104 research outputs found
Resolution of Conflicting Signals at the Single-Cell Level in the Regulation of Cyanobacterial Photosynthesis and Nitrogen Fixation
Unicellular, diazotrophic cyanobacteria temporally separate dinitrogen (N-2) fixation and photosynthesis to prevent inactivation of the nitrogenase by oxygen. This temporal segregation is regulated by a circadian clock with oscillating activities of N-2 fixation in the dark and photosynthesis in the light. On the population level, this separation is not always complete, since the two processes can overlap during transitions from dark to light. How do single cells avoid inactivation of nitrogenase during these periods? One possibility is that phenotypic heterogeneity in populations leads to segregation of the two processes. Here, we measured N-2 fixation and photosynthesis of individual cells using nanometer-scale secondary ion mass spectrometry (nanoSIMS) to assess both processes in a culture of the unicellular, diazotrophic cyanobacterium Crocosphaera watsonii during a dark-light and a continuous light phase. We compared single-cell rates with bulk rates and gene expression profiles. During the regular dark and light phases, C. watsonii exhibited the temporal segregation of N-2 fixation and photosynthesis commonly observed. However, N-2 fixation and photosynthesis were concurrently measurable at the population level during the subjective dark phase in which cells were kept in the light rather than returned to the expected dark phase. At the single-cell level, though, cells discriminated against either one of the two processes. Cells that showed high levels of photosynthesis had low nitrogen fixing activities, and vice versa. These results suggest that, under ambiguous environmental signals, single cells discriminate against either photosynthesis or nitrogen fixation, and thereby might reduce costs associated with running incompatible processes in the same cell
Determinação da dimensão vertical de oclusão em prótese total: revisão de literatura e relato de caso clínico
A busca por métodos e técnicas na determinação de um correto relacionamento maxilomandibular são alvos de diversas discussões na literatura, pois o seu restabelecimento inadequado pode levar ao insucesso de todo o trabalho protético. A reabilitação oral com próteses totais tem por função oferecer conforto ao paciente, permitindo que ele possa falar sem impedimentos, mastigar de forma eficiente, ter uma posição de repouso e, além disso, estar adequadamente bem construída considerando os fatores estéticos. Assim, o objetivo deste trabalho foi o de abordar a importância da tomada correta da dimensão vertical de oclusão, bem como apresentar algumas das principais técnicas para determinação da dimensão vertical de oclusão e representá-las a partir de um relato de caso clínico de um paciente edêntulo. Conclui-se que não existe um método ou alguns métodos que possam ser os mais indicados para se conseguir a perfeição estética do paciente e o seu conforto, mas sim o uso de diversos métodos.
Nitrogen fixation and transfer in open ocean diatom–cyanobacterial symbioses
Many diatoms that inhabit low-nutrient waters of the open ocean live in close association with cyanobacteria. Some of these associations are believed to be mutualistic, where N2-fixing cyanobacterial symbionts provide N for the diatoms. Rates of N2 fixation by symbiotic cyanobacteria and the N transfer to their diatom partners were measured using a high-resolution nanometer scale secondary ion mass spectrometry approach in natural populations. Cell-specific rates of N2 fixation (1.15–71.5 fmol N per cell h−1) were similar amongst the symbioses and rapid transfer (within 30 min) of fixed N was also measured. Similar growth rates for the diatoms and their symbionts were determined and the symbiotic growth rates were higher than those estimated for free-living cells. The N2 fixation rates estimated for Richelia and Calothrix symbionts were 171–420 times higher when the cells were symbiotic compared with the rates estimated for the cells living freely. When combined, the latter two results suggest that the diatom partners influence the growth and metabolism of their cyanobacterial symbionts. We estimated that Richelia fix 81–744% more N than needed for their own growth and up to 97.3% of the fixed N is transferred to the diatom partners. This study provides new information on the mechanisms controlling N input into the open ocean by symbiotic microorganisms, which are widespread and important for oceanic primary production. Further, this is the first demonstration of N transfer from an N2 fixer to a unicellular partner. These symbioses are important models for molecular regulation and nutrient exchange in symbiotic systems
Multidifferential study of identified charged hadron distributions in -tagged jets in proton-proton collisions at 13 TeV
Jet fragmentation functions are measured for the first time in proton-proton
collisions for charged pions, kaons, and protons within jets recoiling against
a boson. The charged-hadron distributions are studied longitudinally and
transversely to the jet direction for jets with transverse momentum 20 GeV and in the pseudorapidity range . The
data sample was collected with the LHCb experiment at a center-of-mass energy
of 13 TeV, corresponding to an integrated luminosity of 1.64 fb. Triple
differential distributions as a function of the hadron longitudinal momentum
fraction, hadron transverse momentum, and jet transverse momentum are also
measured for the first time. This helps constrain transverse-momentum-dependent
fragmentation functions. Differences in the shapes and magnitudes of the
measured distributions for the different hadron species provide insights into
the hadronization process for jets predominantly initiated by light quarks.Comment: All figures and tables, along with machine-readable versions and any
supplementary material and additional information, are available at
https://cern.ch/lhcbproject/Publications/p/LHCb-PAPER-2022-013.html (LHCb
public pages
Study of the decay
The decay is studied
in proton-proton collisions at a center-of-mass energy of TeV
using data corresponding to an integrated luminosity of 5
collected by the LHCb experiment. In the system, the
state observed at the BaBar and Belle experiments is
resolved into two narrower states, and ,
whose masses and widths are measured to be where the first uncertainties are statistical and the second
systematic. The results are consistent with a previous LHCb measurement using a
prompt sample. Evidence of a new
state is found with a local significance of , whose mass and width
are measured to be and , respectively. In addition, evidence of a new decay mode
is found with a significance of
. The relative branching fraction of with respect to the
decay is measured to be , where the first
uncertainty is statistical, the second systematic and the third originates from
the branching fractions of charm hadron decays.Comment: All figures and tables, along with any supplementary material and
additional information, are available at
https://cern.ch/lhcbproject/Publications/p/LHCb-PAPER-2022-028.html (LHCb
public pages
Measurement of the ratios of branching fractions and
The ratios of branching fractions
and are measured, assuming isospin symmetry, using a
sample of proton-proton collision data corresponding to 3.0 fb of
integrated luminosity recorded by the LHCb experiment during 2011 and 2012. The
tau lepton is identified in the decay mode
. The measured values are
and
, where the first uncertainty is
statistical and the second is systematic. The correlation between these
measurements is . Results are consistent with the current average
of these quantities and are at a combined 1.9 standard deviations from the
predictions based on lepton flavor universality in the Standard Model.Comment: All figures and tables, along with any supplementary material and
additional information, are available at
https://cern.ch/lhcbproject/Publications/p/LHCb-PAPER-2022-039.html (LHCb
public pages
Enrichment in <sup>15</sup>N (color scale: <sup>15</sup>N/<sup>14</sup>N) due to N<sub>2</sub> fixation by individual <i>C.</i><i>watsonii</i> cells.
<p>A. Regular dark phase. B. Regular light phase. C. Subjective dark phase. D. Subjective light phase. (Scale bars: 5 µm in A, C and D, 2 µm in B). E–H. Secondary electron images (complementary to A–D.) which are simultaneously recorded during the measurement and showing the individual cells. The aggregation of cells was an artifact of filtration; the <i>C. watsonii</i> cells are unicellular (as per microscopic observation), however, gather in trenches upon filtration due to the unevenness of the filtration devices at the micrometer scale.</p
<sup>15</sup>N<sub>2</sub> fixation and photosynthesis (NaH<sup>13</sup>CO<sub>3</sub> uptake) rates as calculated from the isotopic enrichment of individual cells (each symbol represents one individual cell).
<p>The corresponding dark or light phase is indicated in the upper right corner of each panel. The large variability in the <sup>13</sup>C signal/photosynthesis for the regular dark phase is due to the precision of the nanoSIMS measurement combined with the low labeling during the non-photosynthetic phase.</p
Gene expression analysis shown as enrichment factor of relative transcript abundance.
<p>The genes are indicated in the top right corner of each panel. Filled circles represent the experimental data during the 48 h phase. The grey bars indicate the regular dark phase and the striped grey bars indicate the subjective dark phase. Symbols and error bars represent mean ± SE of triplicate cultures.</p
Summary of single-cell photosynthesis (DIC uptake) and N<sub>2</sub> fixation rates.
<p>Values are in fmol C and N cell<sup>−1</sup> h<sup>−1</sup> for DIC uptake and N<sub>2</sub> fixation, respectively, and represent mean ± SD.</p>*<p>significantly different from all other phases, all other phases are not significantly different from each other.</p>†<p>not significantly different from each other, but from <sup>‡.</sup></p>‡<p>not significantly different from each other, but from <sup>†.</sup></p
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