Curved Tails in Polymerization-Based Bacterial Motility

The curved actin ``comet-tail'' of the bacterium Listeria monocytogenes is a visually striking signature of actin polymerization-based motility. Similar actin tails are associated with Shigella flexneri, spotted-fever Rickettsiae, the Vaccinia virus, and vesicles and microspheres in related in vitro systems. We show that the torque required to produce the curvature in the tail can arise from randomly placed actin filaments pushing the bacterium or particle. We find that the curvature magnitude determines the number of actively pushing filaments, independent of viscosity and of the molecular details of force generation. The variation of the curvature with time can be used to infer the dynamics of actin filaments at the bacterial surface.Comment: 8 pages, 2 figures, Latex2

Search for a Technicolor omega_T Particle in Events with a Photon and a b-quark Jet at CDF

If the Technicolor omega_T particle exists, a likely decay mode is omega_T -> gamma pi_T, followed by pi_T -> bb-bar, yielding the signature gamma bb-bar. We have searched 85 pb^-1 of data collected by the CDF experiment at the Fermilab Tevatron for events with a photon and two jets, where one of the jets must contain a secondary vertex implying the presence of a b quark. We find no excess of events above standard model expectations. We express the result of an exclusion region in the M_omega_T - M_pi_T mass plane.Comment: 14 pages, 2 figures. Available from the CDF server (PS with figs): http://www-cdf.fnal.gov/physics/pub98/cdf4674_omega_t_prl_4.ps FERMILAB-PUB-98/321-

Measurement of the B0 anti-B0 oscillation frequency using l- D*+ pairs and lepton flavor tags

The oscillation frequency Delta-md of B0 anti-B0 mixing is measured using the partially reconstructed semileptonic decay anti-B0 -> l- nubar D*+ X. The data sample was collected with the CDF detector at the Fermilab Tevatron collider during 1992 - 1995 by triggering on the existence of two lepton candidates in an event, and corresponds to about 110 pb-1 of pbar p collisions at sqrt(s) = 1.8 TeV. We estimate the proper decay time of the anti-B0 meson from the measured decay length and reconstructed momentum of the l- D*+ system. The charge of the lepton in the final state identifies the flavor of the anti-B0 meson at its decay. The second lepton in the event is used to infer the flavor of the anti-B0 meson at production. We measure the oscillation frequency to be Delta-md = 0.516 +/- 0.099 +0.029 -0.035 ps-1, where the first uncertainty is statistical and the second is systematic.Comment: 30 pages, 7 figures. Submitted to Physical Review

A Measurement of the Differential Dijet Mass Cross Section in p-pbar Collisions at sqrt{s}=1.8 TeV

We present a measurement of the cross section for production of two or more jets as a function of dijet mass, based on an integrated luminosity of 86 pb^-1 collected with the Collider Detector at Fermilab. Our dijet mass spectrum is described within errors by next-to-leading order QCD predictions using CTEQ4HJ parton distributions, and is in good agreement with a similar measurement from the D0 experiment.Comment: 18 pages including 2 figures and 3 tables. Submitted to Phys. Rev. D Rapid Communication

Search for New Particles Decaying to top-antitop in proton-antiproton collisions at squareroot(s)=1.8 TeV

We use 106 \ipb of data collected with the Collider Detector at Fermilab to search for narrow-width, vector particles decaying to a top and an anti-top quark. Model independent upper limits on the cross section for narrow, vector resonances decaying to \ttbar are presented. At the 95% confidence level, we exclude the existence of a leptophobic \zpr boson in a model of topcolor-assisted technicolor with mass M_{\zpr} $<$ 480 \gev for natural width $\Gamma$ = 0.012 M_{\zpr}, and M_{\zpr} $<$ 780 \gev for $\Gamma$ = 0.04 M_{\zpr}.Comment: The CDF Collaboration, submitted to PRL 25-Feb-200

Search for Kaluza-Klein Graviton Emission in ppˉp\bar{p} Collisions at s=1.8\sqrt{s}=1.8 TeV using the Missing Energy Signature

We report on a search for direct Kaluza-Klein graviton production in a data sample of 84 ${pb}^{-1}$ of \ppb collisions at $\sqrt{s}$ = 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 $3+1+n$-dimensional Kaluza-Klein scenario in which gravity becomes strong at the TeV scale. At 95% confidence level (C.L.) for $n$=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 $b$ and $\bar{b}$-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 $\mu \mu$ and $e \mu$ 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 $b$-flavored hadrons which decay weakly, $\bar{\chi} = 0.152 \pm 0.007$ (stat.) $\pm 0.011$ (syst.), that is significantly larger than the world average $\bar{\chi} = 0.118 \pm 0.005$.Comment: 47 pages, 10 figures, 15 tables Submitted to Phys. Rev.

Interrogation of the perturbed gut microbiota in gouty arthritis patients through in silico metabolic modeling

Recent studies have shown perturbed gut microbiota associated with gouty arthritis, a metabolic disease characterized by an imbalance between uric acid production and excretion. To mechanistically investigate altered microbiota metabolism associated with gout disease, 16S rRNA gene amplicon sequence data from stool samples of gout patients and healthy controls were computationally analyzed through bacterial community metabolic models. Patient-specific community models constructed with the metagenomics modeling pipeline, mgPipe, were used to perform k-means clustering of samples according to their metabolic capabilities. The clustering analysis generated statistically significant partitioning of samples into a Bacteroides-dominated, high gout cluster and a Faecalibacterium-elevated, low gout cluster. The high gout cluster was predicted to allow elevated synthesis of the amino acids D-alanine and L-alanine and byproducts of branched-chain amino acid catabolism, while the low gout cluster allowed higher production of butyrate, the sulfur-containing amino acids L-cysteine and L-methionine, and the L-cysteine catabolic product H2S. By expanding the capabilities of mgPipe to provide taxa-level resolution of metabolite exchange rates, acetate, D-lactate and succinate exchanged from Bacteroides to Faecalibacterium were predicted to enhance butyrate production in the low gout cluster. Model predictions suggested that sulfur-containing amino acid metabolism generally and H2S more specifically could be novel gout disease markers

Intracellular iron uptake is favored in Hfe-KO mouse primary chondrocytes mimicking an osteoarthritis-related phenotype

HFE-hemochromatosis is a disease characterized by a systemic iron overload phenotype mainly associated with mutations in the HFE protein (HFE) gene. Osteoarthritis (OA) has been reported as one of the most prevalent complications in HFE-hemochromatosis patients, but the mechanisms associated with its onset and progression remain incompletely understood. In this study, we have characterized the response to high iron concentrations of a primary culture of articular chondrocytes isolated from newborn Hfe-KO mice and compared the results with that of a similar experiment developed in cells from C57BL/6 wild-type (wt) mice. Our data provide evidence that both wt- and Hfe-KO-derived chondrocytes, when exposed to 50 mu M iron, develop characteristics of an OA-related phenotype, such as an increased expression of metalloproteases, a decreased extracellular matrix production, and a lower expression level of aggrecan. In addition, Hfe-KO cells also showed an increased expression of iron metabolism markers and MMP3, indicating an increased susceptibility to intracellular iron accumulation and higher levels of chondrocyte catabolism. Accordingly, upon treatment with 50 mu M iron, these chondrocytes were found to preferentially differentiate toward hypertrophy with increased expression of collagen I and transferrin and downregulation of SRY (sex-determining region Y)-box containing gene 9 (Sox9). In conclusion, high iron exposure can compromise chondrocyte metabolism, which, when simultaneously affected by an Hfe loss of function, appears to be more susceptible to the establishment of an OA-related phenotype.European Regional Development FundEuropean Union (EU) [EMBRC.PT Alg-01-0145-FEDER-022121, Norte-01-0145-FEDER-000012]Fundacao para a Ciencia e a TecnologiaPortuguese Foundation for Science and Technology [SFRH/BD/77056/2011]Portuguese Foundation for Science and TechnologyPortuguese Foundation for Science and TechnologyPortuguese Science and Technology FoundationPortuguese Foundation for Science and Technologyinfo:eu-repo/semantics/publishedVersio

Invasive Extravillous Trophoblasts Restrict Intracellular Growth and Spread of Listeria monocytogenes

Listeria monocytogenes is a facultative intracellular bacterial pathogen that can infect the placenta, a chimeric organ made of maternal and fetal cells. Extravillous trophoblasts (EVT) are specialized fetal cells that invade the uterine implantation site, where they come into direct contact with maternal cells. We have shown previously that EVT are the preferred site of initial placental infection. In this report, we infected primary human EVT with L. monocytogenes. EVT eliminated ∼80% of intracellular bacteria over 24-hours. Bacteria were unable to escape into the cytoplasm and remained confined to vacuolar compartments that became acidified and co-localized with LAMP1, consistent with bacterial degradation in lysosomes. In human placental organ cultures bacterial vacuolar escape rates differed between specific trophoblast subpopulations. The most invasive EVT—those that would be in direct contact with maternal cells in vivo—had lower escape rates than trophoblasts that were surrounded by fetal cells and tissues. Our results suggest that EVT present a bottleneck in the spread of L. monocytogenes from mother to fetus by inhibiting vacuolar escape, and thus intracellular bacterial growth. However, if L. monocytogenes is able to spread beyond EVT it can find a more hospitable environment. Our results elucidate a novel aspect of the maternal-fetal barrier