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As a result, extremophiles could be used in the elimination of toxic metals from toxic locations

and sludges. However, more research into advancing technology for investigating microbial

surroundings and gaining insight into the pathways analysis which influence microbial activity and

metal degradation metabolic pathways under severe environments is necessary.

10.7 Recombinant DNA Technology for Bioremediation

Genetic engineering methods such as recombinant DNA technology, which include genetic transfer

between bacteria, are used to manipulate the genetic makeup of organisms, which are known as

Genetically Modified Microorganisms (GMM) or Genetically Engineered Microorganisms (GEM).

Microbial Metal Resistance genes (MMRg) are useful genetic strategies for modifying bacteria.

Several MMRg-based bioremediation technologies have been proposed (Zheng et al. 2019).

Genetically modified microorganisms are being used for the effective removal of toxic metals from

the environment. Customized microbial genes in genetically modified organisms provide novel

metabolic pathways that improve the efficiency of bioremediation methods (Holliger and Zehnder

1996). In genetically modified microorganisms, the expression of genes is controlled, which is more

important for the conversion of toxic metals to fewer toxic species/forms (Bondarenko et al. 2008).

The microbial potential has been successfully utilized in different investigations.

The genome sequence of many bacterial communities involved in bioremediation has been

done (Rahman et al. 2017, Yang et al. 2017). The genetic makeup of Pseudomonas sp. KT2440

(6.2 MB) has been analyzed, revealing the presence of genes encoding a wide range of enzymes and

proteins and efflux pumps, each of which plays a critical role in the deterioration of a number of

chemicals. Several additional investigations have revealed that microorganisms are engaged in the

bioremediation of toxic metals, dyes and other chemicals, depending on their genome (Belda et al.

2016, Dangi et al. 2017).

A genetically engineered E. coli strain could successfully remove mercury from the

contaminated area, including water or soil (Sharma and Shukla 2020). Transgenic bacteria with

metallothioneins and polyphosphate kinase genes are appropriate for mercury bioremediation.

Similarly, Cd-contaminated industrial effluent was reported to be treated using genetically modified

Ralstonia metallidurans and Caulobacter spp. (Patel et al. 2010, Azad et al. 2014). Arsenic (As)

may be removed from contaminated soil by transgenic bacteria expressing the ArsM gene through

volatilization (Liu et al. 2019). Bioaccumulation has also been observed in genetically modified

strains of E. coli with enhanced expression of the ArsR gene (Kostal et al. 2004). Nickel is one of

the most refractory pollutants that could be accumulated by genetically engineered E. coli strain

from an aqueous solution (Pacwa-Płociniczak et al. 2011). In another study, the merB and merG

genes were added to the mercury-resistant Cupriavidus metallidurans strain MSR33 to regulate Hg

biodegradation (Rojas et al. 2011).

Even though genetic engineering has devised a number of variants and bacterial species capable

of degrading contaminants, there are many barriers. A major concern towards developed strains

and microorganism’s species is their low bioremediation efficiency. In microbiological ecology,

the use of Stable Isotope Probing (SIP) and related methods have shown that Rhodococcus and

Pseudomonas, which grow faster, are often used as biodegradation hosts but are much less effective

in various natural conditions (Tahri et al. 2013). The main issue with this effective bioremediation

state is keeping the ground conditions for engineered microbes under control. P. fluorescens HK44

has been actively monitored for the optimum ground conditions for bioremediation in the ecosystem

(Ripp et al. 2000). As a result, when it comes to pollution clean-up, GEMs do not appear without

the risks of their introduction into the environment. The adverse field conditions for the designed

microorganisms constitute a significant issue in bioremediation. In naturalistic settings, bacteria

such as E. coli (Bondarenko et al. 2008), B. subtilis (Ivask et al. 2011), and P. putida (Wu et al. 2006)

have been used to focus on ways in which the molecular significance is primarily restricted. The

need for adaptation of created bacterial strains to meet the new challenge is a crucial characteristic