OPM magnetorelaxometry in the presence of a DC bias field

Spatial quantitative information about magnetic nanoparticle (MNP) distributions is a prerequisite for biomedical applications like magnetic hyperthermia and magnetic drug targeting. This information can be gathered by means of magnetorelaxometry (MRX) imaging, where the relaxation of previously aligned MNP’s magnetic moments is measured by sensitive magnetometers and an inverse problem is solved. To remove or minimize the magnetic shielding in which MRX imaging is carried out today, the knowledge of the influence of background magnetic fields on the MNP’s relaxation is a prerequisite. We show MRX measurements using an intensity-modulated optically pumped magnetometer (OPM) in background magnetic fields of up to 100μT. We show that the relaxation parameters alter or may be intentionally altered significantly by applying static fields parallel or antiparallel to the MNP’s alignment direction. Further, not only the relaxation process of the MNP’s magnetic moments could be measured with OPM, but also their alignment due to the MRX excitation field. © 2020, The Author(s)

Eclipses During the 2010 Eruption of the Recurrent Nova U Scorpii

The eruption of the recurrent nova U Scorpii on 28 January 2010 is now the all-time best observed nova event. We report 36,776 magnitudes throughout its 67 day eruption, for an average of one measure every 2.6 minutes. This unique and unprecedented coverage is the first time that a nova has any substantial amount of fast photometry. With this, two new phenomena have been discovered: the fast flares in the early light curve seen from days 9-15 (which have no proposed explanation) and the optical dips seen out of eclipse from days 41-61 (likely caused by raised rims of the accretion disk occulting the bright inner regions of the disk as seen over specific orbital phases). The expanding shell and wind cleared enough from days 12-15 so that the inner binary system became visible, resulting in the sudden onset of eclipses and the turn-on of the supersoft X-ray source. On day 15, a strong asymmetry in the out-of-eclipse light points to the existence of the accretion stream. The normal optical flickering restarts on day 24.5. For days 15-26, eclipse mapping shows that the optical source is spherically symmetric with a radius of 4.1 R_sun. For days 26-41, the optical light is coming from a rim-bright disk of radius 3.4 R_sun. For days 41-67, the optical source is a center-bright disk of radius 2.2 R_sun. Throughout the eruption, the colors remain essentially constant. We present 12 eclipse times during eruption plus five just after the eruption.Comment: ApJ in press. 60 pages, 17 figure

Backbone and side chain NMR assignments of Geobacillus stearothermophilus ZapA allow identification of residues that mediate the interaction of ZapA with FtsZ

Bacterial division begins with the formation of a contractile protein ring at midcell, which constricts the bacterial envelope to generate two daughter cells. The central component of the division ring is FtsZ, a tubulin-like protein capable of self-assembling into filaments which further associate into a higher order structure known as the Z ring. Proteins that bind to FtsZ play a crucial role in the formation and regulation of the Z ring. One such protein is ZapA, a widely conserved 21 kDa homodimeric protein that associates with FtsZ filaments and promotes their bundling. Although ZapA was discovered more than a decade ago, the structural details of its interaction with FtsZ remain unknown. In this work, backbone and side chain NMR assignments for the Geobacillus stearothermophilus ZapA homodimer are described. We titrated FtsZ into (NH)-N-15-H-2-ZapA and mapped ZapA residues whose resonances are perturbed upon FtsZ binding. This information provides a structural understanding of the interaction between FtsZ and ZapA

Characterization of CrgA, a New Partner of the Mycobacterium tuberculosis Peptidoglycan Polymerization Complexes▿†

The role(s) in cell division of the Mycobacterium tuberculosis Rv0011c gene product, a homolog of the Streptomyces CrgA protein that is responsible for coordinating growth and cytokinesis in sporogenic aerial hyphae, is largely unknown. We show that an enhanced cyan fluorescent protein-M. tuberculosis CrgA (ECFP-CrgAMT) fusion protein is localized to the cell membrane, midcell, and cell pole regions in Mycobacterium smegmatis. Furthermore, the ECFP-CrgAMT fusion protein colocalized with FtsZ-enhanced yellow fluorescent protein (EYFP) in M. smegmatis. Bacterial two-hybrid assays indicated strong interactions of M. tuberculosis CrgA with FtsZ, FtsQ, and the class B penicillin-binding proteins, FtsI (PBPB) and PBPA. The midcell localization of CrgAMT was severely compromised under conditions of FtsZ depletion, which indicated that CrgA localizes to the midcell region after assembly of the FtsZ ring. M. tuberculosis cells with reduced CrgA levels were elongated and grew more slowly than wild-type cells, which indicated defects in cell division, whereas CrgA overproduction did not show growth defects. A M. smegmatis ΔcrgA strain exhibited a bulged cell morphology, elongated cells with a chain-like phenotype, cells with polar bulbous structures, and a modest growth defect. FtsZ and FtsI levels were not affected in cells producing altered levels of CrgA. Septal and membrane localization of GFP-FtsI was enhanced by CrgA overproduction and was diminished in a ΔcrgA strain, which indicates that one role of CrgA is to promote and/or stabilize FtsI localization. Overall, these data indicate that CrgA is a novel member of the cell division complex in mycobacteria and possibly facilitates septum formation