hazards to living beings. However, phytoremediation has some disadvantages such
as limitation to the surface area and depth occupied by the roots, slow plant growth,
low biomass production, and contamination possibility of food chain by accumulated contaminants (Macek et al. 2008). Phytoremediation covers several different
strategies such as phytoextraction, rhizofiltration, phytostabilization, phytovolatilization,
etc. (Eapen and D’Souza 2005; Cherian and Oliveira 2005; Doty 2008; Macek et al.
2008).
4 Genetically Engineered Bacteria in Bioremediation
of Heavy Metals and Organic Pollutants
Water and soil are essential components of all living things on earth. But unfortunately these are contaminated by geogenic and anthropogenic activities like mining,
volcanic eruption, heavy rainfall, industrializations, urbanization, and agriculture
waste, which are liable for the pollution of our natural environment and toxicity in
the living beings. Therefore, it is urgent need to adequately treat the contaminated
water and soil to protect the environment and public health. There are several reports
available on the bioremediation of heavy metals and organic pollutants by different
microorganisms (Strong et al. 2000; Barac et al. 2004). Genetically engineered
bacteria reported in the degradation and detoxification of organic and inorganic
pollutants are listed in Table 1.1.
A variety of potential strains of bacteria such as Bacillus idriensis, Ralstonia
eutropha, Sphingomonas desiccabilis, Pseudomonas putida, Escherichia coli,
Mycobacterium marinum, etc. have been genetically engineered for the enhanced
bioremediation of toxic heavy metals in the contaminated matrix (Valls et al. 2000;
Deng et al. 2003; Ackerley et al. 2004; Deng et al. 2005; Kube et al. 2005; Parnell
et al. 2006; Singh et al. 2008; Schue et al. 2009; Liu et al. 2011). Bioremediation of
Hg is mainly facilitated by transgene that confers arsenic resistance to microbes such
as mer operon genes (Jan et al. 2009), mercuric ion transporter gene merC in
Acidithiobacillus ferrooxidans (Sasaki et al. 2005), and mercuric ion transporter
gene merH in Mycobacterium marinum (Schue et al. 2009). The genetically
engineered radiation-resistant bacterium, Deinococcus radiodurans, also showed a
great potential for the bioremediation of radioactive waste containing mercury ion
(Brim et al. 2000). The genetically engineered mercury-resistant bacterium,
Escherichia coli (merT-merP and MT genes), also showed a huge potential for the
removal of Hg
2+ from electrolytic wastewater (Deng and Wilson 2001). It has been
also reported that the accumulation of Cd
2+ was enhanced into Mesorhizobium
huakuii when transformed with a gene that code for phytochelatins from Arabidopsis
thaliana (Sriprang et al. 2003).
Kang et al. (2007) reported that the recombinant E. coli can accumulate Cd up to
25-fold more than control strain. Wu et al. (2006, 2010) studied the alleviation of Cd
toxicity using a metal-binding peptide (EC20) expressing rhizobacterium,
6
G. Saxena et al.
as limitation to the surface area and depth occupied by the roots, slow plant growth,
low biomass production, and contamination possibility of food chain by accumulated contaminants (Macek et al. 2008). Phytoremediation covers several different
strategies such as phytoextraction, rhizofiltration, phytostabilization, phytovolatilization,
etc. (Eapen and D’Souza 2005; Cherian and Oliveira 2005; Doty 2008; Macek et al.
2008).
4 Genetically Engineered Bacteria in Bioremediation
of Heavy Metals and Organic Pollutants
Water and soil are essential components of all living things on earth. But unfortunately these are contaminated by geogenic and anthropogenic activities like mining,
volcanic eruption, heavy rainfall, industrializations, urbanization, and agriculture
waste, which are liable for the pollution of our natural environment and toxicity in
the living beings. Therefore, it is urgent need to adequately treat the contaminated
water and soil to protect the environment and public health. There are several reports
available on the bioremediation of heavy metals and organic pollutants by different
microorganisms (Strong et al. 2000; Barac et al. 2004). Genetically engineered
bacteria reported in the degradation and detoxification of organic and inorganic
pollutants are listed in Table 1.1.
A variety of potential strains of bacteria such as Bacillus idriensis, Ralstonia
eutropha, Sphingomonas desiccabilis, Pseudomonas putida, Escherichia coli,
Mycobacterium marinum, etc. have been genetically engineered for the enhanced
bioremediation of toxic heavy metals in the contaminated matrix (Valls et al. 2000;
Deng et al. 2003; Ackerley et al. 2004; Deng et al. 2005; Kube et al. 2005; Parnell
et al. 2006; Singh et al. 2008; Schue et al. 2009; Liu et al. 2011). Bioremediation of
Hg is mainly facilitated by transgene that confers arsenic resistance to microbes such
as mer operon genes (Jan et al. 2009), mercuric ion transporter gene merC in
Acidithiobacillus ferrooxidans (Sasaki et al. 2005), and mercuric ion transporter
gene merH in Mycobacterium marinum (Schue et al. 2009). The genetically
engineered radiation-resistant bacterium, Deinococcus radiodurans, also showed a
great potential for the bioremediation of radioactive waste containing mercury ion
(Brim et al. 2000). The genetically engineered mercury-resistant bacterium,
Escherichia coli (merT-merP and MT genes), also showed a huge potential for the
removal of Hg
2+ from electrolytic wastewater (Deng and Wilson 2001). It has been
also reported that the accumulation of Cd
2+ was enhanced into Mesorhizobium
huakuii when transformed with a gene that code for phytochelatins from Arabidopsis
thaliana (Sriprang et al. 2003).
Kang et al. (2007) reported that the recombinant E. coli can accumulate Cd up to
25-fold more than control strain. Wu et al. (2006, 2010) studied the alleviation of Cd
toxicity using a metal-binding peptide (EC20) expressing rhizobacterium,
6
G. Saxena et al.