significantly more Cd than the wild type (Zhu et al. 1999). Transgenic plants
expressing glutathione (GSH) have great efficiency for enhancing the Cd
phytoextraction from polluted soils and wastewater. These plants may also show
increased tolerance and accumulation of other heavy metals, because PCs are
thought to play a role in tolerance of a wide range of heavy metals. Simultaneous
expression of Allium sativum phytochelatins synthase (AsPCS1) and yeast cadmium
factor 1 (YCF1) in Arabidopsis led to increase the tolerance to Cd and As and have
higher amounts accumulation of these metals as compared with single-gene transgenic lines and wildtype (Jiangbo et al. 2012).
Transfer of human MT-2 gene to Nicotiana tobacuum, Brassica sp., and
Arabidopsis thaliana resulted in the transgenic plant with enhanced tolerance and
accumulation of cadmium. Development of transgenic cauliflower (Brassica
capitata) having 16-fold higher accumulation of cadmium by transferring CUP
1 gene (Vasavi et al. 2010).
5.3 Factors Affecting Bioremediation of Cadmium
Bioremediation processes are a complex system affected by many environmental
factors such as nutrients, type of soil, pH, moisture content, temperature, and the
presence of oxygen.
(a) Nutrients: Carbon is the most important element for living forms and is required
in large quantities than other elements. Hydrogen, nitrogen, and oxygen also
constitute about 95% of the weight. Contaminated sites are rich source of
organic carbon which is depleted during microbial metabolism. So there is
need of nitrogen, phosphate, and potassium in the contaminated site which
stimulate the cellular metabolism and growth of the microorganisms to augment
the bioremediation. Bioremediation processes require 30:1 carbon-to-phosphorus ratio and 10:1(C:N) carbon-to-nitrogen ratio. However biodegradation of
contaminated soil is much faster with higher C:N (25:1) ratio (Atagana et al.
2003).
(b) Soil structure: Soil can be classified into silt, sand, and clay depending upon the
textures. Granular and well-structured soil provides effective delivery of air,
water, and nutrients to the microorganisms during in situ bioremediation process. To improve soil structure, materials like gypsum or organic matter can be
added. Low soil permeability may not be suitable as it can impede movement of
nutrients, water, and oxygen into soils.
(c) pH: pH from 5.5–8.0 is found to be suitable for the growth of microbes as well to
destroy the contaminants (Vidali 2001).
(d) Moisture content: Water is the primary factor in determining the dielectric
constant of soil and other mediums. Soil moisture content generally ranges
from 25 to 28% (Vidali 2001)
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S. Saini and G. Dhania
expressing glutathione (GSH) have great efficiency for enhancing the Cd
phytoextraction from polluted soils and wastewater. These plants may also show
increased tolerance and accumulation of other heavy metals, because PCs are
thought to play a role in tolerance of a wide range of heavy metals. Simultaneous
expression of Allium sativum phytochelatins synthase (AsPCS1) and yeast cadmium
factor 1 (YCF1) in Arabidopsis led to increase the tolerance to Cd and As and have
higher amounts accumulation of these metals as compared with single-gene transgenic lines and wildtype (Jiangbo et al. 2012).
Transfer of human MT-2 gene to Nicotiana tobacuum, Brassica sp., and
Arabidopsis thaliana resulted in the transgenic plant with enhanced tolerance and
accumulation of cadmium. Development of transgenic cauliflower (Brassica
capitata) having 16-fold higher accumulation of cadmium by transferring CUP
1 gene (Vasavi et al. 2010).
5.3 Factors Affecting Bioremediation of Cadmium
Bioremediation processes are a complex system affected by many environmental
factors such as nutrients, type of soil, pH, moisture content, temperature, and the
presence of oxygen.
(a) Nutrients: Carbon is the most important element for living forms and is required
in large quantities than other elements. Hydrogen, nitrogen, and oxygen also
constitute about 95% of the weight. Contaminated sites are rich source of
organic carbon which is depleted during microbial metabolism. So there is
need of nitrogen, phosphate, and potassium in the contaminated site which
stimulate the cellular metabolism and growth of the microorganisms to augment
the bioremediation. Bioremediation processes require 30:1 carbon-to-phosphorus ratio and 10:1(C:N) carbon-to-nitrogen ratio. However biodegradation of
contaminated soil is much faster with higher C:N (25:1) ratio (Atagana et al.
2003).
(b) Soil structure: Soil can be classified into silt, sand, and clay depending upon the
textures. Granular and well-structured soil provides effective delivery of air,
water, and nutrients to the microorganisms during in situ bioremediation process. To improve soil structure, materials like gypsum or organic matter can be
added. Low soil permeability may not be suitable as it can impede movement of
nutrients, water, and oxygen into soils.
(c) pH: pH from 5.5–8.0 is found to be suitable for the growth of microbes as well to
destroy the contaminants (Vidali 2001).
(d) Moisture content: Water is the primary factor in determining the dielectric
constant of soil and other mediums. Soil moisture content generally ranges
from 25 to 28% (Vidali 2001)
378
S. Saini and G. Dhania