4.1 Bacterial Degradation of Pesticides
The biodegradation of pesticides involves the oxidation of parent compounds to
CO 2 , H 2 O, or less toxic compounds (Abatenh et al. 2017; Doolotkeldieva et al.
2018). Bacterial strains belonging to Burkholderia, Flavobacterium, Arthrobacter,
Azotobacter, and Pseudomonas are known to degrade pesticides (Glazer and
Nikaido 2007). The pesticide degradation depends not only on the enzyme system
of the microorganisms but also on available conditions, such as pH, temperature, and
nutrients (Doolotkeldieva et al. 2018). The methods and processes of pesticide
degradation vary from compound to compounds and the types of bacteria involved
in the process. Both Pseudomonas sp. and Klebsiella pneumoniae have
hydrolases that can degrade organophosphate pesticides and neonicotinoids (Pathak
2018). Sometimes, environmental factors can cause partial degradation of pesticides,
leading to accumulation of pesticide residue in the environment. This may cause
inhibition of microbial populations. Dichlorodiphenyltrichloroethane (DDT), an
organochlorine pesticide, is partially degraded into metabolites of
dichlorodiphenyltrichloroethane (DDD) and dichlorodiphenyldichloroethylene
(DDE), and their toxicity is even higher than the parent compound (Foght et al.
2001). Before introducing microorganisms for pesticide degradation, optimization of
the environmental condition becomes necessary and thus inhibits accumulation of
metabolites in the soil.
4.2 Fungal Degradation of Pesticides
Although both bacterial and fungal species play a vital role in pesticide degradation,
fungi introduce structural changes and then release them into the soil, making them
susceptible to further degradation by bacteria and finally turning pesticides into
nontoxic substances (Gianfreda and Rao 2004). The degradation of pesticides
follows different pathways, depending on its nature, environmental conditions, and
microbe type (Ortiz-Hernández et al. 2013). Phanerochaete chrysosporium are able
to degrade a wide range of pesticides (Singh 2017). The white rot fungi are able to
degrade several types of pesticides, such as lindens, atrazine, durone, tert-butazine,
metalaxyl, DDT, γ-hexachlorocyclohexane, dieldrin, aldrin, heptachlor, chlordane,
and mirex (Pathak 2018). Similarly, fungal species, like Auricularia auricula,
Coriolus versicolor, Agrocybe semiorbicularis, Dichomitus squalens, Stereum
hirsutum, Flammulina velutipes, Pleurotus ostreatus, Avatha discolor, and
Hypholoma fasciculare, have been shown to degrade different types of pesticides
triazines, phenylamide, phenylurea, dicarboximide, chlorinated, and organophosphorus compounds (Bending et al. 2002).
8 Bioremediation: Efficient Technology to Combat Pesticide Pollutants in. . .
157
The biodegradation of pesticides involves the oxidation of parent compounds to
CO 2 , H 2 O, or less toxic compounds (Abatenh et al. 2017; Doolotkeldieva et al.
2018). Bacterial strains belonging to Burkholderia, Flavobacterium, Arthrobacter,
Azotobacter, and Pseudomonas are known to degrade pesticides (Glazer and
Nikaido 2007). The pesticide degradation depends not only on the enzyme system
of the microorganisms but also on available conditions, such as pH, temperature, and
nutrients (Doolotkeldieva et al. 2018). The methods and processes of pesticide
degradation vary from compound to compounds and the types of bacteria involved
in the process. Both Pseudomonas sp. and Klebsiella pneumoniae have
hydrolases that can degrade organophosphate pesticides and neonicotinoids (Pathak
2018). Sometimes, environmental factors can cause partial degradation of pesticides,
leading to accumulation of pesticide residue in the environment. This may cause
inhibition of microbial populations. Dichlorodiphenyltrichloroethane (DDT), an
organochlorine pesticide, is partially degraded into metabolites of
dichlorodiphenyltrichloroethane (DDD) and dichlorodiphenyldichloroethylene
(DDE), and their toxicity is even higher than the parent compound (Foght et al.
2001). Before introducing microorganisms for pesticide degradation, optimization of
the environmental condition becomes necessary and thus inhibits accumulation of
metabolites in the soil.
4.2 Fungal Degradation of Pesticides
Although both bacterial and fungal species play a vital role in pesticide degradation,
fungi introduce structural changes and then release them into the soil, making them
susceptible to further degradation by bacteria and finally turning pesticides into
nontoxic substances (Gianfreda and Rao 2004). The degradation of pesticides
follows different pathways, depending on its nature, environmental conditions, and
microbe type (Ortiz-Hernández et al. 2013). Phanerochaete chrysosporium are able
to degrade a wide range of pesticides (Singh 2017). The white rot fungi are able to
degrade several types of pesticides, such as lindens, atrazine, durone, tert-butazine,
metalaxyl, DDT, γ-hexachlorocyclohexane, dieldrin, aldrin, heptachlor, chlordane,
and mirex (Pathak 2018). Similarly, fungal species, like Auricularia auricula,
Coriolus versicolor, Agrocybe semiorbicularis, Dichomitus squalens, Stereum
hirsutum, Flammulina velutipes, Pleurotus ostreatus, Avatha discolor, and
Hypholoma fasciculare, have been shown to degrade different types of pesticides
triazines, phenylamide, phenylurea, dicarboximide, chlorinated, and organophosphorus compounds (Bending et al. 2002).
8 Bioremediation: Efficient Technology to Combat Pesticide Pollutants in. . .
157