and Ni by the plant (Raskin et al. 1997). It has been studied that Cd stimulates the
synthesis of phytochelatins (PCs), which form a Cd–PC complex of low molecular
weight. Cd–PC complex is then transported into vacuole by Cd/H antiport and
ATP-dependent PC transport protein. The gene (Hmt1) is responsible for
transporting the Cd–PC complex into the vacuole (Sriprand and Murooka 2007).
Metallothioneins (MTs) are cysteine-rich metal-chelating proteins in plants that help
to sequester toxic heavy metal such as cadmium, Hg, Cu, Zn, etc. However there is
requirement that plant biomass must be harvested and removed, followed by metal
reclamation or proper and safe disposal of the biomass.
5.2 Role of Environmental Biotechnology and Genetic
Engineering in Improving Efficient Bioremediation
Various biotechnological approaches such as bioleaching, bioremediation,
bioencapsulation, biostimulation (stimulating living microbial population), biomineralization (synthesis of mineral by living organisms or biomaterials),
mycoremediation (stimulation of fungi), cyanoremediation (stimulating algal biomass), rhizoremediation (plant and microbes) biosorption (dead microbial and
renewable agricultural biomass), and bioextraction are advanced bioremediation
processes to remove heavy metals from the polluted environment.
Environmental biotechnology plays an important role in bioremediation of cadmium from the environment. Understanding the mechanism through which microorganisms capture heavy metals, i.e., metabolism and detoxification pathways, may
lead to the solution of environmental problem associated with heavy metals in a
maximum efficiency. Genes responsible for metal uptake, translocation, sequestration, and bioaccumulation have been identified. Transfer of these genes into organisms will result in the generation of transgenic organism having greater ability for
metal accumulation and detoxification.
Large numbers of bacteria and algae have been genetically engineered to remove
selective heavy metals from polluted soil and water by overexpressing a heavy
metal-binding protein, such as metallothionein, along with a specific metal transport
system (Chen and Wilson 1997; Liu et al. 2011). Various peptides consisting of
metal-binding amino acids (histidine and cysteine residues) have been studied in
bacteria to increase heavy metal accumulation (Liu et al. 2011). Bang et al. (2000)
reported that expression of the thiosulfate reductase gene from Salmonella
typhimurium in Escherichia coli led to increase of the efficiency of removal of
heavy metals from solution and accumulation of cadmium up to 150 mM in 98%
cells. In genetically engineered Ralstonia eutropha, a mouse metallothionein fusion
protein (MTβ) was inserted that displays on the surface of the cell. The MTβ-bearing
cells were able to sequester cadmium from a contaminated soil, partially ameliorating the effects of metal contamination and promoting growth of metal-sensitive
tobacco plants (Lovley and Lloyd 2000) (Fig. 15.5).
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S. Saini and G. Dhania
synthesis of phytochelatins (PCs), which form a Cd–PC complex of low molecular
weight. Cd–PC complex is then transported into vacuole by Cd/H antiport and
ATP-dependent PC transport protein. The gene (Hmt1) is responsible for
transporting the Cd–PC complex into the vacuole (Sriprand and Murooka 2007).
Metallothioneins (MTs) are cysteine-rich metal-chelating proteins in plants that help
to sequester toxic heavy metal such as cadmium, Hg, Cu, Zn, etc. However there is
requirement that plant biomass must be harvested and removed, followed by metal
reclamation or proper and safe disposal of the biomass.
5.2 Role of Environmental Biotechnology and Genetic
Engineering in Improving Efficient Bioremediation
Various biotechnological approaches such as bioleaching, bioremediation,
bioencapsulation, biostimulation (stimulating living microbial population), biomineralization (synthesis of mineral by living organisms or biomaterials),
mycoremediation (stimulation of fungi), cyanoremediation (stimulating algal biomass), rhizoremediation (plant and microbes) biosorption (dead microbial and
renewable agricultural biomass), and bioextraction are advanced bioremediation
processes to remove heavy metals from the polluted environment.
Environmental biotechnology plays an important role in bioremediation of cadmium from the environment. Understanding the mechanism through which microorganisms capture heavy metals, i.e., metabolism and detoxification pathways, may
lead to the solution of environmental problem associated with heavy metals in a
maximum efficiency. Genes responsible for metal uptake, translocation, sequestration, and bioaccumulation have been identified. Transfer of these genes into organisms will result in the generation of transgenic organism having greater ability for
metal accumulation and detoxification.
Large numbers of bacteria and algae have been genetically engineered to remove
selective heavy metals from polluted soil and water by overexpressing a heavy
metal-binding protein, such as metallothionein, along with a specific metal transport
system (Chen and Wilson 1997; Liu et al. 2011). Various peptides consisting of
metal-binding amino acids (histidine and cysteine residues) have been studied in
bacteria to increase heavy metal accumulation (Liu et al. 2011). Bang et al. (2000)
reported that expression of the thiosulfate reductase gene from Salmonella
typhimurium in Escherichia coli led to increase of the efficiency of removal of
heavy metals from solution and accumulation of cadmium up to 150 mM in 98%
cells. In genetically engineered Ralstonia eutropha, a mouse metallothionein fusion
protein (MTβ) was inserted that displays on the surface of the cell. The MTβ-bearing
cells were able to sequester cadmium from a contaminated soil, partially ameliorating the effects of metal contamination and promoting growth of metal-sensitive
tobacco plants (Lovley and Lloyd 2000) (Fig. 15.5).
376
S. Saini and G. Dhania