Insights into the Status of Heavy Metal Resistant Rhizobacterial …
21
and foremost is chromate efflux from the cells, and another one is the reduction of
toxic form Cr
6+ into less toxic form Cr
3+ . The efflux protein of chromate is encoded
by chrAgene, which has homologs in eubacteria, archaea, and also in some eukaryotes (Das et al. 2016). Nies et al. (1998) defined about two chromate efflux pumps
with six transmembrane segments but Diaz-Magana et al. (2009) described that in
E. coli, these two pumps are not separate ones, however together form a heterodimer
of 12 segments.
3.5 Copper
Copper is third oldest abundantly used metal having wide applications in wires,
architecture, motors and medicines. Consuming more amount of copper in the
body causes Copperiedus, leading to the production of Reactive Oxygen Species
(ROS), which have the potential to damage proteins, DNA and lipids. Two oxidation states Cu(I) and Cu(II) involve in copper cycles and dislocate iron (Fe) from
available Fe–S clusters in dehydratases and other iron sulphur proteins (Macomber
and Imlay 2009). Plasmid pRJ1004-mediated copper resistance in bacteria was first
reported by Tetaz and Luke (1983). Later on Bender and Cooksey (1986) identified native pPT23D plasmids in Pseudomonas syringae helping tomato from copper
toxicity. However, the removal of cytoplasmic copper is involved by ATPase-driven
copper efflux system. Periplasmic copper handling, metallochaperones, multicopper
oxidases and Resistance-Nodulation-Division (RND) systems are involved in this
process (Bondarczuk and Piotrowska-Seget 2013).
3.6 Mercury
Compared to other toxic metal pollutants, mercury is one of the most toxic elements in
the earth which has severe health concerns. It is strong in sediments, soils, water and
atmosphere. Through anthropogenic activities mercury enters into the environment.
Mercury resistant bacteria have two operons. One of the operons is narrow-spectrum
mer operon and another one is broad spectrum mer operon (Matsui et al. 2016).
Consensus sequence GMTCAAC is present in the mercury binding site. MerP scavenges inorganic mercury ions and transports them to the MerT protein (Hamlett et al.
1992). merC expression in Arabidopsis thaliana and Nicotiana tabacum has led to
their doubling ability to accumulate mercury (Sasaki et al. 2006).
21
and foremost is chromate efflux from the cells, and another one is the reduction of
toxic form Cr
6+ into less toxic form Cr
3+ . The efflux protein of chromate is encoded
by chrAgene, which has homologs in eubacteria, archaea, and also in some eukaryotes (Das et al. 2016). Nies et al. (1998) defined about two chromate efflux pumps
with six transmembrane segments but Diaz-Magana et al. (2009) described that in
E. coli, these two pumps are not separate ones, however together form a heterodimer
of 12 segments.
3.5 Copper
Copper is third oldest abundantly used metal having wide applications in wires,
architecture, motors and medicines. Consuming more amount of copper in the
body causes Copperiedus, leading to the production of Reactive Oxygen Species
(ROS), which have the potential to damage proteins, DNA and lipids. Two oxidation states Cu(I) and Cu(II) involve in copper cycles and dislocate iron (Fe) from
available Fe–S clusters in dehydratases and other iron sulphur proteins (Macomber
and Imlay 2009). Plasmid pRJ1004-mediated copper resistance in bacteria was first
reported by Tetaz and Luke (1983). Later on Bender and Cooksey (1986) identified native pPT23D plasmids in Pseudomonas syringae helping tomato from copper
toxicity. However, the removal of cytoplasmic copper is involved by ATPase-driven
copper efflux system. Periplasmic copper handling, metallochaperones, multicopper
oxidases and Resistance-Nodulation-Division (RND) systems are involved in this
process (Bondarczuk and Piotrowska-Seget 2013).
3.6 Mercury
Compared to other toxic metal pollutants, mercury is one of the most toxic elements in
the earth which has severe health concerns. It is strong in sediments, soils, water and
atmosphere. Through anthropogenic activities mercury enters into the environment.
Mercury resistant bacteria have two operons. One of the operons is narrow-spectrum
mer operon and another one is broad spectrum mer operon (Matsui et al. 2016).
Consensus sequence GMTCAAC is present in the mercury binding site. MerP scavenges inorganic mercury ions and transports them to the MerT protein (Hamlett et al.
1992). merC expression in Arabidopsis thaliana and Nicotiana tabacum has led to
their doubling ability to accumulate mercury (Sasaki et al. 2006).