Effect of pressure on magnetic properties of magnetic nanoparticles, based on Prussian blue analogues, were studied in pressures up to 1.2 GPa. The Mn 3 [Cr(CN) 6 ] 2 · nH 2 O and Ni 3 [Cr(CN) 6 ] 2 · nH 2 O nanoparticles were prepared by reverse micelle technique. Transmission electron microscopy images show nanoparticles with average diameter of about 3.5 nm embedded in an organic matrix. The characteristic X-ray peaks of nanoparticles are more diffused and broader. Systems of nanoparticles behave as systems of interacting magnetic particles. The Curie temperature TC is reduced from T C = 56 K for Ni-Prussian blue analogues to T C = 21 K for Ni-nanoparticles system and from TC = 65 K for Mn-Prussian blue analogues to T C = 38 K for Mn-nanoparticles system. One can explain this reduction of the Curie temperature and of the saturated magnetization µs by dispersion of nanoparticles in an organic matrix i.e. by a dilution effect. Applied pressure leads to a remarkable increase in T C for system of Mn-nanoparticles (∆T C /∆p = +13 K/GPa) and to only slight decrease in T C for system of Ni-nanoparticles (∆T C /∆p = −3 K/GPa). The pressure effect follows behavior of the mother Prussian blue analogues under pressure. The increase in saturated magnetization, attributed to compression of the organic matrix, is very small. PACS numbers: 75.30.Cr, 75.50.Ee, 75.50.Gg, 75.50.Xx (489) 490 A. Zentko et al.
Pathogenic bacteria employ many strategies to overcome the host immune system for extended survival and propagation in their hosts. Components of the bacterial outer-membrane play an important role in this process. When invading the host, Gram-negative bacteria often use a strategy, known as phase variation, that involves a reversible change in antigenic determinants, frequently polysaccharides. This means that the genes encoding the outer-membrane antigens undergo reversible changes within repeated simple DNA sequence motifs. The antigenic structure of the bacterial outer-membrane is influenced by the character of the host immune system, as well as by the targets for bacterial invasion. When the selection pressure of the immune system is absent or weak, bacteria can fail to synthesise the outer-membrane antigens, which are not needed at that time. Smooth-to-rough (S-R) mutation, an economical and often irreversible process in some Gram-negative bacteria, involves the gradual shortening of the lipopolysaccharide (LPS) O-chain. Under certain conditions, e.g., propagation in embryonated eggs or cell lines, some bacteria will cease synthesis of the complete LPS O-chain because it is an energy-demanding process. A type of gradual shortening of the LPS O-chain by Coxiella burnetii, traditionally called phase variation, is used in serological tests for the diagnosis of Q fever. This review discusses the role and function of polysaccharides, especially LPS produced by some Gram-negative bacteria, in bacterial survival.
The capability of endospores of Bacillus subtilis to withstand extreme environmental conditions is secured by several attributes. One of them, the protein shell that encases the spore and is known as the coat, provides the spore with its characteristic resistance to toxic chemicals, lytic enzymes, and predation by unicellular and multicellular eukaryotes. Despite most of the components of the spore coat having been identified, we have only a vague understanding of how such a complex structure is assembled. Using the yeast two-hybrid system, we attempted to identify direct contacts among the proteins allocated to the insoluble fraction of the spore coat: CotV, CotW, CotX, CotY, and CotZ. We also examined whether they could interact with CotE, one of the most crucial morphogenetic proteins governing outer coat formation and also present in the insoluble fraction. Out of all 21 possible interactions we tested, 4 were found to be positive. Among these interactions, we confirmed the previous observation that CotE forms homo-oligomers. In addition, we observed homotypic interactions of CotY, strong interactions between CotZ and CotY, and relatively weak, yet significant, interactions between CotV and CotW. The results of this yeast two-hybrid analysis were confirmed by size exclusion chromatography of recombinant coat proteins and a pull-down assay.Endospores formed by Bacillus subtilis are encased in a protein shell known as the coat, which is comprised of an organized, multilayered structure. Two distinct layers can be clearly distinguished by electron microscopy: a thick, electron-dense outer layer and a lightly staining inner layer composed of fine lamellae (3, 9). The role of the spore coat, whose synthesis is controlled by sporulation-specific transcription factors, is to protect the spore against lytic enzymes and toxic molecules and to provide the spores with mechanical integrity. On the other hand, the coat is also capable of allowing molecules access to the spore interior: for example, spore germinants that interact with receptors located in the inner spore membrane that is shielded by the coat. Although the spore coat traditionally has been considered as a sieving barrier, some results indicate that it has more active functions (5). In recent years, the spore coat of B. subtilis has been shown to be more complex than previously thought (12, 13). Over 50 different proteins are deposited onto the developing surface of the immature spore known as the forespore. The formation of the coat starts soon after the polar septum is formed. This asymmetrically placed septum divides the cell into two unequal compartments-the larger, mother cell compartment and the smaller forespore. The membranes gradually engulf the forespore, generating a compartmentalized forespore that will mature into the endospore that is then released from the surrounding mother cell. This forespore becomes visible by electron microscopy 4 to 5 h after the initiation of sporulation. The whole process is completed only after mother cell lysis and ...
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