438 research outputs found
Analysis of Six tonB Gene Homologs in Bacteroides Fragilis Revealed That tonB3 is Essential for Survival in Experimental Intestinal Colonization and Intra-Abdominal Infection
The opportunistic, anaerobic pathogen and commensal of the human large intestinal tract, Bacteroides fragilis strain 638R, contains six predicted TonB proteins, termed TonB1-6, four ExbBs orthologs, ExbB1-4, and five ExbDs orthologs, ExbD1-5. The inner membrane TonB/ExbB/ExbD complex harvests energy from the proton motive force (Îp), and the TonB C-terminal domain interacts with and transduces energy to outer membrane TonB-dependent transporters (TBDTs). However, TonBâs role in activating nearly one hundred TBDTs for nutrient acquisition in B. fragilis during intestinal colonization and extraintestinal infection has not been established. In this study, we show that growth was abolished in the ÎtonB3 mutant when heme, vitamin B(12), Fe(III)-ferrichrome, starch, mucin-glycans, or N-linked glycans were used as a substrate for growth in vitro. Genetic complementation of the ÎtonB3 mutant with the tonB3 gene restored growth on these substrates. The ÎtonB1, ÎtonB2, ÎtonB4, ÎtonB5, and ÎtonB6 single mutants did not show a growth defect. This indicates that there was no functional compensation for the lack of TonB3, and it demonstrates that TonB3, alone, drives the TBDTs involved in the transport of essential nutrients. The ÎtonB3 mutant had a severe growth defect in a mouse model of intestinal colonization compared to the parent strain. This intestinal growth defect was enhanced in the ÎtonB3 ÎtonB6 double mutant strain, which completely lost its ability to colonize the mouse intestinal tract compared to the parent strain. The ÎtonB1, ÎtonB2, ÎtonB4, and ÎtonB5 mutants did not significantly affect intestinal colonization. Moreover, the survival of the ÎtonB3 mutant strain was completely eradicated in a rat model of intra-abdominal infection. Taken together, these findings show that TonB3 was essential for survival in vivo. The genetic organization of tonB1, tonB2, tonB4, tonB5, and tonB6 gene orthologs indicates that they may interact with periplasmic and nonreceptor outer membrane proteins, but the physiological relevance of this has not been defined. Because anaerobic fermentation metabolism yields a lower Îp than aerobic respiration and B. fragilis has a reduced redox state in its periplasmic spaceâin contrast to an oxidative environment in aerobesâit remains to be determined if the diverse system of TonB/ExbB/ExbD orthologs encoded by B. fragilis have an increased sensitivity to PMF (relative to aerobic bacteria) to allow for the harvesting of energy under anaerobic conditions
Nicotinamide mononucleotide supplementation reverses vascular dysfunction and oxidative stress with aging in mice
We tested the hypothesis that supplementation of nicotinamide mononucleotide (NMN), a key NAD (+) intermediate, increases arterial SIRT1 activity and reverses ageâassociated arterial dysfunction and oxidative stress. Old control mice (OC) had impaired carotid artery endotheliumâdependent dilation (EDD) (60 ± 5% vs. 84 ± 2%), a measure of endothelial function, and nitric oxide (NO)âmediated EDD (37 ± 4% vs. 66 ± 6%), compared with young mice (YC). This ageâassociated impairment in EDD was restored in OC by the superoxide ([Formula: see text]) scavenger TEMPOL (82 ± 7%). OC also had increased aortic pulse wave velocity (aPWV, 464 ± 31 cm s(â1) vs. 337 ± 3 cm s(â1)) and elastic modulus (EM, 6407 ± 876 kPa vs. 3119 ± 471 kPa), measures of large elastic artery stiffness, compared with YC. OC had greater aortic [Formula: see text] production (2.0 ± 0.1 vs. 1.0 ± 0.1 AU), nitrotyrosine abundance (a marker of oxidative stress), and collagenâI, and reduced elastin and vascular SIRT1 activity, measured by the acetylation status of the p65 subunit of NFÎșB, compared with YC. Supplementation with NMN in old mice restored EDD (86 ± 2%) and NOâmediated EDD (61 ± 5%), reduced aPWV (359 ± 14 cm s(â1)) and EM (3694 ± 315 kPa), normalized [Formula: see text] production (0.9 ± 0.1 AU), decreased nitrotyrosine, reversed collagenâI, increased elastin, and restored vascular SIRT1 activity. Acute NMN incubation in isolated aortas increased NAD (+) threefold and manganese superoxide dismutase (MnSOD) by 50%. NMN supplementation may represent a novel therapy to restore SIRT1 activity and reverse ageârelated arterial dysfunction by decreasing oxidative stress
Energy dependence of elliptic flow over a large pseudorapidity range in Au+Au collisions at RHIC
This paper describes the measurement of the energy dependence of elliptic
flow for charged particles in Au+Au collisions using the PHOBOS detector at the
Relativistic Heavy Ion Collider (RHIC). Data taken at collision energies of
19.6, 62.4, 130 and 200 GeV are shown over a wide range in
pseudorapidity. These results, when plotted as a function of
, scale with approximate linearity throughout ,
implying no sharp changes in the dynamics of particle production as a function
of pseudorapidity or increasing beam energy.Comment: 5 pages, 4 figure
Transverse Momentum and Rapidity Dependence of HBT Correlations in Au+Au Collisions at sqrt(s_NN) = 62.4 and 200 GeV
Two-particle correlations of identical charged pion pairs from Au+Au
collisions at sqrt(s_NN) = 62.4 and 200 GeV were measured by the PHOBOS
experiment at RHIC. Data for the 15% most central events were analyzed with
Bertsch-Pratt and Yano-Koonin-Podgoretskii parameterizations using pairs with
rapidities of 0.4 < y_{\pi\pi} < 1.3 and transverse momenta 0.1 < k_T < 1.4
GeV/c. The Bertsch-Pratt radii R_o and R_l decrease as a function of pair
transverse momentum, while R_s is consistent with a weaker dependence. R_o and
R_s are independent of collision energy, while R_l shows a slight increase. The
source rapidity y_{ykp} scales roughly with the pair rapidity y_{\pi\pi},
indicating strong dynamical correlations.Comment: 5 pages, 4 figures, 2 tables, submitted to Phys. Rev.
Forward-Backward Multiplicity Correlations in sqrt(s_NN) = 200 GeV Gold-Gold Collisions
Forward-backward correlations of charged-particle multiplicities in symmetric
bins in pseudorapidity are studied in order to gain insight into the underlying
correlation structure of particle production in Au+Au collisions. The PHOBOS
detector is used to measure integrated multiplicities in bins centered at eta,
defined within |eta|<3, and covering intervals Delta-eta. The variance
sigma^2_C of a suitably defined forward-backward asymmetry variable C is
calculated as a function of eta, Delta-eta, and centrality. It is found to be
sensitive to short range correlations, and the concept of "clustering'' is used
to interpret comparisons to phenomenological models.Comment: 5 Pages, 5 Figures, submitted to Physical Review C -- Rapid
Communication
Event-by-event fluctuations of azimuthal particle anisotropy in Au+Au collisions at sqrt(s_NN) = 200 GeV
This paper presents the first measurement of event-by-event fluctuations of
the elliptic flow parameter v_2 in Au+Au collisions at sqrt(s_NN) = 200GeV as a
function of collision centrality. The relative non-statistical fluctuations of
the v_2 parameter are found to be approximately 40%. The results, including
contributions from event-by-event elliptic flow fluctuations and from azimuthal
correlations that are unrelated to the reaction plane (non-flow correlations),
establish an upper limit on the magnitude of underlying elliptic flow
fluctuations. This limit is consistent with predictions based on spatial
fluctuations of the participating nucleons in the initial nuclear overlap
region. These results provide important constraints on models of the initial
state and hydrodynamic evolution of relativistic heavy ion collisions.Comment: 5 pages, 2 figures, Published in Phys. Rev. Lett
Non-flow correlations and elliptic flow fluctuations in gold-gold collisions at sqrt(s_NN)= 200 GeV
This paper presents results on event-by-event elliptic flow fluctuations in
Au+Au collisions at sqrt(s_NN)=200Gev, where the contribution from non-flow
correlations has been subtracted. An analysis method is introduced to measure
non-flow correlations, relying on the assumption that non-flow correlations are
most prominent at short ranges (Delta eta < 2). Assuming that non-flow
correlations are of the order that is observed in p+p collisions for long range
correlations (Delta eta > 2), relative elliptic flow fluctuations of
approximately 30-40% are observed. These results are consistent with
predictions based on spatial fluctuations of the participating nucleons in the
initial nuclear overlap region. It is found that the long range non-flow
correlations in Au+Au collisions would have to be more than an order of
magnitude stronger compared to the p+p data to lead to the observed azimuthal
anisotropy fluctuations with no intrinsic elliptic flow fluctuations.Comment: 9 pages, 7 figures, Published in Phys. Rev.
Charged-Particle Pseudorapidity Distributions in Au+Au Collisions at sqrt(s_NN)=62.4 GeV
The charged-particle pseudorapidity density for Au+Au collisions at
sqrt(s_NN)=62.4 GeV has been measured over a wide range of impact parameters
and compared to results obtained at other energies. As a function of collision
energy, the pseudorapidity distribution grows systematically both in height and
width. The mid-rapidity density is found to grow approximately logarithmically
between AGS energies and the top RHIC energy. As a function of centrality,
there is an approximate factorization of the centrality dependence of the
mid-rapidity yields and the overall multiplicity scale. The new results at
sqrt(s_NN)=62.4 GeV confirm the previously observed phenomenon of ``extended
longitudinal scaling'' in the pseudorapidity distributions when viewed in the
rest frame of one of the colliding nuclei. It is also found that the evolution
of the shape of the distribution with centrality is energy independent, when
viewed in this reference frame. As a function of centrality, the total charged
particle multiplicity scales linearly with the number of participant pairs as
it was observed at other energies.Comment: 6 pages, 7 figures, submitted to Phys. Rev. C - Rapid Communication
System Size, Energy, Pseudorapidity, and Centrality Dependence of Elliptic Flow
This paper presents measurements of the elliptic flow of charged particles as
a function of pseudorapidity and centrality from Cu-Cu collisions at 62.4 and
200 GeV using the PHOBOS detector at the Relativistic Heavy Ion Collider
(RHIC). The elliptic flow in Cu-Cu collisions is found to be significant even
for the most central events. For comparison with the Au-Au results, it is found
that the detailed way in which the collision geometry (eccentricity) is
estimated is of critical importance when scaling out system-size effects. A new
form of eccentricity, called the participant eccentricity, is introduced which
yields a scaled elliptic flow in the Cu-Cu system that has the same relative
magnitude and qualitative features as that in the Au-Au system
Latest Results from PHOBOS
This manuscript contains a summary of the latest physics results from PHOBOS,
as reported at Quark Matter 2006. Highlights include the first measurement from
PHOBOS of dynamical elliptic flow fluctuations as well as an explanation of
their possible origin, two-particle correlations, identified particle ratios,
identified particle spectra and the latest results in global charged particle
production.Comment: 9 pages, 7 figures, PHOBOS plenary proceedings for Quark Matter 200
- âŠ