Mass Spectrometric Measurements Research Articles

Krypton-85 chronometry of spent nuclear fuel

Abstract. We describe the use of the radionuclide 85Kr, which is produced by nuclear fission and has a half-life of 10.76 years, to determine the age of spent nuclear fuel. The method is based on mass-spectrometric measurement of the relative abundance of fissiogenic Kr isotopes extracted from a fuel sample, and we show that it can be applied to micron-scale particles of spent fuel that are analogous to particles that have been released into the environment from various nuclear facilities in the past. 85Kr chronometry is potentially valuable for identifying and attributing nuclear materials, grouping samples into collections of common origin that can be used to reconstruct the origin and irradiation history of the material, and verifying declared nuclear activities in the context of international monitoring programs.

Methanol steam reforming over copper supported on apatites

Low-temperature methanol steam (MSR) reforming over Cu is an efficient process for releasing H2 from this promising liquid hydrogen carrier but the Cu contents of commercial catalysts are often exceedingly high. Here we show that Sr-exchanged fluoro and hydroxyapatites with 1wt.% Cu exhibit very high methanol turnover frequencies up to 386h-1 and H2 production rates up to 6569mol H2 kgCu-1 h-1 with CO selectivity as low as ~0.25% at 250 °C. Formaldehyde and methyl formate are the only other byproducts which are especially observed over catalysts with low Sr/P ratio in the hydroxyapatite. The reforming proceeds through methoxy, formaldehyde and formate species according to in situ FTIR and mass spectrometric measurements. The spectroscopic analyses further reveal the involvement of apatitic HPO42- ions in the catalytic sequence. Thus, the catalytic synergy between Cu and apatites provides a basis for highly efficient, bifunctional MSR catalysts with low copper content.

A new multi-analytical procedure for radiocarbon dating of historical mortars

The overarching challenge of this research is setting up a procedure to select the most appropriate fraction from complex, heterogeneous materials such as historic mortars in case of radiocarbon dating. At present, in the international community, there is not a unique and fully accepted way of mortar sample preparation to systematically obtain accurate results. With this contribution, we propose a strategy for selecting suitable mortar samples for radiocarbon dating of anthropogenic calcite in binder or lump. A four-step procedure is proposed: (I) good sampling strategies along with architectural and historical surveys; (II) mineralogical, petrographic, and chemical characterization of mortars to evaluate the feasibility of sample dating; (III) a non-destructive multi-analytical characterization of binder-rich portions to avoid geogenic calcite contamination; (IV) carbonate micro-sample preparation and accelerator mass spectrometer (AMS) measurements. The most innovative feature of the overall procedure relies on the fact that, in case of positive validation in step III, exactly the same material is treated and measured in step IV. The paper aims to apply this procedure to the ancient mortar of the Florentine historical building (Trebbio Castle), selecting micro-samples suitable for dating in natural hydraulic mortars. The discussion of the mortar dating results with the historical-archaeological hypotheses provided significant insights into the construction history of the building.

Simulation Study of Crystalline Al2O3 Thin Films Prepared at Low Temperatures: Effect of Deposition Temperature and Biasing Voltage

In this paper, classical molecular dynamics simulations were used to explore the impact of deposition temperature and bias voltage on the growth of Al2O3 thin films through magnetron sputtering. Ion energy distributions were derived from plasma mass spectrometer measurements. The fluxes of deposited particles (Ar+, Al+, and O−) were categorized into low, medium, and high energies, and the results show that the films are dominated by amorphous Al2O3 at low incident energies without applying bias. As the deposition temperature increased, the crystallinity of the films also increased, with the crystals predominantly consisting of γ-Al2O3. The crystal content of the deposited films increased when biased with −20 V compared to when no bias was applied. Crystalline films were successfully obtained at a deposition temperature of 773 K with a −20 V bias. When biased with −40 V, crystals could be obtained at a lower deposition temperature of 573 K. Increasing the bias enables the particles to have higher energy to overcome the nucleation barrier of the crystallization process, leading to a greater degree of film crystallization. At this stage, the average bond length between Al-O is measured to be approximately 1.89 Å to 1.91 Å, closely resembling that of the crystal.

The Fe-MAN Challenge: Ferrates-Microkinetic Assessment of Numerical Quantum Chemistry.

Organometallic species, such as organoferrate ions, are prototypical nucleophiles prone to reacting with a wide range of electrophiles, including proton donors. In solution, the operation of dynamic equilibria and the simultaneous presence of several organometallic species severely complicate the analysis of these fundamentally important reactions. This can be overcome by gas-phase experiments on mass-selected ions, which allow for the determination of the microscopic reactivity of the target species. In this contribution, we focus on the reactivity of a series of trisarylferrate complexes toward 2,2,2-trifluoroethanol and 2,2-difluoroethanol. By means of mass-spectrometric measurements, we determined the experimental bimolecular rate constants kexp of the gas-phase protolysis reactions of the trisarylferrate anions FePh3- and FeMes3- with the aforementioned acids. Based on these experiments, we carried out a dual blind challenge, inviting theoretical groups to submit their best predictions for the activation barriers and/or theoretical rate constants ktheo. This provides a unique opportunity to evaluate different computational protocols under minimal bias and sets the stage for further benchmarking of quantum chemical methods and data-driven approaches in the future.

Understanding secondary particles in a regional site of Yangtze River Delta: Insights from mass spectrometric measurement

Submicron particulate matter (PM1) poses significant risks to health risks and global climate. In this study, secondary organic aerosols (SOA) and inorganic compositions were examined for their physicochemical characteristics and evolution using high-resolution aerosol instruments in Changzhou over one-month period. The results showed that transport accompanied by regional static conditions leaded to the occurrence of heavy pollution. In addition, regional generation and local emissions also leaded to the occurrence of light and moderate pollution during the observation period in Changzhou. Organic aerosols (OA) and nitrate (NO3−) accounted for 45 % and 23 % of PM1, respectively. The increase in PM1 was dominated by the contribution of NO3− and OA. SOA was dominance in OA (63 % with 40 % MO-OOA), which was higher than primary organic aerosols (POA). Besides, photochemical reactions and the high oxidizing nature of the urban atmosphere promoted the production of OA, especially MO-OOA in Changzhou. Our results highlight that secondary particles contribute significantly to PM pollution in Changzhou, underlining the importance of controlling emissions of gaseous precursors, especially under high oxidation conditions.

The saline infusion test with mass spectrometric measurements of aldosterone in patients tested for primary aldosteronism

The saline infusion test with mass spectrometric measurements of aldosterone in patients tested for primary aldosteronism

Fast and Accurate Disulfide Bridge Detection

Recombinant expression of proteins, propelled by therapeutic antibodies, has evolved into a multibillion dollar industry. Essential here is the quality control assessment of critical attributes, such as sequence fidelity, proper folding, and posttranslational modifications. Errors can lead to diminished bioactivity and, in the context of therapeutic proteins, an elevated risk for immunogenicity. Over the years, many techniques were developed and applied to validate proteins in a standardized and high-throughput fashion. One parameter has, however, so far been challenging to assess. Disulfide bridges, covalent bonds linking two cysteine residues, assist in the correct folding and stability of proteins and thus have a major influence on their efficacy. Mass spectrometry promises to be an optimal technique to uncover them in a fast and accurate fashion. In this work, we present a unique combination of sample preparation, data acquisition, and analysis facilitating the rapid and accurate assessment of disulfide bridges in purified proteins. Through microwave-assisted acid hydrolysis, the proteins are digested rapidly and artifact-free into peptides, with a substantial degree of overlap over the sequence. The nonspecific nature of this procedure, however, introduces chemical background, which is efficiently removed by integrating ion mobility preceding the mass spectrometric measurement. The nonspecific nature of the digestion step additionally necessitates new developments in data analysis, for which we extended the XlinkX node in Proteome Discoverer to efficiently process the data and ensure correctness through effective false discovery rate correction. The entire workflow can be completed within 1 h, allowing for high-throughput, high-accuracy disulfide mapping.

On the simulation and interpretation of substrate-water exchange experiments in photosynthetic water oxidation.

Water oxidation by photosystem II (PSII) sustains most life on Earth, but the molecular mechanism of this unique process remains controversial. The ongoing identification of the binding sites and modes of the two water-derived substrate oxygens ('substrate waters') in the various intermediates (Si states, i = 0, 1, 2, 3, 4) that the water-splitting tetra-manganese calcium penta-oxygen (Mn4CaO5) cluster attains during the reaction cycle provides central information towards resolving the unique chemistry of biological water oxidation. Mass spectrometric measurements of single- and double-labeled dioxygen species after various incubation times of PSII with H218O provide insight into the substrate binding modes and sites via determination of exchange rates. Such experiments have revealed that the two substrate waters exchange with different rates that vary independently with the Si state and are hence referred to as the fast (Wf) and the slow (WS) substrate waters. New insight for the molecular interpretation of these rates arises from our recent finding that in the S2 state, under special experimental conditions, two different rates of WS exchange are observed that appear to correlate with the high spin and low spin conformations of the Mn4CaO5 cluster. Here, we reexamine and unite various proposed methods for extracting and assigning rate constants from this recent data set. The analysis results in a molecular model for substrate-water binding and exchange that reconciles the expected non-exchangeability of the central oxo bridge O5 when located between two Mn(IV) ions with the experimental and theoretical assignment of O5 as WS in all S states. The analysis also excludes other published proposals for explaining the water exchange kinetics.

Cooking emissions are a major source of racial-ethnic air pollution exposure disparities in the United States

Racial-ethnic minority populations in the US are disproportionately exposed to airborne fine particulate matter (PM2.5), but few national studies have focused individually on the sources that contribute to these disparities. We address this gap by conducting a comprehensive analysis of PM2.5 exposure disparities by race-ethnicity in the US, focusing on three source-categories: mobile-sources, cooking, and all other sources combined. Our approach is based on high-resolution, national land-use regression estimates of source-resolved PM2.5 components, derived from high-resolution aerosol mass spectrometer measurements. We find that each of these sources contributes approximately one-third of the overall PM2.5 exposure disparities by race-ethnicity. While the importance of mobile-source tailpipe emissions is well recognized, our study underscores the significance of cooking emissions in creating PM2.5 exposure disparities. This finding represents a potentially significant opportunity to reduce these disparities, as cooking emissions are currently largely unregulated. It has important implications for policymakers and public health advocates aiming to address the persistent issue of racial-ethnic disparities in air pollution.

Fission-track age calibration: Phi and Zeta, never the twain shall meet?

The fission-track method was intended to be an autonomous dating method requiring two track counts and a neutron fluence measurement. It became clear that it was beset with methodological problems, and neutron fluence measurements were abandoned in favour of age standards. The coming of mass-spectrometric uranium measurements eliminated the need for irradiations altogether, and stimulated renewed efforts to establish fission-track dating as an autonomous method. This ran into similar problems as before, and recent publications signal a return to age standards. The attempts at independent dating nevertheless revealed that experts agree on the recommended fission constant and the need to consider experimental factors related to the track counts. In spite of that, the renewed reliance on standards makes that fission-track ages are again not independent, but relative, ages with an uncertain meaning, and from their nature untestable.We report an attempt at standardless and standard-based dating of the Durango and Duluth apatites using neutron irradiation and the external detector method. We start from the assumption that neutron fluence measurements are the most precise and accurate achievable in fission-track dating, a consensus on the recommended fission constant, and on the need to consider experimental factors. One factor (ζ0) accounts for the combined experimental influences; ζ0 can be calculated from identifiable contributions related to track registration, etching and counting; ζ0 can also be determined by experiment and calculated from the ages of standards. This gives three separate, consistent, dimensionless calibration factors that, in contrast to Z and ζ, are independent of the neutron fluence or the uranium content of a reference glass; ζ0 remains a personal factor, however.The standardless fission-track ages of the Durango age standard are in agreement with its reference age and the standardless and standard-based ages of the Duluth apatites are consistent with each other. Furthermore, if ζ0 is used to correct conventional Z- (and by implication ζ-) values for experimental effects, the results are consistent with their definitions in terms of physical parameters. Although ζ0 is a personal factor, the small number of measurements to date is consistent with each other. In contrast, annealing corrections based on the fossil and induced confined fission track lengths overestimate the reference age of Durango and produce incompatible standardless and standard-based ages of the dated apatites. We argue that this points to unresolved issues with the relationship between the age and the fossil track length, and suggest a connection with etching.Plots of the single-grain ages against uranium content and radial plots of the data exhibit conspicuous structure. However statistical factors alone account for the nature and magnitude of the observed correlations. This implies that in the case of the Duluth apatites there is no identifiable effect of radiation damage on the single-grain ages despite their high accumulated α-doses and protracted thermal histories. Spurious correlations must be addressed before attempting to interpret the observed data structure in terms of radiation damage, apatite composition or age components.

Investigation of oil emission mechanisms in a marine medium-speed dual-fuel engine

Pilot-ignition Otto marine engines are known for greatly reduced emissions of air pollutants (sulphur oxides, nitrogen oxide, particulates) compared to marine diesel engines. However, lubricating oil emissions still are about one order of magnitude higher than in land-based systems. To identify reduction potentials, a better understanding of oil emission mechanisms has to be gained. For this purpose, mass spectrometric oil emission measurements and fluorescence lubricating film thickness measurements were performed on a medium-speed marine engine. With the fluorescence measuring system, the varying lubricating oil film on the cylinder wall can be visualised and analysed in sub-crank-angle resolution. By applying the developed calibration method to the measurement data, the oil film thickness can be determined in µm. It is shown that the oil film left by the piston rings on the liner as it moves down is almost halved after ignition compared to during intake stroke. The authors have further been able to detect and time operating point dependent ring rotation and investigations show a connection between ring rotation and cylinder liner temperature distribution. Aligning ring gaps allow blow-by to happen. This and other high intensity events such as engine knock, load shedding or the transition from diesel-mode to gas-mode, heavily disturb the oil layer and cause peaking oil emissions.

Copper(II) complexes with N,O-coordinating thiopseudoureas: syntheses, structures, and properties

Syntheses, characterization, and physical properties of two complexes of copper(II) having the general molecular formula [Cu(L n )2] (1 and 2) with benzyl-N′-(4-R-benzoyl)-N-(2,6-diisopropylphenyl)carbamimidothioates (HL n , where n = 1 and 2 for R = H and Cl, respectively) are reported. Both complexes were characterized by mass spectrometric, magnetic susceptibility, and various spectroscopic (IR, UV–Vis, and EPR) measurements. The molecular structures of 1 and 2 were established by single crystal X-ray crystallographic studies. In each complex, the bivalent metal center is in a near perfect square-planar trans-N2O2 coordination environment assembled by two bidentate six-membered chelate rings forming iminolate-O and azomethine-N donor (L n )− ligands. In the crystal lattice, the packing of 1 is according to the symmetry operations, while intermolecular π⋯π and C–H⋯π interactions assisted self-assembly of 2 leads to a two-dimensional sheet-like structure. Mass spectrometric and infrared and electronic spectroscopic data are in agreement with their molecular formulas and similar structures. The room temperature magnetic moments and EPR spectra of both complexes are consistent with the S = ½ ground state and the square-planar coordination geometry of the metal ion in each complex.

Temperature effects on electrospray current from an externally wetted EMI-Im ionic liquid ion source

Ionic liquid ion sources are expected to be used in a wide range of applications such as space electric propulsion and focused ion beam micromachining. It is known that the backstreaming of secondary charged species generated by ion beam impacts can cause unexpected temperature rise and chemical changes in ionic liquids. This paper reports on results of heating experiments using a sharp needle emitter wetted with an ionic liquid, 1-ethyl-3-methyl imidazolium bis(trifluoromethanesulfonyl)amide, at temperatures in a range from room temperature to 120 °C. Current measurements show that positive and negative electrospray currents from the heated emitter increased as the temperature increased. Time-of-flight (TOF) mass spectrometric measurements reveal that the beam composition changed significantly with increasing temperature, indicating that charged droplets as well as ions were emitted from the heated emitter. The TOF data show that a significant fraction of the current is due to droplets at higher temperatures. On the basis of the results obtained, the size and charge of the emitted droplets are discussed. The beam is roughly estimated to contain charged droplets with a diameter of around 20 nm at 120 °C.

Comprehensive investigation of sputtering deposition pressure effects on a-InGaZnO Schottky diodes

The effects of Ar sputtering deposition pressure on the optical, structural, morphological, and electrical properties of amorphous InGaZnO thin films were investigated. The InGaZnO thin films, which have amorphous structures determined by grazing incidence x-ray diffraction, contained In, Ga, Zn, and O confirmed by secondary ion mass spectrometry method. Additionally, when the thicknesses of the deposited thin films are examined, it was seen that the profilometer measurement results of the crater formed by secondary ion mass spectrometer and scanning electron microscope measurement results are nearly similar, and it is approximately 100 nm. The surface roughness, obtained from Atomic Force Microscopy results, show that decreased up to a particular value with the increase of the working pressure, and then the surface roughness increased. The optical band gaps of the films were obtained in the range of 3.50 eV−3.58 eV via Tauc relation by using the Ultraviolet-Visible measurements carried out in the wavelength range of 200 nm−1100 nm. It was seen that the optical band gap was decreased with the increase in Ar pressure. The electrical properties of InGaZnO thin film-based Schottky diodes, such as the barrier height, ideality factor, saturation current, series resistance, and shunt resistance, have also been studied comprehensively. The electrical results showed that diode properties change with increasing deposition pressure.

A robust methodology for triple (∆47, ∆48, ∆49) clumped isotope analysis of carbonates

Analysis of ∆48 and ∆47 values of CO2 released from phosphoric acid digestion of carbonates enables the rate-limiting kinetic processes involved in carbonate mineralization to be identified and formation temperatures to be determined by accounting for these kinetic biases. This method has the benefit of only requiring analysis of a single carbonate phase. To resolve temperature from the kinetic information, mass spectrometric measurements of highest accuracy and precision are required.Here, we outline a robust methodology for high-precision triple (∆47, ∆48, ∆49) clumped isotope analysis using turbo-pumped gas and carbonate preparation lines, a common acid bath and the dual inlet of a Thermo Scientific 253plus gas source mass spectrometer, equipped with additional m/z47.5 half mass cup. By analysis of >400 replicates each, we report long-term (50 months) ∆47, CDES 90 and ∆48, CDES 90 values for three internationally accepted (ETH-1, -2 and -3) and two internal carbonate standards (GU1, Carrara) unbiased by scale compression. In order to obtain highest accuracy and precisions closest to shot noise limit it is essential to account for a sample size effect, correct raw intensities for a negative background utilizing the half mass cup, avoid pressure imbalances between sample and reference gas and distribute samples evenly across a given analytical session.We confirm ∆47, CDES 90 values that were recently assigned to ETH-1 and ETH-2. Our long-term average ∆47, CDES 90 value of 0.6032 ‰ for ETH-3, on the contrary, occurs 10 ppm lower than its recently assigned value. As a consequence, ∆47, CDES 90 values of samples having relatively low temperatures of formation are not consistent with ∆47, I-CDES values. We show that GU1, a synthetic carbonate deriving from the hydroxylation of CO2 and exhibiting a strong anti-clumped ∆48, CDES 90 value, appears to be homogeneous in its isotopic composition. If used in combination with ETH-1, −2 and − 3, it may allow projection of background corrected raw data without any bias into ∆47-∆48 CDES 90 space, provided our long-term dual clumped isotope values for these carbonate anchors are considered.Stability of mass spectrometric measurements is related to filament age and/or room temperature fluctuations and can be monitored using reference gas m/z49 intensity. Under the most stable analytical conditions, the ∆49, CDES 90 values of equilibrated gases and carbonates reveal a trend with formation temperature. Using data from the most stable sessions, we present a temperature calibration for ∆49, CDES 90 in CO2 evolved from phosphoric acid digestion of carbonates.

Clumped isotope analysis of (bio)apatite using a Kiel IV device in long‐integration dual‐inlet mode

RationaleClumped isotope (Δ47) analysis of bioapatite‐derived CO2 is a powerful tool to determine body temperatures of extinct vertebrates. The common acid bath technique in combination with dual‐inlet‐based mass spectrometric measurements has been the preferred method of choice for this purpose, but the large amount of material necessary and the presence of secondary calcite represent obstacles.MethodsWe analyzed the Δ47 composition of carbonate‐bearing (bio)apatites using a Kiel IV device, which – in general – allows a reduction of sample replicate size by a factor of ~40 over dual‐inlet‐based techniques. The Kiel IV device was tested in two different modes: without and with additional water sinks for improved water removal. Furthermore, we tested a pretreatment technique based on 1 M acetic acid (pH = 5) to selectively remove secondary calcite from the carbonate‐bearing (bio)apatite phase.ResultsSignificantly lower Δ47 values were obtained for a given bioapatite after the installation of the two water sinks. With this setup, Δ47 of (bio)apatites followed a temperature relationship that is indistinguishable from the unified one for pure carbonates, provided a dentine sample, rich in organic matter, was excluded. The original bioapatite Δ47 value was restored from a bioapatite/calcite mixture if the mixed material was treated for 1 h with 1 M acetic acid (pH = 5).Conclusions(Bio)apatites having low organic matter content such as enamel(oid) can be analyzed accurately for Δ47 using a Kiel IV equipped with water sinks that ensure effective removal of water. Secondary calcite can be effectively removed from carbonate‐bearing apatite by pretreatment with 1 M acetic acid (pH = 5) for 1 h.

1D/3D Heterogeneous Assembling Body of Cobalt Nitrides for Highly Efficient Overall Hydrazine Splitting and Supercapacitors.

Herein, the construction of a heterostructured 1D/3D CoN-Co2 N@NF (nickel foam) electrode used for thermodynamically favorable hydrazine oxidation reaction (HzOR), as an alternative to sluggish anodic oxygen evolution reaction (OER) in water splitting for hydrogen production, is reported. The electrode exhibits remarkable catalytic activities, with an onset potential of -0.11V in HzOR and -71mV for a current density of 10mA cm-2 in hydrogen evolution reaction (HER). Consequently, an extraordinary low cell voltage of 53mV is required to achieve 10mA cm-2 for overall hydrazine splitting in a two-electrode system, demonstrating significant energy-saving advantages over conventional water splitting. The HzOR proceeds through the 4e- reaction pathway to release N2 while the 1e- pathway to emit NH3 is uncompetitive, as evidenced by differential electrochemical mass spectrometric measurements. The X-ray absorption spectroscopy, in situ Raman spectroscopy, and theoretical calculations identify cobalt nitrides rather than corresponding oxides/(oxy)hydroxides as catalytic species for HzOR and illustrate advantages of heterostructured CoN-Co2 N in optimizing adsorption energies of intermediates/reagents and promoting catalytic activities toward both HzOR and HER. The CoN-Co2 N@NF is also an excellent supercapacitive material, exhibiting an increased specific capacity (938 F g-1 at 1 A g-1 ) with excellent cycling stability (95.8%, 5000 cycles).

Cyclopalladated complexes with pincer-like ONC-donor N-(4-R-benzoyl)-N′-(9-phenanthrylidene)hydrazines: Regioselective peri‑palladation of the 9-phenanthryl group

Two series of cyclopalladates [Pd(HL1–5)Cl] (1–5) and [Pd(L1–5)(PPh3)] (6–10) with the Schiff bases N-(4-R-benzoyl)-N′-(9-phenanthrylidene)hydrazines (H2Ln, where n = 1–5 for R = H, Cl, OMe, NO2 and NMe2, respectively and 2 Hs represent the amide and the ortho or peri H-atom of the 9-phenanthryl group) are reported. All the complexes were characterized by mass spectrometric and spectroscopic (IR, UV–Vis and fluorescence) measurements. Molecular structures of two Schiff bases (H2L1 and H2L4) and three representative complexes from each series [Pd(HL1,3,5)Cl] (1, 3 and 5) and [Pd(L1,2,4)(PPh3)] (6, 7 and 9) were confirmed by single crystal X-ray crystallographic studies. In each of the two types of complexes (HLn)– or (Ln)2– acts as ONC-donor pincer-like ligand. In [Pd(HL1,3,5)Cl], the metal center is in square-planar ONCCl environment assembled by amide-O, azomethine-N and 9-phenanthryl peri‑C coordinating (HL1,3,5)– and the Cl-atom. On the other hand, in [Pd(L1,2,4)(PPh3)], (L1,2,4)2– coordinate through amidate-O, azomethine-N and 9-phenanthryl peri‑C and the P-atom of PPh3 satisfies the fourth coordination site to form a square-planar ONCP coordination geometry around the metal center. The mass spectrometric and infrared and electronic spectroscopic characteristics of all the complexes are complementary to their molecular structures. All the Schiff bases and the complexes are emissive in solution. Theoretical calculations were carried out with a representative complex to comprehend the regioselective peri‑palladation of the 9-phenanthryl fragment of the tridentate ligand.

Characterization ofantifungal properties of lipopeptide-producing Bacillus velezensis strains and their proteome-based response to the phytopathogens, Diaporthe spp.

Introduction: B. velezensis strains are of interest in agricultural applications due to their beneficial interactions with plants, notable through their antimicrobial activity. The biocontrol ability of two new lipopeptides-producing B. velezensis strains ES1-02 and EFSO2-04, against fungal phytopathogens of Diaporthe spp., was evaluated and compared with reference strains QST713 and FZB42. All strains were found to be effective against the plant pathogens, with the new strains showing comparable antifungal activity to QST713 and slightly lower activity than FZB42. Methods: Lipopeptides and their isoforms were identified by high-performance thin-layer chromatography (HPTLC) and mass spectrometric measurements. The associated antifungal influences were determined in direct in vitro antagonistic dual culture assays, and the inhibitory growth effects on Diaporthe spp. as representatives of phytopathogenic fungi were determined. The effects on bacterial physiology of selected B. velezensis strains were analyzed by mass spectrometric proteomic analyses using nano-LC-MS/MS. Results and Discussion: Lipopeptide production analysis revealed that all strains produced surfactin, and one lipopeptide of the iturin family, including bacillomycin L by ES1-02 and EFSO2-04, while QST713 and FZB42 produced iturin A and bacillomycin D, respectively. Fengycin production was however only detected in the reference strains. As a result of co-incubation of strain ES1-02 with the antagonistic phytopathogen D. longicolla, an increase in surfactin production of up to 10-fold was observed, making stress induction due to competitors an attractive strategy for surfactin bioproduction. An associated global proteome analysis showed a more detailed overview about the adaptation and response mechanisms of B. velezensis, including an increased abundance of proteins associated with the biosynthesis of antimicrobial compounds. Furthermore, higher abundance was determined for proteins associated with oxidative, nitrosative, and general stress response. In contrast, proteins involved in phosphate uptake, amino acid transport, and translation were decreased in abundance. Altogether, this study provides new insights into the physiological adaptation of lipopeptide-producing B. velezensis strains, which show the potential for use as biocontrol agents with respect to phytopathogenic fungi.