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Selenocyanate Derived Se-Incorporation into the Nitrogenase Fe Protein Cluster
No full textThe nitrogenase Fe protein mediates ATP-dependent electron transfer to the nitrogenase MoFe protein during nitrogen fixation, in addition to catalyzing MoFe protein independent substrate (CO₂) reduction and facilitating MoFe protein metallocluster biosynthesis. The precise role(s) of the Fe protein Fe₄S₄ cluster in some of these processes remains ill-defined. Herein, we report crystallographic data demonstrating ATP-dependent chalcogenide exchange at the Fe₄S₄ cluster of the nitrogenase Fe protein when potassium selenocyanate is used as the selenium source. The observed chalcogenide exchange illustrates that this Fe₄S₄ cluster is capable of core substitution reactions under certain conditions, adding to the Fe protein’s repertoire of unique properties
The NICER “Reverberation Machine”: A Systematic Study of Time Lags in Black Hole X-Ray Binaries
No full textWe perform the first systematic search of all NICER archival observations of black hole (and candidate) low-mass X-ray binaries for signatures of reverberation. Reverberation lags result from the light travel time difference between the direct coronal emission and the reflected disk component, and therefore their properties are a useful probe of the disk-corona geometry. We detect new signatures of reverberation lags in eight sources, increasing the total sample from three to 11, and study the evolution of reverberation lag properties as the sources evolve in outbursts. We find that in all of the nine sources with more than one reverberation lag detection, the reverberation lags become longer and dominate at lower Fourier frequencies during the hard-to-soft state transition. This result shows that the evolution in reverberation lags is a global property of the state transitions of black hole low-mass X-ray binaries, which is valuable in constraining models of such state transitions. The reverberation lag evolution suggests that the corona is the base of a jet that vertically expands and/or gets ejected during state transition. We also discover that in the hard state, the reverberation lags get shorter, just as the quasiperiodic oscillations (QPOs) move to higher frequencies, but then in the state transition, while the QPOs continue to higher frequencies, the lags get longer. We discuss the implications of the coronal geometry and physical models of QPOs in light of this new finding
Wave-driven Outbursts and Variability of Low-mass Supernova Progenitors
No full textIn a substantial number of core-collapse supernovae (SNe), early-time interaction indicates a dense circumstellar medium (CSM) that may be produced by outbursts from the progenitor star. Wave-driven mass loss is a possible mechanism to produce these signatures, with previous work suggesting that this mechanism is most effective for low-mass (∼11 M_⊙) SN progenitors. Using one-dimensional hydrodynamic simulations with MESA, we study the effects of this wave heating in SN progenitors of masses M_(ZAMS) = 10–13 M_⊙. This range encompasses stars that experience semidegenerate central neon burning and more degenerate off-center neon ignition. We find that central Ne ignition at M_(ZAMS) = 11 M_⊙ produces a burst of intense wave heating that transmits ∼10⁴⁷ erg of energy at 10 yr before core collapse, whereas other masses experience smaller levels of wave heating. Wave heating does not hydrodynamically drive mass loss in any of our models and is unlikely to produce a very massive CSM on its own. However, wave heating can cause large radial expansion (by more than an order of magnitude), photospheric cooling, and luminosity brightening by up to ∼10⁶ L_⊙ in hydrogen-poor stripped star models. Some Type Ib/c progenitors could drastically change their appearance in the final years of their lives, with brightness in the visual bands increasing by nearly 3 mag. Moreover, interaction with a close binary companion could drive intense mass loss, with implications for Type Ibn and other interaction-powered SNe
Inhibition of gut microbial β-glucuronidase effectively prevents carcinogen-induced microbial dysbiosis and intestinal tumorigenesis
No full textThe bidirectional interaction between carcinogens and gut microbiota that contributes to colorectal cancer is complicated. Reactivation of carcinogen metabolites by microbial β-glucuronidase (βG) in the gut potentially plays an important role in colorectal carcinogenesis. We assessed the chemoprotective effects and associated changes in gut microbiota induced by pre-administration of bacterial-specific βG inhibitor TCH-3511 in carcinogen azoxymethane (AOM)-treated APC^(Min/+) mice. AOM induced intestinal βG activity, which was reflected in increases in the incidence, formation, and number of tumors in the intestine. Notably, inhibition of gut microbial βG by TCH-3511 significantly reduced AOM-induced intestinal βG activity, decreased the number of polyps in both the small and large intestine to a frequency that was similar in mice without AOM exposure. AOM also led to lower diversity and altered composition in the gut microbiota with a significant increase in mucin-degrading Akkermansia genus. Conversely, mice treated with TCH-3511 and AOM exhibited a more similar gut microbiota structure as mice without AOM administration. Importantly, TCH-3511 treatment significant decreased Akkermansia genus and produced a concomitant increase in short-chain fatty acid butyrate-producing gut commensal microbes Lachnoospiraceae NK4A136 group genus in AOM-treated mice. Taken together, our results reveal a key role of gut microbial βG in promoting AOM-induced gut microbial dysbiosis and intestinal tumorigenesis, indicating the chemoprotective benefit of gut microbial βG inhibition against carcinogens via maintaining the gut microbiota balance and preventing cancer-associated gut microbial dysbiosis. Thus, the bacterial-specific βG inhibitor TCH-3511 is a potential chemoprevention agent for colorectal cancer
Retrieving the C and O Abundances of HR 7672 AB: A Solar-type Primary Star with a Benchmark Brown Dwarf
No full textA benchmark brown dwarf (BD) is a BD whose properties (e.g., mass and chemical composition) are precisely and independently measured. Benchmark BDs are valuable in testing theoretical evolutionary tracks, spectral synthesis, and atmospheric retrievals for substellar objects. Here, we report results of atmospheric retrieval on a synthetic spectrum and a benchmark BD, HR 7672 B, with petitRADTRANS. First, we test the retrieval framework on a synthetic PHOENIX BT-Settl spectrum with a solar composition. We show that the retrieved C and O abundances are consistent with solar values, but the retrieved C/O is overestimated by 0.13–0.18, which is about four times higher than the formal error bar. Second, we perform retrieval on HR 7672 B using high spectral-resolution data (R = 35,000) from the Keck Planet Imager and Characterizer and near-infrared photometry. We retrieve [C/H], [O/H], and C/O to be −0.24 ± 0.05, −0.19 ± 0.04, and 0.52 ± 0.02. These values are consistent with those of HR 7672 A within 1.5σ. As such, HR 7672 B is among only a few benchmark BDs (along with Gl 570 D and HD 3651 B) that have been demonstrated to have consistent elemental abundances with their primary stars. Our work provides a practical procedure of testing and performing atmospheric retrieval, and sheds light on potential systematics of future retrievals using high- and low-resolution data
DiI staining of sensory neurons in the entomopathogenic nematode Steinernema hermaphroditum
No full textSteinernema hermaphroditum entomopathogenic nematodes (EPN) and their Xenorhabdus griffiniae symbiotic bacteria have recently been shown to be a genetically tractable system for the study of both parasitic and mutualistic symbiosis. In their infective juvenile (IJ) stage, EPNs search for insect hosts to invade and quickly kill them with the help of the symbiotic bacteria they contain. The mechanisms behind these behaviors have not been well characterized, including how the nematodes sense their insect hosts. In the well-studied free‑living soil nematode Caenorhabditis elegans, ciliated amphid neurons enable the worms to sense their environment, including chemosensation. Some of these neurons have also been shown to control the decision to develop as a stress-resistant dauer larva, analogous to the infective juveniles of EPNs, or to exit from dauer and resume larval development. In C. elegans and other nematodes, dye-filling with DiI is an easy and efficient method to label these neurons. We developed a protocol for DiI staining of S. hermaphroditum sensory neurons. Using this method, we could identify neurons positionally analogous to the C. elegans amphid neurons ASI, ADL, ASK, ASJ, as well as inner labial neurons IL1 and IL2. Similar to findings in other EPNs, we also found that the IJs of S. hermaphroditum are dye-filling resistant
A Mirage or an Oasis? Water Vapor in the Atmosphere of the Warm Neptune TOI-674 b
No full textWe report observations of the recently discovered super-Neptune TOI-674 b (5.25 Earth radii, 23.6 Earth mass) with the Hubble Space Telescope's Wide Field Camera 3 instrument. TOI-674 b is deep into the Neptune desert, an observed paucity of Neptune-size exoplanets at short orbital periods. Planets in the desert are thought to have complex evolutionary histories due to photoevaporative mass loss or orbital migration, making identifying the constituents of their atmospheres critical to understanding their origins. We obtained near-infrared transmission spectroscopy of the planet's atmosphere with the G141 grism, which we detrended and fit. After extracting the transmission spectrum from the data, we used the petitRADTRANS atmospheric spectral synthesis code to perform retrievals on the planet's atmosphere to identify which absorbers are present. These results show evidence for increased absorption at 1.4 μm due to water vapor at 2.1σ (Bayes factor = 3.2). With these results, TOI-674 b joins the exclusive club of exoplanets with featured transmission spectra. TOI-674 b is a strong candidate for further study to refine the water abundance, which is poorly constrained by our data. We also incorporated new TESS short-cadence optical photometry, as well as Spitzer/IRAC data, and re-fit the transit parameters for the planet. We find the planet to have the following transit parameters: R_p/R_∗ = 0.1135±0.0006, T₀ = 2458544.523792 ± 0.000452 BJD, and P = 1.977198 ± 0.00007 d. These measurements refine the planet radius estimate and improve the orbital ephemerides for future transit spectroscopy observations of this highly intriguing warm Neptune
TESS Revisits WASP-12: Updated Orbital Decay Rate and Constraints on Atmospheric Variability
No full textAfter observing WASP-12 in the second year of the primary mission, the Transiting Exoplanet Survey Satellite (TESS) revisited the system in late 2021 during its extended mission. In this paper, we incorporate the new TESS photometry into a reanalysis of the transits, secondary eclipses, and phase curve. We also present a new Ks-band occultation observation of WASP-12b obtained with the Palomar/Wide-field Infrared Camera instrument. The latest TESS photometry spans three consecutive months, quadrupling the total length of the TESS WASP-12 light curve and extending the overall time baseline by almost two years. Based on the full set of available transit and occultation timings, we find that the orbital period is shrinking at a rate of −29.81 ± 0.94 ms yr⁻¹. The additional data also increase the measurement precision of the transit depth, orbital parameters, and phase-curve amplitudes. We obtain a secondary eclipse depth of 466 ± 35 ppm, a 2σ upper limit on the nightside brightness of 70 ppm, and a marginal 6 2 ± 2 8 eastward offset between the dayside hotspot and the substellar point. The voluminous TESS data set allows us to assess the level of atmospheric variability on timescales of days, months, and years. We do not detect any statistically significant modulations in the secondary eclipse depth or day–night brightness contrast. Likewise, our measured K_s-band occultation depth of 2810 ± 390 ppm is consistent with most ∼2.2 μm observations in the literature
Intelligent Bio-Impedance System for Personalized Continuous Blood Pressure Measurement
No full textContinuous blood pressure (BP) measurement is crucial for long-term cardiovascular monitoring, especially for prompt hypertension detection. However, most of the continuous BP measurements rely on the pulse transit time (PTT) from multiple-channel physiological acquisition systems that impede wearable applications. Recently, wearable and smart health electronics have become significant for next-generation personalized healthcare progress. This study proposes an intelligent single-channel bio-impedance system for personalized BP monitoring. Compared to the PTT-based methods, the proposed sensing configuration greatly reduces the hardware complexity, which is beneficial for wearable applications. Most of all, the proposed system can extract the significant BP features hidden from the measured bio-impedance signals by an ultra-lightweight AI algorithm, implemented to further establish a tailored BP model for personalized healthcare. In the human trial, the proposed system demonstrates the BP accuracy in terms of the mean error (ME) and the mean absolute error (MAE) within 1.7 ± 3.4 mmHg and 2.7 ± 2.6 mmHg, respectively, which agrees with the criteria of the Association for the Advancement of Medical Instrumentation (AAMI). In conclusion, this work presents a proof-of-concept for an AI-based single-channel bio-impedance BP system. The new wearable smart system is expected to accelerate the artificial intelligence of things (AIoT) technology for personalized BP healthcare in the future
The DNA–carbon nanotube binding mode determines the efficiency of carbon nanotube-mediated DNA delivery to intact plants
No full textEfficient delivery of DNA, RNA, and genome engineering machinery to plant cells will enable efforts to genetically modify plants for global food security, sustainable energy production, synthetic biology applications, and climate change resilience. For the delivery of functional genetic units into plant cells, charged nanoparticles, particularly carbon nanotubes (CNT), have attracted considerable interest. Although some success has been achieved using CNT-based approaches, the efficiency, batch reproducibility, and the limits of their applicability remain to be assessed. Here, we provide a mechanistic understanding of plasmid DNA-loaded CNTs based transfection of plant cells, and factors affecting the expression of the transformed plasmid. We show that transfection is inherently limited by the presence of the cell wall, Coulomb interactions between DNA and polymer coated CNT, and DNA size, whereas expression of the transformed plasmid is limited by relative gene-to-plasmid size and the intracellular accessibility of DNA. We further show that the formation of partially condensed DNA on the CNT surface is a prerequisite for successful transfection and expression. Furthermore, DNA does not detach completely from the CNT, so the accessibility of the transcription machinery to DNA is the key for transformation efficiency. This irreversible DNA plasmid binding and partial condensation limit the length of DNA that can be expressed, thus negatively affecting efficiency and reproducibility. Understanding the underlying mechanisms and limitations of CNT-mediated delivery of DNA through the plant cell wall is of considerable importance in guiding efforts to design nanomaterials for efficient transformation, trait engineering, and synthetic biology applications