Biodetoxification of Toxic Heavy Metals by Marine Metal Resistant Bacteria- A Novel Approach for Bioremediation of the Polluted Saline Environment

Abstract

Heavy metal contamination of the environment is a serious threat to our biological ecosystem due to their toxicity, carcinogenicity and mutagenicity. In recent years, increased mining, industrialisation and urbanisation activities have increased the flow of toxic metal ions to the environment. Toxic heavy metals such as Cr(VI), Cd(II), Pb(II), As(III/V), etc. are harmful for the environment when present above the critical values. Hence, their removal and detoxification in the environment should be done with utmost priority which can be achieved either by conventional physico-chemical or by bio-detoxification techniques. There are several disadvantages for the conventional physico-chemical metal detoxication techniques such as high cost, production of secondary toxic wastes, inconvenience in treating industrial effluents having low metal concentration, etc. which leads to the emergence of bio-detoxification techniques. Bio-detoxification, a cost-effective, environmental friendly and value added technique, can be used as an alternative treatment technology to overcome the drawbacks of conventional methods. Bio-detoxification of toxic heavy metals includes either transformation of metals from its toxic valency state to less toxic form using biological agents or their removal from the environment by using biosorption techniques. Bacteria from metal polluted habitats are adapted and possess a multiple metal tolerant capacity towards high metal concentration which can be the potential candidates for bio detoxification. Extracellular Polymeric Substances (EPS) of bacterial cell wall plays an important role in heavy metal detoxification. EPS comprising of different components such as peptidoglycan, teichoic and teichuronic acids, phospholipids, lipopolysaccharides and various proteins are responsible for metal binding and transportation across membrane. Most of the industrial effluents are saline in nature and bioremediation of the toxic metals present in such saline environments is a major challenge because it cannot be treated by non-halotolerant microbes due to their growth hindrance in saline rich environments. Metal-resistant and salt tolerant marine bacteria are most efficient agents for rapid adaptation and metal bioremediation from the polluted high saline environment as they are inhabited to the adverse marine environments. Hence, salt tolerant and metal resistant bacteria from marine environment are more suitable for bio-detoxification of heavy metals. The present chapter emphasizes the use of salt tolerant bacteria from different marine habitat for bioremediation of various toxic metals in saline environment.