ArsH of Synechocystis sp. PCC 6803 has the capacity to reduce Cr
6+ (Xue et al.
2014). Actually, these are various genetic adjustment processes present in bacteria
for tolerating chromium toxicity.
12.7.2 Copper
Copper is the third oldest commonly utilized metal which has vast uses in wires,
motors, architecture and medicines. Copperedius results from the extra amount of
copper in the body, which produces ROS and can damage protein, lipids, DNA.
Copper has two oxidation states, Cu(I) and Cu(II), which can dislodge iron (Fe) from
available Fe–S clusters of dehydratases as well as from other iron–sulphur proteins
(Macomber and Imlay 2009). According to the study of Tetaz and Luke (1983), a
plasmid pRJ1004 confers copper resistance in bacteria. Afterwards, Bender and
Cooksey (1986) reported indigenous pPT23D plasmids in P. syringae pv. tomato
helping from copper toxicity. Later on, Mellano and Cooksey (1988) confirmed the
existence of a copper inducible cop operon in the 35-kb pPT23D plasmid. It has a lot
of similarity to the copper resistance genes of P. cichorii and P. fluorescens
(Cooksey et al. 1990). Wunderli-Ye and Solioz (1999) illustrated the process of
copper tolerance in the bacterium Enterococcus hirae, which has four genes:
copYABZ. CopY codes for a repressor in response to copper, while copZ codes
for chaperone protein. It was suggested that copA coding for a protein under
restricted environment to assist in the uptake of copper and CopA as well as CopB
are found to be P-type ATPases. Incidentally Streptomyces sp. AB2A retained
copper in the beginning and later on removed harmful metals which indicated the
activity of extracellular cupric reductase in the organism (Albarracin et al. 2008). In
E. coli, copper tolerance has also been investigated in detail. It was observed that
E. coli possess a dual regulatory procedure for copper tolerance. The first one is the
cus (copper sensing) locus which is a two-component system (Munson et al. 2000).
It consists of two regulator genes, namely, cusR and cuss to make a regulator–sensor
pair to control cusCFBA expression. The CusCBA proteins are like cation/proton
antiporter complexes to remove metal ions from the cell with an influx of H
+
. CusF
binds with copper in the periplasmic space to increase copper storage in the cells
(Yu et al. 2014). A small 10-kDa protein CusF is present in periplasmic space which
is responsible for linking single copper in each polypeptide. It is associated with
copper tolerance and has many methionine, aspartate and histidine residues needed
for linking copper. However, the participation of methionine residues for CusF
linkage with copper was recognized by site-directed mutagenesis. CusF sequence
analysis exposed an N-terminal leader sequence as well as possible cleavage location
of signal peptidase which indicated the periplasmic position of CusF (Franke et al.
2003). The second system is cue or copper efflux system, which is involved with
copper homoeostasis. copA and cueO, the two genes, are under the control of the
regulatory gene cueR. CopA is found to be a P-type ATPase, while multicopper
oxidase is coded by cueO to oxidize Cu
+
. Oxidation of Cu(I) in less harmful Cu
(II) by CueO reduces dioxygen to water in four different single-electron transfer
12 Remediation of Heavy Metals Through Genetically Engineered Microorganism
335
6+ (Xue et al.
2014). Actually, these are various genetic adjustment processes present in bacteria
for tolerating chromium toxicity.
12.7.2 Copper
Copper is the third oldest commonly utilized metal which has vast uses in wires,
motors, architecture and medicines. Copperedius results from the extra amount of
copper in the body, which produces ROS and can damage protein, lipids, DNA.
Copper has two oxidation states, Cu(I) and Cu(II), which can dislodge iron (Fe) from
available Fe–S clusters of dehydratases as well as from other iron–sulphur proteins
(Macomber and Imlay 2009). According to the study of Tetaz and Luke (1983), a
plasmid pRJ1004 confers copper resistance in bacteria. Afterwards, Bender and
Cooksey (1986) reported indigenous pPT23D plasmids in P. syringae pv. tomato
helping from copper toxicity. Later on, Mellano and Cooksey (1988) confirmed the
existence of a copper inducible cop operon in the 35-kb pPT23D plasmid. It has a lot
of similarity to the copper resistance genes of P. cichorii and P. fluorescens
(Cooksey et al. 1990). Wunderli-Ye and Solioz (1999) illustrated the process of
copper tolerance in the bacterium Enterococcus hirae, which has four genes:
copYABZ. CopY codes for a repressor in response to copper, while copZ codes
for chaperone protein. It was suggested that copA coding for a protein under
restricted environment to assist in the uptake of copper and CopA as well as CopB
are found to be P-type ATPases. Incidentally Streptomyces sp. AB2A retained
copper in the beginning and later on removed harmful metals which indicated the
activity of extracellular cupric reductase in the organism (Albarracin et al. 2008). In
E. coli, copper tolerance has also been investigated in detail. It was observed that
E. coli possess a dual regulatory procedure for copper tolerance. The first one is the
cus (copper sensing) locus which is a two-component system (Munson et al. 2000).
It consists of two regulator genes, namely, cusR and cuss to make a regulator–sensor
pair to control cusCFBA expression. The CusCBA proteins are like cation/proton
antiporter complexes to remove metal ions from the cell with an influx of H
+
. CusF
binds with copper in the periplasmic space to increase copper storage in the cells
(Yu et al. 2014). A small 10-kDa protein CusF is present in periplasmic space which
is responsible for linking single copper in each polypeptide. It is associated with
copper tolerance and has many methionine, aspartate and histidine residues needed
for linking copper. However, the participation of methionine residues for CusF
linkage with copper was recognized by site-directed mutagenesis. CusF sequence
analysis exposed an N-terminal leader sequence as well as possible cleavage location
of signal peptidase which indicated the periplasmic position of CusF (Franke et al.
2003). The second system is cue or copper efflux system, which is involved with
copper homoeostasis. copA and cueO, the two genes, are under the control of the
regulatory gene cueR. CopA is found to be a P-type ATPase, while multicopper
oxidase is coded by cueO to oxidize Cu
+
. Oxidation of Cu(I) in less harmful Cu
(II) by CueO reduces dioxygen to water in four different single-electron transfer
12 Remediation of Heavy Metals Through Genetically Engineered Microorganism
335