Role of Enterococcus mundtii in gut of the tomato leaf miner (Tuta absoluta) to detoxification of Chlorantraniliprole

Chlorantraniliprole (CAP) is applied worldwide for the control of caterpillars (Lepidoptera). However, with the overuse of CAP, the resistance problem in pest control is becoming increasingly serious. Recent studies have indicated a central role of the gut symbiont in insect pest resistance to pesticides and these may apply to the tomato leaf miner Tuta absoluta, is one of the most destructive insects worldwide. Here, we successfully isolated seven strains of tolerant CAP bacterium from the CAP-resistant T. absoluta gut, of which Enterococcus mundtii E14 showed the highest CAP tolerance, with a minimum inhibitory concentration (MIC) of 1.6 g/L and CAP degradation rate of 42.4%. Through transcriptomics and metabolism analysis, we studied the detoxification process of CAP by the E. mundtii E14, and found that CAP can be degraded by E. mundtii E14 into non-toxic compounds, such as 3,4-dihydroxy-2-(5-hydroxy-3,7-dimethylocta-2,6-dien-1-yl) benzoic acid and 2-pyridylacetic acid. Additionally, 2-pyridylacetic acid was detected both intracellular and extracellular in E. mundtii E14 treated with CAP. Meanwhile, we identified 52 up-regulated genes, including those associated with CAP degradation, such as RS11670 and RS19130. Transcriptome results annotated using KEGG indicated significant enrichment in up-regulated genes related to the glyoxylate cycle, nitrogen metabolism, and biosynthesis of secondary metabolites. Additionally, we observed that reinfection with E. mundtii E14 may effectively enhance resistance of T. absoluta to CAP. The LC50 values of the antibiotic treatment population of T. absoluta reinfection with E. mundtii E14 is 0.6122 mg/L, which was 18.27 folds higher than before reinfection. These findings offer new insights into T. absoluta resistance to CAP and contribute to a better understanding of the relationship between insecticide resistance and gut symbionts of T. absoluta, which may play a pivotal role in pest management.

Microecological characteristics of water bodies/sediments and microbial remediation strategies after 50 years of pollution exposure in ammunition destruction sites in China

The effects of long-term ammunition pollution on microecological characteristics were analyzed to formulate microbial remediation strategies. Specifically, the response of enzyme systems, N/O stable isotopes, ion networks, and microbial community structure/function levels were analyzed in long-term (50 years) ammunition-contaminated water/sediments from a contamination site, and a compound bacterial agent capable of efficiently degrading trinitrotoluene (TNT) while tolerating many heavy metals was selected to remediate the ammunition-contaminated soil. The basic physical and chemical properties of the water/sediment (pH (up: 0.57-0.64), nitrate (up: 1.31-4.28 times), nitrite (up: 1.51-5.03 times), and ammonium (up: 7.06-70.93 times)) were changed significantly, and the significant differences in stable isotope ratios of N and O (nitrate nitrogen) confirmed the degradability of TNT by indigenous microorganisms exposed to long-term pollution. Heavy metals, such as Pb, Zn, Cu, Cd, Cs, and Sb, have synergistic toxic effects in ammunition-contaminated sites, and significantly decreased the microbial diversity and richness in the core pollution area. However, long-term exposure in the edge pollution area induced microorganisms to use TNT as a carbon and nitrogen sources for life activities and growth and development. The Bacteroidales microbial group was significantly inhibited by ammunition contamination, whereas microorganisms such as Proteobacteria, Acidobacteriota, and Comamonadaceae gradually adapted to this environmental stress by regulating their development and stress responses. Ammunition pollution significantly affected DNA replication and gene regulation in the microecological genetic networks and increased the risk to human health. Mg and K were significantly involved in the internal mechanism of microbial transport, enrichment, and metabolism of TNT. Nine strains of TNT-utilizing microbes were screened for efficient TNT degradation and tolerance to typical heavy metals (copper, zinc and lead) found in contaminated sites, and a compound bacterial agent prepared for effective repair of ammunition-contaminated soil significantly improved the soil ecological environment.

Toxicity analysis of TNT to alfalfa's mineral nutrition and secondary metabolism

Alfalfa has the ability to degrade TNT. TNT exposure caused root disruption of mineral nutrient metabolism. The exposure of TNT imbalanced basal cell energy metabolism. The mechanism of 2,4,6-trinitrotoluene (TNT) toxicity effects was analyzed in alfalfa (Medicago sativa L.) seedlings by examining the mineral nutrition and secondary metabolism of the plant roots. Exposure to 25-100 mg·L^-1 TNT in a hydroponic solution for 72 h resulted in a TNT absorption rate of 26.8-63.0%. The contents of S, K, and B in root mineral nutrition metabolism increased significantly by 1.70-5.46 times, 1.38-4.01 times, and 1.40-4.03 times, respectively, after TNT exposure. Non-targeted metabolomics analysis of the roots identified 189 significantly upregulated metabolites and 420 significantly downregulated metabolites. The altered metabolites were primarily lipids and lipid-like molecules, and the most significant enrichment pathways were alanine, aspartate, and glutamate metabolism and glycerophospholipid metabolism. TNT itself was transformed in the root system into several intermediate products, including 4-hydroxylamino-2,6-dinitrotoluene, 4-amino-2,6-dinitrotoluene, 2-hydroxylamino-4,6-dinitrotoluene, 2,4',6,6'-tetranitro-2',4-azoxytoluene, 4,4',6,6'-tetranitro-2,2'-azoxytoluene, and 2,4-dinitrotoluene. Overall, TNT exposure disturbed the mineral metabolism balance, and significantly interfered with basic plant metabolism.

Lateral Interfaces between Monolayer MoS2 Edges and Armchair Graphene Nanoribbons on Au(111)

The realization of electronic devices based on heterostructures of metallic, semiconducting, or insulating two-dimensional materials relies on the ability to form structurally coherent and clean interfaces between them, vertically or laterally. Lateral two-dimensional heterostructures that fuse together two different materials in a well-controlled manner have attracted recent attention, but the methods to form seamless interfaces between structurally dissimilar materials, such as graphene and transition-metal dichalcogenides (TMDCs), are still limited. Here, we investigate the structure of the lateral interfaces that arise between monolayer MoS₂ flakes on Au(111) and two families of armchair graphene nanoribbons (GNRs) created through on-surface assisted Ullmann coupling using regular organobromine precursors for GNR synthesis. We find that parallel alignment between the GNR armchair edge and MoS₂ leads to van der Waals bonded nanoribbons, whereas a perpendicular orientation is characterized by a single phenyl-group of the GNR covalently bonded to S on the edge. The edge-on bonding is facilitated by a hydrogen treatment of the MoS₂, and temperature control during growth is shown to influence the nanoribbon width and the yield of covalently attached nanoribbons. Interestingly, the temperatures needed to drive the intramolecular dehydrogenation during GNR formation are lowered significantly by the presence of MoS₂, which we attribute to enhanced hydrogen recombination at the MoS₂ edges. These results are a demonstration of a viable method to make laterally bonded graphene nanostructures to TMDCs to be used in further investigations of two-dimensional heterostructure junctions.

The construction of NiFeSx/g-C3N4 composites with high photocatalytic activity towards the degradation of refractory pollutants

In this work, a novel NiFe layered double hydroxide-derived sulfide (NiFeSx)-modified g-C3N4 nanosheet photocatalyst (NiFeSx/g-C3N4) was synthesized, and its morphology, structure and visible light absorption capacity were simultaneously characterized by XRD, SEM, TEM, FT-IR, XPS, UV-Vis DRS, PL techniques and EIS Nyquist plots. Furthermore, it was discovered that at an optimum mass ratio of 3% (NiFeSx to g-C3N4), 3% NiFeSx/g-C3N4 composites exhibited the best degradation efficiency toward tetracycline hydrochloride refractory pollutants. The degradation rate of tetracycline hydrochloride by 3% NiFeSx/g-C3N4 composites was 92.54% under 70 min of visible light illumination, which was about 2.61 times higher than that of pure g-C3N4. The improved degradation activity may be attributed to the synergistic effect between the two constituents of as-synthesized composites, and the formed heterojunction reduced the efficiency of photogenerated carriers. More importantly, this work also gives some inspiration to synthesize some similar photocatalysts for a targeted environmental remediation.

A Density Functional Theory Study toward Ring-Opening Reaction Mechanisms of 2,4,6-Trinitrotoluene's Meisenheimer Complex for the Biodegradation of Old Yellow Enzyme Flavoprotein Reductase

The subsequent degradation pathway of the dihydride-Meisenheimer complex (2H^--TNT), which is the metabolite of 2,4,6-trinitrotoluene (TNT) by old yellow enzyme flavoprotein reductases of yeast and bacteria, was investigated computationally at the SMD/TPSSH/6-311+G(d,p) level of theory. Combining the experimentally detected products, a series of protonation, addition, substitution (dearomatization), and ring-opening reaction processes from 2H^--TNT to alkanes were proposed. By analyzing reaction free energies, we determined that the protonation is more advantageous thermodynamically than the dimerization reaction. In the ring-opening reaction of naphthenic products, the water molecule-mediated proton transfer mechanism plays a key role. The corresponding activation energy barrier is 37.7 kcal·mol^-1, which implies the difficulty of this reaction. Based on our calculations, we gave an optimum pathway for TNT mineralization. Our conclusions agree qualitatively with available experimental results. The details on transition states, intermediates, and free energy surfaces for all proposed reactions are given and make up for a lack of experimental knowledge.

Influence of local microenvironment on the double hydrogen transfer in porphycene

We performed time-resolved transient absorption and fluorescence anisotropy measurements in order to study tautomerization of porphycene in rigid polymer matrices at cryogenic temperatures. Studies were carried out in poly(methyl methacrylate) (PMMA), poly(vinyl butyral) (PVB), and poly(vinyl alcohol) (PVA). The results prove that in all studied media hydrogen tunnelling plays a significant role in the double hydrogen transfer which becomes very sensitive to properties of the environment below approx. 150 K. We also demonstrate that there exist two populations of porphycene molecules in rigid media: "hydrogen-transferring" molecules, in which tautomerization occurs on time scales below 1 ns and "frozen" molecules in which double hydrogen transfer is too slow to be monitored with nanosecond techniques. The number of "frozen" molecules increases when the sample is cooled. We explain this effect by interactions of guest molecules with a rigid host matrix which disturbs symmetry of porphycene and hinders tunnelling. Temperature dependence of the number of hydrogen-transferring molecules suggests that the factor which restores the symmetry of the double-minimum potential well in porphycene are intermolecular vibrations localized in separated regions of the amorphous polymer.

Odd Loop Regions of XenA and XenB Enzymes Modulate Their Interaction with Nitro-explosives Compounds and Provide Structural Support for Their Regioselectivity

The nitro-explosive compounds 2,4,6-trinitrotoluene, 2,4,6-trinitrophenol, and 1,2,3-trinitroglycerol are persistent environmental contaminants. The presence of different functional groups in these molecules represents a great challenge to enzymatic catalysis. The chemical variety of these three substrates is such that they do not bind and interact with catalytic residues within an enzyme with the same affinity. In this context, two Xenobiotic Reductase enzymes produced by the bacteria Pseudomonas putida can catalyze the reduction of these compounds with different affinities and regioselectivity. The structural bases that support this substrate promiscuity and catalytic preferences are unknown. Therefore, through molecular dynamics simulations and free energy calculations, we explored the structural properties driving the specific interactions of these enzymes with their substrates and cofactor. Models of Xenobiotic Reductase A and B enzymes in complex with 2,4,6-trinitrotoluene, 2,4,6-trinitrophenol, or 1,2,3-trinitroglycerol were built, and the ligand enzyme interaction was simulated by molecular dynamics. The structural analysis of the molecular dynamics simulations shows that loops 3, 5, 7, 9, 11, and 13 of Xenobiotic Reductase B, and loops 4, 5, 7, 11, 13, and 15 Xenobiotic Reductase A, are in contact with the ligands during the first stages of the molecular recognition. These loops are the most flexible regions for both enzymes; however, Xenobiotic Reductase B presents a greater range of movement and a higher number of residues interacting with the ligands. Finally, the distance between the cofactor and the different reactive groups in the substrate reflects the regioselectivity of the enzymes, and the free energy calculations are consistent with the substrate specificity of both enzymes studied. The simulation shows a stable interaction between the aromatic ring of the substrates and Xenobiotic Reductase B. In contrast, a less stable interaction with the different nitro groups of the aromatic ligands was observed. In the case of 1,2,3-trinitroglycerol, Xenobiotic Reductase B interacts more closely with the nitro groups of carbon 1 or 3, while Xenobiotic Reductase A is more selective by nitro groups of carbon 2. The obtained results suggest that the flexibility of the loops in Xenobiotic Reductase B and the presence of polar and aromatic residues present in loops 5 and 7 are fundamental to determine the affinity of the enzyme with the different substrates, and they also contribute to the proper orientation of the ligands that directs the catalytic reaction.

Insights into the biotransformation of 2,4,6-trinitrotoluene by the old yellow enzyme family of flavoproteins. A computational study

Biodegradation is a cost-effective and environmentally friendly alternative to removing 2,4,6-trinitrotoluene (TNT) pollution. However, mechanisms of TNT biodegradation have been elusive. To enhance the understanding of TNT biotransformation by the Old Yellow Enzyme (OYE) family, we investigated the crucial first-step hydrogen-transfer reaction by molecular dynamics simulations, docking technologies and empirical valence bond calculations. We revealed the significance of the π-π stacking conformation between the substrate TNT and the reduced flavin mononucleotide (FMNH2) cofactor, which is a prerequisite for the aromatic ring reduction of TNT. Under the π-π stacking conformation, the barrier of the hydrogen-transfer reaction in the aromatic ring reduction is about 16 kcal mol-1 lower than that of nitro group reduction. Then, we confirmed the mechanism of controlling the π-π stacking, that is, the π-π interaction competition mechanism. It indicates that the π-π stacking of TNT and FMNH2 occurs only when the π-π interaction between FMNH2 and TNT is stronger than that between TNT and several key residues with aromatic rings. Finally, based on the competition mechanism, the formation of π-π stacking of TNT and FMNH2 can be successfully enabled by removing the aromatic ring of those key residues in enzymes that originally only transform TNT through the nitro group reduction. This testified the validity of the π-π interaction competition mechanism. This work theoretically clarifies the molecular mechanism of the first-step hydrogen-transfer reaction for the biotransformation of TNT by the OYE family. It is helpful to obtain the enzymes that can biodegrade TNT through the aromatic ring reduction.