Lead Induced Toxicity, Detoxification and Bioremediation 195

by the functional groups present/occurring on their surface to adsorb metal ions (Yin et al. 2016).

In soil, bacteria restricted Pb concentration via fostering insoluble lead complexes with hydroxide,

sulfide and carbonates, transforming the active form into stable insoluble state.

Further, sequestration of toxic ions is mainly through exopolysaccharide, an organic

polysaccharide with smaller proteins and lipids. Many microorganisms like Xanthomonas,

Bacillus, Agrobacterium, Alcaligenes, Pseudomonas spp., etc., have been identified as genera of

EPS-producing organisms to achieve heavy metal remediation by utilizing the charged property of

EPS, where they are incorporated with abundant anionic functional groups (Tayang and Songachan

2021). This mechanism is critical in the process of biomineralization, metal ions biosorption and

bioaccumulation (Thakare et al. 2021). Similarly, Chen et al. (2015) described Bacillus thuringiensis

as a potential biosorbent for Pb (II) transformation. Further, Bacillus cereus could transform Pb into

Pb hydroxyapatite via enzymatic action. An experiment conducted by scientists revealed that the

bacterium Streptomyces and Staphylococcus showed a prominent binding affinity for lead and other

metals. Therefore, they can be effectively used for the biosorption of lead (Sahmoune 2018).

Li et al. (2017) findings revealed that the bacterial strains of Pseudomonas sps., can efficiently

absorb Pb (II) from wastewater sites. For the first time, Borremans et al. (2001) found a lead-

resistance strain, i.e., CH34 in R. metallidurans, which enhances uptake and efflux mechanism by

the pbr operon system. Later many studies have shown the involvement of specific genes expression

for resistance to Pb by metallothionein proteins, specifically in P. aeruginosa (Kumari and Das

2019). Kang et al. (2016) confirmed microbial (bacterial) remediation of Pb-contaminated soils due

to the function of precipitation, sequestration or variation in the oxidation state of Pb. They revealed

the synergistic effect of bacterial consortium (E. cloacae, Sporosarcina, Viridibacillus arenosi, and

Enterobacter cloacae) on a mixture of Pb along with other heavy metals against single strain culture.

These bacteria are accountable for the transformation of HMs by enzymes production (Huang et al.

2009). It was observed that Bacillus iodinium, Klebsiella aerogenes and Bacillus pumilus precipitate

Pb (II) into PbS 9 (Govarthanan et al. 2013).

It has been noted that c‐type cytochromes and porin–cytochrome proteins in outer membrane

proteins in the microbes are involved in declining contaminants toxicity (Shi et al. 2016). Several

studies have shown that microbes transformed the state of metal by changing the valence status of

metals via redox-mediated processes (Dixit et al. 2015, Shi et al. 2016). The bacterial organisms

such as Bacillus sps., A. eutrophus, Pseudomonas sps., produce siderophores enabling extraction of

Pb from soil (Naik and Dubey 2017, Kalita and Joshi 2017). Similarly, in another report, the positive

interaction among siderophores and metal Pb and Ni was revealed by the bacteria P. aeruginosa

(Braud et al. 2009, 2010). The Pteris vittata plant exhibited rapid growth in the Pb-contaminated

area, which was enabled due to Pseudomonas spp., resistance against metal Pb via the process of

extracellular sequestration (Manzoor et al. 2019). Therefore, these examples of evidence show the

significance of siderophore-producing bacteria, which cause extraction and mobilization of Pb from

contaminated soil.

11.4.2 Plants Assisted Remediation of Pb

Phytoremediation, or the use of plants to clean up contaminated soil, is a well-known practice that is both

environmentally beneficial and cost-effective (Ali et al. 2013). Various phytoremediation processes

like phytoextraction, rhizodegradation/rhizofiltration, phytovolatilization, phytodegradation/

phytoaccumulation, phytostabilization and phytorestoration are included in the phytoremediation

of polluted soil. This technique is also performed to eliminate heavy metals through immobilization

or detoxification (Ali et al. 2013). During the process of phytoremediation, heavy metals are

accumulated through the cultivation of hyper accumulator plants as these plants have great potential

to absorb heavy metals and then gather them in the aboveground plant parts (Aliyu and Adamu

2014). Heavy metals are then degraded within the plants through internal (via metabolic aspects)

or external (through the release of some chemicals in the rhizosphere by plant roots) breakdown