and cnrY are present in the periplasm and probably work like antisigma factors. The
cnrCBA codes for an extremely proficient pump which can be induced in the
presence of just micromolar quantity of nickel. These gene products produce an
efflux pump which removes an extra amount of nickel from the cell. Grass et al.
(2005) also described the presence of nre (nickel resistance) operons in
Achromobacter xylosoxidans 31A. They observed the nre locus on the plasmid
pTOM9 and found that just a single gene, nreB, was accountable to provide the
whole tolerance for nickel. However, just like cnr operon, this operon is not
detoxifying Ni
2+ , but removing it from the cell. Previously, Schmidt and Schlegel
(1994) found one other operon ncc operon in the same pTOM9 plasmid, which is
giving joint tolerance for nickel, cobalt and cadmium. However, these processes of
nickel resistance do not participate much in nickel bioremediation. Seven ORFs
were investigated and named as nccYXHCBAN. Nucleotide sequences have a
strong similarity to the cnr as well as czc operons of Alcaligenes eutrophus CH34
(Tibazarwa et al. 2000). The NccX protein is having 76 amino acids with several His
residues which shows that it might be working like a metal-binding protein used for
nickel remediation (Trepreau et al. 2011). Rodrigue et al. (2005) studied the yohM
gene in E. coli and observed that it is coding a membrane-bound polypeptide with
the capacity to tolerate nickel and cobalt. More copies of yohM resulted in a
decreased level of intracellular nickel. yohM, therefore, designated now as rcnA,
was the first nickel efflux system found in E. coli. One more efflux pump for
cadmium–zinc–nickel was found in Helicobacter pylori and designated as cznABC
(Stahler et al. 2006). Of these three genes, cznA and cznC were responsible for
nickel homoeostasis. E. coli JM109 was genetically manipulated to simultaneously
induce nickel transport system and metallothionein gene which can eliminate as well
as recover Ni
2+ from aqueous solution. There is a six-time enhancement in the
nickel-binding ability in comparison to host cells after the linearized Langmuir
isotherm (Deng et al. 2003). In another investigation, the nickel/cobalt transferase
gene, NiCoT of S. aureus ATCC6538, was amplified and ligated into vector pET-3c
which bioaccumulated 11.33 mg/g nickel, three times in comparison to the original
E. coli BL21 strain (Zhang et al. 2007). RcnA nickel (Ni) and cobalt (Co) efflux
systems were repressed genomically for genetically manipulating E. coli to combine
the induction of a particular metallic transporter, NiCoT of Novosphingobium
aromaticivorans which was under plasmid regulation. This Ni/Co buster strain is
accountable for increased nickel (II) and cobalt (II) uptake as well as storage of metal
about 6 mg/g bacterial dry weight in first 10 min of treatment. An extra synthetic
adherence operon was incorporated into the plasmid with the capacity to manufacture bulky biofilm structures in nickel (II) as well as cobalt (II) presence. Thus,
genetic manipulation shows enhanced metal sequestration and biofilm production
through E. coli which can be employed for biofiltration of nickel and cobalt
industrially through immobilized cells (Duprey et al. 2014). Nickel can be
transported to enzyme precursors by protein–protein interactions in a complicated
serial mechanism through nickel metallochaperones. To bind as well as to eliminate
nickel, these metallochaperones can be engineered. Actually, it was reported that
P. cepacia 120S (living and dead biomass) eliminates about 234.4 μg/ml nickel,
12 Remediation of Heavy Metals Through Genetically Engineered Microorganism
341
cnrCBA codes for an extremely proficient pump which can be induced in the
presence of just micromolar quantity of nickel. These gene products produce an
efflux pump which removes an extra amount of nickel from the cell. Grass et al.
(2005) also described the presence of nre (nickel resistance) operons in
Achromobacter xylosoxidans 31A. They observed the nre locus on the plasmid
pTOM9 and found that just a single gene, nreB, was accountable to provide the
whole tolerance for nickel. However, just like cnr operon, this operon is not
detoxifying Ni
2+ , but removing it from the cell. Previously, Schmidt and Schlegel
(1994) found one other operon ncc operon in the same pTOM9 plasmid, which is
giving joint tolerance for nickel, cobalt and cadmium. However, these processes of
nickel resistance do not participate much in nickel bioremediation. Seven ORFs
were investigated and named as nccYXHCBAN. Nucleotide sequences have a
strong similarity to the cnr as well as czc operons of Alcaligenes eutrophus CH34
(Tibazarwa et al. 2000). The NccX protein is having 76 amino acids with several His
residues which shows that it might be working like a metal-binding protein used for
nickel remediation (Trepreau et al. 2011). Rodrigue et al. (2005) studied the yohM
gene in E. coli and observed that it is coding a membrane-bound polypeptide with
the capacity to tolerate nickel and cobalt. More copies of yohM resulted in a
decreased level of intracellular nickel. yohM, therefore, designated now as rcnA,
was the first nickel efflux system found in E. coli. One more efflux pump for
cadmium–zinc–nickel was found in Helicobacter pylori and designated as cznABC
(Stahler et al. 2006). Of these three genes, cznA and cznC were responsible for
nickel homoeostasis. E. coli JM109 was genetically manipulated to simultaneously
induce nickel transport system and metallothionein gene which can eliminate as well
as recover Ni
2+ from aqueous solution. There is a six-time enhancement in the
nickel-binding ability in comparison to host cells after the linearized Langmuir
isotherm (Deng et al. 2003). In another investigation, the nickel/cobalt transferase
gene, NiCoT of S. aureus ATCC6538, was amplified and ligated into vector pET-3c
which bioaccumulated 11.33 mg/g nickel, three times in comparison to the original
E. coli BL21 strain (Zhang et al. 2007). RcnA nickel (Ni) and cobalt (Co) efflux
systems were repressed genomically for genetically manipulating E. coli to combine
the induction of a particular metallic transporter, NiCoT of Novosphingobium
aromaticivorans which was under plasmid regulation. This Ni/Co buster strain is
accountable for increased nickel (II) and cobalt (II) uptake as well as storage of metal
about 6 mg/g bacterial dry weight in first 10 min of treatment. An extra synthetic
adherence operon was incorporated into the plasmid with the capacity to manufacture bulky biofilm structures in nickel (II) as well as cobalt (II) presence. Thus,
genetic manipulation shows enhanced metal sequestration and biofilm production
through E. coli which can be employed for biofiltration of nickel and cobalt
industrially through immobilized cells (Duprey et al. 2014). Nickel can be
transported to enzyme precursors by protein–protein interactions in a complicated
serial mechanism through nickel metallochaperones. To bind as well as to eliminate
nickel, these metallochaperones can be engineered. Actually, it was reported that
P. cepacia 120S (living and dead biomass) eliminates about 234.4 μg/ml nickel,
12 Remediation of Heavy Metals Through Genetically Engineered Microorganism
341