bioremediation does not require external energy sources for their growth and hence
showed enhanced bioremediation (Iwamoto and Minoda 2018). For growth, autotrophic algae need only light, water, carbon dioxide and dissolved minerals.
Recently algal bioremediation showed effective role in remediating sites contaminated with radionuclides. Chlorella vulgaris showed efficient biosorption of uranium, and the rate of biosorption depends on the availability of carboxylic and
phosphate groups. The concentration of uranium, pH and the status of cell is also
directly related to the uranium biosorption (Vogel et al. 2010). Different microalgae
showed effective results in remediation or radionuclides like radioiodine, caesium,
strontium, etc. For example, a green Parachlorella sp. binos microalgae when
cultured under radioiodine condition. It accumulates radioiodine into the cytosol in
light-dependent manner. The microalgae are also able to accumulate strontium and
caesium in light-independent manner, and accumulation of strontium was observed
into the extracellular matrix of Parachlorella sp. (Shimura et al. 2012). Coccomyxa
actinabiotis sp. nov. isolated from nuclear agencies is able to survive under high
ionizing radiation doses up to 20,000 Gy, and it is supposed to be 2000 times lethal
human dose. The microalgae are also able to accumulate high amount of radionuclides like
238 U,
137 Cs,
110m Ag,
60 Co,
54 Mn,
65 Zn and
14 C (Earis 2009).
13.2.4 Genetic Engineering: Bioremediation of Radioactive
Wastes
Due to adverse environmental conditions, it seems impossible for microbes to
survive and remediates pollutants. But there are still some microbes which can resist
extreme environmental conditions but fail to remediate the contaminants (Katarína
et al. 2018). In this case, genetic engineering provides a new insight in the field of
bioremediation as many microbes can be designed in such a way that can remediate
the contaminants which are not done by normal microbes. In this case by altering
gene sequences of desired microbes and enhancing its ability to degrade, digest, and
accumulate contaminants or sometimes reconstructing a microbe by inserting a gene
which has an extraordinary ability to remediate the specific contamination. Thus,
reconstruction of microbes for bioremediation is done specifically (Jaiswal et al.
2019). Deinococcus radiodurans is a well-known radio-resistant bacteria that have
the ability to reduce radioactive wastes like Cr(VI), U(VI) and Tc(VII) (Fredrickson
et al. 2000). Attempts were made to reconstruct Deinococcus radiodurans that has
the ability to reduce the radionuclides along with other contaminants like other
metals and organic pollutants. Incorporation of an E. coli (merA) gene provides
carbon assimilation property for energy generation generated from toluene and
mercury catabolism. Thus, genetically modified Deinococcus radiodurans can be
a promising tool for bioremediation of radionuclides along with other pollutants
(Watanabe 2001). Similarly, expressing the PhoN gene in Deinococcus radiodurans
through rDNA technologies increased 6 months shelf life of the bacteria also
13 Role of Microbes in Bioremediation of Radioactive Waste
345
showed enhanced bioremediation (Iwamoto and Minoda 2018). For growth, autotrophic algae need only light, water, carbon dioxide and dissolved minerals.
Recently algal bioremediation showed effective role in remediating sites contaminated with radionuclides. Chlorella vulgaris showed efficient biosorption of uranium, and the rate of biosorption depends on the availability of carboxylic and
phosphate groups. The concentration of uranium, pH and the status of cell is also
directly related to the uranium biosorption (Vogel et al. 2010). Different microalgae
showed effective results in remediation or radionuclides like radioiodine, caesium,
strontium, etc. For example, a green Parachlorella sp. binos microalgae when
cultured under radioiodine condition. It accumulates radioiodine into the cytosol in
light-dependent manner. The microalgae are also able to accumulate strontium and
caesium in light-independent manner, and accumulation of strontium was observed
into the extracellular matrix of Parachlorella sp. (Shimura et al. 2012). Coccomyxa
actinabiotis sp. nov. isolated from nuclear agencies is able to survive under high
ionizing radiation doses up to 20,000 Gy, and it is supposed to be 2000 times lethal
human dose. The microalgae are also able to accumulate high amount of radionuclides like
238 U,
137 Cs,
110m Ag,
60 Co,
54 Mn,
65 Zn and
14 C (Earis 2009).
13.2.4 Genetic Engineering: Bioremediation of Radioactive
Wastes
Due to adverse environmental conditions, it seems impossible for microbes to
survive and remediates pollutants. But there are still some microbes which can resist
extreme environmental conditions but fail to remediate the contaminants (Katarína
et al. 2018). In this case, genetic engineering provides a new insight in the field of
bioremediation as many microbes can be designed in such a way that can remediate
the contaminants which are not done by normal microbes. In this case by altering
gene sequences of desired microbes and enhancing its ability to degrade, digest, and
accumulate contaminants or sometimes reconstructing a microbe by inserting a gene
which has an extraordinary ability to remediate the specific contamination. Thus,
reconstruction of microbes for bioremediation is done specifically (Jaiswal et al.
2019). Deinococcus radiodurans is a well-known radio-resistant bacteria that have
the ability to reduce radioactive wastes like Cr(VI), U(VI) and Tc(VII) (Fredrickson
et al. 2000). Attempts were made to reconstruct Deinococcus radiodurans that has
the ability to reduce the radionuclides along with other contaminants like other
metals and organic pollutants. Incorporation of an E. coli (merA) gene provides
carbon assimilation property for energy generation generated from toluene and
mercury catabolism. Thus, genetically modified Deinococcus radiodurans can be
a promising tool for bioremediation of radionuclides along with other pollutants
(Watanabe 2001). Similarly, expressing the PhoN gene in Deinococcus radiodurans
through rDNA technologies increased 6 months shelf life of the bacteria also
13 Role of Microbes in Bioremediation of Radioactive Waste
345