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Bioremediation for Sustainable Environmental Cleanup

9.5.5 Modification of Rhizosphere

Rhizosphere bioremediation uses microbes accompanied by roots’ remarkable abilities to break

down organic contaminants and convert hazardous metals. As this plant-based approach is an in-situ

photo restoration method, it is cost-effective, efficient and simple to implement in the field (Kumar

and Fulekar 2018). The toxicity of metals could be reduced by volatilization, phytoextraction and the

degradation process. Metals should usually be physically removed or immobilized, whereas organic

substances can be destroyed. Rhizoremediation has been documented to be a virtuous technique

along with various strategies like microbial augmentation as well as transgenic approaches (Kumar

and Fulekar 2018).

9.5.5.1 Transgenic Technology in Bioremediation

Proteomic, metabolomic, transcriptomic, genomic and metagenomic approaches are being used

to determine traits that maximize the utility of on-ground harvesting techniques and control the

resistance, degradation and accumulation potential of plants and microorganisms to a diversity

of inorganic and organic contaminates by recent advances in omics technologies. Transgenic and

cisgenic techniques can be used to manipulate potential plant species to boost pollutant intake,

transport and degradation, plant development and vitality, root formation and abiotic stress resilience.

Organic matter can be detoxified and inorganic contaminants can be enriched using transgenic

plants (Maestri and Marmiroli 2011). The production of genes that break down pollutants in

prospective bioenergy systems aims to reduce organic contamination of plant tissues and make plant

products from plant protection plantations more accessible. Selected metal transporters expressed in

transgenic plants increase sulfur metabolism output. Chelators that detoxify metals, metallothioneins

and phytochelatins, can also improve heavy metal uptake, transport and accumulation (Ruiz and

Daniell 2009). Transgenic plants expressing three microbial reductases can also promote Hg and Se

volatilization as well as arsenic accumulation in plant shoots. There are also several cases of microbial

genes being successfully incorporated into plant tissue for better biodegradation. These genes code

aid in transporting metals and the breakdown of organic pollutants (Dhankher et al. 2012, Iimura

et al. 2007, Che et al. 2003, Bittsanszkya et al. 2005, Van Dillewijn et al. 2008, Doty et al. 2000). For

instance, to decontaminate explosives (TNT and RDX), transgenic plants were created employing

microbial pollutant-degrading genes (Iimura et al. 2007, Che et al. 2003, Bittsanszkya et al. 2005,

Van Dillewijn et al. 2008). Plants that grow fast and generate a lot of biomasses, including jatropha,

poplar and willow, could be used in two ways- for energy production and phytoremediation.

9.5.5.2 Designer Plant Approach

Organic pollutants are stored and built up in plant tissues, reducing the plant’s lifespan while

negatively impacting the environment by volatilizing through the leaves, that is one of the most

critical limitations of phytoremediation. To address this issue, degrading microorganisms are put on

plant tissues before their transfer to the polluted site, allowing pollutants to degrade in plant tissues

(Aken et al. 2011). In addition, customizing plant-microbial interactions for specific applications is

a new method for pollutant targeting in complex ecosystems (Abhilash et al. 2012).

Phytoremediation will need to be adopted in combination with other multipurpose remediation

techniques in the future (i) conventional biotechnology and (ii stressors, e.g., nutrient deficiency

and location toxicity can be mitigated with integrated bioaugmentation employing advantageous

microorganisms. Such multipurpose remediation systems, once applied, have the potential to

change the remediation domain by providing environmental, economic as well as social advantages

to all the stakeholders involved. Though all phytoremediation technologies are constrained by

economic viability, plant species that provide additional benefits have a better chance of resolving

this problem soon (Abhilash et al. 2012). The remediation of metal(loid)s by the combination of

plants and microbial species are depicted in Table 9.2.