Figure. 10.1. Microbial bioremediation of toxic metals (created by www.biorender)

Metal(loid)s Toxicity and Bacteria Mediated Bioremediation 173

nutrients is an important factor for microbial growth that affects pollutant degradation. Several

microbial mediated approaches are used. Biostimulation is the technique that involves a selective

enrichment of existing soil microbe for efficient bioremediation; bioaugmentation involves the

addition of a microbial strain for biodegradation of specific contaminant; bioaccumulation consists

of the uptake of pollutants in the microbial cells for storage and utilization in metabolic activity

(Mehana et al. 2020). Biofilm biosorption involves the removal of contaminants via surface

adsorption. Bacterial bioremediation has the benefit of being resistant to the presence of particular

pollutants.

10.4.1 Microbial Mechanism for Bioremediation of Toxic Metals

Heavy metals are extremely unsafe for plants, animals and human health. Microbes have developed

defense mechanisms against pollutants by developing biological processes to use heavy metals.

The detoxifying pathways for contaminants include extracellular barrier exclusion, binding of toxic

metals, extracellular polymeric substances, intracellular sequestration (confinement of these toxic

metals in the cytosol), active transport, efflux (microbial efflux machinery to transport away the

toxic elements) and enzyme mediated detoxification (toxic metals are transformed into less or non­

toxic substances). Thus, microbial biodegradation represents an affordable, efficient and economical

approach for the bioremediation of pollutants from the environment.

Microbes aided remediation tries to harness various microbial activities and the metabolic

potentials of important bacteria depending on the specific site conditions. Microbe-mediated

remediation of sediments polluted by heavy and toxic metals involves multiple approaches, including

bioleaching, biosurfactants, bioaccumulation, biosorption, bioprecipitation, biotransformation and

bio volatilization, as shown in Figure 10.1.

Figure 10.1. Microbial bioremediation of toxic metals (created by www.biorender).