Scattered migrating colony formation in the filamentous cyanobacterium, Pseudanabaena sp. NIES-4403.

BACKGROUND: Bacteria have been reported to exhibit complicated morphological colony patterns on solid media, depending on intracellular, and extracellular factors such as motility, cell propagation, and cell-cell interaction. We isolated the filamentous cyanobacterium, Pseudanabaena sp. NIES-4403 (Pseudanabaena, hereafter), that forms scattered (discrete) migrating colonies on solid media. While the scattered colony pattern has been observed in some bacterial species, the mechanism underlying such a pattern still remains obscure. RESULTS: We studied the morphology of Pseudanabaena migrating collectively and found that this species forms randomly scattered clusters varying in size and further consists of a mixture of comet-like wandering clusters and disk-like rotating clusters. Quantitative analysis of the formation of these wandering and rotating clusters showed that bacterial filaments tend to follow trajectories of previously migrating filaments at velocities that are dependent on filament length. Collisions between filaments occurred without crossing paths, which enhanced their nematic alignments, giving rise to bundle-like colonies. As cells increased and bundles aggregated, comet-like wandering clusters developed. The direction and velocity of the movement of cells in comet-like wandering clusters were highly coordinated. When the wandering clusters entered into a circular orbit, they turned into rotating clusters, maintaining a more stable location. Disk-like rotating clusters may rotate for days, and the speed of cells within a rotating cluster increases from the center to the outmost part of the cluster. Using a mathematical modeling with simplified assumption we reproduced some features of the scattered pattern including migrating clusters. CONCLUSION: Based on these observations, we propose that Pseudanabaena forms scattered migrating colonies that undergo a series of transitions involving several morphological patterns. A simplified model is able to reproduce some features of the observed migrating clusters.

Flow cytometric analysis of Xenopus laevis and X. tropicalis blood cells using acridine orange.

Automated blood cell counters can distinguish cells based on their size and the presence or absence of a nucleus. However, most vertebrates have nucleated blood cells that cannot be counted automatically. We established an alternative automatic method for counting peripheral blood cells by staining cells with the fluorescent dye acridine orange (AO) and analysing cell populations using flow cytometry (FCM). As promising new animal models, we chose Xenopus laevis and three inbred strains of X. tropicalis. We compared the haematological phenotypes, including blood cell types, cell sizes, cellular structure, and erythrocyte lifespans/turnover rate among X. laevis and the three inbred strains of X. tropicalis. Each cell type from X. laevis was sorted according to six parameters: forward- and side-scattered light emission, AO red and green fluorescence intensity, and cellular red and green fluorescence. Remarkably, the erythrocyte count was the highest in the Golden line, suggesting that genetic factors were associated with the blood cells. Furthermore, immature erythrocytes in anaemic X. laevis could be separated from normal blood cells based on red fluorescence intensity. These results show that FCM with AO staining allows for an accurate analysis of peripheral blood cells from various species.

Tunable electrical memory characteristics using polyimide:polycyclic aromatic compound blends on flexible substrates.

Resistance switching memory devices with the configuration of poly(ethylene naphthalate)(PEN)/Al/polyimide (PI) blend/Al are reported. The active layers of the PI blend films were prepared from different compositions of poly[4,4'-diamino-4″-methyltriphenylamine-hexafluoroisopropylidenediphthalimide] (PI(AMTPA)) and polycyclic aromatic compounds (coronene or N,N-bis[4-(2-octyldodecyloxy)phenyl]-3,4,9,10-perylenetetracarboxylic diimide (PDI-DO)). The additives of large π-conjugated polycyclic compounds can stabilize the charge transfer complex induced by the applied electric field. Thus, the memory device characteristic changes from the volatile to nonvolatile behavior of flash and write-once-read-many times (WORM) as the additive contents increase in both blend systems. The main differences between these two blend systems are the threshold voltage values and the additive content to change the memory behavior. Due to the stronger accepting ability and higher electron affinity of PDI-DO than those of coronene, the PI(AMTPA):PDI-DO blend based memory devices show a smaller threshold voltage and change the memory behavior in a smaller additive content. Besides, the memory devices fabricated on a flexible PEN substrate exhibit an excellent durability upon the bending conditions. These tunable memory performances of the developed PI/polycyclic aromatic compound blends are advantageous for future advanced memory device applications.

Thermal diffusivity of hexagonal boron nitride composites based on cross-linked liquid crystalline polyimides.

Hexagonal boron nitride (h-BN) composites with the oriented cross-linked liquid crystalline (LC) polyimide have been developed as high thermally conductive materials. Well-dispersed h-BN composite films were obtained, as observed by scanning electron microscopy. The morphology of the composite films was further investigated in detail by the wide-angle X-ray diffraction. The obtained composite films based on the cross-linked LC polyimide showed that the polymer chains vertically aligned in the direction parallel to the films, while those based on the amorphous polyimide showed an isotropic nature. Moreover, the alignment of the cross-linked LC polyimides was maintained, even after increasing the volume fraction of h-BN. This alignment plays an important role in the effective phonon conduction between h-BN and the matrices. Indeed, the thermal diffusivity in the thickness direction of the composite films based on the LC polyimide measured by a temperature wave analysis method was increased to 0.679 mm(2) s(-1) at a 30 vol % h-BN loading, which was higher than that based on the amorphous polyimide.