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Bioremediation for Sustainable Environmental Cleanup

Plants Mediated

Microbes Mediated

Rhizosphere

Lead Bioremediation

Mechanistic Approach by Microbes

Biosorption, Bioaccumulation

Biomineralization via oxidation state

transformation and enzymes

Efflux of ions

Extracellular and intracellular sequestration

Siderophores

Metal chelation

Phytoremediation Processes

Phytoextraction

Phytostabilization,

Bioaccumulation of ions

Rhizofiltration

Phtovolatization

Figure 11.3. Overview of bioremediation strategies to reduce lead toxicity.

11.4.1 Bacteria Assisted Remediation of Pb

Microorganisms are prevalent in the environment and have evolved unique systems for determining

the fate of hazardous heavy metals. Microbes like bacteria, algae, archaebacteria, fungi, etc.,

mediate crucial interactions with ions of metals without unveiling negative effects on their structure,

action and metabolism (Rahman and Singh 2020). However, some toxic metals affect the activities

and survival of microbe cells above the threshold limit by imitating their biological function,

biomolecular denaturation and accelerating ROS production (Prabhakaran et al. 2016). But, due to

the behavior of microorganisms like varying phenotypic expressions, they combat metal toxicity

and show a metal-resistant function (Yin et al. 2019). Recently, a lot of research has been conducted

to unravel the action of microorganisms to diminish the concentration of Pb via biosorption,

oxidation state transformation, efflux, sequestration, metal chelation, use of enzymes, synthesis of

exopolysaccharides, intracellular bioaccumulation, etc. Microbial assisted remediation of Pb shows

key advantages due to their biochemical features like specificity, viability for genetic modulation

and suitability for in situ conditions (Singh and Prasad 2015, Ullah et al. 2015).

Biosorption is a technique where metal ions bind to the peptidoglycan cell wall of bacteria

to confine their entry into the cell and enhance the extracellular sequestration of toxic ions. It is

observed that Pseudomonas aeruginosa biosorb lead, on account of functionally charged groups

available at the surface viz. sulfonate, amine, carboxyl, hydroxyl, phosphonate, etc. (Gabr et al.

2008, Kushwaha et al. 2018). However, efflux is a process to maintain the homeostasis of ions

intracellularly under the action of membrane transport proteins. Several researches revealed that

many ATPase allied transmembrane transporter proteins facilitated lead resistance in microbes, e.g.,

Staphylococcus aureus, R. metallidurans, Cupriavidus metallidurans in the efflux of Pb (Borremans

et al. 2001, Hynninen et al. 2009). The toxicity of HMs to organisms relies on their bioavailability;

thus, microorganisms boost the sequestration of toxic metals at the membrane level. Researchers

have found that exopolysaccharide (EPS) help in bioaccumulation of lead in Pseudomonas

aeruginosa, Marinobacter sp., Acinetobacter junii, etc. (Bramhachari et al. 2007, De and Ramaiah

2007, Kushwaha et al. 2017).

In the environment, the most common microbes are bacteria. During remediation of heavy

metals via bioaccumulation, sequestration and adsorption action, bacteria onset these mechanisms