637 research outputs found
Unexpected Transcripts in Tn7 orf19.2646 C. albicans Mutant Lead to Low Fungal Burden Phenotype In vivo.
The commensal fungus Candida albicans is the major cause of fungal systemic infection in immuno-compromised patients, with a mortality rate approaching 50% in the case of bloodstream infections. There is therefore a clear need to better understand fungal biology during infection to improve treatment. One of the particularities of C. albicans is its capacity to adapt to drastically diverse environments such as brain, bloodstream or gut. Adaptations to environmental change are mediated by transcription factors (TF) that modulate the expression of their target genes. Previous screening of a collection of Tn7 C. albicans TF mutants in vivo identified orf19.2646 as playing a crucial role in the ability of the fungus to survive within its host. Indeed, the orf19.2646 Tn7 interruption mutant strain displayed a reduced fungal burden compared to the wild-type strain. Surprisingly, an independent deletion mutant did not recapitulate the phenotype of the Tn7 interruption mutant. In the present study, we therefore investigated the difference between these two mutants and determined by performing a RACE analysis whether unexpected transcripts of the Tn7 mutant occurred. We found that two such transcripts upstream and downstream of the Tn7 insertion site were produced. The two transcripts were expressed in an orf19.2646 deletion mutant which displayed a significantly reduced fungal burden level compared to the wild-type in G. mellonella. When the regions corresponding to these transcripts were deleted in the Tn7 mutants, the strains lacking both regions displayed a fungal burden similar to that of the wild-type strain. This study shows for the first time that mRNA transcription may occur downstream of a Tn7 sequence. In addition, these results demonstrated that the low fungal burden phenotype observed in the orf19.2646 Tn7 mutant is due to the presence of these two transcripts together participating to an unidentified virulence mechanism to be further elucidated
Exploring the Atmosphere of Neoproterozoic Earth: The Effect of O on Haze Formation and Composition
Previous studies of haze formation in the atmosphere of the Early Earth have
focused on N/CO/CH atmospheres. Here, we experimentally
investigate the effect of O on the formation and composition of aerosols
to improve our understanding of haze formation on the Neoproterozoic Earth. We
obtained in situ size, particle density, and composition measurements of
aerosol particles produced from N/CO/CH/O gas mixtures
subjected to FUV radiation (115-400 nm) for a range of initial
CO/CH/O mixing ratios (O ranging from 2 ppm to 0.2\%).
At the lowest O concentration (2 ppm), the addition increased particle
production for all but one gas mixture. At higher oxygen concentrations (20 ppm
and greater) particles are still produced, but the addition of O
decreases the production rate. Both the particle size and number density
decrease with increasing O, indicating that O affects particle
nucleation and growth. The particle density increases with increasing O.
The addition of CO and O not only increases the amount of oxygen in
the aerosol, but it also increases the degree of nitrogen incorporation. In
particular, the addition of O results in the formation of nitrate bearing
molecules. The fact that the presence of oxygen bearing molecules increases the
efficiency of nitrogen fixation has implications for the role of haze as a
source of molecules required for the origin and evolution of life. The
composition changes also likely affect the absorption and scattering behavior
of these particles but optical properties measurements are required to fully
understand the implications for the effect on the planetary radiative energy
balance and climate.Comment: 15 pages, 3 tables, 8 figures, accepted in Astrophysical Journa
Universality of Probability Distributions Among Two-Dimensional Turbulent Flows
We study statistical properties of two-dimensional turbulent flows. Three
systems are considered: the Navier-Stokes equation, surface quasi-geostrophic
flow, and a model equation for thermal convection in the Earth's mantle. Direct
numerical simulations are used to determine 1-point fluctuation properties.
Comparative study shows universality of probability density functions (PDFs)
across different types of flow. Especially for the derivatives of the
``advected'' quantity, the shapes of the PDFs are the same for the three flows,
once normalized by the average size of fluctuations. Theoretical models for the
shape of PDFs are briefly discussed.Comment: 5 pages, 7 figure
The Relative Humidity in an Isentropic Advection–Condensation Model: Limited Poleward Influence and Properties of Subtropical Minima
An idealized model of advection and condensation of water vapor is considered as a representation of processes influencing the humidity distribution along isentropic surfaces in the free troposphere. Results are presented for how the mean relative humidity distribution varies in response to changes in the distribution of saturation specific humidity and in the amplitude of a tropical moisture source. Changes in the tropical moisture source are found to have little effect on the relative humidity poleward of the subtropical minima, suggesting a lack of poleward influence despite much greater water vapor concentrations at lower latitudes. The subtropical minima in relative humidity are found to be located just equatorward of the inflection points of the saturation specific humidity profile along the isentropic surface. The degree of mean subsaturation is found to vary with the magnitude of the meridional gradient of saturation specific humidity when other parameters are held fixed.
The atmospheric relevance of these results is investigated by comparison with the positions of the relative humidity minima in reanalysis data and by examining poleward influence of relative humidity in simulations with an idealized general circulation model. It is suggested that the limited poleward influence of relative humidity may constrain the propagation of errors in simulated humidity fields
Disorganized attachment in adolescence: Emotional and physiological dysregulation during the Friends and Family Interview and a conflict interaction.
The current study examined the effects of attachment on autonomy, relatedness, and emotion regulation during an attachment interview (Friends and Family Interview; FFI) and a Parent×Child Conflict interaction (Family Interaction Task; FIT) in 49 adolescents (11 to 17 years old). Disorganized adolescents displayed behaviors promoting autonomy and relatedness less frequently and at a lower extent than organized ones in the FIT with mothers but not with fathers. Disorganized adolescents also showed a steeper decrease in heart rate variability (HRV) than organized ones, during both the FFI and the FITs. Moreover, disorganized adolescents responded with a more marked increase in skin conductance level to the FIT with mothers than organized individuals. Dismissing adolescents showed behaviors promoting autonomy and relatedness less frequently and to a lesser extent than secure ones, while displaying more often behaviors undermining autonomy and relatedness in the FITs. Dismissing adolescents also showed a more pronounced decrease in HRV during the FFI than secure and preoccupied individuals; no differences were found between these groups in HRV during the FITs. The results suggest that disorganized adolescents had more difficulties in regulating their emotions during both the FFI and the FITs, whereas dismissing individuals seemed effectively challenged only during the interview
Cluster Dynamics of Planetary Waves
The dynamics of nonlinear atmospheric planetary waves is determined by a
small number of independent wave clusters consisting of a few connected
resonant triads. We classified the different types of connections between
neighboring triads that determine the general dynamics of a cluster. Each
connection type corresponds to substantially different scenarios of energy flux
among the modes. The general approach can be applied directly to various
mesoscopic systems with 3-mode interactions, encountered in hydrodynamics,
astronomy, plasma physics, chemistry, medicine, etc.Comment: 6 pages, 3 figs, EPL, publishe
Increased insolation threshold for runaway greenhouse processes on Earth like planets
Because the solar luminosity increases over geological timescales, Earth
climate is expected to warm, increasing water evaporation which, in turn,
enhances the atmospheric greenhouse effect. Above a certain critical
insolation, this destabilizing greenhouse feedback can "runaway" until all the
oceans are evaporated. Through increases in stratospheric humidity, warming may
also cause oceans to escape to space before the runaway greenhouse occurs. The
critical insolation thresholds for these processes, however, remain uncertain
because they have so far been evaluated with unidimensional models that cannot
account for the dynamical and cloud feedback effects that are key stabilizing
features of Earth's climate. Here we use a 3D global climate model to show that
the threshold for the runaway greenhouse is about 375 W/m, significantly
higher than previously thought. Our model is specifically developed to quantify
the climate response of Earth-like planets to increased insolation in hot and
extremely moist atmospheres. In contrast with previous studies, we find that
clouds have a destabilizing feedback on the long term warming. However,
subsident, unsaturated regions created by the Hadley circulation have a
stabilizing effect that is strong enough to defer the runaway greenhouse limit
to higher insolation than inferred from 1D models. Furthermore, because of
wavelength-dependent radiative effects, the stratosphere remains cold and dry
enough to hamper atmospheric water escape, even at large fluxes. This has
strong implications for Venus early water history and extends the size of the
habitable zone around other stars.Comment: Published in Nature. Online publication date: December 12, 2013.
Accepted version before journal editing and with Supplementary Informatio
Detecting barriers to transport: A review of different techniques
We review and discuss some different techniques for describing local
dispersion properties in fluids. A recent Lagrangian diagnostics, based on the
Finite Scale Lyapunov Exponent (FSLE), is presented and compared to the Finite
Time Lyapunov Exponent (FTLE), and to the Okubo-Weiss (OW) and Hua-Klein (HK)
criteria. We show that the OW and HK are a limiting case of the FTLE, and that
the FSLE is the most efficient method for detecting the presence of
cross-stream barriers. We illustrate our findings by considering two examples
of geophysical interest: a kinematic meandering jet model, and Lagrangian
tracers advected by stratospheric circulation.Comment: 15 pages, 9 figures, submitted to Physica
Precision Measurements of Stretching and Compression in Fluid Mixing
The mixing of an impurity into a flowing fluid is an important process in
many areas of science, including geophysical processes, chemical reactors, and
microfluidic devices. In some cases, for example periodic flows, the concepts
of nonlinear dynamics provide a deep theoretical basis for understanding
mixing. Unfortunately, the building blocks of this theory, i.e. the fixed
points and invariant manifolds of the associated Poincare map, have remained
inaccessible to direct experimental study, thus limiting the insight that could
be obtained. Using precision measurements of tracer particle trajectories in a
two-dimensional fluid flow producing chaotic mixing, we directly measure the
time-dependent stretching and compression fields. These quantities, previously
available only numerically, attain local maxima along lines coinciding with the
stable and unstable manifolds, thus revealing the dynamical structures that
control mixing. Contours or level sets of a passive impurity field are found to
be aligned parallel to the lines of large compression (unstable manifolds) at
each instant. This connection appears to persist as the onset of turbulence is
approached.Comment: 5 pages, 5 figure
Turbulent spectrum of the Earth's ozone field
The Total Ozone Mapping Spectrometer (TOMS) database is subjected to an
analysis in terms of the Karhunen-Loeve (KL) empirical eigenfunctions. The
concentration variance spectrum is transformed into a wavenumber spectrum, . In terms of wavenumber is shown to be in the
inverse cascade regime, in the enstrophy cascade regime with the
spectral {\it knee} at the wavenumber of barotropic instability.The spectrum is
related to known geophysical phenomena and shown to be consistent with physical
dimensional reasoning for the problem. The appropriate Reynolds number for the
phenomena is .Comment: RevTeX file, 4 pages, 4 postscript figures available upon request
from Richard Everson <[email protected]
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