Characterization of ornithine decarboxylase with histidine decarboxylase activity in natural histidine decarboxylase gene deletion Enterobacter hormaechei RH3.

Histamine is predominantly produced in sausages via the decarboxylation of histidine by bacteria. Furthermore, histamine-producing bacteria usually possess the enzyme histidine decarboxylase (hdc). Enterobacter hormaechei RH3 isolated from sausages exhibited significant levels of histamine production despite the absence of hdc. In this study, we elucidated the previously unidentified mechanism underlying histamine production by RH3. We identified an enzyme, NehdX-772, exhibiting the hdc activity from the cell lysate supernatant of RH3, which was annotated as ornithine decarboxylase. The optimal activity of NehdX-772 was recorded at 35 °C and pH 6.0, and it could tolerate a salt concentration of 2.5% (w/v) NaCl. Moreover, artificial inoculation revealed that NehdX-772 was synthesized at significant levels in sausages, leading to an increase in histamine levels. The discovery of NehdX-772 explains the underlying mechanism of histamine production by RH3 and can be applied to decrease histamine production in sausages.

Lactiplantibacillus plantarum RS20D Alleviates Male Reproductive Toxicity Induced by Pubertal Exposure to Di-n-butyl Phthalate and Mono-n-butyl Phthalate.

Phthalate acid esters (PAEs) and their metabolites, such as di-n-butyl phthalate (DBP) and mono-n-butyl phthalate (MBP), are known to cause male reproductive damage. Lactiplantibacillus plantarum RS20D has demonstrated the ability to remove both DBP and MBP in vitro, suggesting its potential as a detoxifying agent against these compounds. This study aimed to investigate the protective effects of RS20D on DBP or MBP-induced male reproductive toxicity in adolescent rats. Oral administration of RS20D significantly mitigated the histological damage to the testes caused by MBP or DBP, restored sperm concentration, morphological abnormalities, and the proliferation index in MBP-exposed rats, and partially reversed spermatogenic damage in DBP-exposed rats. Furthermore, RS20D restored serum levels of estradiol (E2) and testosterone, and superoxide dismutase (SOD) activity in DBP-exposed rats, significantly increased testosterone levels in MBP-exposed rats, and restored copper (Cu) concentrations in the testes after exposure to DBP or MBP. Additionally, RS20D effectively modulated the intestinal microbiota in DBP-exposed rats and partially ameliorated dysbiosis induced by MBP, which may be associated with the alleviation of reproductive toxic effects induced by DBP or MBP. In conclusion, this study demonstrates that RS20D administration can alleviate male reproductive toxicity and gut dysbacteriosis induced by DBP or MBP exposure, providing a dietary strategy for the bioremediation of PAEs and their metabolites.

Research of Multicopper Oxidase and Its Degradation of Histamine in Lactiplantibacillus plantarum LPZN19.

In order to explore the structural changes and products of histamine degradation by multicopper oxidase (MCO) in Lactiplantibacillus plantarum LPZN19, a 1500 bp MCO gene in L. plantarum LPZN19 was cloned, and the recombinant MCO was expressed in E. coli BL21 (DE3). After purification by Ni2+-NTA affinity chromatography, the obtained MCO has a molecular weight of 58 kDa, and it also has the highest enzyme activity at 50 °C and pH 3.5, with a relative enzyme activity of 100%, and it maintains 57.71% of the relative enzyme activity at 5% salt concentration. The secondary structure of MCO was determined by circular dichroism, in which the proportions of the α-helix, ß-sheet, ß-turn and random coil were 2.9%, 39.7%, 21.2% and 36.1%, respectively. The 6xj0.1.A with a credibility of 68.21% was selected as the template to predict the tertiary structure of MCO in L. plantarum LPZN19, and the results indicated that the main components of the tertiary structure of MCO were formed by the further coiling and folding of a random coil and ß-sheet. Histamine could change the spatial structure of MCO by increasing the content of the α-helix and ß-sheet. Finally, the LC-MS/MS identification results suggest that the histamine was degraded into imidazole acetaldehyde, hydrogen peroxide and ammonia.

Untargeted Metabolomics and Physicochemical Analysis Revealed the Quality Formation Mechanism in Fermented Milk Inoculated with Lactobacillus brevis and Kluyveromyces marxianus Isolated from Traditional Fermented Milk.

Traditional fermented milk from the western Sichuan plateau of China has a unique flavor and rich microbial diversity. This study explored the quality formation mechanism in fermented milk inoculated with Lactobacillus brevis NZ4 and Kluyveromyces marxianus SY11 (MFM), the dominant microorganisms isolated from traditional dairy products in western nan. The results indicated that MFM displayed better overall quality than the milk fermented with L. brevis NZ4 (LFM) and K. marxianus SY11 (KFM), respectively. MFM exhibited good sensory quality, more organic acid types, more free amino acids and esters, and moderate acidity and ethanol concentrations. Non-targeted metabolomics showed a total of 885 metabolites annotated in the samples, representing 204 differential metabolites between MFM and LFM and 163 between MFM and KFM. MFM displayed higher levels of N-acetyl-L-glutamic acid, cysteinyl serine, glaucarubin, and other substances. The differential metabolites were mainly enriched in pathways such as glycerophospholipid metabolism, arginine biosynthesis, and beta-alanine metabolism. This study speculated that L. brevis affected K. marxianus growth via its metabolites, while the mixed fermentation of these strains significantly changed the metabolism pathway of flavor-related substances, especially glycerophospholipid metabolism. Furthermore, mixed fermentation modified the flavor and quality of fermented milk by affecting cell growth and metabolic pathways.

Cypermethrin adsorption by Lactiplantibacillus plantarum and its behavior in a simulated fecal fermentation model.

The presence of cypermethrin in the environment and food poses a significant threat to human health. Lactic acid bacteria have shown promise as effective absorbents for xenobiotics and well behaved in wide range of applications. This study aimed to characterize the biosorption behavior of cypermethrin by Lactiplantibacillus plantarum RS60, focusing on cellular components, functional groups, kinetics, and isotherms. Results indicated that RS60 exopolysaccharides played a crucial role removing cypermethrin, with the cell wall and protoplast contributing 71.50% and 30.29% to the overall removal, respectively. Notably, peptidoglycans exhibited a high affinity for cypermethrin binding. The presence of various cellular surface groups including -OH, -NH, -CH3, -CH2, -CH, -P = O, and -CO was responsible for the efficient removal of pollutants. Additionally, the biosorption process demonstrated a good fit with pseudo-second-order and Langmuir-Freundlich isotherm. The biosorption of cypermethrin by L. plantarum RS60 involved complex chemical and physical interactions, as well as intraparticle diffusion and film diffusion. RS60 also effectively reduced cypermethrin residues in a fecal fermentation model, highlighting its potential in mitigating cypermethrin exposure in humans and animals. These findings provided valuable insights into the mechanisms underlying cypermethrin biosorption by lactic acid bacteria and supported the advancement of their application in environmental and health-related contexts. KEY POINTS: • Cypermethrin adsorption by L. plantarum was clarified. • Cell wall and protoplast showed cypermethrin binding ability. • L. plantarum can reduce cypermethrin in a fecal fermentation model.

Class 1 integron carrying qacEΔ1 gene confers resistance to disinfectant and antibiotics in Salmonella.

Salmonella has presented increasingly alarming rates of antimicrobial resistance believed to be a result of a high prevalence of integrons. It is speculated that disinfectant-resistant isolates are due to the expression of qacEΔ1, an efflux pump located in the 3' conserved sequence (3'CS) of class 1 integrons. With this concern, we tested the antibiotic and disinfectant resistance of 581 Salmonella strains collected from different sources, and characterized their integron structures. Gene expression and induction experiments were also performed. Results showed that Salmonella have high resistance to antimicrobials, especially to sulfonamides (SAs, 78.83 %), tetracyclines (TCs, 75.04 %) and benzalkonium chloride (BC, 87.26 %). The multi-drug resistance (MDR) frequency reached up to 63.17 %, and the prevalence of intI1 was 45.78 %. Molecular characterization of class 1 integrons exhibited nine different gene cassette arrays, of these, dfrA12-orf-aadA2 (n = 75), EstX (n = 25) and aadA2 (n = 14) were the most frequent. Importantly, 74.06 % of intI1-positive isolates were carrying qacEΔ1-sul1 genes in the 3'CS. This study also demonstrated that phenotypic resistance to both antibiotics and disinfectants was significantly correlated with the emergence of intI1 (p < 0.05). 91.37 % of qacEΔ1-sul1 positive Salmonella were found with disinfectant resistance. Additionally, expression of qacEΔ1 gene in Escherichia coli confirmed qacEΔ1 is predominantly involved in conferring disinfectant resistance. Disinfectant induction experiments further implicated qacEΔ1 in disinfectant resistance. RT-qPCR revealed a disinfectant-mediated increase in the relative expression of antibiotic-resistant genes (ARGs), aadA2 and dfrA12 on the integron, and efflux pump genes (mdtH and acrD) indicating that disinfectant could trigger co or cross-resistance. Therefore, our study confirmed that using disinfectant could provide selection pressure for strains with acquired resistance to antibiotics, providing new insights into the public health impact of Salmonella and guide continued efforts in antimicrobial stewardship and prevention of antibiotic resistance.

Insight into the acid tolerance mechanism of Acetilactobacillus jinshanensis subsp. aerogenes Z-1.

Several lactic acid bacteria (LAB) are double-edged swords in the production of Sichuan bran vinegar; on the one hand, they are important for the flavour of the vinegar, but on the other hand, they result in vinegar deterioration because of their gas-producing features and their acid resistance. These characteristics intensify the difficulty in managing the safe production of vinegar using strains such as Acetilactobacillus jinshanensis subsp. aerogenes Z-1. Therefore, it is necessary to characterize the mechanisms underlying their acid tolerance. The results of this study showed a survival rate of 77.2% for Z-1 when exposed to pH 3.0 stress for 1 h. This strain could survive for approximately 15 days in a vinegar solution with 4% or 6% total acid content, and its growth was effectively enhanced by the addition of 10 mM of arginine (Arg). Under acidic stress, the relative content of the unsaturated fatty acid C18:1 (n-11) increased, and eight amino acids accumulated in the cells. Meanwhile, based on a transcriptome analysis, the genes glnA, carA/B, arcA, murE/F/G, fabD/H/G, DnaK, uvrA, opuA/C, fliy, ecfA2, dnaA and LuxS, mainly enriched in amino acid transport and metabolism, protein folding, DNA repair, and cell wall/membrane metabolism processes, were hypothesized to be acid resistance-related genes in Z-1. This work paves the way for further clarifying the acid tolerance mechanism of Z-1 and shares applicable perspectives for vinegar brewing.

Exploring the role of Sichuan Baoning vinegar microbiota and the association with volatile flavor compounds at different fermentation depths.

Cereal vinegar is usually produced through solid-state fermentation, and the microbial community plays an important role in fermentation. In this study, the composition and function of Sichuan Baoning vinegar microbiota at different fermentation depths were evaluated by high-throughput sequencing combined with PICRUSt and FUNGuild analysis, and variations in volatile flavor compounds were also determined. The results revealed that no significant differences (p > 0.05) were found in both total acid content and pH of vinegar Pei collected on the same day with different depths. There were significant differences between the bacterial community of samples from the same day with different depths at both phylum and genus levels (p < 0.05), however, no obvious difference (p > 0.05) was observed in the fungal community. PICRUSt analysis indicated that fermentation depth affected the function of microbiota, meanwhile, FUNGuild analysis showed that there were variations in the abundance of trophic mode. Additionally, differences in volatile flavor compounds were observed in samples from the same day with different depths, and significant correlations between microbial community and volatile flavor compounds were observed. The present study provides insights into the composition and function of microbiota at different depths in cereal vinegar fermentation and quality control of vinegar products.

Isolation and characterization of a gas-producing and acid-resistant bacterium from spoiled vinegar.

To understand the deterioration of vinegar that has frequently occurred in China recently and to address such a concern, the physicochemical indicators and bacterial structure of the spoiled vinegar collected from Sichuan were preliminarily investigated. Results showed that Lactobacillaceae was most likely responsible for the decrease of vinegar total sugar and furfural, through which total acid and furfuryl alcohol were generated. Then, an unreported difficult-to-cultivate gas-producing bacterium named Z-1 was isolated using a modified MRS medium. Strain Z-1 was identified as Acetilactobacillus jinshanensis subsp. aerogenes on the basis of physiological, biochemical, molecular biological and whole genome analyses. According to the investigation, such species was present throughout the fermentation process and not limited in Sichuan. The analysis of genetic diversity indicated that all the obtained A. jinshanensis isolates displayed high sequence similarity and an absence of recombination. Although it demonstrated acid resistance, Z-1 could be completely deactivated through heating (60 °C). Based on the above results, suggestions for safe production are made for vinegar enterprises.

A novel cold-adapted pyrethroid-degrading esterase from Bacillus subtilis J6 and its application for pyrethroid-residual alleviation in food matrix.

Prolonged and widespread use of pyrethroid pesticides a significant concern for human health. The initial step in pyrethroid bioremediation involves the hydrolysis of ester-bond. In the present study, the esterase genes est10 and est13, derived from Bacillus subtilis, were successfully cloned and expressed in Escherichia coli. Recombinant Est10 and Est13 were classified within esterase families VII and XIII, respectively, both of which exhibited conserved G-X-G-X-G motifs. These enzymes demonstrated the capability to degrade pyrethroids, with Est13 exhibiting superior efficiency, and thus was selected for further investigation. The degradation products of ß-cypermethrin by Est13 were identified as 3-phenoxybenzoic acid, 3-phenoxybenzaldehyde, and 3-(2,2-Dichloroethenyl)- 2,2-dimethyl-cyclopropanecarboxylate, with key catalytic triads comprising Ser93, Asp192, and His222. Notably, Est13 exhibited the highest ß-cypermethrin-hydrolytic activity at 25 °C and a pH of 7.0, showing robust stability in low and medium temperature environment and a broad range of pH levels. Furthermore, Est13 displayed notable resistance to organic solvents and NaCl, coupled with wide substrate specificity. Moreover, Est13 exhibited substantial efficiency in removing ß-cypermethrin residues from various food items such as milk, meat, vegetables, and fruits. These findings underscore the potential of Est13 for application in the bioremediation of pyrethroid-contaminated environments and reduction of pyrethroid residues in food products.

Facile Synthesis of N, S-Doped Carbon Quantum Dots from Food Waste as Fluorescent Probe for Sensitive Detection of Thiamphenicol and Its Analogues in Real Food Samples along with an Application in Bioimaging.

Herein, N, S co-doped carbon quantum dots (N, S-CDs) with high absolute quantitative yield (Abs-QY) of 50.2% were produced by hydrothermal treatment of food residue crayfish shells. A new detection method of thiamphenicol (TAP) and its analogues was established by discovering the obvious fluorescence response between TAP and N, S-CDs, which achieved a wide linear range of 20-300 µg·L-1 with a detection limit (LOD) of 11.12 µg·L-1. This novel probe exhibited strong sensitivity and shows rapid response in complex food matrices (overall detection time is less than 45 min) mainly induced by static quenching. Spiked food sample recovery ranged from 97.3 to 99.34%. Further, the cell experiments of N, S-CDs were conducted, and the cell viability remained 91.76% under high concentration of N, S-CDs due to the environmentally friendly materials. The low cytotoxicity and good cytocompatibility make these N, S-CDs compatible for cell bioimaging and intracellular detection of TAP.

Antifungal Mechanisms and Application of Lactic Acid Bacteria in Bakery Products: A Review.

Bakery products are nutritious, but they are susceptible to fungal contamination, which leads to a decline in quality and safety. Chemical preservatives are often used to extend the shelf-life of bakery products, but long-term consumption of these preservatives may increase the risk of chronic diseases. Consumers increasingly demand food with fewer chemical preservatives. The application of lactic acid bacteria (LAB) as a novel biological preservative not only prolongs the shelf-life of bakery products but also improves the baking properties of bakery products. This review summarizes different types and action mechanisms of antifungal compounds produced by LAB, factors affecting the production of antifungal compounds, and the effects of antifungal LAB on bakery products, providing a reference for future applications of antifungal LAB in bakery products.

Adsorption Behavior of 3-phenoxybenzoic Acid by Lactobacillus Plantarum and Its Potential Application in Simulated Digestive Juices.

3-PBA is a major degradation intermediate of pyrethroids. Its widespread existence in the environment poses a severe threat to the ecosystem and human health. This study evaluated the adsorption capacity of L. plantarum RS20 toward 3-PBA. Batch adsorption experiments indicated that the optimal adsorption conditions were a temperature of 37 °C and initial pH of 6.0-8.0, under which the removal rate was positively correlated with the cell concentration. In addition, there was no link between the incubation time and adsorption rate. The kinetic study showed that the adsorption process fitted well with the pseudo-second-order model, and the adsorption isotherms could be described by both Langmuir and Freundlich equations. Heat and acid treatments showed that the ability of strain RS20 in removing 3-PBA was independent of microbial vitality. Indeed, it was involved with chemisorption and physisorption via the cell walls. The cell walls made the highest contribution to 3-PBA removal, according to the adsorption experiments using different cellular components. This finding was further reconfirmed by SEM. FTIR spectroscopy analysis indicated that carboxyl, hydroxyl, amino groups, and -C-N were the functional sites for the binding of 3-PBA. The co-culture experiments showed that the adsorption of strain RS20 enhanced the degradation of 3-PBA by strain SC-1. Strain RS20 could also survive and effectively remove 3-PBA in simulated digestive juices. Collectively, strain RS20 could be employed as a biological detoxification agent for humans and animals by eliminating 3-PBA from foods, feeds, and the digestive tract in the future.

Extraction, isolation and identification of four phenolic compounds from Pleioblastus amarus shoots and their antioxidant and anti-inflammatory properties in vitro.

Pleioblastus amarus (P. amarus) shoots, belong to the grass family Gramineae, a traditional green vegetable in China, are rich in nutritional properties, and can provide various health benefits. This study isolated four compounds, namely (1-4), 3-O-coumaroylquinic acid (1), 3-O-feruloylquinic acid (2), 4-O-feruloylquinic acid (3), and 5-O-feruloylquinic acid (4) from Pleioblastus amarus shoots for the first time. The structures of the extracted compounds were determined using detailed spectroscopic (1D/2D NMR), high resolution electrospray ionization mass spectrometry (HR-ESI-MS), and infrared (IR) spectroscopy. The antioxidant capacity of 3-O-feruloylquinic acid (2) was stronger than that of the other compounds, while it also exhibited anti-inflammatory activity, significantly restricting the release of nitric oxide (NO) by lipopolysaccharide (LPS)-induced RAW 264.7 cells, displaying an inhibitory rate of 60.92 percent at a concentration of 400 µg/mL. Furthermore, 3-O-feruloylquinic acid (2) inhibited interleukin-1ß (IL-1ß), interleukin-6 (IL-6), inducible nitric oxide synthase (iNOS), cyclooxygenase-2 (COX-2), and nuclear factor-κB (NF-κB) expression and may be useful for developing novel antioxidant and anti-inflammatory substances.

Optimization and adsorption characteristics of beads based on heat-inactivated bacterial biomaterial towards the pesticide Cypermethrin.

AIMS: Beads containing heat-inactivated bacterial biomaterial (BBBs) were prepared for removal of cypermethrin (CPM) and the conditions for this removal were evaluated and optimized via orthogonal experiments. The adsorption characteristics of BBBs and the binding mechanism were then explored. METHODS AND RESULTS: Single-factor and orthogonal experiments were carried out to optimize five factors affecting the production and effectivity of the beads. The adsorption rate of CPM could reach 98% with beads prepared under optimized conditions: equal volumes of Lactobacillus cell debris derived from 1 × 1011 CFU; 2% hydroxypropyl-ß-cyclodextrin and 2.5% activated carbon concentration, were mixed to give mixture TM, and this and SA, was mixed 1:4 with sodium alginate (SA) and beads were prepared using a 26-Gauge needle). The best adsorption conditions were initial CPM concentration of 10 mg l-1, incubation time of 24 h, and rotational speed of 180 rpm. BBBs have a well-formed structure and abundant surface functional groups, such as -COOH, -OH, -NH, -CH, -CO, -C = C. The adsorption process conformed to pseudo-second-order kinetic, and it was also a Freundlich monolayer adsorption, and the calculated maximum adsorption capacity was 9.69 mg g-1 under optimized conditions. CONCLUSIONS: BBBs showed the highest CPM removal capacity and a good tolerance ability.

Optimization and adsorption characteristics of beads based on heat-inactivated bacterial biomaterial towards the pesticide Cypermethrin.

AIMS: Beads containing heat-inactivated bacterial biomaterial (BBBs) were prepared for removal of cypermethrin (CPM) and the conditions for this removal were evaluated and optimized via single-factor coupled orthogonal experiments based on five factors. The adsorption characteristics of BBBs and the binding mechanism were then explored. METHODS AND RESULTS: Results showed that the adsorption rate of CPM could reach 98% with beads prepared under optimized conditions: equal volumes of Lactobacillus cell debris derived from 1×1011 CFU; 2% hydroxypropyl-ß-cyclodextrin and 2.5% activated carbon concentration, were mixed to give mixture TM, and this and SA, was mixed 1:4 with sodium alginate (SA) and beads were prepared using a 26-Gauge needle). The best adsorption conditions were initial CPM concentration of 10 mg l-1, incubation time of 24 h, and rotational speed of 180 rpm. BBBs have a well-formed structure and abundant surface functional groups, such as -COOH, -OH, -NH, -CH, -CO, -C=C. The adsorption process conformed to pseudo-second-order kinetic, and it was also a Freundlich monolayer adsorption, and the calculated maximum adsorption capacity was 9.69 mg g-1 under optimized conditions. CONCLUSIONS: BBBs showed the highest CPM removal capacity and a good tolerance ability. SIGNIFICANCE AND IMPACT OF THE STUDY: Our results provided a theoretical foundation for developing an adsorbent with heat-inactivated Lactobacillus plantarum (L. plantarum) RS60 for removing CPM in wastewater or drinks.

Multiple rounds of Aspergillus niger biofortification confer relatively stable quality with minor changes of microbial community during industrial-scale Baoning vinegar production.

Vinegar is consumed worldwide as a food condiment, especially in the Chinese diet. The present study optimized the addition of A. niger biofortified-bran Qu (0.3%, 0.45%, and 0.6%) as additional starter to improve total acid content and starch utilization rate in industrial-scale Baoning vinegar production. In addition, this novel study determined the quality and microbial community changes of Baoning vinegar during three-round biofortification in industrial scale. Our results indicated that A. niger biofortified-bran Qu added at 0.6% resulted in higher total acid content and starch utilization rate of vinegar Pei. Biofortification imposed minor changes in the microbial community during three-round biofortification, and more variation was observed in fungal community than that in bacterial community. Most importantly, the quality of Baoning vinegar remained relatively stable. This information further confirmed the feasibility of multiple rounds of A. niger biofortification, and can be used to provide theoretical basis for industrial-scale production.

Heavy Metal Resistance in Salmonella Typhimurium and Its Association With Disinfectant and Antibiotic Resistance.

Metals are widely used in animal feed for their growth-stimulating and antimicrobial effects, yet their use may potentially promote the proliferation of antibiotic resistance through co-selection. We studied the prevalence and associations of metal, antibiotic, and disinfectant resistances of 300 Salmonella Typhimurium isolates from pig meat, pig manure, chicken meat, poultry manure, and human stool from Sichuan, China. Seventy four percent of the 300 Salmonella Typhimurium isolates were considered resistant to Cu, almost 50% to Zn and Cr, over 25% to Mn and Cd, and almost 10% to Co. Most of the isolates carried at least one heavy metal resistance gene (HMRG). The Cr-Zn-Cd-resistance gene czcD was carried by 254 isolates and the Cu-resistance genes pcoR and pcoC by 196 and 179 isolates, respectively. Most of the isolates were resistant to at least one antibiotic and almost 80% were multidrug-resistant. The prevalence of resistance to six antibiotics was higher among the pig meat and manure isolates than among other isolates, and that of streptomycin and ampicillin were highest among the pig meat isolates and that of ciprofloxacin and ofloxacin among the pig manure isolates. From 55 to 79% of the isolates were considered resistant to disinfectants triclosan, trichloroisocyanuric acid, or benzalkonium chloride. The metal resistances and HMRGs were associated with resistance to antibiotics and disinfectants. Especially, Cu-resistance genes were associated with resistance to several antibiotics and disinfectants. The transfer of the Cr-Zn-Cd-resistance gene czcD, Cu-resistance gene pcoC, and Co-Ni-resistance gene cnrA into Escherichia coli and the increased Cu-resistance of the transconjugants implied that the resistance genes were located on conjugative plasmids. Thus, the excessive use of metals and disinfectants as feed additives and in animal care may have the potential to promote antibiotic resistance through co-selection and maintain and promote antibiotic resistance even in the absence of antibiotics.

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 Km and Vmax 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.

A magnetic phosphorescence molecularly imprinted polymers probe based on manganese-doped ZnS quantum dots for rapid detection of trace norfloxacin residual in food.

This paper reports the development of a novel probe based on magnetic room-temperature phosphorescence quantum dots with molecularly imprinted polymers (MQD-MIPs) for the rapid detection of trace norfloxacin (NFX) residual in complex food matrix. The highly selective probe was constructed by surface molecular imprinting technology using magnetic materials (Fe3O4 nanoparticles) as core, Mn-doped ZnS quantum dots (Mn-ZnS QDs) as phosphorescent materials, NFX as template, 3-aminopropyltriethoxysilane as functional monomer, and tetraethoxysilane as crosslinking agent. The as-obtained MQD-MIPs were characterized in detail by transmission electron microscopy, scanning electron microscopy, X-ray powder diffraction, Fourier transform infrared spectrometry, and vibrating sample magnetometer. A magnetic strength of 37.64 emu g-1 was recorded. Also, the probe displayed excellent room temperature phosphorescence properties with excitation/emission peaks at 300/590 nm. Under the optimized conditions, the detection time was less than 40 min, phosphorescence intensity varied linearly with concentration from 1 to 90 µg·L-1, and detection limit reached as low as 0.80 µg·L-1. Furthermore, the MQD-MIPs-based probe successfully detected norfloxacin residues in spiked fish and milk samples with recoveries of 90.92-111.53% and RSD <7%, outperforming the standard control method-HPLC-FLD (recoveries of 85.89-118.28%).