Microbe-Assisted Bioremediation of Pesticides from Contaminated Habitats 113

Figure 7.1. The top 30 countries susceptible to high pesticide pollution risk (Tang et al. 2021).

A bioremediation method can be classified into three subcategories: in-situ, ex-situ solid or ex-situ

slurry. In-situ techniques treat soils and associated groundwater on-site without excavation, while

ex-situ techniques require excavation prior to treatment (Shukla et al. 2010). Three fundamental

principles guide the choice of an appropriate bioremediation technology, namely the ability of the

pollutant to be transformed biologically, the accessibility of the contaminant to microorganisms and

the possibility of optimizing biological activity (Dua et al. 2002). Biological activity is achieved as

microorganisms use the contaminants as nutrients or energy sources. By introducing microorganisms

with desired catalytic capabilities or by supplementing nutrients (nitrogen and phosphorus), electron

acceptors (oxygen) and substrates (methane, phenol, and toluene), the activity of the microbe can

be further stimulated (Shukla et al. 2010). However, the appropriate degrading enzymes and several

environmental factors also contribute to the remediation of pesticides. The possible roles and

applications of microbes for the remediation of pesticides are further summarized.

7.4.1 Bacteria-assisted Degradation

In nature, pesticides continue for many years and travel along various food chains (Kalyabina et al.

2021). The fate of pesticides in the ecosystem is determined by their physico-chemical properties and

inherent biodegradability as a result of their structure (Bernardino et al. 2012). Many pesticides have

insoluble properties, that can cause residues to remain in the environment and then negatively affect

the ecosystem. In order to minimize the impact of pesticides in the environment, several methods

have been developed for pesticide remediation. The traditional methods for pesticide remediation

(physical, chemical and physico-chemical degradation) can, however, produce secondary pollutants

that cause additional harm to the environment. Furthermore, the increased cost involved in using

these techniques makes them unfeasible for pesticide removal from contaminated sites (Rajmohan

et al. 2020). Thus, bioremediation of pesticides by using beneficial living organisms has been

explored as an alternative (Deng and Wang 2016). Bioremediation of pesticide-polluted sites or

samples via microorganisms has become a desired method for decontamination. It is an efficient,

cost-effective technique for remediating pesticides without causing any harm to the environment,

as they metabolize pesticides for nutrients and release CO2 and H2O during the process (Huang

et al. 2018). Several microorganisms, including bacteria, have been isolated and used to degrade

toxic pesticides from contaminated sites (Sarker et al. 2021). Many potential bacterial genera, such

as Pseudomonas, Bacillus, Acinetobacter, Klebsiella and Burkholderia are effective in pesticide