New Phenotype and Mineralization of Biogenic Iron Oxide in Magnetotactic Bacteria

Many magnetotactic bacteria (MTB) biomineralize magnetite crystals that nucleate and grow inside intracellular membranous vesicles originating from invaginations of the cytoplasmic membrane. The crystals together with their surrounding membranes are referred to as magnetosomes. Magnetosome magnetite crystals nucleate and grow using iron transported inside the vesicle by specific proteins. Here, we tackle the question of the organization of magnetosomes, which are always described as constituted by linear chains of nanocrystals. In addition, it is commonly accepted that the iron oxide nanocrystals are in the magnetite-based phase. We show, in the case of a wild species of coccus-type bacterium, that there is a double organization of the magnetosomes, relatively perpendicular to each other, and that the nanocrystals are in fact maghemite. These findings were obtained, respectively, by using electron tomography of whole mounts of cells directly from the environment and high-resolution transmission electron microscopy and diffraction. Structure simulations were performed with the MacTempas software. This study opens new perspectives on the diversity of phenotypes within MTBs and allows to envisage other mechanisms of nucleation and formation of biogenic iron oxide crystals.

PROPERTIES SYSTEMATIZATION FOR POLAR OXIDE CRYSTALS

The systematization of piezoelectic (PE), pyroelectric (PYE), electrooptic (EO), and nonlinear optical (NLO) properties has been carried out for the polar oxide crystals, used in functional electronics. The sharp extremal dependence has been found for the upper envelope of fuzzy sets for these properties taken in pairs. There is no any theoretical analysis of such dependencies in solid state physics up to now. It is shown nevertheless, that general view of such interrelationships is different in detail. The experimental points are near the upper envelope for the NLO-PE interrelationship, but there is still a lack of empirical data for EO-PE interrelationship. The highest acentric properties are observed in crystals of multicomponent oxide relaxors, partially studied only in the last 20 years.

Atomic-resolution STEM-EDS studies of cation ordering in Ti-Nb oxide crystals

Ternary metal oxide compounds, such as Ti-Nb and Nb-W oxides, have renewed research interest in energy storage materials because these oxides contain multivalent metal ions that may be able to control the ion transport in solid lithium batteries. One of these oxides is Ti2Nb10O29, which is composed of metal–oxygen octahedra connected through corner-sharing and edge-sharing to form “block structures”. In the early 1970s Von Dreele and Cheetham proposed a metal-atoms ordering in this oxide crystal using Rietveld refined neutron powder diffraction method. Most recent studies on these oxides, however, have not considered cation ordering in evaluating the battery electrode materials. In this paper, by utilizing the latest scanning transmission electron microscopy combined with energy dispersive X-ray spectroscopy imaging technology, the cation chemical ordering in those oxide crystals was directly revealed at atomic resolution.