1 Introduction
In the last few decades, due to industrialization, increase in population, and daily life
requirements, harmful chemicals have been released into the earth’s air, soil, and
water (Goutam et al. 2018; Gautam et al. 2017; Bharagava et al. 2017a, b; Saxena
et al. 2016; Olugbenga 2017). Excessive mining, agriculture waste, and burning of
fossil fuels consequently release enormous amounts of toxic heavy metals like Hg,
Pb, U, Cd, Zn, Cr, Ni, Co, and Cu and metalloids (As) into the environment which
create mutagenic and carcinogenic effect (Wernick and Themelis 1998; Wijnhoven
et al. 2007). Several chemical industries use and produce wide varieties of hazardous
compounds like benzene, toluene, polychlorinated biphenyls (PCBs), polyaromatic
hydrocarbons (PAHs), dioxins, nitro-aromatics, dyes, polymers, pesticides, explosives, chlorinated organic, and pharmaceuticals (Meagher 2000; Pilon-Smits 2005).
Moreover, many of these substances are non-biodegradable and persistent in
nature that stay long in our natural environment. Many of these substances are
toxic and cause a harmful effect on human health and damage the ecological balance.
However, there is an urgent need to remove these compounds for environmental and
public health safety. The remediation and restoration of sites contaminated with
highly toxic and hazardous pollutants requires eco-friendly and effective approach
for environmental sustainability and to safeguard the public health. Microbial
bioremediation is a waste management technology which uses microorganisms
like bacteria, algae, and fungi to degrade and transform hazardous compounds of
soil and water, while phytoremediation is cost-effective and environmental-friendly
technology that has a potential application to efficiently degrade and transform
organic and inorganic pollutants (Kishor et al. 2018; Saxena and Bharagava
2016; Bharagava et al. 2017c, 2019; Meagher 2000).
Eventually, naturally occurring microorganisms are incapable of degrading all
toxic compounds, especially xenobiotic. To overcome this, serious efforts have been
done to create genetically engineered microorganisms (GEMs) to enhance bioremediation approaches besides degrading xenobiotic (Sayler and Ripp 2000). Thus,
biotechnology is a most important technique that has been applied in different
areas especially in remediation to neutralize various unfit complex environmental
pollutants into nontoxic or simple form and to completely remediate organic wastes
(Iwamoto and Nasu 2001). Recombinant DNA technology has been studied intensively to improve the biodegradation of hazardous pollutants in lab conditions (Dua
et al. 2002). In the late 1970s and early 1980s, the cloning and characterization of
bacterial genes that code for catabolic enzymes for the biodegradation of recalcitrant
pollutants has started. The organism whose genetic material, i.e., DNA, has been
modified/altered in such a way so as to get the required traits is often called as
genetically modified organism (Shukla et al. 2010; Liu et al. 2011). This technology
is often called “gene technology,” or “recombinant DNA technology” (RDT), or
“genetic engineering,” and the resulting organism is said to be “genetically modified,” “genetically engineered,” or “transgenic.”
2
G. Saxena et al.
In the last few decades, due to industrialization, increase in population, and daily life
requirements, harmful chemicals have been released into the earth’s air, soil, and
water (Goutam et al. 2018; Gautam et al. 2017; Bharagava et al. 2017a, b; Saxena
et al. 2016; Olugbenga 2017). Excessive mining, agriculture waste, and burning of
fossil fuels consequently release enormous amounts of toxic heavy metals like Hg,
Pb, U, Cd, Zn, Cr, Ni, Co, and Cu and metalloids (As) into the environment which
create mutagenic and carcinogenic effect (Wernick and Themelis 1998; Wijnhoven
et al. 2007). Several chemical industries use and produce wide varieties of hazardous
compounds like benzene, toluene, polychlorinated biphenyls (PCBs), polyaromatic
hydrocarbons (PAHs), dioxins, nitro-aromatics, dyes, polymers, pesticides, explosives, chlorinated organic, and pharmaceuticals (Meagher 2000; Pilon-Smits 2005).
Moreover, many of these substances are non-biodegradable and persistent in
nature that stay long in our natural environment. Many of these substances are
toxic and cause a harmful effect on human health and damage the ecological balance.
However, there is an urgent need to remove these compounds for environmental and
public health safety. The remediation and restoration of sites contaminated with
highly toxic and hazardous pollutants requires eco-friendly and effective approach
for environmental sustainability and to safeguard the public health. Microbial
bioremediation is a waste management technology which uses microorganisms
like bacteria, algae, and fungi to degrade and transform hazardous compounds of
soil and water, while phytoremediation is cost-effective and environmental-friendly
technology that has a potential application to efficiently degrade and transform
organic and inorganic pollutants (Kishor et al. 2018; Saxena and Bharagava
2016; Bharagava et al. 2017c, 2019; Meagher 2000).
Eventually, naturally occurring microorganisms are incapable of degrading all
toxic compounds, especially xenobiotic. To overcome this, serious efforts have been
done to create genetically engineered microorganisms (GEMs) to enhance bioremediation approaches besides degrading xenobiotic (Sayler and Ripp 2000). Thus,
biotechnology is a most important technique that has been applied in different
areas especially in remediation to neutralize various unfit complex environmental
pollutants into nontoxic or simple form and to completely remediate organic wastes
(Iwamoto and Nasu 2001). Recombinant DNA technology has been studied intensively to improve the biodegradation of hazardous pollutants in lab conditions (Dua
et al. 2002). In the late 1970s and early 1980s, the cloning and characterization of
bacterial genes that code for catabolic enzymes for the biodegradation of recalcitrant
pollutants has started. The organism whose genetic material, i.e., DNA, has been
modified/altered in such a way so as to get the required traits is often called as
genetically modified organism (Shukla et al. 2010; Liu et al. 2011). This technology
is often called “gene technology,” or “recombinant DNA technology” (RDT), or
“genetic engineering,” and the resulting organism is said to be “genetically modified,” “genetically engineered,” or “transgenic.”
2
G. Saxena et al.