Ferroelectric materials are widely used in modern electric devices such as memory elements, filtering devices and high-performance insulators. Ferroelectric crystals have a spontaneous electric polarization arising from the coherent arrangement of electric dipoles (specifically, a polar displacement of anions and cations). First-principles calculations and electron density analysis of ferroelectric materials have revealed that the covalent bond between the anions and cations, or the orbital hybridization of electrons on both ions, plays a key role in establishing the dipolar arrangement. However, an alternative model-electronic ferroelectricity-has been proposed in which the electric dipole depends on electron correlations, rather than the covalency. This would offer the attractive possibility of ferroelectric materials that could be controlled by the charge, spin and orbital degrees of freedom of the electron. Here we report experimental evidence for ferroelectricity arising from electron correlations in the triangular mixed valence oxide, LuFe(2)O(4). Using resonant X-ray scattering measurements, we determine the ordering of the Fe(2+) and Fe(3+) ions. They form a superstructure that supports an electric polarization consisting of distributed electrons of polar symmetry. The polar ordering arises from the repulsive property of electrons-electron correlations-acting on a frustrated geometry.

Genetic and phenotypic studies on the strains biochemically identified as Shewanella putrefaciens, which had a G+C content ranging from 52 to 54 mol% were conducted. The moles percent G+C of the type strain of S. putrefaciens is 46. Surprisingly, DNA homology experiments revealed that all these strains are genetically related to Shewanella d g a (which was reported to produce tetrodotoxin), not to the type strain of S. putrefaciens. In this study, we reidentified clinical strains of S. putrefaciens which have a high range of moles percent G+C, as does S. alga. We also characterized the reidentified strains and found that the original description of S. alga (U. Simidu, K. Kita-Tsukamoto, T. Yasumoto, and M. Yotsu, Int. J. Syst. Bacteriol. 4k331-336, 1990) is insufficient to identify this strain. An emended description of S. alga is given.The organism now called Shewanella putrefaciens was first described in 1931 and classified as a member of the genus Achromobacter (4). In 1941, it was transferred to the genus Pseudomonas (16) on the basis of morphology. In 1972, it was transferred to the genus Alteromonas (1) on the basis of G+C content. Finally, in 1985, it was transferred to a new genus, Shewanella, on the basis of comparative 5s rRNA sequences (17). The type species of Shewanella is S. putrefaciens (17).Many of the strains classified as S. putrefaciens were isolated from diverse sources, including environmental sources, such as spoilage flora of foods (12, 14, 18,28), oil fields (24), and the ocean (1, 13), and diverse clinical sources, such as patients with otitis, bronchitis, pneumonia, and urinary tract infections (3, 6, 9, 14, 15, 21, 22,29). However, the collected strains were heterogeneous and there were differences between environmental and clinical isolates (9,14,20,21,23,24,28). Owen et al. (20) divided the 10 environmental strains and 16 clinical strains into four groups. Group IV consisted of nine clinical strains. The moles percent G+C value for group IV (52.6) was clearly higher than those for the other three groups (43.9 to 46.9). All four groups retained the species identification of S. putrefaciens, despite the obvious heterogeneity and moles percent G+C values ranging from 43 to 55 (2).Recently, we noticed that most strains isolated from human clinical specimens and identified as S. putrefaciens showed beta-hemolysis on sheep blood agar. However, environmental strains were nonhemolytic. These hemolytic strains had 52 to 54 mol% G+C. Although the hemolytic strains are biochemically identified as S. putrefaciens according to the description in the Manual of Clinical Microbiology (7), they exhibited high levels of DNA homology with the type strain of S. alga. In this study, we present evidence that these clinical strains of S. putrefaciens should be identified as S. alga and emend the description of S. alga * Corresponding author. S. alga is known to be a tetrodotoxin (lTX)-producing bacterium (25,26). Production of TTX by some newly reidentified strains was examined. This is the first report o...

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Depth-related changes in whole-community structure were evaluated in a coastal marine sediment using a molecular fingerprinting method, terminal restriction fragment length polymorphism (T-RFLP) analysis, and a chemotaxonomic technique (quinone profiling). Dendrograms derived from both T-RFLP analysis and quinone profiling indicated a significant variation in microbial community structure between the 0-2 cm layer and deeper layers. This corresponded to the dramatic change in the redox potential, acid-volatile sulphide-sulphur and bacterial numbers observed at 0-2 cm and 2-4 cm depths. A significant change in the number of terminal restriction fragments (T-RFs) was also detected at this transition depth. However, the change in major T-RFs with depth was not seen in electropherograms. The population changes were primarily variations in minor ribotypes. Most quinone homologues were detected at all depths, although the quinone composition changed with depth. Therefore, quinone profiling also suggested that the depth-related variation was primarily attributable to minor bacterial groups rather than change in the major population structure. 16S rDNA clone library analysis revealed that clones belonging to the genera Vibrio and Serratia predominated as major bacterial groups at all depths. Our data suggested that the sediment community might result from sedimentation effects of sinking particles. Overall, our results demonstrated that the combined methods of T-RFLP analysis and quinone profiling were effective for assessing depth-related microbial populations.