thought that pbrA exports Pb(II) from the cytoplasm, which is changed to a phosphate salt through inorganic phosphate formed by PbrB. Hynninen et al. (2009)
reported that pbrB is coding for an undecaprenyl pyrophosphate phosphatase. A Pb
(II)-binding protein was coded by pbrD which is present downstream of pbrC and is
critical for lead sequestration. Under the lead’s presence, the regulator pbrR activates
the transcription of pbrABCD operon. Pbr operon is controlled through pbrR, which
is having similarity to the family of heavy metal ion-sensing regulatory genes merR.
pbrR activated the induction of pbrABCD like single transcriptional unit under Pb
2
+
presence. pbrABC combination is thought to have some role in lead efflux, while
pbrD is believed to have role in Pb
2+ storage (Borremans et al. 2001). PbrD consists
of a possible cysteine-rich metal-binding motif (Cys-7XCys-Cys-7X-Cys-7X-His14X-Cys) and also possesses many proline and serine residues (Jarosławiecka and
Piotrowska-Seget 2014). Monchy et al. (2007) illustrated that gene pbrU is also
present and is induced under the presence of Pb
2+ . However, pbrU encodes a
permease which belongs to the main facilitator superfamily (MFS) present at the
inner membrane of C. metallidurans (Taghavi et al. 2009). Cupriavidus
metallidurans was identified as Ralstonia metallidurans, and the name of some of
the genes in the Deutsche Sammlung von Mikroorganismen und Zellkulturen
(DSMZ) database are still starts with BRme meaning R. metallidurans (von Rozycki
and Nies 2009). Roane (1999) studied the intracellular compartmentalization of
0.6 mM lead through metallothionein-like proteins in B. megaterium. Bacterial
metallothionein (BmtA) is present in P. aeruginosa strain WI-1 of Mandovi estuary
which stored intracellularly 26.5 mg lead/g dry weight of cells to decrease the
harmful influences of lead (Naik et al. 2012a). Salmonella choleraesuis and Proteus
penneri stored 19 and 22 mg lead, respectively, as an expression of metallothionein
protein of smtAB gene was enhanced in them (Naik et al. 2012b). Thus, the
occurrence of metallothioneins in bacteria may be exploited for bioremedaiting
lead at polluted sites. Metal immobilization through extracellular sequestration is
critical for the regulation of metal toxicity. Extracellular polymeric substances (EPS)
have different substances like polysaccharides, proteins, nucleic acids, humic
substances and lipids which possess numerous functional groups such as hydroxyl,
carboxyl, amides and phosphoryls having a strong attraction for heavy metals with
greater specificity and affinity (Bhaskar and Bhosle 2006; Bramhachari et al. 2007).
De et al. (2007) also studied the binding of lead through negatively charged
compounds of EPS in P. aeruginosa CH07. Pseudomonas marginalis is capable
of tolerating up to 2.5 mM lead through sequestration of lead in an exopolymer
(Roane 1999). In the same way, in Paenibacillus jamilae, biosorption of 303.03 mg
lead/g EPS through EPS from lead solution takes place (Morillo et al. 2008). There
are various enzymatic activities in the bacterial EPS which help in transforming
harmful metals through chemical reaction, precipitation or entrapment (Pal and Paul
2008). Thus, lead-resistant bacterial strains which generate EPS may function as a
potential bioremediative agent, i.e. as lead biosorbent in those places which are
polluted by lead. Another approach to decrease metal bioavailability as well as
toxicity is to make insoluble complex through bioprecipitation of dangerous metals.
Precipitation of lead into lead sulphide (PbS) was observed in B. iodonium GP13 and
12 Remediation of Heavy Metals Through Genetically Engineered Microorganism
337
reported that pbrB is coding for an undecaprenyl pyrophosphate phosphatase. A Pb
(II)-binding protein was coded by pbrD which is present downstream of pbrC and is
critical for lead sequestration. Under the lead’s presence, the regulator pbrR activates
the transcription of pbrABCD operon. Pbr operon is controlled through pbrR, which
is having similarity to the family of heavy metal ion-sensing regulatory genes merR.
pbrR activated the induction of pbrABCD like single transcriptional unit under Pb
2
+
presence. pbrABC combination is thought to have some role in lead efflux, while
pbrD is believed to have role in Pb
2+ storage (Borremans et al. 2001). PbrD consists
of a possible cysteine-rich metal-binding motif (Cys-7XCys-Cys-7X-Cys-7X-His14X-Cys) and also possesses many proline and serine residues (Jarosławiecka and
Piotrowska-Seget 2014). Monchy et al. (2007) illustrated that gene pbrU is also
present and is induced under the presence of Pb
2+ . However, pbrU encodes a
permease which belongs to the main facilitator superfamily (MFS) present at the
inner membrane of C. metallidurans (Taghavi et al. 2009). Cupriavidus
metallidurans was identified as Ralstonia metallidurans, and the name of some of
the genes in the Deutsche Sammlung von Mikroorganismen und Zellkulturen
(DSMZ) database are still starts with BRme meaning R. metallidurans (von Rozycki
and Nies 2009). Roane (1999) studied the intracellular compartmentalization of
0.6 mM lead through metallothionein-like proteins in B. megaterium. Bacterial
metallothionein (BmtA) is present in P. aeruginosa strain WI-1 of Mandovi estuary
which stored intracellularly 26.5 mg lead/g dry weight of cells to decrease the
harmful influences of lead (Naik et al. 2012a). Salmonella choleraesuis and Proteus
penneri stored 19 and 22 mg lead, respectively, as an expression of metallothionein
protein of smtAB gene was enhanced in them (Naik et al. 2012b). Thus, the
occurrence of metallothioneins in bacteria may be exploited for bioremedaiting
lead at polluted sites. Metal immobilization through extracellular sequestration is
critical for the regulation of metal toxicity. Extracellular polymeric substances (EPS)
have different substances like polysaccharides, proteins, nucleic acids, humic
substances and lipids which possess numerous functional groups such as hydroxyl,
carboxyl, amides and phosphoryls having a strong attraction for heavy metals with
greater specificity and affinity (Bhaskar and Bhosle 2006; Bramhachari et al. 2007).
De et al. (2007) also studied the binding of lead through negatively charged
compounds of EPS in P. aeruginosa CH07. Pseudomonas marginalis is capable
of tolerating up to 2.5 mM lead through sequestration of lead in an exopolymer
(Roane 1999). In the same way, in Paenibacillus jamilae, biosorption of 303.03 mg
lead/g EPS through EPS from lead solution takes place (Morillo et al. 2008). There
are various enzymatic activities in the bacterial EPS which help in transforming
harmful metals through chemical reaction, precipitation or entrapment (Pal and Paul
2008). Thus, lead-resistant bacterial strains which generate EPS may function as a
potential bioremediative agent, i.e. as lead biosorbent in those places which are
polluted by lead. Another approach to decrease metal bioavailability as well as
toxicity is to make insoluble complex through bioprecipitation of dangerous metals.
Precipitation of lead into lead sulphide (PbS) was observed in B. iodonium GP13 and
12 Remediation of Heavy Metals Through Genetically Engineered Microorganism
337