8

Bioremediation for Sustainable Environmental Cleanup

now concentrated on the creation of a less expensive bioremediation strategy, however, physical

and chemical treatments are often costly. Bioremediation, which uses microorganisms capable of

digesting harmful substances, is regarded as a viable, ecologically beneficent and economically

advantageous technique for getting rid of PCBs (Dercova et al. 2015). PCB bioremediation relies

primarily on bacterial aerobic utilization of the pollutant molecules, while benzoic acids that can be

further degraded by specialized strains of bacteria or substances with lower toxicity are typically the

products of biphenyl dioxygenase-initiated degradation (Murínová et al. 2014). The microorganisms

used in the remediation/degradation of PCBs are given in Table 1.2.

Table 1.2. Polychlorinated biphenyls (PCBs) degrading microorganisms.

PCBs

Microorganism

References

PCB (Delor 103)

Achromobacter xylosoxidans, Stenotrophomonas

maltophilia, Rhodococcus ruber

Horváthová et al. 2018

PCB

Paraburkholderia xenovorans LB400

Bako et al. 2021

PCBs (18, 52, 77)

Streptococcus sp. SPco

Lin et al. 2022

bph- gene

Bacterial gene (Ralstonia, Cupriavidus)

Jiang et al. 2018

PCB

Rhodococcus biphenylivorans strain TG9T

Ye et al. 2020

PCB

Klebsiella Lw3

Zhu et al. 2022

PCB

Eisenia fetida

Eslami et al. 2022

Trichlorobiphenyl

Rhodococcus strains KT112-7, CH628, P25

Gorbunova et al. 2021

PCB

Ligninolytic fungi

Šrédlová et al. 2021

PCB

Ascomycetesstrain

Germain et al. 2021

1.5.3 Bioremediation of Pesticides

Pesticides are organic chemical compounds which are frequently used in agricultural applications

to control or eradicate pests and boost crop yields. These are inexpensive, simple to make and

easily accessible. Globally more than half of the pesticides are used in Asia. India is third in Asia

behind China and Turkey in terms of pesticide-usage, ranking 12th globally (Nayak and Solanki

2021). Pesticides can be categorized into the following groups: insecticides, fungicides, herbicides,

rodenticides and fumigants, etc. Pesticides that dissolve quickly are known as non-persistent,

whereas those that resist degradation are known as persistent. They accumulate across the food

chain and cause severe hazards as a result of their excessive use and persistence. Different types

of degradation procedures are involved in the remediation of pesticides such as biodegradation,

chemical degradation, hydrolysis, oxidation-reduction (redox), ionization and photo-degradation

(Zhang and Qiao 2002). The metabolic activity of different types of microorganisms plays a crucial

part in the degradation process. Some of the pesticide-degrading microorganisms are given in

Table 1.3.

Different types of enzymes play a crucial role in the biodegradation of pesticides. The

biodegradation of pesticides involves a series of enzyme-catalyzed processes which includes

oxidation, reduction, dechlorination, dehydration and hydrolysis. The compound enters the body of

the microorganism in a specific way, and after a series of physiological and biochemical reactions

involving various enzymes, the pesticide could be completely degraded or broken down into smaller

molecular compounds (CO2 and H2O) with no or low toxicity (Chen et al. 2011, Tang 2018).

A majority of the genes encoding for the degradation of pesticides have been reported to be

on catabolic plasmids of Pseudomonas sp., Micrococcus sp., Actinobacter sp., Rhodoccus sp.,

Fusarium sp., and Arthrobacter sp., Actinomycetes could also be used for the biotransformation as

well as biodegradation of pesticides.