Investigating staphyloferrin B biosynthesis in Staphylococcus aureus

In S. aureus, the iron-scavenging siderophores staphyloferrin A and staphyloferrin B are synthesized by enzymes encoded within the sfa and sbn gene clusters, respectively. This work details the in vitro functional characterization of the Sbn enzymes responsible for synthesizing staphyloferrin B. As demonstrated through UV-vis spectrophotometric enzymatic assays and LC-ESI-MS experiments, staphyloferrin B can be synthesized in vitro by incubating purified Sbn enzymes (SbnCEFH) with fundamental components of the siderophore such as L-2,3-diaminopropionic acid, citric acid, and alpha-ketoglutaric acid. Furthermore, a novel iron-regulated citrate synthase has been characterized and is named SbnG, which condenses acetyl-CoA with oxaloacetate to form the citric acid component o f staphyloferrin B. Finally, in vitro prepared staphyloferrin B was biologically active in that it was capable of binding and supplying iron, through the SirABC transporter, to S. aureus. With functional characterization of the Sbn enzymes and their corresponding reaction products, a biosynthetic pathway for staphyloferrin B is proposed

What Has COVID-19 Paved the Way for Social Work Practice Teaching?

The future is undoubtedly unpredictable which is vividly proved by the 2020 pandemic. Educators primarily focused for the well-being of the students in this time of crisis, panic and ambivalence. In present milieu, social work practice teaching has been made online. This is high time which calls for the retrofitting of the previous discussions where the emphasis should now be laid upon a better quality of teaching, curriculum restructuring, and capacity building of clinical practice educators. Yet, there are multitudes of underlying predicaments, i.e. e-teaching versus e-learning, synchronous versus asynchronous modalities, and educator versus youtuber, which need to be analyzed and evaluated before stepping in and getting lost in the new era

Volatility and Agent Adaptability in a Self-Organizing Market

We present results for the so-called `bar-attendance' model of market behavior: $p$ adaptive agents, each possessing $n$ prediction rules chosen randomly from a pool, attempt to attend a bar whose cut-off is $s$. The global attendance time-series has a mean near, but not equal to, $s$. The variance, or `volatility', can show a minimum with increasing adaptability of the individual agents.Comment: 8 pages, 3 figs. [email protected], [email protected]

Paper Session II-B - Solid State Oxygen Sensor Development

To anticipate future long-duration mission needs for life support sensors, we explored the feasibility of using thin-film metal-oxide semiconductors. The objective of this task was to develop gas sensors for life support applications which would be suitable for long-duration missions. Metal oxides, such as ZnO, SnO2, and TiO2 have been shown to react with oxygen molecules. Oxygen lowers the metal oxide\u27s electrical resistance. Critical to the performance is the application of the oxide in a thin film on an inert substrate: the thinner the film, the more readily the oxygen penetration and hence the more rapid and sensitive the sensor. Metal oxides are not limited to oxygen detection, rather, oxides offer detection and quantification applications to the complete range of gases of interest, not only for life support systems, but for propellants as well

Mutation of L-2,3-diaminopropionic acid synthase genes blocks staphyloferrin B synthesis in Staphylococcus aureus

BACKGROUND: Staphylococcus aureus synthesizes two siderophores, staphyloferrin A and staphyloferrin B, that promote iron-restricted growth. Previous work on the biosynthesis of staphyloferrin B has focused on the role of the synthetase enzymes, encoded from within the sbnA-I operon, which build the siderophore from the precursor molecules citrate, alpha-ketoglutarate and L-2,3-diaminopropionic acid. However, no information yet exists on several other enzymes, expressed from the biosynthetic cluster, that are thought to be involved in the synthesis of the precursors (or synthetase substrates) themselves. RESULTS: Using mutants carrying insertions in sbnA and sbnB, we show that these two genes are essential for the synthesis of staphyloferrin B, and that supplementation of the growth medium with L-2,3-diaminopropionic acid can bypass the block in staphyloferrin B synthesis displayed by the mutants. Several mechanisms are proposed for how the enzymes SbnA, with similarity to cysteine synthase enzymes, and SbnB, with similarity to amino acid dehydrogenases and ornithine cyclodeaminases, function together in the synthesis of this unusual nonproteinogenic amino acid L-2,3-diaminopropionic acid. CONCLUSIONS: Mutation of either sbnA or sbnB result in abrogation of synthesis of staphyloferrin B, a siderophore that contributes to iron-restricted growth of S. aureus. The loss of staphyloferrin B synthesis is due to an inability to synthesize the unusual amino acid L-2,3-diaminopropionic acid which is an important, iron-liganding component of the siderophore structure. It is proposed that SbnA and SbnB function together as an L-Dap synthase in the S. aureus cell

Optical coherence tomography and non-linear microscopy for paintings – a study of the complementary capabilities and laser degradation effects

This paper examines for the first time the potential complementary imaging capabilities of Optical coherence tomography (OCT) and non-linear microscopy (NLM) for multi-modal 3D examination of paintings following the successful application of OCT to the in situ, non-invasive examination of varnish and paint stratigraphy of historic paintings and the promising initial studies of NLM of varnish samples. OCT provides image contrast through the optical scattering and absorption properties of materials, while NLM provides molecular information through multi-photon fluorescence and higher harmonics generation (second and third harmonic generation). OCT is well-established in the in situ non-invasive imaging of the stratigraphy of varnish and paint layers. While NLM examination of transparent samples such as fresh varnish and some transparent paints showed promising results, the ultimate use of NLM on paintings is limited owing to the laser degradation effects caused by the high peak intensity of the laser source necessary for the generation of non-linear phenomena. The high intensity normally employed in NLM is found to be damaging to all non-transparent painting materials from slightly scattering degraded varnish to slightly absorbing paint at the wavelength of the laser excitation source. The results of this paper are potentially applicable to a wide range of materials given the diversity of the materials encountered in paintings (e.g. minerals, plants, insects, oil, egg, synthetic and natural varnish)

Discovery of Gamma-ray Pulsations from the Transitional Redback PSR J1227-4853

The 1.69 ms spin period of PSR J1227-4853 was recently discovered in radio observations of the low-mass X-ray binary XSS J12270-4859 following the announcement of a possible transition to a rotation-powered millisecond pulsar state, inferred from decreases in optical, X-ray, and gamma-ray flux from the source. We report the detection of significant (5$\sigma$) gamma-ray pulsations after the transition, at the known spin period, using ~1 year of data from the Large Area Telescope on board the Fermi Gamma-ray Space Telescope. The gamma-ray light curve of PSR J1227-4853 can be fit by one broad peak, which occurs at nearly the same phase as the main peak in the 1.4 GHz radio profile. The partial alignment of light-curve peaks in different wavebands suggests that at least some of the radio emission may originate at high altitude in the pulsar magnetosphere, in extended regions co-located with the gamma-ray emission site. We folded the LAT data at the orbital period, both pre- and post-transition, but find no evidence for significant modulation of the gamma-ray flux. Analysis of the gamma-ray flux over the mission suggests an approximate transition time of 2012 November 30. Continued study of the pulsed emission and monitoring of PSR J1227-4853, and other known redback systems, for subsequent flux changes will increase our knowledge of the pulsar emission mechanism and transitioning systems.Comment: 5 figures, 1 table, accepted for publication in ApJ, updated to reflect accepted version and add additional coautho

The Enhancon, Black Holes, and the Second Law

We revisit the physics of five-dimensional black holes constructed from D5- and D1-branes and momentum modes in type IIB string theory compactified on K3. Since these black holes incorporate D5-branes wrapped on K3, an enhancon locus appears in the spacetime geometry. With a `small' number of D1-branes, the entropy of a black hole is maximised by including precisely half as many D5-branes as there are D1-branes in the black hole. Any attempts to introduce more D5-branes, and so reduce the entropy, are thwarted by the appearance of the enhancon locus above the horizon, which then prevents their approach. The enhancon mechanism thereby acts to uphold the Second Law of Thermodynamics. This result generalises: For each type of bound state object which can be made of both types of brane, we show that a new type of enhancon exists at successively smaller radii in the geometry, again acting to prevent any reduction of the entropy just when needed. We briefly explore the appearance of the enhancon in the black hole interior.Comment: 22 pages, 2 figures, latex, epsfig (v2: Fixed trivial typos.

2FGL J0846.0+2820: A new neutron star binary with a giant secondary and variable γ\gamma-ray emission

We present optical photometric and spectroscopic observations of the likely stellar counterpart to the unassociated \emph{Fermi}-Large Area Telescope (LAT) $\gamma$-ray source 2FGL J0846.0+2820, selected for study based on positional coincidences of optical variables with unassociated LAT sources. Using optical spectroscopy from the SOAR telescope, we have identified a late-G giant in an eccentric ($e$ = 0.06) 8.133 day orbit with an invisible primary. Modeling the spectroscopy and photometry together lead us to infer a heavy neutron star primary of $\sim 2 M_{\odot}$ and a partially stripped giant secondary of $\sim 0.8 M_{\odot}$. H$\alpha$ emission is observed in some of the spectra, perhaps consistent with the presence of a faint accretion disk. We find the $\gamma$-ray flux of 2FGL J0846.0+2820 dropped substantially in mid-2009, accompanied by an increased variation in the optical brightness, and since then it has not been detected by \emph{Fermi}. The long period and giant secondary are reminiscent of the $\gamma$-ray bright binary 1FGL J1417.7--4407, which hosts a millisecond pulsar apparently in the final stages of the pulsar recycling process. The discovery of 2FGL J0846.0+2820 suggests the identification of a new subclass of millisecond pulsar binaries that are the likely progenitors of typical field millisecond pulsars.Comment: 12 pages, 8 figures, 3 tables. Accepted for publication in Ap

Astrophysical Lasers Operating in optical Fe II Lines Lines in Stellar Ejecta of Eta Carinae

After the discovery of space masers based on OH radicals (Weaver et al, 1965) and H2O (Cheung et al, 1969) such microwave lasers have been found to work in more than 100 molecular species (Elitzur, 1992; Townes, 1997), as well as in highly excited H atoms (Strelnitski et al,1996). In the IR region (10 microns), the effect of stimulated emission of radiation in the CO2 molecule has been discovered in the Martian and Venus' atmospheres (Betz et al, 1976; Mumma et al, 1981). We report here on the discovery of laser action in the range 0.9-2 micr. in several spectral lines of Fe II, which are associated with transitions from "pseudo-metastable" states populated by spontaneous transitions from Ly-alpha pumped Fe II levels. The intense Ly-alpha radiation is formed in the HII region of gas condensations close to the star Eta Carinae. The laser transitions form together with spontaneous transitions closed radiative cycles, one of which includes the extremely bright 2507/09 A lines. Closed radiative cycles, together with an accidental mixing of energy levels, may provide an explanation of the abnormal intensities of these UV non-lasing lines. Using the complicated energy level diagram of Fe II we present those peculiar features, which are essential for the inverted population and laser effect: the pumping, the level mixing, and the "bottle neck" for spontaneous decay. The laser action is a new indicator of non-equilibrium and spatially non-homogeneous physical conditions as well as a high brightness temperature of Ly-alpha in ejecta from eruptive stars. Such conditions are very difficult to probe by existing methods, and we propose some future experiments. The fact, that the lasing near-IR lines appear in the spectrum with about the same inten- sity as non-lasing lines is discussed and compared with the situation in masers.Comment: 27 pages, 11 figures; to be published in A&A; also available at http://130.235.102.158/blackhole/astrolaser.pd