Environmental and Agricultural Microbiology. Группа авторов

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process or mechanism. But later, it is discovered that they are not only lethal but their existence can persuade different mechanism of metal resistance in microorganisms. Microbes and metal ion communication can take place through different mechanisms. These mechanisms are classified depending on the pathway of communication of metal ions with microbes such as active and passive uptake of metal ions [63]. The biological interaction of microbes and metal ions transform the ions from toxic to less toxic or few accessible forms or arrest metal ions to inhibit their opening into bioprocess (Figure 3.1). The various interactive mechanisms are available such as biosorption, bioleaching, biovolatilization, bioimmobilization, and bioaccumulation. The EPS of biofilm bacterial cell also interact with metal ions, due to communication among positive charge metal ions and negative charge EPS of cell surface [64].

      The accumulation of heavy metals in food chain and their toxicity affects to biological system creates various problems. These can also enter to water bodies and contaminate soil through agricultural extract, industrial wastes, domestic runoff, and other commercial activities. We can eliminate or reduce heavy metal from contaminated sources. Therefore, there are different types of detoxification technology that have been utilized to eliminate heavy metals from contaminated sources. These detoxification technologies are briefly described as follows:

       ➢ Biosorption

       ➢ Bioleaching

       ➢ Biovolatilization

       ➢ Bioimmobilization

      3.5.1 Biosorption

      Active process: This process is metabolism dependent and also called as bioaccumulation process. In this process, transport of metal through the membrane of cell with a subsequent accumulation of intracellular metal facilitated through metabolism of cell. Only viable cells can perform bioaccumulation, which are also often linked with a mechanism of resistance initiated through microorganism in the existence of a toxic metal [66].

      Passive process: This process is a metabolism-independent process, otherwise known as biosorption. This is a physic-chemical process, normally includes four mechanism (adsorption, ion-exchange, complexation, and precipitation) and this mechanism helps to transport metal inside the cell [66].

      Adsorption: The adsorption occurs with the help of van der Waals’ force [52, 64]. The selective materials for adsorption of Cr(VI) and Ni(II) are “crushed initiated carbon > bagasse > fly ash” and “crushed initiated carbon >fly ash >bagasse”, respectively. The lower pH of 6.0 is suitable for removal of Cr(VI) and pH 8.0 is appropriate condition for removal of Ni(II) ions. The limitation of adsorption is that the ability is very low and their use for industrial runoffs treatment cannot be defensible [22].

      Ion-exchange: In biosorption process, the ion-exchange method was first introduced by Volesky and Holan (1995) and is backing through numerous current studies [66]. In passive absorption, the ion exchange method has essential role. In this mechanism, the biomass is displayed toward metal because the first metal aliquots are continuously discharged in to the solution while the second metal is combined, and a portion of second metal is combined to the bio-sorbent. This assay is suitable for Cu2+ and Pb2+ removal [67].

      Complexion: In this method, the complex formation on the cell surface after communication between metals and functional groups of microorganisms occurs for metal removal from the solution. The magnesium, copper, calcium, mercury, zinc, and cadmium accumulation via Pseudomonas syringae takes place and is removed by simply complexion mechanism. The organic acid may produce by microorganisms may chelate toxic metals, resulting in makeup of metallo-organic molecules [65].

      3.5.2 Bioleaching

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