. Therefore, the present investigation was carried out to study the effect of 10–7 to 10–3 molar concentrations of imidacloprid for a period of 24, 48, 72 and 96 h on three antioxidant enzymes superoxide dismutase, catalase and peroxidase in *Bacillus* *weihenstephanensis*. Further, the genes for the three enzymes involved in the antioxidant defense process in soil isolate *Bacillus weihenstephanensis* were sequenced and identified.
