2,112 research outputs found
Photosynthesis is widely distributed among Proteobacteria as demonstrated by the phylogeny of PufLM reaction center proteins
Two different photosystems for performing bacteriochlorophyll-mediated photosynthetic energy conversion are employed in different bacterial phyla. Those bacteria employing a photosystem II type of photosynthetic apparatus include the phototrophic purple bacteria (Proteobacteria), Gemmatimonas and Chloroflexus with their photosynthetic relatives. The proteins of the photosynthetic reaction center PufL and PufM are essential components and are common to all bacteria with a type-II photosynthetic apparatus, including the anaerobic as well as the aerobic phototrophic Proteobacteria. Therefore, PufL and PufM proteins and their genes are perfect tools to evaluate the phylogeny of the photosynthetic apparatus and to study the diversity of the bacteria employing this photosystem in nature. Almost complete pufLM gene sequences and the derived protein sequences from 152 type strains and 45 additional strains of phototrophic Proteobacteria employing photosystem II were compared. The results give interesting and comprehensive insights into the phylogeny of the photosynthetic apparatus and clearly define Chromatiales, Rhodobacterales, Sphingomonadales as major groups distinct from other Alphaproteobacteria, from Betaproteobacteria and from Caulobacterales (Brevundimonas subvibrioides). A special relationship exists between the PufLM sequences of those bacteria employing bacteriochlorophyll b instead of bacteriochlorophyll a. A clear phylogenetic association of aerobic phototrophic purple bacteria to anaerobic purple bacteria according to their PufLM sequences is demonstrated indicating multiple evolutionary lines from anaerobic to aerobic phototrophic purple bacteria. The impact of pufLM gene sequences for studies on the environmental diversity of phototrophic bacteria is discussed and the possibility of their identification on the species level in environmental samples is pointed out. © 2018 Imhoff, Rahn, Künzel and Neulinger
Positionally dependent ^(15)N fraction factors in the UV photolysis of N_2O determined by high resolution FTIR spectroscopy
Positionally dependent fractionation factors for the photolysis of isotopomers of N_2O in natural abundance have been determined by high resolution FTIR spectroscopy at three photolysis wavelengths. Fractionation factors show clear 15N position and photolysis wavelength dependence and are in qualitative agreement with theoretical models but are twice as large. The fractionation factors increase with photolysis wavelength from 193 to 211 nm, with the fractionation factors at 207.6 nm for ^(14)N^(15)N^916)O, ^(15)N^(14)N^(16)O and ^(14)N^(14)N^(18)O equal to −66.5±5‰,−27.1±6‰ and −49±10‰, respectively
Spin resonance in the superconducting state of LiFeODFeSe observed by neutron spectroscopy
We have performed inelastic neutron scattering measurements on a powder
sample of the superconductor lithium iron selenide hydroxide
LiFeODFeSe (, \,K). The spectrum shows an enhanced intensity below over an
energy range , where is the
superconducting gap, with maxima at the wave vectors \,\AA and \,\AA. The behavior of this
feature is consistent with the spin resonance mode found in other
unconventional superconductors, and strongly resembles the spin resonance
observed in the spectrum of the molecular-intercalated iron selenide,
Li(ND)(ND)FeSe. The signal can
be described with a characteristic two-dimensional wave vector
in the Brillouin zone of the iron square lattice, consistent with the nesting
vector between electron Fermi sheets
Fluid Simulations of Three-Dimensional Reconnection that Capture the Lower-Hybrid Drift Instability
Fluid models that approximate kinetic effects have received attention
recently in the modelling of large scale plasmas such as planetary
magnetospheres. In three-dimensional reconnection, both reconnection itself and
current sheet instabilities need to be represented appropriately. We show that
a heat flux closure based on pressure gradients enables a ten moment fluid
model to capture key properties of the lower-hybrid drift instability (LHDI)
within a reconnection simulation. Characteristics of the instability are
examined with kinetic and fluid continuum models, and its role in the
three-dimensional reconnection simulation is analysed. The saturation level of
the electromagnetic LHDI is higher than expected which leads to strong kinking
of the current sheet. Therefore, the magnitude of the initial perturbation has
significant impact on the resulting turbulence.Comment: 20 pages, 9 figure
Bioenergetic Profiling of Zebrafish Embryonic Development
Many debilitating conditions are linked to bioenergetic defects. Developing screens to probe the genetic and/or chemical basis for such links has proved intractable. Furthermore, there is a need for a physiologically relevant assay of bioenergetics in whole organisms, especially for early stages in life where perturbations could increase disease susceptibility with aging. Thus, we asked whether we could screen bioenergetics and mitochondrial function in the developing zebrafish embryo. We present a multiplexed method to assay bioenergetics in zebrafish embryos from the blastula period (3 hours post-fertilization, hpf) through to hatching (48 hpf). In proof of principle experiments, we measured respiration and acid extrusion of developing zebrafish embryos. We quantified respiratory coupling to various bioenergetic functions by using specific pharmacological inhibitors of bioenergetic pathways. We demonstrate that changes in the coupling to ATP turnover and proton leak are correlated with developmental stage. The multiwell format of this assay enables the user to screen for the effects of drugs and environmental agents on bioenergetics in the zebrafish embryo with high sensitivity and reproducibility
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