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1 * Corresponding author: [email protected]
3
Biodetoxification of Heavy Metals Using Biofilm Bacteria
Adyasa Barik1, Debasish Biswal2, A. Arun1 and Vellaisamy Balasubramanian1*
1Department of Microbiology, Alagappa University, Karaikudi, Tamil Nadu, India
2Department of Biotechnology, Ravenshaw University, Cuttack, Odisha, India
Abstract
Heavy metal wastes are produced from various sources including anthropogenic and industrial activities. These metals create severe problem to our environment and cause different diseases in human such as cancer, skin lesions, birth defect, cerebral and bodily retention, disability to gain knowledge, and malfunction of liver and kidney. Therefore, heavy metals detoxification is a big challenge for researchers. Strategies have been employed to exploit the biofilm bacteria for detoxification of heavy metal. The drastic growth of biofilm bacteria occurs in polluted water environment through accumulating heavy metals. It is resistance to heavy metal through extra polymeric substances (EPSs) play a major role in detoxification of heavy metal. Polysaccharides, uronic acid, and sugar have functional group such as carboxylic acid and amino acid groups. These are the chemical composition of EPS. These functional groups could be acidic and retain the ability to bind or detoxify the heavy metal ions. The proteinaceous part of EPS plays an important role in complexation of metal ions. Several studies demonstrated that, the metal resistance genes (MRGs) and antibiotic resistance genes (ARGs) co-occur in bacteria isolated from water bodies polluted with heavy metal wastes. These kinds of studies give a little clue about the heavy metal resistance potential of antibiotic resistance strains. The stability and structure of biofilm together with diverse range of arrays will have more number of unexplored metabolic characteristics features of biofilm bacterial community’s toward the biofilm-mediated detoxification of heavy metal.
Keywords: Heavy metals, detoxification, biofilm bacteria, EPS, polysaccharides, functional groups, acidic, metal ions, MRGs, ARGs
3.1 Introduction
In current days, industrial, domestic, agriculture, and anthropogenic activity increase due to increasing population and demand of society. Therefore, new pollutants are present in different sources. Some of them are not degradable or take several years for degradation like xenobiotic and heavy metals. They are present in many forms in soil and water, enter in food chain of animal, plant, and human, and create diseases and several physical and physiological disorders. In recent days, heavy metal waste production is more from anthropogenic and industrial sources and these are creating serious problem to our surrounding and causing several diseases like cancer, skin lesions, birth defect, cerebral and bodily retention, gain knowledge disability, and malfunction of liver and kidney [1]. Therefore, heavy metal pollution has become a headache to our society. The metals and metalloids are heavy metals and biologically classified into two categories: essential [manganese (Mn), zinc (Zn), cobalt (Co), copper (Cu), and chromium (Cr)] and nonessential [cadmium (Cd), lead (Pb), and mercury (Hg)] elements [2]. The low concentration of essential heavy metal is required for animal, plant, and human nutrition, and non-essential element is generally known as toxic element for living beings [3, 4]. The treatment of toxic elements by biological process is better than physical and chemical process because of cost effectiveness and environmental compatibility. The potential of biofilm communities for biodetoxification methods has currently been realized [5]. The biodetoxification of heavy metals can be possible by immobilization, volatilization, concentration, and separating to an environmental part, thereby reducing estimated vulnerabilities [6, 7]. Development of biofilm of microbes and formation of their Extracellular Polymeric Substance (EPS) are commonly linked with resistance, ability to tolerate, and bioremediation of metal [8]. EPS of microbes has vital importance on development of biofilm and cell mass that gives safeguard to cells against antagonistic atmosphere and can tie substantial amount of heavy metals [8]. Biofilm EPS has high resistance capacity to entrapment of metal precipitate like cupper reducing bacteria, sulfur reducing bacteria, and another some bacteria. In polluted water, growth of biofilm is easy and accumulates heavy metals and resistance to heavy metal [9]. Polysaccharides, uronic acid, sugar, and proteins have functional groups such as carboxylic acid and amino acid groups, which are the composition of EPS, and these functional groups could be acidic and have ability to bind metal ions [1, 9]. In some studies, the polysaccharide part of EPS is essential
