Biodegradation and extracellular enzymatic activities of Pseudomonas aeruginosa strain GF31 on β-cypermethrin

Bioremediation of environmental organic pollutants by Pseudomonas aeruginosa: Mechanisms, methods and challenges

The development of the chemical industry has led to a boom in daily consumption and convenience, but has also led to the release of large amounts of organic pollutants, such as petroleum hydrocarbons, plastics, pesticides, and dyes. These pollutants are often recalcitrant to degradation in the environment, whereby the most problematic compounds may even lead to carcinogenesis, teratogenesis and mutagenesis in animals and humans after accumulation in the food chain. Microbial degradation of organic pollutants is efficient and environmentally friendly, which is why it is considered an ideal method. Numerous studies have shown that Pseudomonas aeruginosa is a powerful platform for the remediation of environmental pollution with organic chemicals due to its diverse metabolic networks and its ability to secrete biosurfactants to make hydrophobic substrates more bioavailable, thereby facilitating degradation. In this paper, the mechanisms and methods of the bioremediation of environmental organic pollutants (EOPs) by P. aeruginosa are reviewed. The challenges of current studies are highlighted, and new strategies for future research are prospected. Metabolic pathways and critical enzymes must be further deciphered, which is significant for the construction of a bioremediation platform based on this powerful organism.

Insights into the recent advances in nano-bioremediation of pesticides from the contaminated soil

In the present scenario, the uncontrolled and irrational use of pesticides is affecting the environment, agriculture and livelihood worldwide. The excessive application of pesticides for better production of crops and to maintain sufficient food production is leading to cause many serious environmental issues such as soil pollution, water pollution and also affecting the food chain. The efficient management of pesticide use and remediation of pesticide-contaminated soil is one of the most significant challenges to overcome. The efficiency of the current methods of biodegradation of pesticides using different microbes and enzymes depends on the various physical and chemical conditions of the soil and they have certain limitations. Hence, a novel strategy is the need of the hour to safeguard the ecosystem from the serious environmental hazard. In recent years, the application of nanomaterials has drawn attention in many areas due to their unique properties of small size and increased surface area. Nanotechnology is considered to be a promising and effective technology in various bioremediation processes and provides many significant benefits for improving the environmental technologies using nanomaterials with efficient performance. The present article focuses on and discusses the role, application and importance of nano-bioremediation of pesticides and toxic pollutants to explore the potential of nanomaterials in the bioremediation of hazardous compounds from the environment.

Isolation of Dibutyl Phthalate-Degrading Bacteria and Its Coculture with Citrobacter freundii CD-9 to Degrade Fenvalerate

Continued fenvalerate use has caused serious environmental pollution and requires large-scale remediation. Dibutyl phthalate (DBP) was discovered in fenvalerate metabolites degraded by Citrobacter freundii CD-9. Coculturing is an effective method for bioremediation, but few studies have analyzed the degradation pathways and potential mechanisms of cocultures. Here, a DBP-degrading strain (BDBP 071) was isolated from soil contaminated with pyrethroid pesticides (PPs) and identified as Stenotrophomonas acidaminiphila. The optimum conditions for DBP degradation were determined by response surface methodology (RSM) analysis to be 30.9 mg/l DBP concentration, pH 7.5, at a culture temperature of 37.2°C. Under the optimized conditions, approximately 88% of DBP was degraded within 48 h and five metabolites were detected. Coculturing C. freundii CD-9 and S. acidaminiphila BDBP 071 promoted fenvalerate degradation. When CD-9 was cultured for 16 h before adding BDBP 071, the strain inoculation ratio was 5:5 (v/v), fenvalerate concentration was 75.0 mg/l, fenvalerate was degraded to 84.37 ± 1.25%, and DBP level was reduced by 5.21 mg/l. In addition, 12 fenvalerate metabolites were identified and a pathway for fenvalerate degradation by the cocultured strains was proposed. These results provide theoretical data for further exploration of the mechanisms used by this coculture system to degrade fenvalerate and DBP, and also offer a promising method for effective bioremediation of PPs and their related metabolites in polluted environments.

Biodegradation of λ-cyhalothrin through cell surface display of bacterial carboxylesterase

Pyrethroids are the third widespread used insecticides globally which have been extensively applied in agricultural or household environments. Due to continuous applications, pyrethroids have been detected both in living cells and environments. The permanent exposure to pyrethroids have caused substantial health risks and ecosystem concerns. In this work, a λ-cyhalothrin (one kind of pyrethroid insecticides) degrading bacterium Bacillus velezensis sd was isolated and a carboxylesterase gene, CarCB2 was characterized. A whole cell biocatalyst was developed for λ-cyhalothrin biodegradation by displaying CarCB2 on the surface of Escherichia coli cells. CarCB2 was successfully displayed and functionally expressed on E. coli cells with optimal pH and temperature of 7.5 and 30 °C, using p-NPC₄ as substrate, respectively. The whole cell biocatalyst exhibited better stability than the purified CarCB2, and approximately 120%, 60% or 50% of its original activity at 4 °C, 30 °C or 37 °C over a period of 35 d was retained, respectively. No enzymatic activity was detected when incubated the purified CarCB2 at 30 °C for 120 h, or 37 °C for 72 h, respectively. Additionally, 30 mg/L of λ-cyhalothrin was degraded in citrate-phosphate buffer by 10 U of the whole cell biocatalyst in 150 min. This work reveals that the whole cell biocatalyst affords a promising approach for efficient biodegradation of λ-cyhalothrin, and might have the potential to be applied in further environmental bioremediation of other different kinds of pyrethroid insecticides.

Novel Mechanism and Kinetics of Tetramethrin Degradation Using an Indigenous Gordonia cholesterolivorans A16

Tetramethrin is a pyrethroid insecticide that is commonly used worldwide. The toxicity of this insecticide into the living system is an important concern. In this study, a novel tetramethrin-degrading bacterial strain named A16 was isolated from the activated sludge and identified as Gordonia cholesterolivorans. Strain A16 exhibited superior tetramethrin degradation activity, and utilized tetramethrin as the sole carbon source for growth in a mineral salt medium (MSM). High-performance liquid chromatography (HPLC) analysis revealed that the A16 strain was able to completely degrade 25 mg·L⁻¹ of tetramethrin after 9 days of incubation. Strain A16 effectively degraded tetramethrin at temperature 20–40 °C, pH 5–9, and initial tetramethrin 25–800 mg·L⁻¹. The maximum specific degradation rate (q_max), half-saturation constant (K_s), and inhibition constant (K_i) were determined to be 0.4561 day⁻¹, 7.3 mg·L⁻¹, and 75.2 mg·L⁻¹, respectively. The Box–Behnken design was used to optimize degradation conditions, and maximum degradation was observed at pH 8.5 and a temperature of 38 °C. Five intermediate metabolites were identified after analyzing the degradation products through gas chromatography–mass spectrometry (GC-MS), which suggested that tetramethrin could be degraded first by cleavage of its carboxylester bond, followed by degradation of the five-carbon ring and its subsequent metabolism. This is the first report of a metabolic pathway of tetramethrin in a microorganism. Furthermore, bioaugmentation of tetramethrin-contaminated soils (50 mg·kg⁻¹) with strain A16 (1.0 × 10⁷ cells g⁻¹ of soil) significantly accelerated the degradation rate of tetramethrin, and 74.1% and 82.9% of tetramethrin was removed from sterile and non-sterile soils within 11 days, respectively. The strain A16 was also capable of efficiently degrading a broad spectrum of synthetic pyrethroids including D-cyphenothrin, chlorempenthrin, prallethrin, and allethrin, with a degradation efficiency of 68.3%, 60.7%, 91.6%, and 94.7%, respectively, after being cultured under the same conditions for 11 days. The results of the present study confirmed the bioremediation potential of strain A16 from a contaminated environment.

Purification and characterization of a novel cypermethrin-hydrolyzing esterase from Bacillus licheniformis B-1

Cypermethrin (CY) is a synthetic pyrethroid widely used to control insect pests and it elicits a toxic effect on the human body. In this study, Bacillus licheniformis B-1 isolated from tea garden soil was used to degrade CY effectively. A specific enzyme was mainly localized in the extracellular compartments of B-1. This enzyme was identified as an esterase that could be produced without CY. The enzyme was purified 23.03-fold to apparent homogeneity with 8.38% overall recovery by ammonium sulfate precipitation, anion exchange chromatography, and gel filtration chromatography. The molecular mass of the CY-degrading enzyme was 66.4 kDa, and its optimal pH and temperature were 8.5 and 40 °C, respectively. Appropriate Zn²⁺ , Mn²⁺ , Mg²⁺ , Tween 80, SDS, Triton X-100, and BSA concentrations could greatly increase the activity of this enzyme. By contrast, EDTA, 1,10-phenanthroline, NaF, and PMSF strongly inhibited its activity. The purified enzyme showed K_m and V_max values were 5.532 nmol/mL and 33.445 nmol/min. The CY residue in lettuce and cherry tomatoes could be removed more than 50% under the conditions of the treatment concentration for 500 mg/L and the enzyme preparation dilution of 100 times. These results suggested that the CY-degrading enzyme, a constitutive enzyme that mainly exists in the extracellular space, was a novel esterase that might be used to detoxify CY, and could remove CY in vegetables effectively. PRACTICAL APPLICATION: Our research found a novel cypermethrin-hydrolyzing esterase from Bacillus licheniformis B-1 and proved that the enzyme could remove cypermethrin in vegetables effectively.

Biodegradation and metabolic pathway of fenvalerate by Citrobacter freundii CD-9

Fenvalerate is a pyrethroid insecticide with rapid action, strong targeting, broad spectrum, and high efficiency. However, continued use of fenvalerate has resulted in its widespread presence as a pollutant in surface streams and soils, causing serious environmental pollution. Pesticide residues in the soil are closely related to food safety, yet little is known regarding the kinetics and metabolic behaviors of fenvalerate. In this study, a fenvalerate-degrading microbial strain, CD-9, isolated from factory sludge, was identified as Citrobacter freundii based on morphological, physio-biochemical, and 16S rRNA sequence analysis. Response surface methodology analysis showed that the optimum conditions for fenvalerate degradation by CD-9 were pH 6.3, substrate concentration 77 mg/L, and inoculum amount 6% (v/v). Under these conditions, approximately 88% of fenvalerate present was degraded within 72 h of culture. Based on high-performance liquid chromatography and gas chromatography-mass spectrometry analysis, ten metabolites were confirmed after the degradation of fenvalerate by strain CD-9. Among them, o-phthalaldehyde is a new metabolite for fenvalerate degradation. Based on the identified metabolites, a possible degradation pathway of fenvalerate by C. freundii CD-9 was proposed. Furthermore, the enzyme localization method was used to study CD-9 bacteria and determine that its degrading enzyme is an intracellular enzyme. The degradation rate of fenvalerate by a crude enzyme solution for over 30 min was 73.87%. These results showed that strain CD-9 may be a suitable organism to eliminate environmental pollution by pyrethroid insecticides and provide a future reference for the preparation of microbial degradation agents and environmental remediation.

New Insights into the Microbial Degradation of D-Cyphenothrin in Contaminated Water/Soil Environments

Persistent use of the insecticide D-cyphenothrin has resulted in heavy environmental contamination and public concern. However, microbial degradation of D-cyphenothrin has never been investigated and the mechanism remains unknown. During this study, for the first time, an efficient D-cyphenothrin-degrading bacterial strain Staphylococcus succinus HLJ-10 was identified. Response surface methodology was successfully employed by using Box-Behnken design to optimize the culture conditions. At optimized conditions, over 90% degradation of D-cyphenothrin (50 mg·L⁻¹) was achieved in a mineral salt medium within 7 d. Kinetics analysis revealed that its half-life was reduced by 61.2 d, in comparison with the uninoculated control. Eight intermediate metabolites were detected in the biodegradation pathway of D-cyphenothrin including cis-D-cyphenothrin, trans-D-cyphenothrin, 3-phenoxybenzaldehyde, α-hydroxy-3-phenoxy-benzeneacetonitrile, trans-2,2-dimethyl-3-propenyl-cyclopropanol, 2,2-dimethyl-3-propenyl-cyclopropionic acid, trans-2,2-dimethyl-3-propenyl-cyclopropionaldehyde, and 1,2-benzenedicarboxylic acid, dipropyl ester. This is the first report about the degradation of D-cyphenothrin through cleavage of carboxylester linkage and diaryl bond. In addition to degradation of D-cyphenothrin, strain HLJ-10 effectively degraded a wide range of synthetic pyrethroids including permethrin, tetramethrin, bifenthrin, allethrin, and chlorempenthrin, which are also widely used insecticides with environmental contamination problems. Bioaugmentation of D-cyphenothrin-contaminated soils with strain HLJ-10 substantially enhanced its degradation and over 72% of D-cyphenothrin was removed from soils within 40 d. These findings unveil the biochemical basis of a highly efficient D-cyphenothrin-degrading bacterial isolate and provide potent agents for eliminating environmental residues of pyrethroids.

New insights into the microbial degradation and catalytic mechanism of synthetic pyrethroids

The significant applications of pyrethroid insecticides in agro-ecosystem and household environments have raised serious environmental concerns. Environmental bioremediation has emerged as an effective and eco-friendly approach to remove or neutralize hazardous compounds. Bioaugmentation accelerates pyrethroid degradation in liquid cultures and soil. Pyrethroid-degrading microorganisms have been extensively studied to cope with pyrethroid residues. Microorganisms primarily hydrolyze the ester bonds of pyrethroids, and their degradation pathways have been elaborated. The functional genes and enzymes involved in microbial degradation have also been screened and studied. Carboxylesterase plays a key role in pyrethroid degradation by cleaving its carboxylester linkage. The catalytic mechanism is dependent on a specific catalytic triad, consisting of three amino acid residues (glutamine, histidine, and serine) within the active site of the carboxylesterase enzyme. Pyrethroid-degrading strains and enzymes have proven to be effective for the bioremediation of pyrethroid-contaminated environments. In this review, we have summarized newly isolated pyrethroid-degrading strains and proposed the degradation pathways along with key functional genes/enzymes. To develop an efficient bioremediation strategy, pyrethroid-degrading microorganisms should be comprehensively explored.

Effective biodegradation of pentachloronitrobenzene by a novel strain Peudomonas putida QTH3 isolated from contaminated soil

To eliminate pentachloronitrobenzene (PCNB) residue in PCNB-contaminated environment, the degradation potential of Pseudomonas putida QTH3 to PCNB was evaluated in this study. Peudomonas putida QTH3 could grow well in mineral salt medium (MSM) containing PCNB as sole carbon and was able to degrade PCNB efficiently, whereas the degradation rate of P. putida QTH3 to PCNB increased gradually, and reached 49.84% in 35 days. The degradation rates of P. putida QTH3 to 13 tested organochlorine compounds found to be 10.85%-42.51% after 14 days. The metabolites during PCNB biodegradation by P. putida QTH3 were identified as catechol, 2, 3, 5, 6-tetrachloroaniline (TCA), 2, 3, 4, 5- TCA, 2, 3, 4, 5, 6-pentachloroaniline (PCA) and pentachlorothioanisole (PCTAs). Furthermore, possible degradation pathway of PCNB by P. putida QTH3 was proposed. The degradation rates of intracellular enzyme and extracellular enzyme were 44.73% and 8.93% after incubation with 100 mg L^-1 PCNB for 30 min, respectively. Thus, intracellular enzyme is a major enzyme responsible for PCNB degradation. The results indicate that P. putida QTH3 can be a suitable organism for the degradation of PCNB, and facilitate its potential for the bioremediation of the environments contaminated with major organochlorine compounds used during this study.

Screening of a beta-cypermethrin-degrading bacterial strain Brevibacillus parabrevis BCP-09 and its biochemical degradation pathway

A novel beta-cypermethrin (Beta-CP)-degrading strain isolated from activated sludge was identified as Brevibacillus parabrevis BCP-09 based on its morphological and physio-biochemical characteristics, and 16S rRNA gene analysis. Strain BCP-09 could effectively degrade Beta-CP at pH 5.0-9.0, 20-40 °C, and 10-500 mg L^-1 Beta-CP. Under optimal conditions (pH 7.41, 38.9 °C, 30.9 mg L^-1 Beta-CP), 75.87% Beta-CP was degraded within 3 days. Beta-CP degradation (half-life, 33.45 h) and strain BCP-09 growth were respectively described using first-order-kinetic and logistic-kinetic models. Seven metabolites were detected by high-performance liquid chromatography and gas chromatography-mass spectrometry- methyl salicylate, catechol, phthalic acid, salicylic acid, 3-(2,2-dichlorovinyl)-2,2-dimethylcyclopropanecarboxylic acid, 3-phenoxybenzaldehyde, and 3-phenoxybenzoic acid (3-PBA). The major Beta-CP metabolite, 3-PBA was further degraded into phenol, benzoic acid, and 4-methylhexanoic acid. BCP-09 also degraded aromatic compounds such as phenol, catechol, and protocatechuic acid. Beta-CP appears to be mainly degraded into 3-PBA, which is continuously degraded into smaller benzene or chain compounds. Thus, strain BCP-09 could form a complete degradation system for Beta-CP and might be considered a promising strain for application in the bioremediation of environments and agricultural products polluted by Beta-CP.

Screening cyhalothrin degradation strains from locust epiphytic bacteria and studying Paracoccus acridae SCU-M53 cyhalothrin degradation process

All locust epiphytic bacteria were screened and a total of 62 epiphytic bacteria were obtained from samples of Acrida cinerea. Via phylogenetic analysis, the 62 epiphytic bacteria were allocated to 27 genera, 18 families, 13 orders, six classes, and four phylums. Then, cyhalothrin degradation experiments were conducted, and the 10 strains that degraded more than 30% cyhalothrin and Paracoccus acridae SCU-M53 showed the highest cyhalothrin degradation rate of 70.5%. Furthermore, Paracoccus acridae SCU-M53 was selected for optimal cyhalothrin biodegradation conditions via the response surface method (Design-Expert). Under the optimum conditions (28 °C, 75 mg/L, and 180 rpm), the cyhalothrin degradation rate reached 79.84% after 2 days. This suggests the possibility that isolating biodegradation cyhalothrin strains from Acrida cinerea is feasible.

Purification and Characterization of a Novel β-Cypermethrin-Degrading Aminopeptidase from Pseudomonas aeruginosa GF31

In this study, a novel β-cypermethrin-degrading enzyme was isolated and purified by 32.8 fold from the extracellular cell-free filtrate of Pseudomonas aeruginosa GF31with the protein recovery of 26.6%. The molecular mass of the enzyme was determined to be 53 kDa. The optimum temperature for the activity was surprisingly 60 °C, and moreover, the purified enzyme showed a good pH stability, maintaining over 85% of its initial activity in the pH 5.0-9.0 range. Most of the common metal ions exhibited little influence on the activity except for Hg²⁺, Ag⁺, and Cu²⁺. After the complete gene sequence of the degrading enzyme was obtained by subcloning, sequence analyses as well as enzymatic properties demonstrated that the islolated enzyme should be an aminopeptidase. This is the first reported aminopeptidase for pyrethroid hydrolase, providing new potential enzyme resources for the degradation of this type of pesticide.