Mussel-inspired tissue adhesive composite hydrogel with photothermal and antioxidant properties prepared from pectin for burn wound healing.

Biodegradable self-healing hydrogels with antibacterial property attracted growing attentions in biomedication as wound dressings since they can prevent bacterial infection and promote wound healing process. In this research, a biodegradable self-healing hydrogel with ROS scavenging performance and enhanced tissue adhesion was fabricated from dopamine grafted oxidized pectin (OPD) and naphthoate hydrazide terminated PEO (PEO NH). At the same time, Fe3+ ions were incorporated to endow the hydrogel with near-infrared (NIR) triggered photothermal property to obtain antibacterial activity. The composite hydrogel showed good hemostasis performance based on mussel inspired tissue adhesion with biocompatibility well preserved. As expected, the composition of FeCl3 improved conductivity and endowed photothermal property to the hydrogel. The in vivo wound repairing experiment revealed the 808 nm NIR light triggered photothermal behavior of the hydrogel reduced the inflammation response and promoted wound repairing rate. As a result, this composite FeCl3/hydrogel shows great potential to be an excellent wound dressing for the treatment of infection prong wounds with NIR triggers.

Differential Resistance to Acetyl-CoA Carboxylase Inhibitors in Rice: Insights from Two Distinct Target-Site Mutations.

Weeds present a significant challenge to agricultural productivity, and acetyl-CoA carboxylase (ACCase)-inhibiting herbicides have proven to be effective in managing weed populations in rice fields. To develop ACCase-inhibiting herbicide-resistant rice, we generated mutants of rice ACCase (OsACC) featuring Ile-1792-Leu or Gly-2107-Ser substitutions through ethyl methyl sulfonate (EMS) mutagenesis. The Ile-1792-Leu mutant displayed cross-resistance to aryloxyphenoxypropionate (APP) and phenylpyrazoline (DEN) herbicides, whereas the Gly-2107-Ser mutants primarily exhibited cross-resistance to APP herbicides with diminished resistance to the DEN herbicide. In vitro assays of the OsACC activity revealed an increase in resistance to haloxyfop and quizalofop, ranging from 4.84- to 29-fold in the mutants compared to that in wild-type. Structural modeling revealed that both mutations likely reduce the binding affinity between OsACC and ACCase inhibitors, thereby imparting resistance. This study offers insights into two target-site mutations, contributing to the breeding of herbicide-resistant rice and presenting alternative weed management strategies in rice cultivation.

Multifunctional Ultrathin Metasurface with a Low Radar Cross Section and Variable Infrared Emissivity.

The development of stealth devices that are compatible with both infrared (IR) and radar systems remains a significant challenge, as the material properties required for effective IR and radar stealth are often contradictory. In this work, based on an IR electrochromic device (IR-ECD), concepts of metamaterial manipulating electromagnetic waves are applied to develop a multifunctional ultrathin metasurface with a low radar cross section (RCS) and variable infrared emissivity. This paper presents a linear-to-linear polarization conversion metasurface (PCM) designed by hollowing the IR-ECD. In this way, the IR-ECD based on polyaniline (PANI) can also modulate the reflection waves in the microwave band without affecting its features in the infrared region. Thus, the proposed metasurface integrates both microwave stealth and variable infrared emissivity through a single layer. The measured results show that a 10 dB RCS reduction is achieved in the band of 8.46-9.5 GHz, and the infrared emissivity can be adjusted from 0.870 to 0.513 in the infrared stealth band of 8-14 µm. Due to the ultrathin thickness (only 0.081λ0 at 9 GHz), low RCS in the X-band, and variable infrared emissivity, the designed multifunctional stealth metasurface has promising applications on military platforms with various surrounding environments.

Whole transcriptome scanning and validation of negatively related genes in UC-MSCs.

Background: Human umbilical cord mesenchymal stem cells (UC-MSCs) are one of the most extensively researched stem cell types due to their potential for multi-lineage differentiation, secretion of regenerative factors, modulations of immunological activities, and the release of regenerative substances and influence immunological processes. Since UC-MSCs must be cultivated on a large scale for clinical use, selecting the appropriate storing passage, such as the usage-based passage of UC-MSCs, is critical for long-term autologous or allogeneic usage. Long-term cultivation of stem cells, on the other hand, causes them to lose their pluripotent differentiation capacity. As a result, distinguishing between high and low passages of UC-MSCs and identifying the particular variations associated with stem cells and their modes of action is essential for regenerative medicine. Therefore, we investigated the biological features and transcriptional changes of UC-MSCs over passages. Methods: UC-MSCs were isolated from the tissues of the human umbilical cord, and UC-MSCs from five passages (P1, P3, P5, P10 and P15) with three repetitions were compared and identified based on morphology, cell markers, differentiation capacity, and aging-related characteristics. It was previously assumed that the phenotype of cells before the P10 passage was stable, defined as early passage, and that culture could be continued until the 15th passage, defined as late passage. Next, the five passages of UC-MSCs were sequenced using high-throughput complete transcriptome sequencing. Fuzzy C-Means Clustering (FCM) and Weighted Gene Co-expression Network Analysis (WGCNA) were used to find hub genes, and gene silencing was performed to investigate the impact of missing genes on the stemness of UC-MSC cells. Results: UC-MSCs of different passages displayed similar surface markers, including CD73, CD105, CD90, CD34, CD45 and HLA-DR. However, the proliferation time of late-phase UC-MSCs was longer than that of early-phase UC-MSCs, and the expression of the senescence-associated (SA)-ß-gal staining marker was higher. At the same time, pluripotency markers (NANOG, OCT4, SOX2 and KIF4A) were down-regulated, and the multi-differentiation potential was reduced. Meanwhile, KIFC1 and UBE2C were down-regulated in late-phase UC-MSCs, which were involved in the maintenance of stemness. Conclusions: KIFC1 and UBE2C were highly expressed in early-UC-MSCs and showed a downward gradient trend with cell expansion in vitro. They regulated UC-MSC proliferation, colony sphere formation, multiple differentiation, stemness maintenance, and other biological manifestations. Therefore, they are anticipated to be new biomarkers for UC-MSCs quality identification in regenerative medicine applications.

In vitro digestion under simulated saliva, gastric and small intestinal conditions and fermentation of nicotinamide mononucleotide, and its effects on the gut microbiota.

Nicotinamide Mononucleotide (NMN) is a derivative of vitamin B3, which plays a significant role in a plethora of metabolic reactions in the human body and is intricately associated with both immunity and metabolism. Nonetheless, in the intestine metabolic pathway of NMN and the relationship between NMN, gut microbiota, and SCFAs remain hitherto obscure. This study examined the digestion of NMN in simulated saliva, gastric, and small intestine environments, as well as exploring the interaction between NMN and human gut microbiota utilizing an in vitro fermentation model. NMN was progressively degraded into nicotinamide ribose (NR), nicotinamide (NAM), and ribose, with niacinate (NA) constituting the ultimate degradation product due to hydrolysis and metabolism by microbiota. NMN was ingested by human intestinal microbiota with a slower fermentation rate. As a result of NMN ingestion by human gut bacteria，the concentrations of propionate and butyrate increased by 88% and 23%, respectively, compared to the blank control group, the proliferation of beneficial gut bacteria (Bifidobacterium, Phascolarctobacterium, Faecalibacteriun, and Alistipes) significantly increased, while the proliferation of some harmful bacteria (Sutterella, Desulfovibrio and Pseudomonas) drastically declined. These findings illustrated the metabolic processes of NMN in the intestine, elaborating the relationship between NMN, SCFAs and gut microbiota. NMN might be a potential prebiotic to improve intestinal health.

Morpholine-modified polyacrylamides with Polymerization-Induced emission and its specific detection to Cu2+ ions.

In this work, three morpholine-modified polyacrylamide derivatives (MMPAm) were successfully prepared by free radical polymerization of monomers with morpholine moiety. The intramolecular aggregation of morpholine rings on macromolecular backbone gives MMPAm a significant polymerization-induced emission (PIE). Particularly, poly(N-morpholine acrylamide) (PNMPA) has the characteristics of strong fluorescence at 450 nm, and its fluorescence quantum yield reaches 2.87 %. The introduction of morpholine moiety, the length of CH2 spacer between morpholine ring and the backbone and the molecular weight play the important roles in PIE properties of PNMPA. Interestingly, PNMPA can recognize and detect Cu2+ specifically even in the presence of 12 other metal ions by thorough fluorescence quenching, and the detection limit of PNMPA is 17.3 µM. Furthermore, the dynamic quenching of PNMPA by Cu2+ ions and the complexation ratio of 1:2 according to JOB's working diagram were confirmed by fluorescence titration. Under the assistance of EDTA, a reversible detection system for Cu2+ is achieved, and a portable test paper from PNMPA for the detection of Cu2+ was also made. In conclusion, PNMPA is endowed with a significant PIE effect by the intramolecular aggregation of morpholine rings along the backbone in the polymerization of non-fluorescent monomer, and is expected to be a promising material for specific detection to Cu2+ ions.

Comprehensive investigation into the effects of yeast dietary fiber and temperature on konjac glucomannan/kappa-carrageenan for the development of fat analogs.

In this study, yeast dietary fiber (YDF) was incorporated into konjac glucomannan/kappa-carrageenan (KGM/κ-KC) for the development of fat analogs, and the impact of YDF on the gelation properties and behavior of KGM/κ-KC composite gels was assessed. YDF improved the composite gel whiteness value, and affected the mechanical properties of the composite gel, especially enhancing its hardness, and decreasing its chewiness, elasticity, and gel strength, making it more similar to porcine back fat. When the yeast dietary fiber content was 0.033 g/mL and the heating temperature was 80 °C (T80-2), the textural properties of the composite gel were closest to porcine back fat. The frequency sweep results suggested that YDF incorporation led to enhancement of the intermolecular interaction and intermixing and interaction among more easily at higher processing temperatures (80 °C and 90 °C). By scanning electron microscopy, the fatty surface of porcine back fat was flat and covered with a large amount of oil, while KGM/κ-KC/YDF composite gels developed a dense, stacked network structure. YDF caused more fragmented, folded, and uneven structures to emerge. Overall, YDF could influence the gel behavior of KGM/κ-KC composite gels, and change their colors and mechanical properties. This work could serve as a guide for preparing fat analogs with KGM/κ-KC composite gels.

A Near-Infrared Fluorogenic Probe for Rapid, Specific, and Ultrasensitive Detection of Sphingosine in Living Cells and In Vivo.

Sphingosine (Sph) plays important roles in various complex biological processes. Abnormalities in Sph metabolism can result in various diseases, including neurodegenerative disorders. However, due to the lack of rapid and accurate detection methods, understanding sph metabolic in related diseases is limited. Herein, a series of near-infrared fluorogenic probes DMS-X (X = 2F, F, Cl, Br, and I) are designed and synthesized. The fast oxazolidinone ring formation enables the DMS-2F to detect Sph selectively and ultrasensitively, and the detection limit reaches 9.33 ± 0.41 nm. Moreover, it is demonstrated that DMS-2F exhibited a dose- and time-dependent response to Sph and can detect sph in living cells. Importantly, for the first time, the changes in Sph levels induced by Aß42 oligomers and H2 O2 are assessed through a fluorescent imaging approach, and further validated the physiological processes by which Aß42 oligomers and reactive oxygen species (ROS)-induce changes in intracellular Sph levels. Additionally, the distribution of Sph in living zebrafish is successfully mapped by in vivo imaging of a zebrafish model. This work provides a simple and efficient method for probing Sph in living cells and in vivo, which will facilitate investigation into the metabolic process of Sph and the connection between Sph and disease pathologies.

Coupling of Nd doping and oxygen-rich vacancy in CoMoO4@NiMoO4 nanoflowers toward advanced supercapacitors and photocatalytic degradation.

In this paper, we successfully prepared rare earth element-doped 0.8% Nd-CoMoO4@NiMoO4 nanoflowers with a large specific surface area using the sol-gel method for the first time. In the experiment, we added a structure-directing agent to successfully assemble the nanosheets into a three-dimensional ordered micro-flower shape. By using the strategy of forming a flower-shaped morphology with a structure-directing agent and doping Nd elements to generate oxygen vacancies, the problems of the collapse of the active material structure and slow reaction kinetics were solved. Through relevant electrochemical performance tests, it was found that when the rare earth element Nd was doped at a concentration of 0.8%, the material exhibited exceptional specific capacitance (2387 F g-1 at 1 A g-1) and cycling stability (99.3% after 10 000 cycles at 5 A g-1). These performance characteristics far surpassed those of the other synthesized products. We assembled 0.8% Nd-CoMoO4@NiMoO4 with hydrophilic CNTs into an asymmetric device, 0.8% Nd-CoMoO4@NiMoO4//CNTs. This device exhibited high specific capacitance (262 F g-1 at 1 A g-1) and cycling stability (99.2% after 3000 cycles), with a good energy storage effect. In addition, 0.8% Nd-CoMoO4@NiMoO4 has a low band gap, which broadens the absorption range of the product and improves the utilization rate of visible light. The photocatalyst showed good degradation efficiency (all exceeding 96%) and cycling stability (96%) for all four dyes. This paper provides a new strategy and method for preparing doped polymetallic mixtures, which has potential application value.

Regulation of low-density lipoprotein on lipid metabolism in macrophages of large yellow croaker (Larimichthys crocea).

Low-density lipoprotein (LDL) is the main carrier of cholesterol transport in plasma, which participates in regulating lipid homeostasis. Studies in mammals have shown that high levels of LDL in plasma absorbed by macrophages trigger the formation of lipid-rich foam cells, leading to the development of atherosclerotic plaques. Although lipid-rich atherosclerosis-like lesions have been discovered in the aorta of several fish species, the physiological function of LDL in fish macrophages remains poorly understood. In the present study, LDL was isolated from the plasma of large yellow croaker (Larimichthys crocea), and mass spectrometry analysis identified two truncated forms of apolipoprotein B100 in the LDL protein profile. Transcriptomic analysis of LDL-stimulated macrophages revealed that differentially expressed genes (DEGs) were enriched in various pathways related to lipid metabolism, as confirmed by the fact that LDL increased total cholesterol and cholesteryl esters content. Meanwhile, the gene and protein expression levels of perilipin2 (PLIN2), a DEG enriched in the PPAR signaling pathway, were upregulated in response to LDL stimulation. Importantly, knocking down plin2 significantly attenuates LDL-induced cholesterol accumulation and promotes cholesterol efflux. Furthermore, the transcription factor PPARγ, which is upregulated in response to LDL stimulation, can enhance the promoter activity of plin2. In conclusion, this study suggests that LDL may upregulate plin2 expression through PPARγ, resulting in cholesterol accumulation in fish macrophages. This study will facilitate the investigation of the function of LDL in regulating lipid homeostasis in macrophages and shed light on the evolutionary origin of LDL metabolism in vertebrates.

Phosphatidylethanolamine alleviates OX-LDL-induced macrophage inflammation by upregulating autophagy and inhibiting NLRP1 inflammasome activation.

Oxidized low-density lipoprotein (OX-LDL)-induced inflammation and autophagy dysregulation are important events in the progression of atherosclerosis. Phosphatidylethanolamine (PE), a multifunctional phospholipid that is enriched in cells, has been proven to be directly involved in autophagy which is closely associated with inflammation. However, whether PE can influence OX-LDL-induced autophagy dysregulation and inflammation has not been reported. In the present study, we revealed that OX-LDL significantly induced macrophage inflammation through the CD36-NLRP1-caspase-1 signaling pathway in fish. Meanwhile, cellular PE levels were significantly decreased in response to OX-LDL induction. Based on the relationship between PE and autophagy, we then examined the effect of PE supplementation on OX-LDL-mediated autophagy impairment and inflammation induction in macrophages. As expected, exogenous PE restored impaired autophagy and alleviated inflammation in OX-LDL-stimulated cells. Notably, autophagy inhibitors reversed the inhibitory effect of PE on OX-LDL-induced maturation of IL-1ß, indicating that the regulation of PE on OX-LDL-induced inflammation is dependent on autophagy. Furthermore, the positive effect of PE on OX-LDL-induced inflammation was relatively conserved in mouse and fish macrophages. In conclusion, we elucidated the role of the CD36-NLRP1-caspase-1 signaling pathway in OX-LDL-induced inflammation in fish and revealed for the first time that altering PE abundance in OX-LDL-treated cells could alleviate inflammasome-mediated inflammation by inducing autophagy. Given the relationship between OX-LDL-induced inflammation and atherosclerosis, this study prompts that the use of PE-rich foods promises to be a new strategy for atherosclerosis treatment in vertebrates.

Yeast protein as a novel dietary protein source: Comparison with four common plant proteins in physicochemical properties.

Currently, with the preference for a healthy diet and increased awareness of reducing the carbon footprint, the demand for protein is becoming more and more diversified. In this study, the physicochemical properties of yeast protein (YP) and four common plant proteins (soy protein isolate, pea protein isolate, wheat gluten, and peanut protein) were compared. The most prevalent secondary structure in YP is the ß-sheet. Furthermore, YP is in an aggregated state, and it has a high surface hydrophobicity. The tryptophan residues are primarily exposed on the polar surface of YP. The results of in vitro digestibility indicated that YP (84.91 ± 0.52%) was a high-quality protein. Moreover, YP has a higher thermal stability and relatively stable low apparent viscosity, which provides ample possibility for its application in food processing and in foods for people with swallowing difficulties. This study provides theoretical basis in the potential of YP as an alternative protein source.

Glycerol monolaurate improved intestinal barrier, antioxidant capacity, inflammatory response and microbiota dysbiosis in large yellow croaker (Larimichthys crocea) fed with high soybean oil diets.

Glycerol monolaurate (GML) is a potential candidate for regulating metabolic syndrome and inflammatory response. However, the role of GML in modulating intestinal health in fish has not been well determined. In this study, a 70-d feeding trial was conducted to evaluate the effect of GML on intestinal barrier, antioxidant capacity, inflammatory response and microbiota community of large yellow croaker (13.05 ± 0.09 g) fed with high level soybean oil (SO) diets. Two basic diets with fish oil (FO) or SO were formulated. Based on the SO group diet, three different levels of GML 0.02% (SO0.02), 0.04% (SO0.04) and 0.08% (SO0.08) were supplemented respectively. Results showed that intestinal villus height and perimeter ratio were increased in SO0.04 treatment compared with the SO group. The mRNA expressions of intestinal physical barrier-related gene odc and claudin-11 were significantly up-regulated in different addition of GML treatments compared with the SO group. Fish fed SO diet with 0.04% GML addition showed higher activities of acid phosphatase and lysozyme compared with the SO group. The content of malonaldehyde was significantly decreased and activities of catalase and superoxide dismutase were significantly increased in 0.02% and 0.04% GML groups compared with those in the SO group. The mRNA transcriptional levels of inflammatory response-related genes (il-1ß, il-6, tnf-α and cox-2) in 0.04% GML treatment were notably lower than those in the SO group. Meanwhile, sequencing analysis of bacterial 16S rRNA V4-V5 region showed that GML addition changed gut microbiota structure and increased alpha diversity of large yellow croaker fed diets with a high level of SO. The correlation analysis results indicated that the change of intestinal microbiota relative abundance strongly correlated with intestinal health indexes. In conclusion, these results demonstrated that 0.02%-0.04% GML addition could improve intestinal morphology, physical barrier, antioxidant capacity, inflammatory response and microbiota dysbiosis of large yellow croaker fed diets with a high percentage of SO.

Core-Shell-Structured Electrorheological Fluid with a Polarizability-Tunable Nanocarbon Shell for Enhanced Stimuli-Responsive Activity.

The incorporation of nanocarbon-based materials into electrorheological fluids has been shown to be an effective means of improving the electrorheological (ER) response. However, the mechanism of the sp2/sp3-hybridized carbon structure and high ER response is still under investigation. Herein, barium titanate@nanocarbon shell (BTO@NCs) composites are proposed and prepared by introducing carbonized polydopamine (C-PDA) into a shell. When the polymerization time of dopamine is tuned, the shell thickness, surface polar functional groups, and sp2/sp3-hybridized carbon can be effectively controlled. The maximum yield stress of the BTO@NCs-24 h ER fluid reaches 2.5 kPa under an electric field of 4 kV mm-1, which is attributed to the increased content of sp3 C-OH and oxygenous functional groups within the shell, resulting in a rapidly achievable polarization. Furthermore, the SiO2@NCs and TiO2@NCs ER fluids are also prepared with enhanced ER behavior in these phenomena, confirming an approach to high-performance ER fluids based on nanocarbon composites.

Faraday cage-type ECL biosensor for the detection of circulating tumor cell MCF-7.

Herein, a Faraday cage-type electrochemiluminescence biosensor was designed for the detection of human breast cancer cell MCF-7. Two kinds of nanomaterials, Fe3O4-APTs and GO@PTCA-APTs, were synthesized as capture unit and signal unit, respectively. In presence of the target MCF-7, the Faraday cage-type electrochemiluminescence biosensor was constructed by forming a complex "capture unit-MCF-7-signal unit". In this case, lots of electrochemiluminescence signal probes were assembled and could participate in the electrode reaction, achieving a significant increase in sensitivity. In addition, the double aptamer recognition strategy was adopted to improve the capture, enrichment efficiency and detection reliability. Under optimal experimental conditions, the limit of detection was 3 cells/mL. And, the sensor could afford the detection of actual human blood samples, which is the first report on the detection of intact circulating tumor cells by the Faraday cage-type electrochemiluminescence biosensor.

Assessment of the Effects of Structural Modification of Gastrodia elata Polysaccharide on Anti-Breast Cancer Activity Using Asymmetrical Flow Field-Flow Fractionation.

Gastrodia elata ("Tian Ma" in Chinese) is used as a food and medical ingredient in traditional Chinese medicine. In this study, to enhance the anti-breast cancer activity of Gastrodia elata polysaccharide (GEP), GEPs were modified via sulfidation (SGEP) and acetylation (AcGEP). The physicochemical properties (such as solubility and substitution degree) and structural information (such as molecular weight Mw and radius of gyration Rg) of GEP derivatives were determined by Fourier transformed infrared (FTIR) spectroscopy and asymmetrical flow field-flow fractionation (AF4) coupled online with multiangle light scattering (MALS) and differential refractive index (dRI) detectors (AF4-MALS-dRI). The effects of the structural modification of GEP on the proliferation, apoptosis, and cell cycle of MCF-7 cell were studied systematically. The ability of MCF-7 cell for the uptake of GEP was studied by laser scanning confocal microscopy (LSCM). The results suggested that the solubility and anti-breast cancer activity of GEP were enhanced and the average Rg and Mw of GEP decreased after chemical modification. The AF4-MALS-dRI results showed that the chemical modification process simultaneously caused the degradation and aggregation of GEPs. The LSCM results revealed that more SGEP can enter the MCF-7 cell interior compared with AcGEP. The results indicated that the structure of AcGEP could play a dominating role in antitumor activity. The data obtained in this work can be used as a starting point for investigating the structure-bioactivity of GEPs.

A Stretchable, Transparent, and Mechanically Robust Silver Nanowire-Polydimethylsiloxane Electrode for Electrochromic Devices.

The application of flexible indium tin oxide (ITO-free) electrochromic devices has steadily attracted widespread attention in wearable devices. Recently, silver nanowire/poly(dimethylsiloxane) (AgNW/PDMS)-based stretchable conductive films have raised great interest as ITO-free substrate for flexible electrochromic devices. However, it is still difficult to achieve high transparency with low resistance due to the weak binding force between AgNW and PDMS with low surface energy because of the possibility of detaching and sliding occurring at the interface. Herein, we propose a method to pattern the pre-cured PDMS (PT-PDMS) by stainless steel film as a template through constructed micron grooves and embedded structure, to prepare a stretchable AgNW/PT-PDMS electrode with high transparency and high conductivity. The stretchable AgNW/PT-PDMS electrode can be stretched (5000 cycles), twisted, and surface friction (3M tape for 500 cycles) without significant loss of conductivity (ΔR/R ≈ 16% and 27%). In addition, with the increase of stretch (stretching to 10-80%), the AgNW/PT-PDMS electrode transmittance increased, and the conductivity increased at first and then decreased. It is possible that the AgNWs in the micron grooves are spread during PDMS stretching, resulting in a larger spreading area and higher transmittance of the AgNWs film; at the same time, the nanowires between the grooves come into contact, thus increasing conductivity. An electrochromic electrode constructed with the stretchable AgNW/PT-PDMS exhibited excellent electrochromic behavior (transmittance contrast from ~61% to ~57%) even after 10,000 bending cycles or 500 stretching cycles, indicating high stability and mechanical robustness. Notably, this method of preparing transparent stretch electrodes based on patterned PDMS provides a promising solution for developing electronic devices with unique structures and high performance.

Visualizing Atomic Quantum Defects in Ultrathin 1T-PtTe2.

Defects are of significant importance to determine and improve the distinct properties of 2D materials, such as electronic, optical, and catalytic performance. In this report, we observe four types of point defects in atomically thin flakes of 1T-PtTe2 by using low-temperature scanning tunnelling microscopy and spectroscopy (STM/S). Through the combination of STM imaging and simulations, such defects are identified as a single tellurium vacancy from each side of the top PtTe2 layer and a single platinum vacancy from the topmost and next layer. The density functional theory (DFT) calculations reveal that the platinum vacancies from both the monolayer and bilayer exhibit a local magnetic moment. In bilayer PtTe2, the interlayer coulomb screening effect reduces the local magnetic momentum of the single platinum vacancy. Our research provides meaningful guidance for further experiments about the effects of intrinsic defects on potential functions of thin 1T-PtTe2, such as catalysis and spintronic applications.

Human-associated bacteria adopt an unusual route for synthesizing 3-acetylated tetramates for environmental adaptation.

BACKGROUND: Tetramates or tetramic acid-containing compounds (TACs) are a group of bioactive natural products featuring a pyrrolidine-2,4-dione ring acknowledged being closed via Dieckmann cyclization. The cariogenic Streptococcus mutans strains bearing a muc biosynthetic gene cluster (BGC) can synthesize mutanocyclin (MUC), a 3-acetylated TAC that can inhibit both leukocyte chemotaxis and filamentous development in Candida albicans. Some strains can also accumulate reutericyclins (RTCs), the intermediates of MUC biosynthesis with antibacterial activities. However, the formation mechanism of the pyrrolidine-2,4-dione ring of MUC and the distribution of muc-like BGCs along with their ecological functions has not been explored extensively. RESULTS: We demonstrated that a key intermediate of MUC biosynthesis, M-307, is installed by a hybrid nonribosomal peptide synthetase-polyketide synthase assembly line and its pyrrolidine-2,4-dione ring is closed via an unprecedented lactam bond formation style. Subsequent C-3 acetylation will convert M-307 to RTCs, which is then hydrolyzed by a deacylase, MucF, to remove the N-1 fatty acyl appendage to generate MUC. Distribution analysis showed that the muc-like BGCs distribute predominantly in human-associated bacteria. Interestingly, most of the muc-like BGCs possessing a mucF gene were isolated from human or livestock directly, indicating their involvement in alleviating the host's immune attacks by synthesizing MUC; while those BGCs lacking mucF gene distribute mainly in bacteria from fermented products, suggesting that they tend to synthesize RTCs to compete with neighboring bacteria. It is noteworthy that many bacteria in the same habitats (e.g., the oral cavity) lack the muc-like BGC, but possess functional MucF homologues to "detoxify" RTCs to MUC, including several competitive bacteria of S. mutans. We also comparably studied the distribution of TAS1, a fungal enzyme responsible for the production of phytotoxic tenuazonic acids (TeAs), a class of 3-acetylated TACs with similar structure but distinct biosynthetic mechanism to MUC, and found that it mainly exists in plants or crops. CONCLUSIONS: The in vivo and in vitro experiments revealed that the pyrrolidine-2,4-dione ring of MUC is closed via lactam bond formation, which may be adopted by many TACs without 3-acyl decorations. Besides, we found that muc-like BGCs are widespread in human-associated bacteria and their shapes and main products can be influenced by the habitat environment and vice versa. By comparing with TeAs, we provided thought-provoking insights into how ecological and evolutionary forces drive bacteria and fungi to construct a common 3-acetylated pyrrolidine-2,4-dione core through different routes, and how the biosynthetic processes are delicately controlled to generate diverse 3-acetylated TACs for environmental adaptation. Video Abstract.