Preyssler-type phosphotungstate is a new family of negative-staining reagents for the TEM observation of viruses

Systematic Comparison of Commercial Uranyl-Alternative Stains for Negative- and Positive-Staining Transmission Electron Microscopy of Organic Specimens

Negative- and positive-staining transmission electron microscopy (ns/psTEM) is a cornerstone of research and diagnostics, enabling nanometer-resolution analysis of organic specimens from nanoparticles to cells without requiring costly cryo-equipment. For nearly 70 years, uranyl salts like uranyl acetate (UA) have been the gold-standard ns/psTEM-stains. However, mounting safety concerns due to their high toxicity and radioactivity have led to stricter regulations and expensive licensing requirements. Consequently, there is an urgent global demand for safer, more sustainable stains that deliver uranyl-comparable, high-quality ns/psTEM. Here, the commercially available stain-alternatives UranyLess, UAR, UA-Zero, PTA, STAIN 77, Nano-W, NanoVan, and lead citrate are systematically assessed against UA. The stains are evaluated regarding their contrast, resolution, stain-distribution, and ease-of-use in ns/psTEM across a diverse sample set, including polymethylmethacrylate-nanoplastics, phosphatidylcholine-liposomes, Influenza-A viruses, globular ferritin, fibrillar pyruvate kinase amyloids, and human lung-carcinoma cell-sections. It is shown that for this variety of samples, a ready-to-use uranyl-alternative is commercially available with comparable or even superior ns/psTEM-performance to UA using an efficient staining-protocol. Furthermore, the GUIDE4U tool is developed for the fast identification of the appropriate uranyl-replacements for each sample of interest, saving ns/psTEM-users time and costs while ensuring excellent staining results for ultrastructural analysis, thereby further catalyzing the use of safer stains.

New Morganella morganii Phage vB_Mm5 with Tolerance to Cu2+ Ions

Background

Research on phages targeting Morganella morganii is still emerging, with limited studies compared with other phage-host systems. Interest in these phages has increased due to rising antibiotic resistance and their potential for controlling M. morganii spread in the environment.

Materials and Methods

This study investigates the biology and genetics of the novel M. morganii-infecting myophage vB_Mm5 and evaluates its stability under Cu2+ exposure.

Results

Phage vB_Mm5 has a 10-min latent period and a burst size of 30 (±5). It shows high tolerance to elevated temperatures and Cu2+. The phage genome, comprising 163,232 bp dsDNA with 229 open reading frames, encodes genes that not only enhance the phage's predatory capabilities but also confer resistance to host defense mechanisms.

Conclusions

vB_Mm5 is highly distinct from other sequenced M. morganii phages, does not contain any known virulence genes, and holds potential as a therapeutic agent against M. morganii infections.

Molecular mechanisms behind the anti corona virus activity of small metal oxide nanoparticles

The recent COVID-19 pandemic has set a strong quest for advanced understanding of possible tracks in abating and eliminating viral infections. In the view that several families of "pristine" small oxide nanoparticles (NPs) have demonstrated viricidal activity against SARS-CoV-2, we studied the effect of two NPs, with presumably different reactivity, on two viruses aiming to evaluate two "primary suspect" routes of their antiviral activity, either specific blocking of surface proteins or causing membrane disruption. The chosen NPs were non-photoactive 3.5 nm triethanolamine terminated (surface capped) titania TiO2 NPs (TATT) and ultrasmall (1.1 nm) silicotungstate polyoxometalate (POM) NPs. The former were expected to both, interact with viral surface proteins as well as strongly complex with phosphate groups whereas the latter was not expected to form surface complexes. We demonstrated that expectedly, POM NPs up to 1.25 mM (4.5 mg l-1) had no significant antiviral activity towards neither of the used viruses, an enveloped transmissible gastroenteritis virus (TGEV) belonging to coronaviruses and non-enveloped encelomyocarditis virus (EMCV). At the same time, TATT NPs exhibited statistically significant (p < 0.05) antiviral activity against TGEV starting from 0.125 mM (12 μg ml-1). However, no antiviral activity of TATT against non-enveloped EMCV was detected. The observation that TATT NPs showed activity only against enveloped viruses and at relatively high concentrations suggests that the effect could be related with complexation with phospholipids. Possible chemical mechanism of viral membrane disruption was investigated by a variable temperature NMR study of NP complexation with model organic phosphate molecules, proving TATT to strongly interact with them and POM remain unreacted. Viral membrane disruption by TATT NPs was additionally confirmed by demonstraing RNA leackage from TGEV upon contact with those NPs. Therefore, our study proved a new mechanism of antiviral action of titania NPs in the dark which involved membrane disruption proceeding via direct surface complexation.

Comparative metabolomics analysis of Citrus medica var. sarcodactylis Swingle and Limonia acidissima Linn. Fruits and leaves cultivated in Egypt in context to their antiviral effects

A comprehensive study of fruits and leaves extracts of Citrus medica var. sarcodactylis Swingle and Limonia acidissima L. family Rutaceae was accomplished to investigate their antiviral activity along with their zinc oxide nanoparticles formulation (ZnONPs) against the avian influenza H5N1 virus. A thorough comparative phytochemical investigation of C. medica and L.acidissima leaves and fruits was performed using UPLC-QTOF-MS-MS. Antiviral effects further aided by molecular docking proved the highly significant potential of using C. medica and L.acidissima extracts as medicinal agents. Antiviral potency is ascendingly arranged as L. acidissima leaves (LAL) > L. acidissima fruits (LAF) > C. medica leaves (CML) at 160 μg. Nano formulation of LAF has the most splendid antiviral upshot. The metabolomic profiling of CMF and LAL revealed the detection of 48 & 74 chromatographic peaks respectively. Docking simulation against five essential proteins in survival and replication of the influenza virus revealed that flavonoid di-glycosides (hesperidin, kaempferol-3-O-rutinoside, and kaempferol-7-neohesperidoside) have shown great affinity toward the five investigated proteins and achieved docking scores which approached or even exceeded that achieved by the native ligands. Hesperidin has demonstrated the best binding affinity toward neuraminidase (NA), haemagglutinin (HA), and polymerase protein PB2 (-10.675, -8.131, and -10.046 kcal/mol respectively. We propose using prepared crude methanol extracts of both plants as an antiviral agent.

Structure Transformation of Methylammonium Polyoxomolybdates via In-Solution Acidification and Solid-State Heating from Methylammonium Monomolybdate and Application as Negative Staining Reagents for Coronavirus Observation

We prepared polyoxomolybdates with methylammonium countercations from methylammonium monomolybdate, (CH3NH3)2[MoO4], through two dehydrative condensation methods, acidifying in the aqueous solution and solid-state heating. Discrete (CH3NH3)10[Mo36O112(OH)2(H2O)14], polymeric ((CH3NH3)8[Mo36O112(H2O)14])n, and polymeric ((CH3NH3)4[γ-Mo8O26])n were selectively isolated via pH control of the aqueous (CH3NH3)2[MoO4] solution. The H2SO4-acidified solution of pH < 1 produced "sulfonated α-MoO3", polymeric ((CH3NH3)2[(MoO3)3(SO4)])n. The solid-state heating of (CH3NH3)2[MoO4] in air released methylamine and water to produce several methylammonium polyoxomolybdates in the sequence of discrete (CH3NH3)8[Mo7O24-MoO4], discrete (CH3NH3)6[Mo7O24], discrete (CH3NH3)8[Mo10O34], and polymeric ((CH3NH3)4[γ-Mo8O26])n, before their transformation into molybdenum oxides such as hexagonal-MoO3 and α-MoO3. Notably, some of their polyoxomolybdate structures were different from polyoxomolybdates produced from ammonium molybdates, such as (NH4)2[MoO4] or (NH4)6[Mo7O24], indicating that countercation affected the polyoxomolybdate structure. Moreover, among the tested polyoxomolybdates, (CH3NH3)6[Mo7O24] was the best negative staining reagent for the observation of the SARS-CoV-2 virus using transmission electron microscopy.

Hexalacunary [α-H2 P2 W12 O48 ]12- Wells-Dawson Anion: X-ray Crystal Structural Evidence and Oligomerization to WO(OH2 )4+ -Bridged Dimer and Trimers

We report the first single-crystal X-ray structural evidence of the potassium salt of the hexalacunary [α-H2 P2 W12 O48 ]12- (abbreviated as {P2 W12 }) anion after its discovery by Contant and Ciabrini in 1977. In addition, we observed oligomerization of {P2 W12 } into a {WO(OH2 )}4+ -bridged Pacman-shaped [{WO(OH2 )}(α-HP2 W12 O48 )2 ]22- ({P4 W25 }) dimer and a cyclic [{WO(OH2 )}3 (P2 W12 O48 )3 ]30- ({P6 W39 }) trimer. The three phosphotungstate anions were synthesized through recrystallization of (NH4 )12 [α-H2 P2 W12 O48 ] from slightly alkaline (HOCH2 )3 CNH2 /KCl, CH3 NH3 Cl/KCl, and CH3 NH3 Cl/NH4 Cl solutions. The structure of {P2 W12 } is derived from [α-P2 W18 O62 ]6- that has six tungsten atoms one from each polar group and four from the belt-removed, and the center of the lacunary site is capped by a potassium cation. Structures of {P4 W25 } and {P6 W39 } are constructed by connecting two and three {P2 W12 } units with {WO(OH2 )}4+ , respectively. The isolation of a pure {P6 W39 } phosphotungstate framework without coordination with transition metal cations is unprecedented. Powder X-ray diffraction confirmed the bulk purity of these compounds, indicating that selective crystallization was achieved through the selection of countercations and pH.

Limonene anti-TMV activity and its mode of action

The main component of orange peel essential oil is limonene. Limonene is a natural active monoterpene with multiple functions, such as antibacterial, antiseptic and antitumor activity, and has important development value in agriculture. This study found that limonene exhibited excellent anti-tobacco mosaic virus (TMV) bioactivity, with results showing that its protection activity, inactivation activity, and curative activity at 800 μg/mL were 84.93%, 59.28%, and 58.89%, respectively-significantly higher than those of chito-oligosaccharides. A direct effect of limonene on TMV particles was not observed, but limonene triggered the hypersensitive response (HR) in tobacco. Further determination of the induction activity of limonene against TMV demonstrated that it displayed good induction activity at 800 μg/mL, with a value of 60.59%. The results of physiological and biochemical experiments showed that at different treatment days, 800 μg/mL limonene induced the enhancement of defense enzymes activity in tobacco, including of SOD, CAT, POD, and PAL, which respectively increased by 3.2, 4.67, 4.12, and 2.33 times compared with the control (POD and SOD activities reached highest on the seventh day, and PAL and CAT activities reached highest on the fifth day). Limonene also enhanced the relative expression levels of pathogenesis related (PR) genes, including NPR1, PR1, and PR5, which were upregulated 3.84-fold, 1.86-fold and 1.71-fold, respectively. Limonene induced the accumulation of salicylic acid (SA), and increased the relative expression levels of genes related to SA biosynthesis (PAL) and reactive oxygen species (ROS) burst (RBOHB), which respectively increased by 2.76 times and 4.23 times higher than the control. Systemic acquired resistance (SAR) is an important plant immune defense against pathogen infection. The observed accumulation of SA, the enhancement of defense enzymes activity and the high-level expression of defense-related genes suggested that limonene may induce resistance to TMV in tobacco by activating SAR mediated by the SA signaling pathway. Furthermore, the experimental results demonstrated that the expression level of the chlorophyll biosynthesis gene POR1 was increased 1.72-fold compared to the control in tobacco treated with 800 μg/mL limonene, indicating that limonene treatment may increase chlorophyll content in tobacco. The results of pot experiment showed that 800 μg/mL limonene induced plant resistance against Sclerotinia sclerotiorum (33.33%), Phytophthora capsici (54.55%), Botrytis cinerea (50.00%). The bioassay results indicated that limonene provided broad-spectrum and long-lasting resistance to pathogen infection. Therefore, limonene has good development and utilization value, and is expected to be developed into a new botanical-derived anti-virus agent and plant immunity activator in addition to insecticides and fungicides.

Rapid microbial viability assay using scanning electron microscopy: a proof-of-concept using Phosphotungstic acid staining

Multiple stains have been historically utilized in electron microscopy to provide proper contrast and superior image quality enabling the discovery of ultrastructures. However, the use of these stains in microbiological viability assessment has been limited. Phosphotungstic acid (PTA) staining is a common negative stain used in scanning electron microscopy (SEM). Here, we investigate the feasibility of a new SEM-PTA assay, aiming to determine both viable and dead microbes. The optimal sample preparation was established by staining bacteria with different PTA concentrations and incubation times. Once the assay conditions were set, we applied the protocol to various samples, evaluating bacterial viability under different conditions, and comparing SEM-PTA results to culture. The five minutes 10% PTA staining exhibited a strong distinction between viable micro-organisms perceived as hypo-dense, and dead micro-organisms displaying intense internal staining which was confirmed by high Tungsten (W) peak on the EDX spectra. SEM-PTA viability count after freezing, freeze-drying, or oxygen exposure, were concordant with culture. To our knowledge, this study is the first contribution towards PTA staining of live and dead bacteria. The SEM-PTA strategy demonstrated the feasibility of a rapid, cost-effective and efficient viability assay, presenting an open-view of the sample, and providing a potentially valuable tool for applications in microbiome investigations and antimicrobial susceptibility testing.

Thermal Structure Transformation of Methylammonium Vanadate and it's Application as a Negative Staining Reagent for Observing SARS-CoV-2

The solid-state thermal structure transformation of methylammonium vanadate, (CH3NH3)VO3, from -150 °C to 350 °C is reported. Variable-temperature X-ray single-crystal structure analysis at 23, 0, -50, -100, and -150 °C reveal (CH3NH3)VO3 comprises of methylammonium cations and "snake-like" ([VO3]-)n anion chains propagating along the c-direction in the Pna21 space group. In between -150 and -100 °C, we observe a reversible structural transformation due to the re-orientation of the methylammonium cations in the crystal packing, which is also confirmed by the reversible profiles observed in differential scanning calorimetry. The methylammonium vanadate is stable until at ca. 100 °C and further heating releases methylamine and water and V2O5 is formed at ca. 275 °C . Furthermore, we show that the methylammonium vanadate can be used as a negative staining reagent for visualizing SARS-CoV-2, allowing us to discern the spike proteins from the body of the virus using transmission electron microscopy.

Coordination of Pt(IV) by {P8W48} Macrocyclic Inorganic Cavitand: Structural, Solution, and Electrochemical Studies

Hydrothermal reaction of a macrocyclic inorganic POM cavitand Li₁₇(NH₄)₂₁H₂[P₈W₄₈O₁₈₄] with [Pt(H₂O)₂(OH)₄] results in coordination of up to six {Pt(H₂O)_x(OH)_4-x} fragments to the internal surface of the polyoxoanion. The product was isolated as K₂₂(NH₄)₉H₃[{Pt(OH)₃(H₂O)}₆P₈W₄₈O₁₈₄]·79H₂O (1) and characterized by multiple techniques in the solid state (SCXRD, XRPD, XPS, FTIR, and TGA) and in solution (NMR, ESI-MS, and HPLC-ICP-AES). Electrochemical properties were studied both in solution and as components of the paste electrode. The complex shows electrocatalytic activity in water oxidation.