A micro-focusing and high-flux-throughput beamline design using a bending magnet for microscopic XAFS at the High Energy Photon Source.

An optical design study of a bending-magnet beamline, based on multi-bend achromat storage ring lattices, at the High Energy Photon Source, to be built in Beijing, China, is described. The main purpose of the beamline design is to produce a micro-scale beam from a bending-magnet source with little flux loss through apertures. To maximize the flux of the focal spot, the synchrotron source will be 1:1 imaged to a virtual source by a toroidal mirror; a mirror pair will be used to collimate the virtual source into quasi-parallel light which will be refocused by a Kirkpatrick-Baez mirror pair. In the case presented here, a beamline for tender X-rays ranging from 2.1 keV to 7.8 keV, with a spot size of approximately 7 µm (H) × 6 µm (V) and flux up to 2 × 1012 photons s-1, can be achieved for the purpose of X-ray absorption fine-structure (XAFS)-related experiments, such as scanning micro-XAFS and full-field nano-XAFS.

SIRT1 suppresses self-renewal of adult hippocampal neural stem cells.

The balance between self-renewal and differentiation of adult neural stem cells (aNSCs) is essential for the maintenance of the aNSC reservoir and the continuous supply of new neurons, but how this balance is fine-tuned in the adult brain is not fully understood. Here, we investigate the role of SIRT1, an important metabolic sensor and epigenetic repressor, in regulating adult hippocampal neurogenesis in mice. We found that there was an increase in SIRT1 expression during aNSC differentiation. In Sirt1 knockout (KO) mice, as well as in brain-specific and inducible stem cell-specific conditional KO mice, the proliferation and self-renewal rates of aNSCs in vivo were elevated. Proliferation and self-renewal rates of aNSCs and adult neural progenitor cells (aNPCs) were also elevated in neurospheres derived from Sirt1 KO mice and were suppressed by the SIRT1 agonist resveratrol in neurospheres from wild-type mice. In cultured neurospheres, 2-deoxy-D-glucose-induced metabolic stress suppressed aNSC/aNPC proliferation, and this effect was mediated in part by elevating SIRT1 activity. Microarray and biochemical analysis of neurospheres suggested an inhibitory effect of SIRT1 on Notch signaling in aNSCs/aNPCs. Inhibition of Notch signaling by a γ-secretase inhibitor also largely abolished the increased aNSC/aNPC proliferation caused by Sirt1 deletion. Together, these findings indicate that SIRT1 is an important regulator of aNSC/aNPC self-renewal and a potential mediator of the effect of metabolic changes.

Differential utilization and transformation of sulfur allotropes, µ-S and α-S8, by moderate thermoacidophile Sulfobacillus thermosulfidooxidans.

The utilization of amorphous µ-S and orthorhombic α-S8 by thermoacidophile Sulfobacillus thermosulfidooxidans was firstly investigated in terms of cell growth and sulfur oxidation behavior. The morphology and surface sulfur speciation transformation were evaluated by using scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform-infrared spectroscopy (FT-IR), Raman spectroscopy and sulfur K-edge X-ray absorption near edge structure (XANES) spectroscopy. The results showed that the strain grown on µ-S entered slower (about 1 day later) into the exponential phase, while grew faster in exponential phase and attained higher maximal cell density and lower pH than on α-S8. After bio-corrosion, both sulfur samples were evidently eroded, but only µ-S surface presented much porosity, while α-S8 maintained glabrous. µ-S began to be gradually converted into α-S8 from day 2 when the bacterial cells entered the exponential phase, with a final composition of 62.3% µ-S and 37.7% α-S8 on day 4 at the stationary phase. α-S8 was not found to transform into other species in the experiments with or without bacteria. These data indicated S. thermosulfidooxidans oxidized amorphous µ-S faster than orthorhombic α-S8, but the chain-like µ-S was transformed into cyclic α-S8 by S. thermosulfidooxidans.

Sulfur oxidation activities of pure and mixed thermophiles and sulfur speciation in bioleaching of chalcopyrite.

The sulfur oxidation activities of four pure thermophilic archaea Acidianus brierleyi (JCM 8954), Metallosphaera sedula (YN 23), Acidianus manzaensis (YN 25) and Sulfolobus metallicus (YN 24) and their mixture in bioleaching chalcopyrite were compared. Meanwhile, the relevant surface sulfur speciation of chalcopyrite leached with the mixed thermophilic archaea was investigated. The results showed that the mixed culture, with contributing significantly to the raising of leaching rate and accelerating the formation of leaching products, may have a higher sulfur oxidation activity than the pure cultures, and jarosite was the main passivation component hindering the dissolution of chalcopyrite, while elemental sulfur seemed to have no influence on the dissolution of chalcopyrite. In addition, the present results supported the former speculation, i.e., covellite might be converted from chalcocite during the leaching experiments, and the elemental sulfur may partially be the derivation of covellite and chalcocite.

Investigation of elemental sulfur speciation transformation mediated by Acidithiobacillus ferrooxidans.

The speciation transformation of elemental sulfur mediated by the leaching bacterium Acidithiobacillus ferrooxidans was investigated using an integrated approach including scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, energy dispersive X-ray spectroscopy, and X-ray absorption near edge spectroscopy (XANES). Our results showed that when grown on elemental sulfur powder, At. ferrooxidans ATCC23270 cells were first attached to sulfur particles and modified the surface sulfur with some amphiphilic compounds. In addition, part of the elemental sulfur powder might be converted to polysulfides. Furthermore, sulfur globules were accumulated inside the cells. XANES spectra of these cells suggested that these globules consisted of elemental sulfur bound to thiol groups of protein.