Keywords

6.1 Introduction

Pyrethroids are a synthetic organic compound similar in structure to natural pyrethrums extracted from Chrysanthemum cinerariaefolium. Their acid and alcohol parts are bound by ester bonds and usually contain 1–3 chiral centers. As a chiral compound, pyrethroids usually have 4–8 stereoisomers (Bhatt et al. 2020a). Different isomers exhibit different insecticidal activities and have enantioselective degradation characteristics during microbial metabolism (Garcia et al. 2017). Pyrethroids can be divided into two categories based on the presence or absence of cyano-group on the α-chiral carbon: type II pyrethroids with cyano-group and type I pyrethroids without cyano-group.

Allethrin is the first type I pyrethroid synthesized in the USA in 1949, which is to control domestic sanitary pests (Bhatt et al. 2020d). Compared with type II pyrethroids, pyrethroids of type I had structural diversity and were generally less toxic than type II due to the absence of cyano-group (Zhang et al. 2016). In addition to the cyano-group, pyrethroids have introduced halogens such as fluorine, chlorine, and bromine to increase insecticidal activity (Tang et al. 2018b; Zhan et al. 2018; Cycoń et al. 2014).

Pyrethroids have been used worldwide for more than 40 years since they were synthesized in the middle of the last century. With the increasing restrictions on organophosphorus and organochlorine pesticides by governments, the use of pyrethroids has increased year by year, from 25% of the world pesticide market in 2010 to more than 30% in 2018 (Zhai et al. 2012; Cycoń and Piotrowska-Seget 2016). A pyrethroid is a broad-spectrum insecticide with selective toxicity to Diptera, Hymenoptera, and mammals (Thatheyus and Gnana Selvam 2013). To improve the insecticidal activity and environmental stability of active ingredients, piperonyl butoxide and piperonyl sulfoxide were added to commercial pyrethroids (Thatheyus and Gnana Selvam 2013).

Pyrethroids are highly hydrophobic and will be adsorbed in sediment rapidly after entering the water body (Delgado-Moreno et al. 2011). Subsequently, some of them are utilized by indigenous microorganisms, and the other part enters the aquatic food web, which may eventually accumulate in the human body through biological amplification (Liu et al. 2012; Cycoń et al. 2017). A large number of results have confirmed that pyrethroids have high toxicity to aquatic organisms (Mendis et al. 2018; Mulla et al. 2017; He et al. 2008). Long-term exposure to pyrethroids can affect the quality of human semen (Ham et al. 2020). A series of environmental problems caused by the irrational use of pyrethroids has aroused public concern in recent years. At present, diverse methods have been developed to remove pyrethroids from the environment.

In this chapter, we are summarizing the previously isolated and characterized degrading microorganisms and introduce the metabolic pathways of common pyrethroids. In the last two decades, many researchers have reported pyrethroid hydrolases encoded by genes with open reading frames (ORF). We will discuss these functional enzymes and describe the metabolic mechanisms that catalyze the triad (Serine, Histidine, Aspartate) at the active site of the degrading enzyme.

6.2 Potential of Microbes in Pyrethroid Degradation

Pesticide-degrading microorganisms have become a scientific research hotspot and effective strategy to treat pesticide residues over 30 years of development due to their unique advantages. Microbes can catabolize the large-molecular heterologous pollutants remaining in the environment into nontoxic or low-toxic inorganic small-molecule compounds in various ways (Huang et al. 2021; Lin et al. 2020; Mishra et al. 2020; Chen et al. 2012a). Generally, it is an effective way to use enrichment culture technology to screen functional microorganisms from soil, water, and activated sludge contaminated by pesticides (Zhang et al. 2021; Zhan et al. 2020; Lin et al. 2011). There are also reports that it is feasible to obtain degrading functional bacteria from resistant insects and fermented food (Cho et al. 2009). Type II pyrethroids are lethal to aquatic organisms which are often used as ship detergents to prevent the adhesion of marine organisms (Feng et al. 2009). Therefore, seawater has also been reported commonly as an important source of pyrethroid degrading microorganisms.

To date, a great number of studies have confirmed that bacteria and fungi can effectively degrade pyrethroid residues in water and soil (Table 6.1). There are also a few reports on yeast and algae (Pang et al. 2020). Microorganisms can use pyrethroids as the sole energy source or with the help of other nutrients to remove pyrethroids through co-metabolism (Zhao et al. 2019b). Bacillus subtilis 1D has been reported to hydrolyze 95% of cypermethrin within 15 days. And 700 bp esterase and 1200 bp laccase were extracted from strain 1D, which indicates that esterase and laccase are involved in the cypermethrin metabolism (Gangola et al. 2018). Wang et al. (2019) isolated a strain of Photobacterium ganghwense 6046 from seawater. This strain can grow with cyfluthrin as the sole carbon source and degrade 60% of cyfluthrin (100 mg∙L−1) for 72 h (Wang et al. 2019). The intermediate products of cyfluthrin were identified, and the cyano-group was not found. It is speculated that cyano-groups may be metabolized by strain 6046 first. Paracoccus acridae SCU-M53 is an epiphytic bacterium isolated from locusts, which can metabolize 79.84% of cyhalothrin in 48 h (Tian et al. 2018).

Table 6.1 Pyrethroid-degrading microbes obtained from various sources
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Response surface methodology (RSM) is a common method to optimize microbial growth and degradation conditions. Based on the Box-Behnken design, Zhan et al. (2018) used RSM to optimize the degradation conditions of Acinetobacter baumannii ZH-14. Under the conditions of 30 °C and pH 7, permethrin with a concentration of 50 mg∙L−1 was completely removed within 72 h. Bacillus thuringiensis ZS-19 obtained from activated sludge can completely eliminate 100 mg∙L−1 cyhalothrin in 72 h and can continue to work effectively when the concentration is as high as 800 mg∙L−1. In addition to cyhalothrin, strain ZS-19 can also efficiently metabolize fenpropathrin, deltamethrin, beta-cypermethrin, and cyfluthrin (Chen et al. 2015). Allethrin is the earliest synthesized pyrethroid, but reports on allethrin degradation bacteria are not common. Acidomonas sp. degraded 70% of allethrin at a concentration of 16 mM in MSM medium during 72 h and proposed a metabolic pathway (Paingankar et al. 2005). Recently, Bhatt et al. (2020b) manifested that Sphingomonas trueperi strain CW3 utilized allethrin as the sole source of energy and remove 93% of 100 mg∙L−1 allethrin after 7 days. The optimal culture conditions are pH 7, temperature 30 °C, and inoculation amount of 0.1 g L−1.

While earlier studies focused on the degradation kinetics of single strains, more studies now suggested that microbial consortia may exhibit higher degradation capabilities than single strains (Feng et al. 2020a, b). The previous results of Tang et al. (2020) showed that when the ratio of Klebsiella pneumoniae BPBA052 and Acinetobacter Junii LH-1-1 was 2.5:7.5, the dissipation of 75 mg∙L−1 deltamethrin in 96 h was 94.25%. Streptomyces aureus HP-S-01 and B. Cereus ZH-3 can 100% metabolize cypermethrin (50 mg∙L−1) within 72 h (Chen et al. 2012b). A consortium composed of four beta-cypermethrin-degrading bacteria, which was Streptomyces sp. GXZQ4, Enterobacter sp. GXZQ6, Streptomyces sp. GXZQ7, and Pseudomonas sp. GXZQ13, was obtained by enrichment culture and high-throughput sequencing. The consortium’s degradation rate of beta-cypermethrin (100 mg∙L−1) was up to 89.84% after 96 h (Qi and Wei 2017).

Among the published pyrethroid degrading bacteria, only a few strains can degrade pyrethroid 100% in a short time. Pyrethroids are similar in structure, which means that the same strain may degrade many different pyrethroid pesticides (Bhatt et al. 2020f). The essence of microbial metabolism is an enzymatic reaction, in which complex macromolecular compounds are gradually broken down under the action of various enzymes (Feng et al. 2020a; Zhang et al. 2020; Bhatt et al. 2021a). 3-Phenoxybenzoic acid is the main intermediate metabolite of most pyrethroids. 3-PBA has high water solubility and antibacterial properties, which is one of the reasons limiting the further metabolism of pyrethroids (Zhao et al. 2019a). It is a new attempt to solve the toxicity of 3-phenoxybenzoic acid (3-PBA) through co-culture. Two strains of Aspergillus oryzae M-4 and B. licheniformis B-1 were combined by Zhao et al. (2016). After 72 h of cocultivation, 100 mg∙L−1 β-cypermethrin was removed by 78.85%. The toxic intermediate product 3-PBA formed by the hydrolysis of β-cypermethrin with B. licheniformis B-1 was effectively utilized by A. oryzae M-4, the gallic acid produced by the metabolism of beta-cypermethrin with A. oryzae M-4 was effectively degraded by B. licheniformis B-1.

6.3 Genes and Enzymes Involved in Pyrethroid Metabolism

Carboxylesterase is a very important class of pyrethroid hydrolases. It is a subtype of esterase and had classified in subtype 3.1.1 by the International Union of Biochemistry (Bhatt et al. 2021b). Carboxylesterase/lipase is divided into eight families (I–VIII). Group I esterases are true lipases, while group II–VIII esterases are carboxylesterase (Zhan et al. 2020). Carboxylesterase is the most studied enzyme among pyrethroid hydrolases. It is widely found in resistant insects, mammals, and microbial cells. It can hydrolyze a variety of organic compounds containing esters, such as carbamate and pyrethroid, and produce nontoxic acids and alcohols (Liu et al. 2017). The active site of esterase contains serine residues, which are located in the conserved pentapeptide motif (Gly-X-Ser-X-Gly) (Diegelmann et al. 2015).

Many pyrethroid degradation genes, such as pye3, pytY, estA, pytZ, pytH, est3385, mes1, and sys410, have been cloned and identified (Wang et al. 2009; Li et al. 2008; Ruan et al. 2013; Luo et al. 2018). Phylogenetic analysis indicated that Est3385 derived from Rhodopseudomonas palustris PSB-S belong to the esterase group I, Sys410 belongs to esterase V family, and the pyrethroid carboxylesterase PytY encoded by pytY gene is a member of esterase VI families (Luo et al. 2018; Ruan et al. 2013; Fan et al. 2012). Most pyrethroid hydrolase activities have been reported to require no cofactor, but the presence of some metal ions can severely inhibit enzyme activity. The pyrethroid hydrolase extracted from A. niger ZD11 has a pI value of 5.4 and a molecular weight (MW) of 56 kDa; a pyrethroid esterase, Pye3, with an open reading frame (ORF) of 819 bp and an MW of about 31 kDa, was obtained from the soil by using metagenomics tools; and the esterase EstP with an ORF of 1914 bp was extracted from Klebsiella sp. strain ZD112 cells. These three enzymes can be strongly inhibited by Hg2+ and Ag+ (Wu et al. 2006; Li et al. 2008; Liang et al. 2005).

Due to the similarity in the structure of pyrethroid pesticides, most pyrethroid functional enzymes show broad-spectrum substrate specificity to pyrethroids. Pyrethroid hydrolytic esterase (EstP) was isolated from Klebsiella sp. ZD112 and encoded by gene estP, has an ORF of 1914 bp. The molecular weight of EstP is about 73 kDa, which contains 637 amino acid residues (Wu et al. 2006). No similarity was found with the reported nucleotide sequences of esterase/lipase family members by multiple sequence alignment. The purified EstP has a broad spectrum of substrate utilization. The Km and kcat values of EstP hydrolyzing trans- and cis-permethrin indicated that EstP hydrolyzes pyrethroids more efficiently than carboxylesterases obtained from insect-resistant insects and mammals.

The ORF of the pyrethroid hydrolytic gene est 3385 contains 963 nucleotides, and the optimum pH and temperature are 6.0 and 35 °C, respectively (Luo et al. 2018). The enzyme can metabolize a variety of pyrethroid pesticides, and fenpropathrin is the best substrate. The enzyme degradation kinetics indicated that the Vmax and Km values of hydrolyzed fenpropathrin were 0.918 ± 0.025 U/microg and 0.734 ± 0.013 mmol/L, respectively. The pytH cloned from Sphingobium sp. strain JZ-1 encodes the carboxylesterase PytH. In addition to hydrolyzing a variety of pyrethroids, PytH can also convert short-chain fatty acids (Wang et al. 2009). Studies have shown that transferring the carboxylesterase encoding gene pytH into Pseudomonas putida KT2440 can completely hydrolyze 0.2 mM permethrin, fenpropathrin, and cypermethrin within 48 h (Zuo et al. 2015).

Previous results showed that there is enantioselective degradation of pyrethroid hydrolase. The pyrethroid hydrolase extracted from the A. Niger ZD11 was able to detoxification various pyrethroids, but compared with cis-permethrin, the substrate utilization of trans-permethrin was higher (Liang et al. 2005). A pyrethroid hydrolase esterase gene pytY containing 897 bp ORF was isolated from Ochrobactrum Anthropi YZ-1 by Ruan et al. (2013). PytY can hydrolyze different pyrethroids, but it showed the highest hydrolysis activity with lambda-cyhalothrin as the substrate. The kinetic constants of Vmax and Km were 56.33 nmol/min and 2.34 mmol/L, respectively.

The beta-cypermethrin-degrading monooxygenase CMO was first identified by Chen et al. (2013b) from environmental microorganisms. The natural enzyme showed that the CMO has a pI of 5.4 and an MW of 41 kDa. The enzyme exerted the greatest activity against beta-cypermethrin at 30 °C and pH 7.5. Fe2+ can significantly enhance the activity of CMO, while Cu2+, Al3+, and Ag+ have a strong inhibitory effect on CMO activity. Most of the pyrethroid hydrolases are extracted from the cells of organisms. It has been proved that it is feasible to extract pyrethroid metabolizing enzymes from extracellular regions. A functional enzyme was isolated from Pseudomonas aeruginosa strain GF31 cells. The molecular weight of the enzyme was 53.7 kDa, and the pI value was 7.67. The ORF contained a 1611 bp DNA fragment, encoding 536 amino acids. Through phylogenetic analysis, it was highly similar to aminopeptidases (Tang et al. 2017).

6.4 Catalytic Mechanisms of Pyrethroids

Pyrethroid hydrolases are members of the α/β superfamily. Most of the active site amino acids of carboxylesterase have conservative sites, with the active site amino acids contain a catalytic triad composed of nucleophiles, basic groups, and acidic groups (Bhatt et al. 2020a). Hydrolase folds into a complex three-dimensional structure in space, and the different residues of the catalytic triad (Ser-His-Asp) come together during the folding process. The triad is hidden in the enzyme protein molecule, and the serine residue at the active site is masked by the alpha helix. Through the folding of enzyme protein, the catalytic triad of carboxylesterase activity site is combined with a pyrethroid.

Aspartate and histidine combine with two hydrogen bonds to increase the pKa value (acidity coefficient) of the triad and activate the nucleophile serine. After the hydroxyl molecule of the serine is activated by catalytic histidine/aspartate, the latter obtains electrons from the hydroxyl molecule of the nucleophile. The active site of pyrethroid hydrolases contains serine residues, which is situated in the common pentapeptide sequence Gly-X-Ser-X-Gly of esterases. It acts as a nucleophile to attack the carbonyl group of pyrethroids through hydroxyl (OH), then releases alcohols, and produces a covalent intermediate of acylation (Bhatt et al. 2019). The basic group (His) and the acidic group (Asp) obtain hydrogen ions from the OH of serine, and the carbonyl group’s nucleophilic attack of pyrethroid is performed by hydroxyl anion generated from serine. These two processes are carried out simultaneously.

The carbon atom of the ester bond of pyrethroid is attacked by serine (nucleophile) and forces the oxygen atom of the ester bond to accept electrons, forming a tetrahedral intermediate. Restoration of the intermediate carbonyl leads to the transfer of histidine protons to the carbon atoms of pyrethroids adjacent to the α-chiral carbons. Subsequently, water molecules replace serine as a nucleophile to supply a proton to histidine, and the remaining OH attacks the carbonyl carbon atom to form a complex intermediate (Bhatt et al. 2020a). Furthermore, the serine in the enzyme regains protons from the basic group histidine, which further hydrolyzes the complex intermediate into nontoxic acids and alcohols. The specific metabolic process is shown in Fig. 6.1.

Fig. 6.1
figure 1

Catalytic mechanisms of pyrethroids

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6.5 Metabolic Pathways of Pyrethroid Biodegradation

The main intermediate metabolites detected in pyrethroids during microbial metabolism are 3-phenoxybenzyl alcohol, 3-phenoxyebenzoic acid (3-PBA), and 3-phenoxybenzaldehyde. The metabolite α-hydroxy-3-phenoxybenzeneacetonitrile is a unique intermediate product of pyrethroid II due to the absence of cyanogen in I pyrethroid (Guo et al. 2021; Bhatt et al. 2021c). Under alkaline conditions, pyrethroids are easily hydrolyzed into cyclopropane-containing acid and α-hyroxy-3-phenoxybenzeneacetonitrile, and then quickly converted into 3-phenoxybenzaldehyde (Chen et al. 2011a). In the presence of dehydrogenase, 3-phenoxybenzaldehyde is further oxidized to 3-PBA (Deng et al. 2015). 3-PBA is an endocrine disruptor which stables in the environment, has higher water solubility than the parent compound, and is frequently detected in human urine. When monitoring the residues of pyrethroids, 3-PBA is often used as a detection indicator (Hongsibsong et al. 2019).

Most of the time, microorganisms follow the same metabolic pattern and metabolize the parent pesticide into 3-PBA (Chen et al. 2012d). Staphylococcus succinus HLJ-10 converts D-cyphenothrin through the cleavage of ester bonds and diaryl bonds. 3-PBA, 3-phenoxybenzaldehyde, and α-hyroxy-3-phenoxybenzeneacetonitrile were detected in this process (Huang et al. 2020); B. licheniformis B-1, A. niger YAT, B. subtilis BSF01, and Brevibacillus parabrevis BCP-09 have been reported to have similar metabolic steps on beta-cypermethrin (Tang et al. 2018a; Deng et al. 2015; Xiao et al. 2015). However, after the formation of 3-PBA, different strains hydrolyze 3-PBA in completely different ways (Fig. 6.2). Under the catalysis of dioxygenase, 3-PBA may have a variety of downstream metabolic mechanisms. Bacillus licheniformis CY-012 can hydrolyze 3-PBA into benzoic acid and phenol (Tang et al. 2018b). Subsequently, phenol is hydrolyzed to catechol by hydrolase, and benzoic acid is further generated into 3-hydroxybenzoate. Another approach is performed by A. niger YAT; 3-PBA was hydrolyzed into protocatechuic acid and phenol (Deng et al. 2015). Protocatechuic acid undergoes aromatic ring cleavage with the assistance of dioxygenase to form 3-carboxy-muconic acid.

Fig. 6.2
figure 2

Microbial degradation pathways of pyrethroids

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3-Phenoxybenzoic acid is one of the most studied pyrethroid intermediates. An interesting phenomenon was observed by Zhu et al. (2016) that 3-phenoxybenzyl alcohol and 3-PBA can be converted to each other, but will soon be hydrolyzed further. In addition, Candida pelliculosa ZS-02 and A. oryzae M-4 revealed another possibility of transforming 3-PBA into 3,5-dimethoxyphenyl or gallic acid (Chen et al. 2012a). After the formation of phenol into catechol, dioxygenase played an important catalytic role in the further decomposition of the aromatic ring to muconic acid (Zhao et al. 2019a). Ultimately, it is mineralized into nontoxic water molecules and carbon dioxide.

Until now, there are few reports on the biodegradation pathway of type I pyrethroids. In recent years, microbial degrading strains which can efficiently degrade permethrin, bifenthrin, d-cypermethrin, and permethrin have been screened from different sources, and their metabolic pathways have been demonstrated. Bhatt et al. (2020b) first hydrolyzed the ester bond of permethrin by S. trueperi CW3 to produce chrysanthemic acid and alcohol 2-(1,4,4-trimethyl-cy-clohex-2-enyl) ethanol. Then, the alcohol was oxidized to 1,4,4-trimethylcyclohex-2-ethylene carboxylic acid, which was further transformed into chrysanthemyl alcohol. Under the metabolism of Acinetobacter baumannii ZH-14, permethrin first formed 2,2-dimethyl-3-(2,2-dichlorovinyl) cyclopropanecarboxylic acid and 3-phenoxybenzenemethane, and then transformed into 3-phenyl benzaldehyde by redox. Finally, 3-Phenoxybenzaldehyde converted to 1,2-benzenedicarboxylic acid with the diaryl cleavage (Zhan et al. 2018).

6.6 Bioremediation of Pyrethroid-Contaminated Environments

The large-scale application of pyrethroids has caused ecological pollution of soil, sediments, and surface water, as well as serious indoor residues (Yoshida 2009; Chen et al. 2012c). After applying pyrethroids in the environment, as long as a small part of the active ingredients reach the target organism, most of them remain on the surface of plants and soil (Bhatt et al. 2020e; Huang et al. 2019). Most of the pyrethroid residues that contact the surface of plants and soil will be degraded by solar radiation. A small proportion of pyrethroids are utilized by indigenous microorganisms as a carbon source for growth. However, there are reports that the presence of deltamethrin can interfere with indigenous microbial communities (Braganca et al. 2019).

The long-term residues of pyrethroids in the soil force indigenous microorganisms to induce the expression of pyrethroid-related metabolic genes, thereby accelerating the metabolism of pyrethroid residues in contaminated environments. In addition to their own enzyme activities, soil temperature, pH, initial pyrethroid concentration, soil water content, and organic matter content also affect the soil bioremediation process by pyrethroid-degrading microbes (Bhatt et al. 2021d; Mishra et al. 2021). Zhang et al. (2016) collected a B. cereus strain Y1 from soil contaminated with deltamethrin, which can metabolize 74.9% of deltamethrin within 24 days. Bacillus sp. ISTDS2 was isolated from the marble mining area and was observed to use beta-cypermethrin as the sole source of nitrogen and carbon for growth (Sundaram et al. 2013). The β-cypermethrin with a concentration of 100 mg/L is thoroughly hydrolyzed by strain ISTDS2 in the field after 30 days. Recently, Bhatt et al. (2020c) obtained a B. thuringiensis SG4 from farmland. The experimental results suggested that 83.3% of 100 mg/L cypermethrin was removed from soil after 15 days of incubation.

6.7 Conclusions and Future Perspectives

Microbial degradation of pesticides in the environment faces many different problems. The metabolic activity of purified strain in soil has been the focus of previous research. Studies have shown that some microorganisms will give priority to the use of nutrients in soil media, leading to a decrease in the utilization of pyrethroids. The biodegradative efficiency of hydrophobic pyrethroids by microorganisms is related to the bioavailability of cells to pesticide molecules. The degradation rate of pyrethroids can be improved by adding appropriate surfactants Tween-80 and BRIj-35. The transformed pyrethroids pose another challenge to the environment. Pyrethroids metabolites are more water-soluble and have biological toxicity than the original pyrethroids. In the past 30 years, although a variety of microorganisms have been screened out and have the ability to hydrolyze pyrethroids. However, only a few strains can metabolize 3-PBA and pyrethroids simultaneously.

In order to solve these problems, many governance schemes have been proposed in recent years. Microorganisms that can utilize different substrates were combined to form consortia, which often exhibits a higher biodegradation effect than a single strain. Most microorganisms in nature cannot be obtained directly. Metagenomics provides a powerful tool for obtaining novel microbial enzyme resources. At present, the main pyrethroid degrading enzymes reported are carboxylesterase, monooxygenase, CYP, and laccase. However, not all enzymes have all the characteristics of high stability, high productivity, and high enzyme activity, which is essential for practical field application. Random mutagenesis, as another powerful tool, can enhance the catalytic activity and stability of enzymes through molecular modification, providing the possibility to obtain more potential enzymes.

Based on multidisciplinary results, many studies on immobilized degradation strains have been reported. Using calcium alginate in the form of microcapsules can immobilize a single purified strain or a multi-strain consortium. Compared with free cells, the immobilized strain has a higher substrate utilization rate. By regulating the flow rate, the number of repetitions of fixed strains can also be prolonged. With the development of materials science, many kinds of substrates for fixing cells have been developed, showing different advantages. In addition to immobilizing living cells, the immobilization of degrading enzymes has also been reported. Most of these experiments are currently in the laboratory research stage, and there are still many studies that need to be further carried out before the real large-scale application.