Antioxidant defense systems in bioremediation of organic pollutants

Rapid industrialization, urban waste, and natural activities can results in the addition of massive quantities of extremely toxic organic pollutants, that is, polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), petroleum hydrocarbons, halogenated and nitro aromatic compounds, polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs), solvents, explosives, and pesticides in both aquatic and soil ecosystems. Organic pollutants attained worldwide attention due to their toxic effects on both plants and humans. These are highly persistent in the environment and are earlier treated by biochemical and physical processes, which are costly and produced toxic by-products. An alternative technique, called bioremediation, is a process of removal of these organic pollutants by the use of specific microbial species, algae, fungi, and hyperaccumulator plants. The plants when exposed to these organic pollutants showed stunted growth due to the production of oxidative stress. Oxidative stress was induced by the generation of reactive oxygen species (ROS), which in response alter the balance between free radicals and reactive species, which showed cytotoxic responses. Hyperaccumulator plants and microbes that were used for bioremediation have a capability to detoxify the effects of ROS by activating antioxidant defense systems. Antioxidant defense system is composed of various enzymatic (peroxidase, ascorbate peroxidase, superoxide dismutase, ascorbate peroxidase, catalase, glutathione reductase, and polyphenol oxidase) and nonenzymatic (α-tocopherol, β-carotenes, ascorbic acid, proline, reduced glutathione, and carotenoids) antioxidants. This chapter will discuss in detail the activation of antioxidant systems present in microbes and plants during the bioremediation of organic pollutants.