495 research outputs found
Propionibacterium acnes bacteriophages display limited genetic diversity and broad killing activity against bacterial skin isolates.
UnlabelledInvestigation of the human microbiome has revealed diverse and complex microbial communities at distinct anatomic sites. The microbiome of the human sebaceous follicle provides a tractable model in which to study its dominant bacterial inhabitant, Propionibacterium acnes, which is thought to contribute to the pathogenesis of the human disease acne. To explore the diversity of the bacteriophages that infect P. acnes, 11 P. acnes phages were isolated from the sebaceous follicles of donors with healthy skin or acne and their genomes were sequenced. Comparative genomic analysis of the P. acnes phage population, which spans a 30-year temporal period and a broad geographic range, reveals striking similarity in terms of genome length, percent GC content, nucleotide identity (>85%), and gene content. This was unexpected, given the far-ranging diversity observed in virtually all other phage populations. Although the P. acnes phages display a broad host range against clinical isolates of P. acnes, two bacterial isolates were resistant to many of these phages. Moreover, the patterns of phage resistance correlate closely with the presence of clustered regularly interspaced short palindromic repeat elements in the bacteria that target a specific subset of phages, conferring a system of prokaryotic innate immunity. The limited diversity of the P. acnes bacteriophages, which may relate to the unique evolutionary constraints imposed by the lipid-rich anaerobic environment in which their bacterial hosts reside, points to the potential utility of phage-based antimicrobial therapy for acne.ImportancePropionibacterium acnes is a dominant member of the skin microflora and has also been implicated in the pathogenesis of acne; however, little is known about the bacteriophages that coexist with and infect this bacterium. Here we present the novel genome sequences of 11 P. acnes phages, thereby substantially increasing the amount of available genomic information about this phage population. Surprisingly, we find that, unlike other well-studied bacteriophages, P. acnes phages are highly homogeneous and show a striking lack of genetic diversity, which is perhaps related to their unique and restricted habitat. They also share a broad ability to kill clinical isolates of P. acnes; phage resistance is not prevalent, but when detected, it appears to be conferred by chromosomally encoded immunity elements within the host genome. We believe that these phages display numerous features that would make them ideal candidates for the development of a phage-based therapy for acne
Antiferromagnetic spin fluctuations in CeRhSn probed by 119Sn NMR
We have carried out 119Sn nuclear magnetic resonance (NMR) measurements on the quasi-Kagomé compound CeRhSn. We found that 119Sn Knight shift (119K) is highly anisotropic and shows Curie-Weiss type temperature (T) dependence above 25 K. In this T range, the NMR relaxation rate shows 119(1/T1)α√T and is enhanced by magnetic fluctuations. At low T's, 119K stays constant and the enhanced Korringa relation of 119(T1TK2) = const is observed, differently from the non-Fermi-liquid behavior observed for bulk measurements. The present NMR results suggest that antiferromagnetic spin fluctuations exist in CeRhSn
Bubbling AdS and droplet descriptions of BPS geometries in IIB supergravity
This paper focuses on supergravity duals of BPS states in N=4 super
Yang-Mills. In order to describe these duals, we begin with a sequence of
breathing mode reductions of IIB supergravity: first on S^3, then S^3 x S^1,
and finally on S^3 x S^1 x CP^1. We then follow with a complete supersymmetry
analysis, yielding 1/8, 1/4 and 1/2 BPS configurations, respectively (where in
the last step we take the Hopf fibration of S^3). The 1/8 BPS geometries, which
have an S^3 isometry and are time-fibered over a six-dimensional base, are
determined by solving a non-linear equation for the Kahler metric on the base.
Similarly, the 1/4 BPS configurations have an S^3 x S^1 isometry and a
four-dimensional base, whose Kahler metric obeys another non-linear,
Monge-Ampere type equation.
Despite the non-linearity of the problem, we develop a universal bubbling AdS
description of these geometries by focusing on the boundary conditions which
ensure their regularity. In the 1/8 BPS case, we find that the S^3 cycle
shrinks to zero size on a five-dimensional locus inside the six-dimensional
base. Enforcing regularity of the full solution requires that the interior of a
smooth, generally disconnected five-dimensional surface be removed from the
base. The AdS_5 x S^5 ground state corresponds to excising the interior of an
S^5, while the 1/8 BPS excitations correspond to deformations (including
topology change) of the S^5 and/or the excision of additional droplets from the
base. In the case of 1/4 BPS configurations, by enforcing regularity
conditions, we identify three-dimensional surfaces inside the four-dimensional
base which separate the regions where the S^3 shrinks to zero size from those
where the S^1 shrinks.Comment: 94 pages, 6 figures, latex, typos corrected, references added, one
new Appendi
A Chandra Survey of Supermassive Black Holes with Dynamical Mass Measurements
We present Chandra observations of 12 galaxies that contain supermassive
black holes with dynamical mass measurements. Each galaxy was observed for 30
ksec and resulted in a total of 68 point source detections in the target
galaxies including supermassive black hole sources, ultraluminous X-ray
sources, and extragalactic X-ray binaries. Based on our fits of the X-ray
spectra, we report fluxes, luminosities, Eddington ratios, and slope of the
power-law spectrum. Normalized to the Eddington luminosity, the 2--10 keV band
X-ray luminosities of the SMBH sources range from to , and
the power-law slopes are centered at with a slight trend towards
steeper (softer) slopes at smaller Eddington fractions, implying a change in
the physical processes responsible for their emission at low accretion rates.
We find 20 ULX candidates, of which six are likely ( chance) to be true
ULXs. The most promising ULX candidate has an isotropic luminosity in the
0.3--10 keV band of erg/s.Comment: Accepted by ApJ. 16 pages, 8 figures, 5 table
Heavy-fermion weak-ferromagnet YbRhSb
A new Yb-based compound YbRhSb with the orthorhombic -TiNiSi-type structure has been synthesized. The magnetic-susceptibility, magnetization, and specific-heat (Cp) measurements of single crystals revealed a ferromagnetic transition at TC = 2.7 K. An extrapolation of the Cp/T data below 1 K yields 370 mJ/mol K2 as the value, and the magnetic entropy reaches only 0.25R ln 2 at TC. The spontaneous moment is unusually small, 3×10–3µB/Yb for B||b, while the magnetization increases to 1.4µB/Yb when the field of 15 T is applied along the a axis. We ascribe the weak ferromagnetism to a canted antiferromagnetic structure based on the observation of a metamagnetic transition and the decrease of TC with the increase of magnetic field
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