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Cells of Flavobacterium johnsoniae and of many other members of the phylum Bacteroidetes exhibit rapid gliding motility over surfaces by a unique mechanism. These cells do not have flagella or pili; instead, they rely on a novel motility apparatus composed of Gld and Spr proteins. SprB, a 669-kDa cell-surface adhesin, is required for efficient gliding. SprB was visualized by electron microscopy as thin 150-nm-long filaments extending from the cell surface. Fluorescence microscopy revealed movement of SprB proteins toward the poles of the cell at ∼2 μm/s. The fluorescent signals appeared to migrate around the pole and continue at the same speed toward the opposite pole along an apparent left-handed helical closed loop. Movement of SprB, and of cells, was rapidly and reversibly blocked by the addition of carbonyl cyanide m -chlorophenylhydrazone, which dissipates the proton gradient across the cytoplasmic membrane. In a gliding cell, some of the SprB protein appeared to attach to the substratum. The cell body moved forward and rotated with respect to this point of attachment. Upon reaching the rear of the cell, the attached SprB often was released from the substratum, and apparently recirculated to the front of the cell along a helical path. The results suggest a model for Flavobacterium gliding, supported by mathematical analysis, in which adhesins such as SprB are propelled along a closed helical loop track, generating rotation and translation of the cell body.

Confined spaces are omnipresent in the micro-environments, including soil aggregates and intestinal crypts, yet little is known about how bacteria behave under such conditions where movement is challenging due to spatial confinement that limited effective diffusion. Stinkbug symbiont Caballeronia insecticola navigates a narrow gut passage about one micrometer in diameter to reach the stinkbug’s symbiotic organ. Here, we developed a microfluidic device mimicking the host’s sorting organ, wherein bacterial cells are confined in a quasi-one-dimensional fashion, and revealed that this bacterium wraps flagellar filaments around its cell body like a screw thread to control fluid flow and generate propulsion for smooth and directional movement in narrow passages. Physical simulations and genetic experiments revealed that hook flexibility is essential for this wrapping; increasing hook rigidity impaired both wrapping motility and infectivity. Thus, flagellar wrapping likely represents an evolutionary innovation, enabling bacteria to break through confined environments using their motility machinery. Yoshioka et al. show that bacteria wrap their flagella to squeeze through near cell-width confinements, which allows symbiotic microbes to navigate constricted gut regions within insect hosts.

The magnetocaloric properties of (MnFeRu)2(PSiGe) have been studied by monitoring the differential scanning calorimetry (DSC) and the adiabatic temperature change. The compounds have the Curie temperature of 340–360 K. The DSC curves show sharp peaks, indicating a first-order magnetic transition. The thermal hysteresis is less than 2.3 K. Using our previous data, we examined the correlation between the DSC peak and the magnetic entropy change ΔSM. A strong positive correlation between these two quantities is observed. The analyses also suggest that ΔSM of (MnFeRu)2(PSiGe) reaches 11–16 J/ K kg in a field change of 1.5 T. The direct measurements of the adiabatic temperature change ΔTad have revealed ΔTad of 1.7–1.8 K at 1 T for (MnFeRu)2(PSiGe). These results suggest that (MnFeRu)2(PSiGe) compounds are potential candidates for magnetic refrigerant materials above room temperature up to 90 °C (~ 360 K).

Ternary La(Fe 1- x Si x ) 13 compounds undergo a first-order magnetic transition at the Curie temperature T C . Above T C , the compounds exhibit the itinerant electron metamagnetism. We have studied Hall effect and thermal conductivity of La(Fe 1- x Si x ) 13 . The Hall resistivity was measured as a function of the magnetic field B at various temperatures. Using the magnetization data, we separated the normal Hall effect (NHE) and the anomalous Hall effect (AHE) in the ferromagnetic state. It is found that NHE is positive at low temperatures, while it becomes negative near T C . The large AHE was observed for x  = 0.12. Our analyses revealed that the skew scattering is dominant in the AHE. The temperature dependence of thermal conductivity λ exhibits a peak at T C for x  = 0.12 and 0.14, while abrupt reduction in λ was observed at T C for x  = 0.10 both on cooling and on heating. We discuss the physical origins of these anomalies in the transport properties of La(Fe 1- x Si x ) 13 .

We have scaled up the production process of magnetic refrigerants near room temperature. The Mn2−yFey−xRuxP1−zSiz compounds with 0.03 ≤ x ≤ 0.16, y ≈ 0.75, and z ≈ 0.55 were synthesized and their magnetocaloric properties were examined. By changing the compositions and the annealing temperature, the Curie temperature was tuned between 275 and 315 K with 2~3 K steps. All the compounds underwent a first-order magnetic transition accompanied by thermal hysteresis of less than 2 K. The compounds showed excellent magnetocaloric properties: the magnetic entropy change was more than 10 J/K·kg and the refrigerant capacity was about 115 J/kg in a field change of 1.5 T. The detailed instructions to synthesize high-performance (MnFe)2PSi materials are given.

An intermediate valence compound YbPd undergoes successive structural transitions at 105 K and 125 K. The recent inelastic X-ray scattering measurement have revealed softening of longitudinal acoustic (LA) mode around X point, q (0, 0, 0.5). We have attempted to reproduce this softening from first-principles calculations. The calculated results with fixed valence Yb do not show any anomaly in the LA mode around X. To include valence change in the lattice vibrations, the nearest-neighbor valence-lattice interaction has been added. The interaction reduces the energy of the LA mode around X as observed by the experiment. This soft mode leads to the structure below 105 K. On the other hand, the lowest energy is found at the slightly different wavevector, q (0.1, 0.1, 0.5). This wavevector corresponds to the superlattice reflection observed by the experiment in the intermediate incommensurate phase between 105 K and 125 K. Therefore, the successive structural transitions of YbPd can be correctly reproduced by including this valence-lattice interaction.

We report the effects of a magnetic field on a pressure-induced valence transition in EuRh2Si2 by using magnetization measurements under high pressure. The M-H curves at 2 K under various pressures up to 1.18 GPa exhibit no anomalies associated with a field-induced valence transition. On the other hand, the M-H curves under a pressure of ∼ 1 GPa, where a temperature-induced valence transition occurs at around 30 K, show a clear metamagnetic transition with a large hysteresis at around 30 K. This behavior corresponds to a field-induced valence transition. The M-T curves in magnetic fields indicate that with increasing magnetic field, the temperature-induced valence transition shifts toward lower temperature and that its thermal hysteresis becomes larger. Cooling the sample under a pressure of ∼ 1 GPa in a magnetic field of 7 T collapses the valence transition and stabilizes the magnetic high-temperature phase down to 2 K. Besides, with decreasing magnetic field, three sharp valence transitions toward the nonmagnetic Eu3+ direction are observed: 4.65, 2.65 and 1.93 T.

EuPtP is known to exhibit two valence ordering transitions, one at T1 = 235 K and the other at T2 = 190 K. For T > T1, the Eu ions are in the valence fluctuating state. For T2 < T < T1, the Eu valence state is ordered along the c-axis with the sequence of Eu2+-Eu2+-Eu3+-Eu2+-Eu2+-Eu3+. Moreover, the stacking is replaced by another sequence of Eu2+-Eu3+-Eu2+-Eu3+ at temperatures below T2. The substitution of As for P expands the lattice and decreases both T1 and T2. In this paper, we report the magnetic susceptibility and electrical resistivity of EuPtP1−xAsx single crystals. We observed two valence ordering transitions for 0 ≤ x ≤ 0.4, while a single valence ordering transition was detected for 0.55 ≤ x ≤ 0.6. No valence ordering transitions were observed for x = 0.7 down to the lowest temperature. Based on the experimental results, we present the phase diagram of EuPtP1−xAsx and discuss the Eu valence state in this system.

The hexagonal layered compound EuPtP exhibits two valence transitions at T1 240 K and T2 198 K. We present field-induced shift of temperature of the two valence transitions and magnetic field versus temperature phase diagram in EuPtP. Magnetic field dependence of the valence transition temperatures, T1 and T2, is similar to that reported in Eu(Pd1−xPtx)2Si2 and YbIn1−xAgxCu4.

intestinal crypts, yet little is known about how bacteria behave under such conditions where movement is challenging due to limited diffusion. Stinkbug symbiont Caballeronia insecticola navigates a narrow gut passage about one micrometer in diameter to reach the stinkbug's symbiotic organ. Here, we developed a microfluidic device mimicking the host's sorting organ, wherein bacterial cells are confined in a quasi-one-dimensional fashion, and revealed that this bacterium wraps flagellar filaments around its cell body like a screw thread to control fluid flow and generate propulsion for smooth and directional movement in narrow passages. Physical simulations and genetic experiments revealed that hook flexibility is essential for this wrapping; increasing hook rigidity impaired both wrapping motility and infectivity. Thus, flagellar wrapping likely represents an evolutionary innovation, enabling bacteria to break through confined environments using their motility machinery.Competing Interest StatementThe authors have declared no competing interest.