Heterologous expression and characterization of a malathion-hydrolyzing carboxylesterase from a thermophilic bacterium, Alicyclobacillus tengchongensis

Uridine Diphosphate-Glycosyltransferase RpUGT344D38 Contributes to λ-Cyhalothrin Resistance in Rhopalosiphum padi

Uridine diphosphate-glycosyltransferase (UGT) is a key phase II enzyme in the insect detoxification system. Pyrethroids are commonly used to control the destructive wheat aphid Rhopalosiphum padi. In this study, we found a highly expressed UGT gene, RpUGT344D38, in both λ-cyhalothrin (LCR)- and bifenthrin (BTR)-resistant strains of R. padi. After exposure to λ-cyhalothrin and bifenthrin, the expression levels of RpUGT344D38 were significantly increased in the resistant strains. Knockdown of RpUGT344D38 did not affect the resistance of BTR, but it did significantly increase the susceptibility of LCR aphids to λ-cyhalothrin. Molecular docking analysis demonstrated that RpUGT344D38 had a stable binding interaction with both bifenthrin and λ-cyhalothrin. The recombinant RpUGT344D38 was able to metabolize 50% of λ-cyhalothrin. This study provides a comprehensive analysis of the role of RpUGT344D38 in the resistance of R. padi to bifenthrin and λ-cyhalothrin, contributing to a better understanding of aphid resistance to pyrethroids.

Characterization of the role of esterases in the biodegradation of organophosphate, carbamate, and pyrethroid pesticides

Ester-containing organophosphate, carbamate, and pyrethroid (OCP) pesticides are used worldwide to minimize the impact of pests and increase agricultural production. The toxicity of these chemicals to humans and other organisms has been widely reported. Chemically, these pesticides share an ester bond in their parent structures. A particular group of hydrolases, known as esterases, can catalyze the first step in ester-bond hydrolysis, and this initial regulatory metabolic reaction accelerates the degradation of OCP pesticides. Esterases can be naturally found in plants, animals, and microorganisms. Previous research on the esterase enzyme mechanisms revealed that the active sites of esterases contain serine residues that catalyze reactions via a nucleophilic attack on the substrates. In this review, we have compiled the previous research on esterases from different sources to determine and summarize the current knowledge of their properties, classifications, structures, mechanisms, and their applications in the removal of pesticides from the environment. This review will enhance the understanding of the scientific community when studying esterases and their applications for the degradation of broad-spectrum ester-containing pesticides.

An integrated overview of bacterial carboxylesterase: Structure, function and biocatalytic applications

Carboxylesterases (CEs) are members of prominent esterase, and as their name imply, they catalyze the cleavage of ester linkages. By far, a considerable number of novel CEs have been identified to investigate their exquisite physiological and biochemical properties. They are abundant enzymes in nature, widely distributed in relatively broad temperature range and in various sources; both macroorganisms and microorganisms. Given the importance of these enzymes in broad industries, interest in the study of their mechanisms and structural-based engineering are greatly increasing. This review presents the current state of knowledge and understanding about the structure and functions of this ester-metabolizing enzyme, primarily from bacterial sources. In addition, the potential biotechnological applications of bacterial CEs are also encompassed. This review will be useful in understanding the molecular basis and structural protein of bacterial CEs that are significant for the advancement of enzymology field in industries.

Biotechnological basis of microbial consortia for the removal of pesticides from the environment

The application of microbial strains as axenic cultures has frequently been employed in a diverse range of sectors. In the natural environment, microbes exist as multispecies and perform better than monocultures. Cell signaling and communication pathways play a key role in engineering microbial consortia, because in a consortium, the microorganisms communicate via diffusible signal molecules. Mixed microbial cultures have gained little attention due to the lack of proper knowledge about their interactions with each other. Some ideas have been proposed to deal with and study various microbes when they live together as a community, for biotechnological application purposes. In natural environments, microbes can possess unique metabolic features. Therefore, microbial consortia divide the metabolic burden among strains in the group and robustly perform pesticide degradation. Synthetic microbial consortia can perform the desired functions at naturally contaminated sites. Therefore, in this article, special attention is paid to the microbial consortia and their function in the natural environment. This review comprehensively discusses the recent applications of microbial consortia in pesticide degradation and environmental bioremediation. Moreover, the future directions of synthetic consortia have been explored. The review also explores the future perspectives and new platforms for these approaches, besides highlighting the practical understanding of the scientific information behind consortia.

Microbial Enzymes Used in Bioremediation

Emerging pollutants in nature are linked to various acute and chronic detriments in biotic components and subsequently deteriorate the ecosystem with serious hazards. Conventional methods for removing pollutants are not efficient; instead, they end up with the formation of secondary pollutants. Significant destructive impacts of pollutants are perinatal disorders, mortality, respiratory disorders, allergy, cancer, cardiovascular and mental disorders, and other harmful effects. The pollutant substrate can recognize different microbial enzymes at optimum conditions (temperature/pH/contact time/concentration) to efficiently transform them into other rather unharmful products. The most representative enzymes involved in bioremediation include cytochrome P450s, laccases, hydrolases, dehalogenases, dehydrogenases, proteases, and lipases, which have shown promising potential degradation of polymers, aromatic hydrocarbons, halogenated compounds, dyes, detergents, agrochemical compounds, etc. Such bioremediation is favored by various mechanisms such as oxidation, reduction, elimination, and ring-opening. The significant degradation of pollutants can be upgraded utilizing genetically engineered microorganisms that produce many recombinant enzymes through eco-friendly new technology. So far, few microbial enzymes have been exploited, and vast microbial diversity is still unexplored. This review would also be useful for further research to enhance the efficiency of degradation of xenobiotic pollutants, including agrochemical, microplastic, polyhalogenated compounds, and other hydrocarbons.

Characterization of a novel hyper-thermostable and chlorpyrifos-hydrolyzing carboxylesterase EstC: A representative of the new esterase family XIX

Carboxylesterases have widely been used in a series of industrial applications, especially, the detoxification of pesticide residues. In the present study, EstC, a novel carboxylesterase from Streptomyces lividans TK24, was successfully heterogeneously expressed, purified and characterized. Phylogenetic analysis showed that EstC can be assigned as the first member of a novel family XIX. Multiple sequence alignment indicated that EstC has highly conserved structural features, including a catalytic triad formed by Ser155, Asp248 and His278, as well as a canonical Gly-His-Ser-Ala-Gly pentapeptide. Biochemical characterization indicated that EstC exhibited maximal activity at pH 9.0 (Tris-HCl buffer) and 55 °C. It also showed higher activity towards short-chain substrates, with the highest activity for p-nitrophenyl acetate (pNPA2) (K_m = 0.31 ± 0.02 mM, k_cat/K_m = 1923.35 ± 9.62 s^-1 mM^-1) compared to other pNP esters used in this experiment. Notably, EstC showed hyper-thermostability and good alkali stability. The activity of EstC had no significant changes when it was incubated under 55 °C for 100 h and reached half-life after incubation at 100 °C for 8 h. Beyond that, EstC also showed stability at pH ranging from 6.0 to 11.0 and about 90% residual activity still reserved after treatment at pH 8.0 or 9.0 for 26 h, especially. Furthermore, EstC had outstanding potential for bioremediation of chlorpyrifos-contaminated environment. The recombinant enzyme (0.5 U mL^-1) could hydrolyze 79.89% chlorpyrifos (5 mg L^-1) at 37 °C within 80 min. These properties will make EstC have a potential application value in various industrial productions and detoxification of chlorpyrifos residues.

Facile One-Pot Immobilization of a Novel Thermostable Carboxylesterase from Geobacillus uzenensis for Continuous Pesticide Degradation in a Packed-Bed Column Reactor

The novel carboxylesterase gene (est741) was cloned from Geobacillus uzenensis. The optimal pH and temperature of Est741 were 8.0 and 50 °C. Through site-directed mutation, the optimum temperature of the mutant M160K(EstM160K) was increased from 50 to 60 °C, and showed enhanced T1/2 of 2.5 h at 70 °C in comparison to the wild type (1.3 h). EstM160K was successfully expressed Pichia pastoris and EstM160K fermentation broth was directly immobilized on epoxy-functionalized supports via a one-pot strategy to obtain the immobilized enzyme lx-EstM160K. Additionally, lx-EstM160K showed enhanced T1/2 of 36.8 h at 70 °C in comparison to free enzyme. lx-EstM160K could degrade various pyrethroid pesticides. After 40 min reaction with 50 U of the lx-EstM160K, the malathion removal was 95.8% with a malathion concentration of 20 mg/L. When 2.5 g lx-EstM160K was added to the 10 mL column reactor with the concentration of bifenthrin was 500 mg/L and the transfer rate of the pump was 0.7 mL/min, the degradation rate of lx-EstM160K to bifenthrin was 90.4%. lx-EstM160K exhibited high operational stability and maintained 72% initial activity after ten batches of continuous reaction for bifenthrin pesticide biodegradation.

A comprehensive review on enzymatic degradation of the organophosphate pesticide malathion in the environment

A comprehensive review of available bioremediation technologies for the pesticide malathion is presented. This review article describes the usage and consequences of malathion in the environment, along with a critical discussion on modes of metabolism of malathion as a sole source of carbon, phosphorus, and sulfur for bacteria, and fungi along with the biochemical and molecular aspects involved in its biodegradation. Additionally, the recent approaches of genetic engineering are discussed for the manipulation of important enzymes and microorganisms for enhanced malathion degradation along with the challenges that lie ahead.

Presence of esterase and laccase in Bacillus subtilis facilitates biodegradation and detoxification of cypermethrin

Ubiquitous presence of cypermethrin as a contaminant in surface stream and soil necessitates to develop potential bioremediation methods to degrade and eliminate this pollutant from the environment. A cypermethrin utilizing bacterial strain (MIC, 450  ppm) was isolated from the soil of pesticide contaminated agriculture field and characterized by using polyphasic approach. On molecular basis bacterial isolate showed 98% homology with Bacillus subtilis strain 1D. Under optimized growth conditions, bacteria showed 95% degradation of cypermethrin after 15 days and the end products of cypermethrin biodegradation under aerobic conditions were cyclododecylamine, phenol, 3-(2,2-dichloroethenyl 2,2-dimethyl cyclopropane carboxylate,1-decanol,chloroacetic acid, acetic acid, cyclopentan palmitoleic acid, and decanoic acid. Amplification of esterase (700 bp) and laccase (1200 bp) genes was confirmed by PCR which showed a possible role of these enzymes in biodegradation of cypermethrin. In the presence of cypermethrin Km value(s) of both the enzymes was low than the control. A nobel cypermethrin degradation pathway followed by B. subtilis was proposed on the basis of characterization of biodegraded products of cypermethrin using GC-MS. Cypermethrin biodegradation ability of Bacillus subtilis strain 1D without producing any toxic end product reveals the potential of this organism in cleaning of pesticide contaminated soil and water.

Functional Analysis of a Carboxylesterase Gene Associated With Isoprocarb and Cyhalothrin Resistance in Rhopalosiphum padi (L.)

Carboxylesterase (CarE) is an important class of detoxification enzymes involved in insecticide resistance. However, the molecular mechanism of CarE-mediated insecticide resistance in Rhopalosiphum padi, a problematic agricultural pest, remains largely unknown. In the present study, an isoprocarb-resistant (IS-R) strain and a cyhalothrin-resistant (CY-R) strain were successively selected from a susceptible (SS) strain of R. padi. The enzyme activity indicated that enhanced carboxylesterase activity contributes to isoprocarb and cyhalothrin resistance. The expression levels of putative CarE genes were examined and compared among IS-R, CY-R, and SS strains, and only the R. padi carboxylesterase gene (RpCarE) was significantly over expressed in both the IS-R and CY-R strains compared to the SS strain. The coding region of the RpCarE gene was cloned and expressed in Escherichia coli. The purified RpCarE protein was able to catalyze the model substrate, α-naphtyl acetate (Kcat = 5.50 s^-1; Km = 42.98 μM). HPLC assay showed that the recombinant protein had hydrolase activity against isoprocarb and cyhalothrin. The modeling and docking analyses consistently indicated these two insecticide molecules fit snugly into the catalytic pocket of RpCarE. Taken together, these findings suggest that RpCarE plays an important role in metabolic resistance to carbamates and pyrethroids in R. padi.

Preparation of Stable Cross-Linked Enzyme Aggregates (CLEAs) of a Ureibacillus thermosphaericus Esterase for Application in Malathion Removal from Wastewater

In this study, the active and stable cross-linked enzyme aggregates (CLEAs) of the thermostable esterase estUT1 of the bacterium Ureibacillus thermosphaericus were prepared for application in malathion removal from municipal wastewater. Co-expression of esterase with an E. coli chaperone team (KJE, ClpB, and ELS) increased the activity of the soluble enzyme fraction up to 200.7 ± 15.5 U mg−1. Response surface methodology (RSM) was used to optimize the preparation of the CLEA-estUT1 biocatalyst to maximize its activity and minimize enzyme loss. CLEA-estUT1 with the highest activity of 29.4 ± 0.5 U mg−1 (90.6 ± 2.7% of the recovered activity) was prepared with 65.1% (w/v) ammonium sulfate, 120.6 mM glutaraldehyde, and 0.2 mM bovine serum albumin at 5.1 h of cross-linking. The biocatalyst has maximal activity at 80 °С and pH 8.0. Analysis of the properties of CLEA-estUT1 and free enzyme at 50–80 °C and pH 5.0–10.0 showed higher stability of the biocatalyst. CLEA-estUT1 showed marked tolerance against a number of chemicals and high operational stability and activity in the reaction of malathion hydrolysis in wastewater (up to 99.5 ± 1.4%). After 25 cycles of malathion hydrolysis at 37 °С, it retained 55.2 ± 1.1% of the initial activity. The high stability and reusability of CLEA-estUT1 make it applicable for the degradation of insecticides.

New Insights into the Microbiota of Moth Pests

In recent years, next generation sequencing (NGS) technologies have helped to improve our understanding of the bacterial communities associated with insects, shedding light on their wide taxonomic and functional diversity. To date, little is known about the microbiota of lepidopterans, which includes some of the most damaging agricultural and forest pests worldwide. Studying their microbiota could help us better understand their ecology and offer insights into developing new pest control strategies. In this paper, we review the literature pertaining to the microbiota of lepidopterans with a focus on pests, and highlight potential recurrent patterns regarding microbiota structure and composition.

Detection of carboxylesterase and esterase activity in culturable gut bacterial flora isolated from diamondback moth, Plutella xylostella (Linnaeus), from India and its possible role in indoxacarb degradation

Diamondback moth (DBM), Plutella xylostella (Linnaeus), is a notorious pest of brassica crops worldwide and is resistant to all groups of insecticides. The insect system harbors diverse groups of microbiota, which in turn helps in enzymatic degradation of xenobiotic-like insecticides. The present study aimed to determine the diversity of gut microflora in DBM, quantify esterase activity and elucidate their possible role in degradation of indoxacarb. We screened 11 geographic populations of DBM in India and analyzed them for bacterial diversity. The culturable gut bacterial flora underwent molecular characterization with 16S rRNA. We obtained 25 bacterial isolates from larvae (n=13) and adults (n=12) of DBM. In larval gut isolates, gammaproteobacteria was the most abundant (76%), followed by bacilli (15.4%). Molecular characterization placed adult gut bacterial strains into three major classes based on abundance: gammaproteobacteria (66%), bacilli (16.7%) and flavobacteria (16.7%). Esterase activity from 19 gut bacterial isolates ranged from 0.072 to 2.32μmol/min/mg protein. Esterase bands were observed in 15 bacterial strains and the banding pattern differed in Bacillus cereus - KC985225 and Pantoea agglomerans - KC985229. The bands were characterized as carboxylesterase with profenofos used as an inhibitor. Minimal media study showed that B. cereus degraded indoxacarb up to 20%, so it could use indoxacarb for metabolism and growth. Furthermore, esterase activity was greater with minimal media than control media: 1.87 versus 0.26μmol/min/mg protein. Apart from the insect esterases, bacterial carboxylesterase may aid in the degradation of insecticides in DBM.

Decontamination of heavy metal laden sewage sludge with simultaneous solids reduction using thermophilic sulfur and ferrous oxidizing species

A possibility of using simultaneous sewage sludge digestion and metal leaching (SSDML) process at the thermophilic temperature to remove heavy metals and suspended solids from sewage sludge is explored in this study. Though thermophilic sludge digestion efficiently produces a stable sludge, its inability to remove heavy metals requires it to be used in tandem with another process like bioleaching for metal reduction. Previously, different temperature optima were known for the heterotrophs (thermophilic) responsible for the sludge digestion and the autotrophs involved in bioleaching (mesophilic), because of which the metal concentration was brought down separately in a different reactor. In our study, SSDML process was carried out at 50 °C (thermophilic) by using ferrous sulfate (batch-1) and sulfur (batch-2) as the energy source in two reactors. The concentration of volatile suspended solids reduced by >40% in both batches, while that of heavy metals zinc, copper, chromium, cadmium and nickel decreased by >50% in both batch-1 and batch-2. Lead got leached out only in batch-1. Using 16S rRNA gene-based PCR-denaturing gradient gel electrophoresis analysis, Alicyclobacillus tolerans was found to be the microorganism responsible for lowering the pH in both the reactors at thermophilic temperature. The indicator organism count was also below the maximum permissible limit making sludge suitable for agricultural use. Our results indicate that SSDML at thermophilic temperature can be effectively used for reduction of heavy metals and suspended solids from sewage sludge.

Identification and Characterization of a New 7-Aminocephalosporanic Acid Deacetylase from Thermophilic Bacterium Alicyclobacillus tengchongensis

Deacetylation of 7-aminocephalosporanic acid (7-ACA) at position C-3 provides valuable starting material for producing semisynthetic β-lactam antibiotics. However, few enzymes have been characterized in this process before now. Comparative analysis of the genome of the thermophilic bacterium Alicyclobacillus tengchongensis revealed a hypothetical protein (EstD1) with typical esterase features. The EstD1 protein was functionally cloned, expressed, and purified from Escherichia coli BL21(DE3). It indeed displayed esterase activity, with optimal activity at around 65°C and pH 8.5, with a preference for esters with short-chain acyl esters (C2 to C4). Sequence alignment revealed that EstD1 is an SGNH hydrolase with the putative catalytic triad Ser15, Asp191, and His194, which belongs to carbohydrate esterase family 12. EstD1 can hydrolyze acetate at the C-3 position of 7-aminocephalosporanic acid (7-ACA) to form deacetyl-7-ACA, which is an important starting material for producing semisynthetic β-lactam antibiotics. EstD1 retained more than 50% of its initial activity when incubated at pH values ranging from 4 to 11 at 65°C for 1 h. To the best of our knowledge, this enzyme is a new SGNH hydrolase identified from thermophiles that is able to hydrolyze 7-ACA.

IMPORTANCE

Deacetyl cephalosporins are highly valuable building blocks for the industrial production of various kinds of semisynthetic β-lactam antibiotics. These compounds are derived mainly from 7-ACA, which is obtained by chemical or enzymatic processes from cephalosporin C. Enzymatic transformation of 7-ACA is the main method because of the adverse effects chemical deacylation brought to the environment. SGNH hydrolases are widely distributed in plants. However, the tools for identifying and characterizing SGNH hydrolases from bacteria, especially from thermophiles, are rather limited. Here, our work demonstrates that EstD1 belongs to the SGNH family and can hydrolyze acetate at the C-3 position of 7-ACA. Moreover, this study can enrich our understanding of the functions of these enzymes from this family.

Functional Analysis of Esterase TCE2 Gene from Tetranychus cinnabarinus (Boisduval) involved in Acaricide Resistance

The carmine spider mite, Tetranychus cinnabarinus is an important pest of crops and vegetables worldwide, and it has the ability to develop resistance against acaricides rapidly. Our previous study identified an esterase gene (designated TCE2) over-expressed in resistant mites. To investigate this gene's function in resistance, the expression levels of TCE2 in susceptible, abamectin-, fenpropathrin-, and cyflumetofen-resistant strains were knocked down (65.02%, 63.14%, 57.82%, and 63.99%, respectively) via RNA interference. The bioassay data showed that the resistant levels to three acaricides were significantly decreased after the down-regulation of TCE2, indicating a correlation between the expression of TCE2 and the acaricide-resistance in T. cinnabarinus. TCE2 gene was then re-engineered for heterologous expression in Escherichia coli. The recombinant TCE2 exhibited α-naphthyl acetate activity (483.3 ± 71.8 nmol/mg pro. min(-1)), and the activity of this enzyme could be inhibited by abamectin, fenpropathrin, and cyflumetofen, respectively. HPLC and GC results showed that 10 μg of the recombinant TCE2 could effectively decompose 21.23% fenpropathrin and 49.70% cyflumetofen within 2 hours. This is the first report of a successful heterologous expression of an esterase gene from mites. This study provides direct evidence that TCE2 is a functional gene involved in acaricide resistance in T. cinnabarinus.