The Potential Binding Interaction and Hydrolytic Mechanism of Carbaryl with the Novel Esterase PchA in Pseudomonas sp. PS21

cAMP-Mediated Biofilm eDNA Transfer Facilitates the Resilience of Soil Microbiome to Agrochemical Stress

Soil microorganisms utilize extracellular DNA (eDNA)-based biofilms as a defense against xenobiotics. However, the specific effects and transfer pathways of eDNA under persistent agrochemical exposure remain unclear. This study examined the transfer dynamics of carbofuran-hydrolase gene pchA from Pseudomonas stutzeri PS21. During biofilm formation, pchA was released from eDNA, leading to an enrichment of beneficial microorganisms such as Acidobacteria and Elusimicrobia, which enhanced organic compound metabolism and improved soil microbiome resilience. An increase in the pchA-associated mobile genetic elements and the colocalization of pchA with other bacterial species indicated the potential horizontal gene transfer (HGT) under carbofuran exposure. Additionally, carbofuran triggered a cAMP-dependent apoptotic pathway, leading to a 59.6% increase in pchA copy number, which suggested that cAMP played a role in initiating HGT. In conclusion, the cAMP-mediated interspecific transfer of pchA could enhance microbial coadaptation to carbofuran contamination, thereby strengthening the collective defense of soil microbiome against agrochemical stress.

Cloning and Expression of the Isoprocarb Hydrolase Gene cehA from the Newly Isolated Isoprocarb-Degrading Strain Sphingobium sp. R-7

To remove the isoprocarb residues from the environment, a bacterial strain that was capable of degrading isoprocarb was isolated from agricultural soils where isoprocarb has been applied for a long period, and named R-7. On the basis of its cellular morphology and phenotypic features and 16S rRNA phylogenetic analysis, strain R-7 was preliminarily identified as Sphingobium sp. This strain could grow on isoprocarb as a sole carbon source and degrade 98.3% of 0.5 mM of isoprocarb within 16 h in batch liquid culture. The metabolite produced was identified as 2-isopropylphenol by high-performance liquid chromatography and tandem mass spectrometry (HPLC-MS/MS) analysis. Strain R-7 hydrolysed the ester bond of isoprocarb to generate 2-isopropylphenol, but this metabolite was not further degraded. Upon the genome comparison, the isoprocarb hydrolase gene cehA was cloned from strain R-7 and expressed in Escherichia coli BL21. The purified CehAR-7 displayed maximal enzymatic activity at 40 °C and pH 7.0. The apparent Km and kcat values of CehAR-7 for isoprocarb were 169.12 ± 7.74 µmol L-1 and 347 ± 17.73 min-1, respectively. CehAR-7 could hydrolyse carbaryl and isoprocarb efficiently, although its ability to hydrolyse carbofuran, oxamyl and methomyl was poor. In conclusion, this study provided an efficient isoprocarb-degrading microorganism, and identified the isoprocarb hydrolase CehA from strain R-7, which has potential applications for microbial remediation of isoprocarb-polluted environments.

Characterization and Mechanism Study of a Novel Ethanol Acetyltransferase from Hanseniaspora uvarum (EatH) with Good Thermostability, pH Stability, and Broad Alcohol Substrate Specificity

Ethyl acetate, one of the most essential industrial compounds, has a broad range of applications, including flavors, fragrances, pharmaceuticals, cosmetics, and green solvents. Eat1 is accountable for bulk ethyl acetate production in yeasts, yet its properties and molecular mechanism are not well characterized. In this study, an eat1 gene from Hanseniaspora uvarum was obtained through gene mining. EatH showed the highest activity at pH 7.5 and 35 °C and preferred short-chain acyl substrates but had a broad alcohol substrate spectrum from short-chain primary alcohols to aromatic alcohols. Its Km and kcat/Km values toward pNPA were measured to be 1.16 mM and 29.03 L·mmol-1·s-1, respectively. The structure of EatH was composed of a lid domain and a core catalytic domain, with the catalytic triad of Ser124, Asp148, and His296. Additionally, crucial residues and their mechanism were analyzed through molecular docking, site-directed mutagenesis, and molecular dynamics simulation. The mutants N149A, N149K, and N149S showed enhanced enzyme activity toward pNP-hexanoate to 5.0-, 6.6-, and 3.6-fold, and Y204S enhanced enzyme activity for pNP-butyrate by 2.6 times via creating a wider substrate binding pocket and enhancing hydrophobicity. Collectively, this work provided a theoretical basis for the further rational design of EatH and enriched the understanding of the Eat family.

Abridgement of Microbial Esterases and Their Eminent Industrial Endeavors

Esterases are hydrolases that contribute to the hydrolysis of ester bonds into both water-soluble acyl esters and emulsified glycerol-esters containing short-chain acyl groups. They have garnered significant attention from biotechnologists and organic chemists due to their immense commercial value. Esterases, with their diverse and significant properties, have become highly sought after for various industrial applications. Synthesized ubiquitously by a wide range of living organisms, including animals, plants, and microorganisms, these enzymes have found microbial esterases to be the preferred choice in industrial settings. The cost-effective production of microbial esterases ensures higher yields, unaffected by seasonal variations. Their applications span diverse sectors, such as food manufacturing, leather tanneries, paper and pulp production, textiles, detergents, cosmetics, pharmaceuticals, biodiesel synthesis, bioremediation, and waste treatment. As the global trend shifts toward eco-friendly and sustainable practices, industrial processes are evolving with reduced waste generation, lower energy consumption, and the utilization of biocatalysts derived from renewable and unconventional raw materials. This review explores the background, structural characteristics, thermostability, and multifaceted roles of bacterial esterases in crucial industries, aiming to optimize and analyze their properties for continued successful utilization in diverse industrial processes. Additionally, recent advancements in esterase research are overviewed, showcasing novel techniques, innovations, and promising areas for further exploration.

OBP83b and OBP49a Involved in the Perception of Female-Derived Pheromones in Bactrocera dorsalis (Hendel)

In Bactrocera dorsalis, both males and females release chemical signals to attract mates. In our previous study, we identified ethyl laurate, ethyl myristate, and ethyl palmitate as potent female-derived pheromones that contribute to mate attraction. However, the mechanisms underlying the olfactory recognition remain unclear. In this study, we observed strong antennal and behavioral responses in male B. dorsalis to these female-derived pheromones, and further investigation revealed significant upregulation of OBP49a and OBP83b following exposure to these compounds. Through fluorescence competitive binding assays and RNA interference techniques, we demonstrated the crucial roles of OBP49a and OBP83b in detecting female-derived pheromones. Finally, molecular docking analysis identified key residues, including His134 in OBP83b and a lysine residue in OBP49a, which formed hydrogen bonds with female-derived pheromones, facilitating their binding. These findings not only advance our understanding of olfactory recognition of pheromones in B. dorsalis but also offer potential targets for developing olfaction-interfering techniques for pest control.

Removal, transformation and ecological risk assessment of pesticide in rural wastewater by field-scale horizontal flow constructed wetlands of treated effluent

Constructed wetlands (CWs) are widely used in sewage treatment in rural areas, but there are only a few studies on field-scale CWs in treating wastewater-borne pesticides. In this study, the treatment and metabolic transformation of 29 pesticides in rural domestic sewage by 10 field-scale horizontal flow CWs (HF-CWs), each with a treatment scale of 36‒5000 m3/d and operated for 2‒10 years, in Guangzhou, Southern China was investigated. The risk of pesticides in treated effluent and main factors influencing such risk were evaluated. Results demonstrated that HF-CWs could remove pesticides in sewage and reduce their ecological risk in effluent, but the degree varied among types of pesticides. Herbicides had the highest mean removal rate (67.35 %) followed by insecticides (60.13 %), and the least was fungicides (53.22 %). In terms of single pesticide compounds, the mean removal rate of butachlor was the highest (73.32 %), then acetochlor (69.41 %), atrazine (68.28 %), metolachlor (58.40 %), and oxadixyl (53.28 %). The overall removal rates of targeted pesticides in each HF-CWs ranged from 11 %‒57 %, excluding two HF-CWs showing increases in pesticides in treated effluent. Residues of malathion, phorate, and endosulfan in effluent had high-risks (RQ > 5). The pesticide concentration in effluent was mainly affected by that in influent (P = 0.042), and source control was the key to reducing risk. The main metabolic pathways of pesticide in HF-CWs were oxidation, with hydroxyl group to carbonyl group or to form sulfones, the second pathways by hydrolysis, aerobic condition was conducive to the transformation of pesticides. Sulfones were generally more toxic than the metabolites produced by hydrolytic pathways. The present study provides a reference on pesticides for the purification performance improvement, long-term maintenance, and practical sustainable application of field-scale HF-CWs.

Substrate-enzyme interactions and catalytic mechanism in a novel family VI esterase with dibutyl phthalate-hydrolyzing activity

Microbial degradation has been confirmed as effective and environmentally friendly approach to remediate phthalates from the environment, and hydrolase is an effective element for contaminant degradation. In the present study, a novel dibutyl phthalate (DBP)-hydrolyzing carboxylesterase (named PS06828) from Pseudomonas sp. PS1 was heterogeneously expressed in E. coli, which was identified as a new member of the lipolytic family VI. Purified PS06828 could efficiently degrade DBP with a wide range of temperature (25-37 °C) and pH (6.5-9.0). Multi-spectroscopy methods combined with molecular docking were employed to study the interaction of PS06828 with DBP. Fluorescence and UV-visible absorption spectra revealed the simultaneous presence of static and dynamic component in the fluorescence quenching of PS06828 by DBP. Synchronous fluorescence and circular dichroism spectra showed inconspicuous alteration in micro-environmental polarity around amino acid residues but obvious increasing of α-helix and reducing of β-sheet and random coil in protein conformation. Based on the information on exact binding sites of DBP on PS06828 provided by molecular docking, the catalytic mechanism mediated by key residues (Ser113, Asp166, and His197) was proposed and subsequently confirmed by site-directed mutagenesis. The results can strengthen our mechanistic understanding of family VI esterase involved in hydrolysis of phthalic acid esters, and provide a solid foundation for further enzymatic modification.

Heterogeneous distribution of carbofuran shaped by Pseudomonas stutzeri biofilms enhances biodegradation of agrochemicals

Biodegradation, harnessing the metabolic versatility of microorganisms to reduce agrochemical contaminations, is commonly studied with enriched planktonic cells but overlooking the dominant lifestyle of microorganisms is to form biofilms, which compromises the efficiency of biodegradation in natural environment. Here, we employed a carbofuran-degrading bacterium Pseudomonas stutzeri PS21 to investigate how the bacterial biofilms formed and responded to agrochemicals. First, the PS21 biofilms formed with a core of bacterial cells enclosing with extracellular polymeric substances (EPSs), and the biofilms were active and resilient when exposed to carbofuran (up to 50 mg L^-1). The formation was regulated by the second messenger bis-(3'-5')-cyclic di-guanosine monophosphate signaling, which strengthened the structural resistance and metabolic basis of biofilms to remain the degrading efficiency as comparable as the planktonic cells. Second, carbofuran distributed heterogeneously in the near-biofilm microenvironment via the covalent adsorption of biofilms, which provided a spontaneous force that enhanced the combination of carbofuran with biofilms to maintain high degrading activity. Additionally, we elucidated the biodegradation was driven by the integrated metabolic system of biofilms involving the extracellular enzymes located in the EPSs. This study exhibited the structural and metabolic advantages of microbial biofilms, highlighting the attractive potentials of exploring biofilm-based strategies to facilitate the in-situ bioremediation of organic contaminations.

Microbial elimination of carbamate pesticides: specific strains and promising enzymes

Carbamate pesticides are widely used in the environment, and compared with other pesticides in nature, they are easier to decompose and have less durability. However, due to the improper use of carbamate pesticides, some nontarget organisms still may be harmed. To this end, it is necessary to investigate effective removal or elimination methods for carbamate pesticides. Current effective elimination methods could be divided into four categories: physical removal, chemical reaction, biological degradation, and enzymatic degradation. Physical removal primarily includes elution, adsorption, and supercritical fluid extraction. The chemical reaction includes Fenton oxidation, photo-radiation, and net electron reduction. Biological degradation is an environmental-friendly manner, which achieves degradation by the metabolism of microorganisms. Enzymatic degradation is more promising due to its high substrate specificity and catalytic efficacy. All in all, this review primarily summarizes the property of carbamate pesticides and the traditional degradation methods as well as the promising biological elimination. KEY POINTS: • The occurrence and toxicity of carbamate pesticides were shown. • Biological degradation strains against carbamate pesticides were presented. • Promising enzymes responsible for the degradation of carbamates were discussed.