1,511 research outputs found
Simultaneous Effects of Light Intensity and Phosphorus Supply on the Sterol Content of Phytoplankton
Sterol profiles of microalgae and their change with environmental conditions are of great interest in ecological food web research and taxonomic studies alike. Here, we investigated effects of light intensity and phosphorus supply on the sterol content of phytoplankton and assessed potential interactive effects of these important environmental factors on the sterol composition of algae. We identified sterol contents of four common phytoplankton genera, Scenedesmus, Chlamydomonas, Cryptomonas and Cyclotella, and analysed the change in sterol content with varying light intensities in both a high-phosphorus and a low-phosphorus approach. Sterol contents increased significantly with increasing light in three out of four species. Phosphorus-limitation reversed the change of sterol content with light intensity, i.e., sterol content decreased with increasing light at low phosphorus supply. Generally sterol contents were lower in low-phosphorus cultures. In conclusion, both light and phosphorus conditions strongly affect the sterol composition of algae and hence should be considered in ecological and taxonomic studies investigating the biochemical composition of algae. Data suggest a possible sterol limitation of growth and reproduction of herbivorous crustacean zooplankton during summer when high light intensities and low phosphorus supply decrease sterol contents of algae
Conservation of the role of INNER NO OUTER in development of unitegmic ovules of the Solanaceae despite a divergence in protein function
The P-SlINO::SlINO-GFP transgene continues to be expressed after fertilization during the onset of fruit development. A-C: Ovules from P-SlINO::SlINO-GFP plants. D, E: Ovules from control plants. Images A (confocal) and B (DIC overlaid with GFP channel) show expression in the outer cell layer in an ovule post-anthesis. C-E are images of the surface cells of the integument of ovules taken from 3–4 mm fruits. C and D are images taken on an epifluorescence microscope (Axioplan) using a Chroma GFP filter set 41017 (Chroma, Bellows Falls, VT). E is a dark-field image of the same ovule in D. These images show expression is present in developing fruit. Scale bar in B represents 20 μm, scale bar in E represents 20 μm in C-E. (TIF 4435 kb
Involvement of Iron in Biofilm Formation by Staphylococcus aureus
Staphylococcus aureus is a human pathogen that forms biofilm on catheters and medical implants. The authors' earlier study established that 1,2,3,4,6-penta-O-galloyl-β-D-glucopyranose (PGG) inhibits biofilm formation by S. aureus by preventing the initial attachment of the cells to a solid surface and reducing the production of polysaccharide intercellular adhesin (PIA). Our cDNA microarray and MALDI-TOF mass spectrometric studies demonstrate that PGG treatment causes the expression of genes and proteins that are normally expressed under iron-limiting conditions. A chemical assay using ferrozine verifies that PGG is a strong iron chelator that depletes iron from the culture medium. This study finds that adding FeSO4 to a medium that contains PGG restores the biofilm formation and the production of PIA by S. aureus SA113. The requirement of iron for biofilm formation by S. aureus SA113 can also be verified using a semi-defined medium, BM, that contains an iron chelating agent, 2, 2′-dipyridyl (2-DP). Similar to the effect of PGG, the addition of 2-DP to BM medium inhibits biofilm formation and adding FeSO4 to BM medium that contains 2-DP restores biofilm formation. This study reveals an important mechanism of biofilm formation by S. aureus SA113
The genomes of two key bumblebee species with primitive eusocial organization
Background: The shift from solitary to social behavior is one of the major evolutionary transitions. Primitively eusocial bumblebees are uniquely placed to illuminate the evolution of highly eusocial insect societies. Bumblebees are also invaluable natural and agricultural pollinators, and there is widespread concern over recent population declines in some species. High-quality genomic data will inform key aspects of bumblebee biology, including susceptibility to implicated population viability threats. Results: We report the high quality draft genome sequences of Bombus terrestris and Bombus impatiens, two ecologically dominant bumblebees and widely utilized study species. Comparing these new genomes to those of the highly eusocial honeybee Apis mellifera and other Hymenoptera, we identify deeply conserved similarities, as well as novelties key to the biology of these organisms. Some honeybee genome features thought to underpin advanced eusociality are also present in bumblebees, indicating an earlier evolution in the bee lineage. Xenobiotic detoxification and immune genes are similarly depauperate in bumblebees and honeybees, and multiple categories of genes linked to social organization, including development and behavior, show high conservation. Key differences identified include a bias in bumblebee chemoreception towards gustation from olfaction, and striking differences in microRNAs, potentially responsible for gene regulation underlying social and other traits. Conclusions: These two bumblebee genomes provide a foundation for post-genomic research on these key pollinators and insect societies. Overall, gene repertoires suggest that the route to advanced eusociality in bees was mediated by many small changes in many genes and processes, and not by notable expansion or depauperation
Search for Kaluza-Klein Graviton Emission in Collisions at TeV using the Missing Energy Signature
We report on a search for direct Kaluza-Klein graviton production in a data
sample of 84 of \ppb collisions at = 1.8 TeV, recorded
by the Collider Detector at Fermilab. We investigate the final state of large
missing transverse energy and one or two high energy jets. We compare the data
with the predictions from a -dimensional Kaluza-Klein scenario in which
gravity becomes strong at the TeV scale. At 95% confidence level (C.L.) for
=2, 4, and 6 we exclude an effective Planck scale below 1.0, 0.77, and 0.71
TeV, respectively.Comment: Submitted to PRL, 7 pages 4 figures/Revision includes 5 figure
Measurement of the average time-integrated mixing probability of b-flavored hadrons produced at the Tevatron
We have measured the number of like-sign (LS) and opposite-sign (OS) lepton
pairs arising from double semileptonic decays of and -hadrons,
pair-produced at the Fermilab Tevatron collider. The data samples were
collected with the Collider Detector at Fermilab (CDF) during the 1992-1995
collider run by triggering on the existence of and candidates
in an event. The observed ratio of LS to OS dileptons leads to a measurement of
the average time-integrated mixing probability of all produced -flavored
hadrons which decay weakly, (stat.)
(syst.), that is significantly larger than the world average .Comment: 47 pages, 10 figures, 15 tables Submitted to Phys. Rev.
Measurement of Lifetime and Decay-Width Difference in B0s -> J/psi phi Decays
We measure the mean lifetime, tau=2/(Gamma_L+Gamma_H), and the width
difference, DeltaGamma=Gamma_L-Gamma_H, of the light and heavy mass eigenstates
of the B0s meson, B0sL and B0sH, in B0s -> J/psi phi decays using 1.7 fb^-1 of
data collected with the CDF II detector at the Fermilab Tevatron ppbar
collider. Assuming CP conservation, a good approximation for the B0s system in
the Standard Model, we obtain DeltaGamma = 0.076^+0.059_-0.063 (stat.) +- 0.006
(syst.) ps^-1 and tau = 1.52 +- 0.04 (stat.) +- 0.02 (syst.) ps, the most
precise measurements to date. Our constraints on the weak phase and DeltaGamma
are consistent with CP conservation.
Dedicated to the memory of our dear friend and colleague, Michael P. Schmid
Search for Pair Production of Scalar Top Quarks Decaying to a tau Lepton and a b Quark in ppbar Collisions at sqrt{s}=1.96 TeV
We search for pair production of supersymmetric top quarks (~t_1), followed
by R-parity violating decay ~t_1 -> tau b with a branching ratio beta, using
322 pb^-1 of ppbar collisions at sqrt{s}=1.96 TeV collected by the CDF II
detector at Fermilab. Two candidate events pass our final selection criteria,
consistent with the standard model expectation. We set upper limits on the
cross section sigma(~t_1 ~tbar_1)*beta^2 as a function of the stop mass
m(~t_1). Assuming beta=1, we set a 95% confidence level limit m(~t_1)>153
GeV/c^2. The limits are also applicable to the case of a third generation
scalar leptoquark (LQ_3) decaying LQ_3 -> tau b.Comment: 7 pages, 2 eps figure
Precision measurement of the top quark mass from dilepton events at CDF II
We report a measurement of the top quark mass, M_t, in the dilepton decay
channel of
using an integrated luminosity of 1.0 fb^{-1} of p\bar{p} collisions collected
with the CDF II detector. We apply a method that convolutes a leading-order
matrix element with detector resolution functions to form event-by-event
likelihoods; we have enhanced the leading-order description to describe the
effects of initial-state radiation. The joint likelihood is the product of the
likelihoods from 78 candidate events in this sample, which yields a measurement
of M_{t} = 164.5 \pm 3.9(\textrm{stat.}) \pm 3.9(\textrm{syst.})
\mathrm{GeV}/c^2, the most precise measurement of M_t in the dilepton channel.Comment: 7 pages, 2 figures, version includes changes made prior to
publication by journa
Cross Section Measurements of High- Dilepton Final-State Processes Using a Global Fitting Method
We present a new method for studying high- dilepton events
(, , ) and simultaneously
extracting the production cross sections of , , and p\bar{p} \to \ztt at a center-of-mass energy of TeV. We perform a likelihood fit to the dilepton data in a parameter
space defined by the missing transverse energy and the number of jets in the
event. Our results, which use of data recorded with the CDF
II detector at the Fermilab Tevatron Collider, are pb, pb, and
\sigma(\ztt) =291^{+50}_{-46} pb.Comment: 20 pages, 2 figures, to be submitted to PRD-R
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