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Discovery of new strains of bacteria that inhibit pathogen growth can facilitate improvements in biocontrol and probiotic strategies. Traditional, plate-based co-culture approaches that probe microbial interactions can impede this discovery as these methods are inherently low-throughput, labor-intensive, and qualitative. We report a second-generation, photo-addressable microwell device, developed to iteratively screen interactions between candidate biocontrol agents existing in bacterial strain libraries and pathogens under increasing pathogen pressure. Microwells (0.6 pl volume) provide unique co-culture sites between library strains and pathogens at controlled cellular ratios. During sequential screening iterations, library strains are challenged against increasing numbers of pathogens to quantitatively identify microwells containing strains inhibiting the highest numbers of pathogens. Ring-patterned 365 nm light is then used to ablate a photodegradable hydrogel membrane and sequentially release inhibitory strains from the device for recovery. Pathogen inhibition with each recovered strain is validated, followed by whole genome sequencing. To demonstrate the rapid nature of this approach, the device was used to screen a 293-membered biovar 1 agrobacterial strain library for strains inhibitory to the plant pathogen Agrobacterium tumefaciens sp. 15955. One iterative screen revealed nine new inhibitory strains. For comparison, plate-based methods did not uncover any inhibitory strains from the library (n = 30 plates). The novel pathogen-challenge screening mode developed here enables rapid selection and recovery of strains that effectively suppress pathogen growth from bacterial strain libraries, expanding this microwell technology platform toward rapid, cost-effective, and scalable screening for probiotics, biocontrol agents, and inhibitory molecules that can protect against known or emerging pathogens.

 

Combining archival photometric observations from multiple large-area surveys spanning the past 17 years, we detect long-term variability in the light curves of ZTF J032833.52−121945.27 (ZTF J0328−1219), ZTF J092311.41+423634.16 (ZTF J0923+4236), and WD 1145+017, all known to exhibit transits from planetary debris. ZTF J0328−1219 showed an overall fading in brightness from 2011 through to 2015, with a maximum dimming of ≃0.3 mag, and still remains ≃0.1 mag fainter compared to 2006. We complement the analysis of the long-term behaviour of these systems with high-speed photometry. In the case of ZTF J0923+4236 and WD 1145+017, the time-series photometry exhibits vast variations in the level of transit activity, both in terms of numbers of transits, as well as their shapes and depths, and these variations correlate with the overall brightness of the systems. Inspecting the current known sample of white dwarfs with transiting debris, we estimate that similar photometric signatures may be detectable in one in a few hundred of all white dwarfs. Accounting for the highly aligned geometry required to detect transits, our estimates imply that a substantial fraction of all white dwarfs exhibiting photospheric metal pollution from accreted debris host close-in planetesimals that are currently undergoing disintegration.

 

We present photometry and spectroscopy of the slowly evolving superluminous Type IIn supernova (SN) 2015da. SN 2015da is extraordinary for its very high peak luminosity, and also for sustaining a high luminosity for several years. Even at 8 yr after explosion, SN 2015da remains as luminous as the peak of a normal SN II-P. The total radiated energy integrated over this time period (with no bolometric correction) is at least $1.6 \times 10^{51}$ erg (or 1.6 FOE). Including a mild bolometric correction, adding kinetic energy of the expanding cold dense shell of swept-up circumstellar material (CSM), and accounting for asymmetry, the total explosion kinetic energy was likely 5–10 FOE. Powering the light curve with CSM interaction requires an energetic explosion and 20 M$_{\odot }$ of H-rich CSM, which in turn implies a massive progenitor system $\gt $30 M$_{\odot }$. Narrow P Cyg features show steady CSM expansion at 90 km s$^{-1}$, requiring a high average mass-loss rate of $\sim$0.1 M$_{\odot }$ yr$^{-1}$ sustained for two centuries before explosion (although ramping up toward explosion time). No current theoretical model for single-star pre-SN mass-loss can account for this. The slow CSM, combined with broad wings of H $\alpha$ indicating H-rich material in the unshocked ejecta, disfavours a pulsational pair instability model for the pre-SN mass-loss. Instead, violent pre-SN binary interaction is a likely culprit. Finally, SN 2015da exhibits the characteristic asymmetric blueshift in its emission lines from shortly after peak until the present epoch, adding another well-studied superluminous SNe IIn with unambiguous evidence of post-shock dust formation.

 

For aging to evolve, selection against mortality must decrease with age. This prevailing view in the evolutionary theory of senescence posits that mutations with deleterious effects happening late in life—when purging selection is weak—may become fixed via genetic drift in the germline, and produce a senescent phenotype. Theory, however, has focused primarily on growing populations and the fate of single deleterious mutations. In a mathematical model, we demonstrate that relaxing both of these simplifying assumptions leads to unrealistic outcomes. In density-regulated populations, previously fixed deleterious mutations should promote the fixation of other deleterious mutations that lead to senescence at ever younger ages, until death necessarily occurs at sexual maturity. This sequential fixation of deleterious mutations is not promoted by a decrease in population size, but is due to a change in the strength of selection. In an individual-based model, we also show that such evolutionary dynamics should lead to the extinction of most populations. Our models therefore make rather unrealistic predictions, underlining the need for a reappraisal of current theories. In this respect, we have further assumed in our models that the deleterious effects of mutations can only occur at certain ages, marked, for instance, by somatic or physiological changes. Under this condition, we show that the catastrophic accumulation of deleterious mutations in the germline can stop. This new finding emphasizes the importance of investigating somatic factors, as well as other mechanisms underlying the deleterious effects of mutations, to understand senescence evolution. More generally, our model therefore establishes that patterns of senescence in nature depend not only on the decrease in selection strength with age but also on any mechanism that stops the catastrophic accumulation of mutations.

 

We measure the CO-to-H₂conversion factor (α_CO) in 37 galaxies at 2 kpc resolution, using the dust surface density inferred from far-infrared emission as a tracer of the gas surface density and assuming a constant dust-to-metal ratio. In total, we have ∼790 and ∼610 independent measurements ofα_COfor CO (2–1) and (1–0), respectively. The mean values forα_{CO (2–1)}andα_{CO (1–0)}are${9.3}_{-5.4}^{+4.6}$and${4.2}_{-2.0}^{+1.9}{M}_{\odot }{\mathrm{pc}}^{-2}{(\mathrm{K}\mathrm{km}{\mathrm{s}}^{-1})}^{-1}$, respectively. The CO-intensity-weighted mean is 5.69 forα_{CO (2–1)}and 3.33 forα_{CO (1–0)}. We examine howα_COscales with several physical quantities, e.g., the star formation rate (SFR), stellar mass, and dust-mass-weighted average interstellar radiation field strength ($\overline{U}$). Among them,$\overline{U}$, Σ_SFR, and the integrated CO intensity (W_CO) have the strongest anticorrelation with spatially resolvedα_CO. We provide linear regression results toα_COfor all quantities tested. At galaxy-integrated scales, we observe significant correlations betweenα_COandW_CO, metallicity,$\overline{U}$, and Σ_SFR. We also find thatα_COin each galaxy decreases with the stellar mass surface density (Σ_⋆) in high-surface-density regions (Σ_⋆≥ 100M_⊙pc⁻²), following the power-law relations${\alpha }_{\mathrm{CO}(2–1)}\propto {\mathrm{\Sigma }}_{\star }^{-0.5}$and${\alpha }_{\mathrm{CO}(1–0)}\propto {\mathrm{\Sigma }}_{\star }^{-0.2}$. The power-law index is insensitive to the assumed dust-to-metal ratio. We interpret the decrease inα_COwith increasing Σ_⋆as a result of higher velocity dispersion compared to isolated, self-gravitating clouds due to the additional gravitational force from stellar sources, which leads to the reduction inα_CO. The decrease inα_COat high Σ_⋆is important for accurately assessing molecular gas content and star formation efficiency in the centers of galaxies, which bridge “Milky Way–like” to “starburst-like” conversion factors.

 

In this paper, we discuss some of the key challenges in the study of time-dependent processes and non-equilibrium behaviour in warm dense matter. We outline some of the basic physics concepts that have underpinned the definition of warm dense matter as a subject area in its own right and then cover, in a selective, non-comprehensive manner, some of the current challenges, pointing along the way to topics covered by the papers presented in this volume. This article is part of the theme issue ‘Dynamic and transient processes in warm dense matter’. 

The geometry of the blood vessel wall plays a regulatory role on the motion of red blood cells (RBCs). The overall topography of the vessel wall depends on many features, among which the endothelial lining of the endothelial surface layer (ESL) is an important one. The endothelial lining of vessel walls presents a large surface area for exchanging materials between blood and tissues. The ESL plays a critical role in regulating vascular permeability, hindering leukocyte adhesion as well as inhibiting coagulation during inflammation. Changes in the ESL structure are believed to cause vascular hyperpermeability and entrap immune cells during sepsis, which could significantly alter the vessel wall geometry and disturb interactions between RBCs and the vessel wall, including the wall-induced migration of RBCs and the thickening of a cell-free layer. To investigate the influence of the vessel wall geometry particularly changed by the ESL under various pathological conditions, such as sepsis, on the motion of RBCs, we developed two models to represent the ESL using the immersed boundary method in two dimensions. In particular, we used simulations to study how the lift force and drag force on a RBC near the vessel wall vary with different wall thickness, spatial variation, and permeability associated with changes in the vessel wall geometry. We find that the spatial variation of the wall has a significant effect on the wall-induced migration of the RBC for a high permeability, and that the wall-induced migration is significantly inhibited as the vessel diameter is increased. 

Warm dense matter is a material state in the region of parameter space connecting condensed matter to classical plasma physics. In this intermediate regime, we investigate the significance of non-adiabatic electron-ion interactions upon ion dynamics. To disentangle non-adiabatic from adiabatic electron-ion interactions, we compare the ion self-diffusion coefficient from the non-adiabatic electron force field computational model with an adiabatic, classical molecular dynamics simulation. A classical pair potential developed through a force-matching algorithm ensures the only difference between the models is due to the electronic inertia. We implement this new method to characterize non-adiabatic effects on the self-diffusion of warm dense hydrogen over a wide range of temperatures and densities. Ultimately we show that the impact of non-adiabatic effects is negligible for equilibrium ion dynamics in warm dense hydrogen. This article is part of the theme issue ‘Dynamic and transient processes in warm dense matter’.