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81.
82.
Patricia A. Burrowes María Celeste Martes Mónica Torres-Ríos Ana V. Longo 《Journal of Natural History》2017,51(11-12):643-656
Pathogen-mediated changes in host behaviour can result from hosts altering their habitat preferences. Although infection risk with pathogenic fungus Batrachochytrium dendrobatidis in amphibians is associated with environments favouring its growth, the relationship with microhabitat use has not been examined. Here, we aim to determine if microhabitats used by frogs during their nocturnal activity predict B. dendrobatidis prevalence and infection intensity. Our focal host, Eleutherodactylus coqui, is a habitat generalist that uses multiple habitats from the forest floor to the canopy. We analysed data on B. dendrobatidis occurrence in 157 adults and 122 juveniles at El Yunque National forest in Puerto Rico. We categorized each individual’s nocturnal microhabitat as forest floor, curled palm fronds in the floor, arboreal bromeliads and foliage or tree trunks 50 cm to 2.5 m above ground. We found that frogs on the forest floor had the greatest B. dendrobatidis prevalence (73%), compared with those active in vegetation above ground (55%). Overall, the probability of B. dendrobatidis infection in frogs using microhabitats on the forest floor was twice as great as for those on arboreal substrates. Differences in B. dendrobatidis prevalence and intensity in E. coqui may be explained by specific abiotic conditions of microenvironments (temperature and humidity) affecting both pathogen and host, and by the age-specific ecological requirements of hosts. Adults were found to be most active in microhabitats where individuals had lower infection burdens, suggesting pathogen-modulated habitat choice. This work has important implications for the evolutionary dynamics of enzootic diseases and provides data that may inform potential mitigation strategies against a generalist amphibian pathogen. 相似文献
83.
Andrey V. Kulikov Alexander S. Vdovin Boris Zhivotovsky Vladimir Gogvadze 《Cellular and molecular life sciences : CMLS》2014,71(12):2325-2333
Rapidly proliferating tumor cells easily become hypoxic. This results in acquired stability towards treatment with anticancer drugs. Here, we show that cells grown at 0.1 % oxygen are more resistant towards treatment with the conventionally used anticancer drugs doxorubicin and cisplatin. The stimulation of apoptosis, as assessed by the number of cells in the SubG1 fraction of the cell cycle, release of cytochrome c into the cytosol, activation of caspase-3, and cleavage of PARP, was markedly suppressed under low oxygen content or when hypoxia was mimicked by deferoxamine. Hypoxia or deferoxamine treatment was accompanied by stabilization of the hypoxia-inducible factor (HIF-1). The downregulation of HIF-1 using siRNA technique restored cell sensitivity to treatment under hypoxic conditions to the levels detected under normoxic conditions. In contrast to cisplatin or doxorubicin, α-tocopheryl succinate (α-TOS), a compound that targets mitochondria, stimulated cell death irrespective of the oxygen concentration. Moreover, under hypoxic condition cell death induced by α-TOS was even enhanced. Thus, α-TOS can successfully overcome resistance to treatment caused by hypoxia, which makes α-TOS an attractive candidate for antitumor therapy via mitochondrial targeting. 相似文献
84.
Lígia O. Martins Paulo Durão Vânia Brissos Peter F. Lindley 《Cellular and molecular life sciences : CMLS》2015,72(5):911-922
The ubiquitous members of the multicopper oxidase family of enzymes oxidize a range of aromatic substrates such as polyphenols, methoxy-substituted phenols, amines and inorganic compounds, concomitantly with the reduction of molecular dioxygen to water. This family of enzymes can be broadly divided into two functional classes: metalloxidases and laccases. Several prokaryotic metalloxidases have been described in the last decade showing a robust activity towards metals, such as Cu(I), Fe(II) or Mn(II) and have been implicated in the metal metabolism of the corresponding microorganisms. Many laccases, with a superior efficiency for oxidation of organic compounds when compared with metals, have also been identified and characterized from prokaryotes, playing roles that more closely conform to those of intermediary metabolism. This review aims to present an update of current knowledge on prokaryotic multicopper oxidases, with a special emphasis on laccases, anticipating their enormous potential for industrial and environmental applications. 相似文献
85.
86.
Ohne Zusammenfassung9. Mitt. Untersuchungen über Organextrakte; 8. Mitt. vgl. Helv. chim. acta28 im Druck. 相似文献
87.
Proteomic studies have yielded detailed lists of the proteins present in a cell. Comparatively little is known, however, about how these proteins interact and are spatially arranged within the 'functional modules' of the cell: that is, the 'molecular sociology' of the cell. This gap is now being bridged by using emerging experimental techniques, such as mass spectrometry of complexes and single-particle cryo-electron microscopy, to complement traditional biochemical and biophysical methods. With the development of integrative computational methods to exploit the data obtained, such hybrid approaches will uncover the molecular architectures, and perhaps even atomic models, of many protein complexes. With these structures in hand, researchers will be poised to use cryo-electron tomography to view protein complexes in action within cells, providing unprecedented insights into protein-interaction networks. 相似文献
88.
Piccioni G Drossart P Sanchez-Lavega A Hueso R Taylor FW Wilson CF Grassi D Zasova L Moriconi M Adriani A Lebonnois S Coradini A Bézard B Angrilli F Arnold G Baines KH Bellucci G Benkhoff J Bibring JP Blanco A Blecka MI Carlson RW Di Lellis A Encrenaz T Erard S Fonti S Formisano V Fouchet T Garcia R Haus R Helbert J Ignatiev NI Irwin PG Langevin Y Lopez-Valverde MA Luz D Marinangeli L Orofino V Rodin AV Roos-Serote MC Saggin B Stam DM Titov D Visconti G 《Nature》2007,450(7170):637-640
Venus has no seasons, slow rotation and a very massive atmosphere, which is mainly carbon dioxide with clouds primarily of sulphuric acid droplets. Infrared observations by previous missions to Venus revealed a bright 'dipole' feature surrounded by a cold 'collar' at its north pole. The polar dipole is a 'double-eye' feature at the centre of a vast vortex that rotates around the pole, and is possibly associated with rapid downwelling. The polar cold collar is a wide, shallow river of cold air that circulates around the polar vortex. One outstanding question has been whether the global circulation was symmetric, such that a dipole feature existed at the south pole. Here we report observations of Venus' south-polar region, where we have seen clouds with morphology much like those around the north pole, but rotating somewhat faster than the northern dipole. The vortex may extend down to the lower cloud layers that lie at about 50 km height and perhaps deeper. The spectroscopic properties of the clouds around the south pole are compatible with a sulphuric acid composition. 相似文献
89.
Diaconescu B Pohl K Vattuone L Savio L Hofmann P Silkin VM Pitarke JM Chulkov EV Echenique PM Farías D Rocca M 《Nature》2007,448(7149):57-59
Nearly two-dimensional (2D) metallic systems formed in charge inversion layers and artificial layered materials permit the existence of low-energy collective excitations, called 2D plasmons, which are not found in a three-dimensional (3D) metal. These excitations have caused considerable interest because their low energy allows them to participate in many dynamical processes involving electrons and phonons, and because they might mediate the formation of Cooper pairs in high-transition-temperature superconductors. Metals often support electronic states that are confined to the surface, forming a nearly 2D electron-density layer. However, it was argued that these systems could not support low-energy collective excitations because they would be screened out by the underlying bulk electrons. Rather, metallic surfaces should support only conventional surface plasmons-higher-energy modes that depend only on the electron density. Surface plasmons have important applications in microscopy and sub-wavelength optics, but have no relevance to the low-energy dynamics. Here we show that, in contrast to expectations, a low-energy collective excitation mode can be found on bare metal surfaces. The mode has an acoustic (linear) dispersion, different to the dependence of a 2D plasmon, and was observed on Be(0001) using angle-resolved electron energy loss spectroscopy. First-principles calculations show that it is caused by the coexistence of a partially occupied quasi-2D surface-state band with the underlying 3D bulk electron continuum and also that the non-local character of the dielectric function prevents it from being screened out by the 3D states. The acoustic plasmon reported here has a very general character and should be present on many metal surfaces. Furthermore, its acoustic dispersion allows the confinement of light on small surface areas and in a broad frequency range, which is relevant for nano-optics and photonics applications. 相似文献
90.
In 2005, plumes were detected near the south polar region of Enceladus, a small icy satellite of Saturn. Observations of the south pole revealed large rifts in the crust, informally called 'tiger stripes', which exhibit higher temperatures than the surrounding terrain and are probably sources of the observed eruptions. Models of the ultimate interior source for the eruptions are under consideration. Other models of an expanding plume require eruptions from discrete sources, as well as less voluminous eruptions from a more extended source, to match the observations. No physical mechanism that matches the observations has been identified to control these eruptions. Here we report a mechanism in which temporal variations in tidal stress open and close the tiger-stripe rifts, governing the timing of eruptions. During each orbit, every portion of each tiger stripe rift spends about half the time in tension, which allows the rift to open, exposing volatiles, and allowing eruptions. In a complementary process, periodic shear stress along the rifts also generates heat along their lengths, which has the capacity to enhance eruptions. Plume activity is expected to vary periodically, affecting the injection of material into Saturn's E ring and its formation, evolution and structure. Moreover, the stresses controlling eruptions imply that Enceladus' icy shell behaves as a thin elastic layer, perhaps only a few tens of kilometres thick. 相似文献