302 research outputs found
Specificity of Association between Paenibacillus spp. and the Entomopathogenic Nematodes, Heterorhabditis spp.
Endospore-forming bacteria, Paenibacillus spp., have
recently been isolated in association with insect pathogenic
nematodes Heterorhabditis spp. Sporangia adhere
to nematode infective juveniles (J3) and are carried
with them into insects. Paenibacillus proliferates in the
killed insect along with Heterorhabditis and its obligate
bacterial symbiont, Photorhabdus, despite the antibiotic
production of the latter. Nematode infective juveniles
leave the insect cadaver with Paenibacillus sporangia
attached. The specificity of the relationship between
Paenibacillus and Heterorhabditis was investigated.
Sporangia of nematode-associated Paenibacillus adhered
to infective juveniles (but not other stages) of all Heterorhabditis species tested, and to infective juveniles of vertebrate parasitic Strongylida species, but not to a
variety of other soil nematodes tested. Paenibacillus
species that were not isolated from nematodes, but
were phylogenetically close to the nematode-associated
strains, did not adhere to Heterorhabditis, and they
were also sensitive to Photorhabdus antibiotics in vitro,
whereas the nematode-associated strains were not.
Unusual longevity of the sporangium and resistance to
Photorhabdus antibiotics may represent specific adaptations
of the nematode-associated Paenibacillus strains
to allow them to coexist with and be transported by
Heterorhabditis. Adaptation to specific Heterorhabditis-
Photorhabdus strains is evident among the three nematode-
associated Paenibacillus strains (each from a different
nematode strain). Paenibacillus NEM1a and
NEM3 each developed best in cadavers with the nematode
from which it was isolated and not at all with the
nematode associate of the other strain. Differences between
nematode-associated Paenibacillus strains in
cross-compatibility with the various Heterorhabditis
strains in cadavers could not be explained by differential
sensitivity to antibiotics produced by the nematodes'
Photorhabdus symbionts in vitro
Specificity of Association between Paenibacillus spp. and the Entomopathogenic Nematodes, Heterorhabditis spp.
Endospore-forming bacteria, Paenibacillus spp., have
recently been isolated in association with insect pathogenic
nematodes Heterorhabditis spp. Sporangia adhere
to nematode infective juveniles (J3) and are carried
with them into insects. Paenibacillus proliferates in the
killed insect along with Heterorhabditis and its obligate
bacterial symbiont, Photorhabdus, despite the antibiotic
production of the latter. Nematode infective juveniles
leave the insect cadaver with Paenibacillus sporangia
attached. The specificity of the relationship between
Paenibacillus and Heterorhabditis was investigated.
Sporangia of nematode-associated Paenibacillus adhered
to infective juveniles (but not other stages) of all Heterorhabditis species tested, and to infective juveniles of vertebrate parasitic Strongylida species, but not to a
variety of other soil nematodes tested. Paenibacillus
species that were not isolated from nematodes, but
were phylogenetically close to the nematode-associated
strains, did not adhere to Heterorhabditis, and they
were also sensitive to Photorhabdus antibiotics in vitro,
whereas the nematode-associated strains were not.
Unusual longevity of the sporangium and resistance to
Photorhabdus antibiotics may represent specific adaptations
of the nematode-associated Paenibacillus strains
to allow them to coexist with and be transported by
Heterorhabditis. Adaptation to specific Heterorhabditis-
Photorhabdus strains is evident among the three nematode-
associated Paenibacillus strains (each from a different
nematode strain). Paenibacillus NEM1a and
NEM3 each developed best in cadavers with the nematode
from which it was isolated and not at all with the
nematode associate of the other strain. Differences between
nematode-associated Paenibacillus strains in
cross-compatibility with the various Heterorhabditis
strains in cadavers could not be explained by differential
sensitivity to antibiotics produced by the nematodes'
Photorhabdus symbionts in vitro
The Nakhlites Sample Multiple Igneous Units: Evidence From 40Ar/39Ar Chronology And Geochemistry
No abstract available
Anomalous rotational properties of Bose-Einstein condensates in asymmetric traps
We study the rotational properties of a Bose-Einstein condensate confined in
a rotating harmonic trap for different trap anisotropies. Using simple
arguments, we derive expressions for the velocity field of the quantum fluid
for condensates with or without vortices. While the condensed gas describes
open spiraling trajectories, on the frame of reference of the rotating trap the
motion of the fluid is against the trap rotation. We also find explicit
formulae for the angular momentum and a linear and Thomas-Fermi solutions for
the state without vortices. In these two limits we also find an analytic
relation between the shape of the cloud and the rotation speed. The predictions
are supported by numerical simulations of the mean field Gross-Pitaevskii
model.Comment: 4 RevTeX pages, 2 EPS figures; typos fixed, reference adde
Adiabatic Output Coupling of a Bose Gas at Finite Temperatures
We develop a general theory of adiabatic output coupling from trapped atomic
Bose-Einstein Condensates at finite temperatures. For weak coupling, the output
rate from the condensate, and the excited levels in the trap, settles in a time
proportional to the inverse of the spectral width of the coupling to the output
modes. We discuss the properties of the output atoms in the quasi-steady-state
where the population in the trap is not appreciably depleted. We show how the
composition of the output beam, containing condensate and thermal component,
may be controlled by changing the frequency of the output coupler. This
composition determines the first and second order coherence of the output beam.
We discuss the changes in the composition of the bose gas left in the trap and
show how nonresonant output coupling can stimulate either the evaporation of
thermal excitations in the trap or the growth of non-thermal excitations, when
pairs of correlated atoms leave the condensate.Comment: 22 pages, 6 Figs. To appear in Physical Review A All the typos from
the previous submission have been fixe
Solutions of Gross-Pitaevskii equations beyond the hydrodynamic approximation: Application to the vortex problem
We develop the multiscale technique to describe excitations of a
Bose-Einstein condensate (BEC) whose characteristic scales are comparable with
the healing length, thus going beyond the conventional hydrodynamical
approximation. As an application of the theory we derive approximate explicit
vortex and other solutions. The dynamical stability of the vortex is discussed
on the basis of the mathematical framework developed here, the result being
that its stability is granted at least up to times of the order of seconds,
which is the condensate lifetime. Our analytical results are confirmed by the
numerical simulations.Comment: To appear in Phys. Rev.
The role of apolipoprotein N-acyl transferase, Lnt, in the lipidation of factor H binding protein of Neisseria meningitidis strain MC58 and its potential as a drug target
BACKGROUND AND PURPOSE
The level of cell surface expression of the meningococcal vaccine antigen, Factor H binding protein (FHbp) varies between and within strains and this limits the breadth of strains that can be targeted by FHbp-based vaccines. The molecular pathway controlling expression of FHbp at the cell surface, including its lipidation, sorting to the outer membrane and export, and the potential regulation of this pathway have not been investigated until now. This knowledge will aid our evaluation of FHbp vaccines.
EXPERIMENTAL APPROACH
A meningococcal transposon library was screened by whole cell immuno-dot blotting using an anti-FHbp antibody to identify a mutant with reduced binding and the disrupted gene was determined.
KEY RESULTS
In a mutant with markedly reduced binding, the transposon was located in the lnt gene which encodes apolipoprotein N-acyl transferase, Lnt, responsible for the addition of the third fatty acid to apolipoproteins prior to their sorting to the outer membrane. We provide data indicating that in the Lnt mutant, FHbp is diacylated and its expression within the cell is reduced 10 fold, partly due to inhibition of transcription. Furthermore the Lnt mutant showed 64 fold and 16 fold increase in susceptibility to rifampicin and ciprofloxacin respectively.
CONCLUSION AND IMPLICATIONS
We speculate that the inefficient sorting of diacylated FHbp in the meningococcus results in its accumulation in the periplasm inducing an envelope stress response to down-regulate its expression. We propose Lnt as a potential novel drug target for combination therapy with antibiotics
Metabolome-wide association study on ABCA7 indicates a role of ceramide metabolism in Alzheimerâs disease
Genome-wide association studies (GWASs) have identified genetic loci associated with the risk of Alzheimerâs disease (AD), but the molecular mechanisms by which they confer risk are largely unknown. We conducted a metabolome-wide association study (MWAS) of AD-associated loci from GWASs using untargeted metabolic profiling (metabolomics) by ultraperformance liquid chromatographyâmass spectrometry (UPLC-MS). We identified an association of lactosylceramides (LacCer) with AD-related single-nucleotide polymorphisms (SNPs) in ABCA7 (P = 5.0 Ă 10â5 to 1.3 Ă 10â44). We showed that plasma LacCer concentrations are associated with cognitive performance and genetically modified levels of LacCer are associated with AD risk. We then showed that concentrations of sphingomyelins, ceramides, and hexosylceramides were altered in brain tissue from Abca7 knockout mice, compared with wild type (WT) (P = 0.049â1.4 Ă 10â5), but not in a mouse model of amyloidosis. Furthermore, activation of microglia increases intracellular concentrations of hexosylceramides in part through induction in the expression of sphingosine kinase, an enzyme with a high control coefficient for sphingolipid and ceramide synthesis. Our work suggests that the risk for AD arising from functional variations in ABCA7 is mediated at least in part through ceramides. Modulation of their metabolism or downstream signaling may offer new therapeutic opportunities for AD
Dark soliton states of Bose-Einstein condensates in anisotropic traps
Dark soliton states of Bose-Einstein condensates in harmonic traps are
studied both analytically and computationally by the direct solution of the
Gross-Pitaevskii equation in three dimensions. The ground and self-consistent
excited states are found numerically by relaxation in imaginary time. The
energy of a stationary soliton in a harmonic trap is shown to be independent of
density and geometry for large numbers of atoms. Large amplitude field
modulation at a frequency resonant with the energy of a dark soliton is found
to give rise to a state with multiple vortices. The Bogoliubov excitation
spectrum of the soliton state contains complex frequencies, which disappear for
sufficiently small numbers of atoms or large transverse confinement. The
relationship between these complex modes and the snake instability is
investigated numerically by propagation in real time.Comment: 11 pages, 8 embedded figures (two in color
Stabilization and pumping of giant vortices in dilute Bose-Einstein condensates
Recently, it was shown that giant vortices with arbitrarily large quantum
numbers can possibly be created in dilute Bose-Einstein condensates by
cyclically pumping vorticity into the condensate. However, multiply quantized
vortices are typically dynamically unstable in harmonically trapped nonrotated
condensates, which poses a serious challenge to the vortex pump procedure. In
this theoretical study, we investigate how the giant vortices can be stabilized
by the application of a Gaussian potential peak along the vortex core. We find
that achieving dynamical stability is feasible up to high quantum numbers. To
demonstrate the efficiency of the stabilization method, we simulate the
adiabatic creation of an unsplit 20-quantum vortex with the vortex pump.Comment: 8 pages, 6 figures; to be published in J. Low Temp. Phys., online
publication available at http://dx.doi.org/10.1007/s10909-010-0216-
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