Stage of infection with Mycobacterium avium subsp. paratuberculosis impacts expression of Rab5, Rab7, and CYP27B1 in macrophages within the ileum of naturally infected cows

Introduction

Macrophages are the preferential target of Mycobacterium avium subsp. paratuberculosis (MAP), the etiologic agent of ruminant paratuberculosis. Uptake of pathogens by intestinal macrophages results in their trafficking through endosomal compartments, ultimately leading to fusion with an acidic lysosome to destroy the pathogen. MAP possesses virulence factors which disrupt these endosomal pathways. Additionally, levels of serum vitamin D₃ have proven relevant to host immunity. Dynamics of endosomal trafficking and vitamin D₃ metabolism have been largely unexplored in bovine paratuberculosis.

Methods

This study aimed to characterize expression of early and late endosomal markers Rab5 and Rab7, respectively, within CD68+ macrophages in frozen mid-ileum sections harvested from cows at different stages of natural paratuberculosis infection. Additionally, factors of vitamin D₃ signaling and metabolism were characterized through expression of vitamin D₃ activating enzyme 1α-hydroxylase (CYP27B1), vitamin D₃ inactivating enzyme 24-hydroxylase (CYP24A1), and vitamin D₃ receptor (VDR) within CD68+ ileal macrophages.

Results and discussion

Cows with clinical paratuberculosis had significantly greater macrophage and MAP burden overall, as well as intracellular MAP. Total expression of Rab5 within macrophages was reduced in clinical cows; however, Rab5 and MAP colocalization was significantly greater in this group. Intracellular Rab7 colocalization with MAP was not detected in subclinical or Johne's Disease negative (JD-) control cows but was present in clinical cows. Additionally, macrophage CYP27B1 expression was significantly reduced in clinical cows. Taken together, the results from this study show disparate patterns of expression for key mediators in intracellular MAP trafficking and vitamin D metabolism for cows at different stages of paratuberculosis.

A secondary metabolite drives intraspecies antagonism in a gut symbiont that is inhibited by cell-wall acetylation

The mammalian microbiome encodes numerous secondary metabolite biosynthetic gene clusters; yet, their role in microbe-microbe interactions is unclear. Here, we characterized two polyketide synthase gene clusters (fun and pks) in the gut symbiont Limosilactobacillus reuteri. The pks, but not the fun, cluster encodes antimicrobial activity. Forty-one of 51 L. reuteri strains tested are sensitive to Pks products; this finding was independent of strains' host origin. Sensitivity to Pks was also established in intraspecies competition experiments in gnotobiotic mice. Comparative genome analyses between Pks-resistant and -sensitive strains identified an acyltransferase gene (act) unique to Pks-resistant strains. Subsequent cell-wall analysis of wild-type and act mutant strains showed that Act acetylates cell-wall components, providing resistance to Pks-mediated killing. Additionally, pks mutants lost their competitive advantage, while act mutants lost their Pks resistance in in vivo competition assays. These findings provide insight into how closely related gut symbionts can compete and co-exist in the gastrointestinal tract.

Controlling Near-Surface Ni Composition in Octahedral PtNi(Mo) Nanoparticles by Mo Doping for a Highly Active Oxygen Reduction Reaction Catalyst

We report and study the translation of exceptionally high catalytic oxygen electroreduction activities of molybdenum-doped octahedrally shaped PtNi(Mo) nanoparticles from conventional thin-film rotating disk electrode screenings (3.43 ± 0.35 A mg_Pt^-1 at 0.9 V_RHE) to membrane electrode assembly (MEA)-based single fuel cell tests with sustained Pt mass activities of 0.45 A mg_Pt^-1 at 0.9 V_cell, one of the highest ever reported performances for advanced shaped Pt alloys in real devices. Scanning transmission electron microscopy with energy dispersive X-ray analysis (STEM-EDX) reveals that Mo preferentially occupies the Pt-rich edges and vertices of the element-anisotropic octahedral PtNi particles. Furthermore, by combining in situ wide-angle X-ray spectroscopy, X-ray fluorescence, and STEM-EDX elemental mapping with electrochemical measurements, we finally succeeded to realize high Ni retention in activated PtNiMo nanoparticles even after prolonged potential-cycling stability tests. Stability losses at the anodic potential limits were mainly attributed to the loss of the octahedral particle shape. Extending the anodic potential limits of the tests to the Pt oxidation region induced detectable Ni losses and structural changes. Our study shows on an atomic level how Mo adatoms on the surface impact the Ni surface composition, which, in turn, gives rise to the exceptionally high experimental catalytic ORR reactivity and calls for strategies on how to preserve this particular surface composition to arrive at performance stabilities comparable with state-of-the-art spherical dealloyed Pt core-shell catalysts.

X-ray powder diffraction to analyse bimetallic core–shell nanoparticles (gold and palladium; 7–8 nm)

A comparative X-ray powder diffraction study on poly(N-vinyl pyrrolidone) (PVP)-stabilized palladium and gold nanoparticles and bimetallic Pd–Au nanoparticles (both types of core–shell nanostructures) was performed.

Strain and electric-field control of magnetism in supercrystalline iron oxide nanoparticle-BaTiO3 composites

The manipulation of the magnetism of self-assembled iron oxide nanoparticle (NP) monolayers on top of BaTiO₃ (BTO) single crystals is reported. We observe strain induced magnetoelectric coupling (MEC) as shown by measurements of both the magnetization and magneto-electric AC susceptibility (MEACS). The magnetization, coercivity, remanent magnetization and MEACS signal as a function of temperature show abrupt jumps at the BTO phase transition temperatures. Hereby the jump values are opposite for in-plane and out-of-plane measurements. Grazing incidence small angle X-ray scattering (GISAXS) and scanning electron microscopy (SEM) confirm a hexagonal close-packed supercrystalline order of the NP monolayers. Cross-sectional scanning transmission electron microscopy (STEM) experiments provide information about the layer structure of the sample. This work opens up viable possibilities for fabricating energy-efficient electronic devices by self-assembly techniques.

Conjugation of thiol-terminated molecules to ultrasmall 2 nm-gold nanoparticles leads to remarkably complex 1H-NMR spectra

Gold nanoparticles, functionalized by aliphatic and aromatic mercapto-functionalized carboxylic acids and by two small peptides (CG and CGGRGD), respectively, were synthesized by the reduction of HAuCl₄ with NaBH₄ in the presence of the above ligands.

Nanostructure of wet-chemically prepared, polymer-stabilized silver–gold nanoalloys (6 nm) over the entire composition range

Bimetallic silver–gold nanoparticles were prepared by co-reduction using citrate and tannic acid in aqueous solution and colloidally stabilized with poly(N-vinylpyrrolidone) (PVP).

In situ fabrication of ultrathin porous alumina and its application for nanopatterning Au nanocrystals on the surface of ion-sensitive field-effect transistors

In situ fabrication in a single step of thin films of alumina exhibiting a thickness of less than 100 nm and nanopores with a highly regular diameter distribution in order to pattern nanostructures over field-effect devices is a critical issue and has not previously been demonstrated. Here we report the fabrication in situ of 50 nm thick ultrathin nanoporous alumina membranes with a regular pore size directly over metal-free gate ion-sensitive field-effect transistors. Depositing thin films of aluminum by an electron beam at a relatively low rate of deposition on top of chips containing the transistors and using a conventional single-step anodization process permits the production of a well-adhering nanoporous ultrathin layer of alumina on the surface of the devices. The anodization process does not substantially affect the electrical properties of the transistors. The small thickness and pore size of ultrathin alumina membranes allow them to be sequentially employed as masks for patterning Au nanocrystals grown by an electroless approach directly on the top of the transistors. The patterning process using a wet chemical approach enables the size of the patterned crystals to be controlled not only by the dimensions of the pores of alumina, but also by the concentration of the reactants employed. Surface modification of these nanocrystals with alkanethiol molecules demonstrates that the electrostatic charge of the functional groups of the molecules can modulate the electrical characteristics of the transistors. These results represent substantial progress towards the development of novel nanostructured arrays on top of field-effect devices that can be applied for chemical sensing or non-volatile memories.

Al13Fe4 as a low-cost alternative for palladium in heterogeneous hydrogenation

Replacing noble metals in heterogeneous catalysts by low-cost substitutes has driven scientific and industrial research for more than 100 years. Cheap and ubiquitous iron is especially desirable, because it does not bear potential health risks like, for example, nickel. To purify the ethylene feed for the production of polyethylene, the semi-hydrogenation of acetylene is applied (80 × 10(6) tons per annum; refs 1-3). The presence of small and separated transition-metal atom ensembles (so-called site-isolation), and the suppression of hydride formation are beneficial for the catalytic performance. Iron catalysts necessitate at least 50 bar and 100 °C for the hydrogenation of unsaturated C-C bonds, showing only limited selectivity towards semi-hydrogenation. Recent innovation in catalytic semi-hydrogenation is based on computational screening of substitutional alloys to identify promising metal combinations using scaling functions and the experimental realization of the site-isolation concept employing structurally well-ordered and in situ stable intermetallic compounds of Ga with Pd (refs 15-19). The stability enables a knowledge-based development by assigning the observed catalytic properties to the crystal and electronic structures of the intermetallic compounds. Following this approach, we identified the low-cost and environmentally benign intermetallic compound Al(13)Fe(4) as an active and selective semi-hydrogenation catalyst. This knowledge-based development might prove applicable to a wide range of heterogeneously catalysed reactions.

Geometric origin of magnetic frustration in the μ-Al₄Mn giant-unit-cell complex intermetallic

The structurally ordered μ-Al(4)Mn complex intermetallic phase with 563 atoms in the giant unit cell shows the typical broken-ergodicity phenomena of a magnetically frustrated spin system. The low-field zero-field-cooled and field-cooled magnetic susceptibilities show splitting below the spin freezing temperature T(f) = 2.7 K. The ac susceptibility exhibits a frequency-dependent cusp, associated with a frequency-dependent freezing temperature T(f)(ν). The decay of the thermoremnant magnetization is logarithmically slow in time and shows a dependence on the aging time t(w) and the cooling field H(fc) typical of an ultraslow out-of-equilibrium dynamics of a nonergodic spin system that approaches thermal equilibrium, but can never reach it on the experimentally accessible time scale. The above features classify the μ-Al(4)Mn complex intermettalic among spin glasses. The origin of frustration of magnetic interactions was found to be geometrical due to the distribution of a significant fraction of Mn spins on triangles with antiferromagnetic coupling. The μ-Al(4)Mn phase is a geometrically frustrated spin glass.

Plastic-deformation mechanism in complex solids

In simple crystalline materials, plastic deformation mostly takes place by the movement of dislocations. Although the underlying mechanisms in these materials are well explored, in complex metallic alloys--crystalline solids containing up to thousands of atoms per unit cell--the defects and deformation mechanisms remain essentially unknown. Owing to the large lattice parameters of these materials, extended dislocation concepts are required. We investigated a typical complex metallic alloy with 156 atoms per unit cell using atomic-resolution aberration-corrected transmission electron microscopy. We found a highly complex deformation mechanism, based on the movement of a dislocation core mediating strain and separate escort defects. On deformation, the escort defects move along with the dislocation core and locally transform the material structure for the latter. This mechanism implies the coordinated movement of hundreds of atoms per elementary glide step, and nevertheless can be described by simple rearrangement of basic structural subunits.