Recycled stellar ejecta as fuel for star formation and implications for the origin of the galaxy mass-metallicity relation

We use cosmological, hydrodynamical simulations from the Evolution and Assembly of GaLaxies and their Environments and OverWhelmingly Large Simulations projects to assess the significance of recycled stellar ejecta as fuel for star formation. The fractional contributions of stellar mass-loss to the cosmic star formation rate (SFR) and stellar mass densities increase with time, reaching 35 and 19 per cent, respectively, at z = 0. The importance of recycling increases steeply with galaxy stellar mass forM* < 1010.5M_, and decreases mildly at higher mass. This trend arises from the mass dependence of feedback associated with star formation and AGN, which preferentially suppresses star formation fuelled by recycling. Recycling is more important for satellites than centrals and its contribution decreases with galactocentric radius. The relative contribution of asymptotic giant branch (AGB) stars increases with time and towards galaxy centres. This is a consequence of the more gradual release of AGB ejecta compared to that of massive stars, and the preferential removal of the latter by star formation driven outflows and by lock up in stellar remnants. Recycling-fuelled star formation exhibits a tight, positive correlation with galaxy metallicity, with a secondary dependence on the relative abundance of alpha elements (which are predominantly synthesized in massive stars), that is insensitive to the subgrid models for feedback. Hence, our conclusions are directly relevant for the origin of the mass–metallicity relation and metallicity gradients. Applying the relation between recycling and metallicity to the observed mass–metallicity relation yields our best estimate of the mass-dependent contribution of recycling. For centrals with a mass similar to that of the Milky Way, we infer the contributions of recycled stellar ejecta to the SFR and stellar mass to be 35 and 20 per cent, respectively

Flickering AGN can explain the strong circumgalactic O VI observed by COS-Halos

Proximity zone fossils (PZFs) are ionization signatures around recently active galactic nuclei (AGNs) where metal species in the circumgalactic medium remain overionized after the AGNs have shut off due to their long recombination time scales. We explore cosmological zoom hydrodynamic simulations, using the EAGLE (Evolution and Assembly of GaLaxies and their Environments) model paired with a non-equilibrium ionization and cooling module including time-variable AGN radiation to model PZFs around star-forming disc galaxies in the z ∼ 0.2 Universe. Previous simulations typically underestimated the O VI content of galactic haloes, but we show that plausible PZF models increase O VI column densities by 2 − 3 × to achieve the levels observed around COS-Halos star-forming galaxies out to 150 kpc. Models with AGN bolometric luminosities 1043.6erg s−1, duty cycle fractions 10 per cent, and AGN lifetimes 106 yr are the most promising, because their supermassive black holes grow at the cosmologically expected rate and they mostly appear as inactive AGN, consistent with COS-Halos. The central requirement is that the typical star-forming galaxy hosted an active AGN within a time-scale comparable to the recombination time of a high metal ion, which for circumgalactic O VI is ≈107 yr. H I, by contrast, returns to equilibrium much more rapidly due to its low neutral fraction and does not show a significant PZF effect. O VI absorption features originating from PZFs appear narrow, indicating photoionization, and are often well aligned with lower metal ion species. PZFs are highly likely to affect the physical interpretation of circumgalactic high ionization metal lines if, as expected, normal galaxies host flickering AGN

The Wellesley News (06-10-1957)

https://repository.wellesley.edu/wcnews/1157/thumbnail.jp

Molecular analysis of the interaction between the probiotic Lactobacillus rhamnosus GG and intestinal epithelial cells

Probiotics are defined as live micro-organisms which, when administered in adequate amounts, confer a health bene&#64257;t on the host . Growing numbers of intervention trials show that certain bacterial strains or mixtures of strains, generally lactobacilli and bifidobacteria, can confer specific health benefits. Many of the interactions between probiotic bacteria and the host are thought to be mediated by molecular structures, known as microbe-associated molecular patterns (MAMPs), which can be recognized by the host through specific pattern recognition receptors (PRRs), such as Toll-like receptors (TLRs). Unfortunately, in human intervention trials, there is often a lack of attention to mechanisms of actions. Nevertheless, we believe that for an optimized application of probiotics, it is imperative to understand the mechanisms of interaction with the host in detail. Lactobacillus rhamnosus GG is one of the best described probiotic strains with proven health benefits including promotion of gastro-intestinal health, prevention of respiratory tract infections and modulation of the immune system. In this PhD research, we aimed to develop a platform for the elucidation of PRR-mediated probiotic mechanisms, in specific with intestinal epithelial cells (IECs). We chose to focus on previously described cell wall components of L. rhamnosus GG: lipoteichoic acid (LTA), the spaCBA pili and the major secreted proteins Msp1 and Msp2. Earlier research indicated that the promiscuous TLR-2 might be an important PRR for L. rhamnosus GG. First, we developed TLR reporter cell lines in a simple HEK293T model cell to analyze whether the bacterial cell wall compounds could activate TLR-mediated NF-&#954;B signaling. An important innovative step in this PhD thesis was the development of a stable TLR-2/TLR-6 expressing cell line. Hereby, we aimed to investigate the roll of bacterial cell wall compounds as MAMPs by their co-incubation with these reporter cell lines under different forms: purified fractions (with or without chemical modification), recombinant proteins, and mutant strains that allow to investigate the presentation of MAMPs in their cellular context. We also aimed to elucidate structure-activity relationships (SAR) of MAMP-PRR interactions in a second step. In a third step, we aimed to confirm the initial findings in a more complex setting in IEC lines.LTA is generally regarded as the Gram-positive counterpart of Gram-negative lipopolysaccharides. In this work, we used highly purified LTA and a mutant with a modified LTA structure to show that LTA is an important MAMP of L. rhamnosus GG for the interaction with TLR-2, only when present in a heterodimer with TLR-6, resulting in NF-&#954;B activation. The SAR analysis confirmed that the acyl chains of the glycolipid anchor are critical for binding to the receptor. These findings could be confirmed in the Caco-2 IEC line, as LTA induced the pro-inflammatory chemokine IL-8. These data support a key role for LTA in immune stimulatory actions of L. rhamnosus GG.SpaCBA pili are proteinaceous protrusions of the cell surface that play a crucial role in the excellent adherence capacity of L. rhamnosus GG. We analyzed isogenic single and double mutants of L. rhamnosus GG for their capacity to interact with TLR-2/TLR-6. The data suggest that the SpaCBA pili, when presented on live cells, negatively interfere with TLR-2/TLR-6 mediated NF-&#954;B induction by other ligands, such as LTA. To gain better insights in the immunomodulatory role of L. rhamnosus GG, we optimized a purification protocol to obtain native SpaCBA pili in pure form. Surprisingly, the first data with these purified pili show that they can significantly activate NF-&#954;B signaling in the TLR-2/TLR-6 cell line when presented under this form at a concentration of 5 µg/ml. The major secreted proteins Msp1 and Msp2 were previously shown to promote homeostasis in IECs, dependent on the Akt signaling pathway. Here, we show that 10-100 µg/ml of the recombinant proteins could induce TLR-2/TLR-6 mediated NF-&#954;B signaling. Moreover, the purified native glycosylated Msp1 did also induce NF-&#954;B activation in the TLR-2/TLR-6 cell line, indicating that the glycosylation does not play a major role in this interaction. Whether Msp1/2 mediated TLR-2/TLR-6 signaling is also involved in Akt activation, remains under investigation. In this PhD work, we contributed to better molecular insights on MAMP-TLR2/6 interactions of L. rhamnosus GG, although many details remain to be unraveled. Nevertheless, we are convinced that the unique set-up with the use of both proteins (recombinant and purified) and mutant strains can help elucidate MAMP-PRR interactions and SAR. This platform could further help to clarify probiotic modes of action and could help the design of novel applications, not only in L. rhamnosus GG, but also in other strains.nrpages: 165status: publishe

Molecular analysis of the interaction between the probiotic **Lactobacillus rhamnosus** GG and intestinal epithelial cells

Probiotics are defined as live micro-organisms which, when administered in adequate amounts, confer a health bene&#64257;t on the host . Growing numbers of intervention trials show that certain bacterial strains or mixtures of strains, generally lactobacilli and bifidobacteria, can confer specific health benefits. Many of the interactions between probiotic bacteria and the host are thought to be mediated by molecular structures, known as microbe-associated molecular patterns (MAMPs), which can be recognized by the host through specific pattern recognition receptors (PRRs), such as Toll-like receptors (TLRs). Unfortunately, in human intervention trials, there is often a lack of attention to mechanisms of actions. Nevertheless, we believe that for an optimized application of probiotics, it is imperative to understand the mechanisms of interaction with the host in detail. Lactobacillus rhamnosus GG is one of the best described probiotic strains with proven health benefits including promotion of gastro-intestinal health, prevention of respiratory tract infections and modulation of the immune system. In this PhD research, we aimed to develop a platform for the elucidation of PRR-mediated probiotic mechanisms, in specific with intestinal epithelial cells (IECs). We chose to focus on previously described cell wall components of L. rhamnosus GG: lipoteichoic acid (LTA), the spaCBA pili and the major secreted proteins Msp1 and Msp2. Earlier research indicated that the promiscuous TLR-2 might be an important PRR for L. rhamnosus GG. First, we developed TLR reporter cell lines in a simple HEK293T model cell to analyze whether the bacterial cell wall compounds could activate TLR-mediated NF-&#954;B signaling. An important innovative step in this PhD thesis was the development of a stable TLR-2/TLR-6 expressing cell line. Hereby, we aimed to investigate the roll of bacterial cell wall compounds as MAMPs by their co-incubation with these reporter cell lines under different forms: purified fractions (with or without chemical modification), recombinant proteins, and mutant strains that allow to investigate the presentation of MAMPs in their cellular context. We also aimed to elucidate structure-activity relationships (SAR) of MAMP-PRR interactions in a second step. In a third step, we aimed to confirm the initial findings in a more complex setting in IEC lines.LTA is generally regarded as the Gram-positive counterpart of Gram-negative lipopolysaccharides. In this work, we used highly purified LTA and a mutant with a modified LTA structure to show that LTA is an important MAMP of L. rhamnosus GG for the interaction with TLR-2, only when present in a heterodimer with TLR-6, resulting in NF-&#954;B activation. The SAR analysis confirmed that the acyl chains of the glycolipid anchor are critical for binding to the receptor. These findings could be confirmed in the Caco-2 IEC line, as LTA induced the pro-inflammatory chemokine IL-8. These data support a key role for LTA in immune stimulatory actions of L. rhamnosus GG.SpaCBA pili are proteinaceous protrusions of the cell surface that play a crucial role in the excellent adherence capacity of L. rhamnosus GG. We analyzed isogenic single and double mutants of L. rhamnosus GG for their capacity to interact with TLR-2/TLR-6. The data suggest that the SpaCBA pili, when presented on live cells, negatively interfere with TLR-2/TLR-6 mediated NF-&#954;B induction by other ligands, such as LTA. To gain better insights in the immunomodulatory role of L. rhamnosus GG, we optimized a purification protocol to obtain native SpaCBA pili in pure form. Surprisingly, the first data with these purified pili show that they can significantly activate NF-&#954;B signaling in the TLR-2/TLR-6 cell line when presented under this form at a concentration of 5 µg/ml. The major secreted proteins Msp1 and Msp2 were previously shown to promote homeostasis in IECs, dependent on the Akt signaling pathway. Here, we show that 10-100 µg/ml of the recombinant proteins could induce TLR-2/TLR-6 mediated NF-&#954;B signaling. Moreover, the purified native glycosylated Msp1 did also induce NF-&#954;B activation in the TLR-2/TLR-6 cell line, indicating that the glycosylation does not play a major role in this interaction. Whether Msp1/2 mediated TLR-2/TLR-6 signaling is also involved in Akt activation, remains under investigation. In this PhD work, we contributed to better molecular insights on MAMP-TLR2/6 interactions of L. rhamnosus GG, although many details remain to be unraveled. Nevertheless, we are convinced that the unique set-up with the use of both proteins (recombinant and purified) and mutant strains can help elucidate MAMP-PRR interactions and SAR. This platform could further help to clarify probiotic modes of action and could help the design of novel applications, not only in L. rhamnosus GG, but also in other strains.nrpages: 165status: publishe

Towards a better understanding of **Lactobacillus rhamnosus** GG - host interactions

Lactobacillus rhamnosus GG (LGG) is one of the most widely used probiotic strains. Various health effects are well documented including the prevention and treatment of gastro-intestinal infections and diarrhea, and stimulation of immune responses that promote vaccination or even prevent certain allergic symptoms. However, not all intervention studies could show a clinical benefit and even for the same conditions, the results are not univocal. Clearly, the host phenotype governed by age, genetics and environmental factors such as the endogenous microbiota, plays a role in whether individuals are responders or non-responders. However, we believe that a detailed knowledge of the bacterial physiology and the LGG molecules that play a key role in its host-interaction capacity is crucial for a better understanding of its potential health benefits. Molecules that were yet identified as important factors governing host interactions include its adhesive pili or fimbriae, its lipoteichoic acid molecules, its major secreted proteins and its galactose-rich exopolysaccharides, as well as specific DNA motifs. Nevertheless, future studies are needed to correlate specific health effects to these molecular effectors in LGG, and also in other probiotic strains

Energy Efficiency in School Buildings: The Need for a Tailor-Made Business Model

Energy efficiency (EE) for buildings can be an essential aid to the climate objectives regarding the reduction of greenhouse gas emissions (GHG). More and more, the potential of maintenance and energy performance contract (EPC) is being recognized for this implementation, with the help of an energy service company (ESCO) whether accompanied by a facilitator. Clustering buildings can be an additional asset: since in this way the risks for the ESCO can be spread, the projects with a quick and high return on investment are a catalyst for long-term projects and finally, because of the higher absolute amount of investment these projects become more interested for/in the financial partners, which can be realized through adapted business models. In this article, we discuss two cases related to the pooling of buildings for higher and secondary education institutions. The university of applied sciences PXL with 12 buildings, all under own management and the association of schools in Sint-Niklaas (54 different location in the city), belongs to four different school communities. For both cases, the limits of the “classical” maintenance EPC are discussed and an adjusted approach with the corresponding business model is reported. As the educational value for both institutions is also of great importance, the link between energy efficiency and the didactic component, as well as the interaction with other stakeholders in the buildings (in- and extern) is explained

Metals in the circumgalactic medium are out of ionization equilibrium due to fluctuating active galactic nuclei

We study the effect of a fluctuating active galactic nucleus (AGN) on the abundance of circumgalactic OVI in galaxies selected from the EAGLE simulations. We follow the time-variable OVI abundance in post-processing around four galaxies - two at $z=0.1$ with stellar masses of $M_{\ast} \sim 10^{10}$ M$_{\odot}$ and $M_{\ast} \sim 10^{11}$ M$_{\odot}$, and two at $z=3$ with similar stellar masses - out to impact parameters of twice their virial radii, implementing a fluctuating central source of ionizing radiation. Due to delayed recombination, the AGN leave significant `AGN proximity zone fossils' around all four galaxies, where OVI and other metal ions are out of ionization equilibrium for several megayears after the AGN fade. The column density of OVI is typically enhanced by $\approx 0.3-1.0$ dex at impact parameters within $0.3R_{\rm vir}$, and by $\approx 0.06-0.2$ dex at $2R_{\rm vir}$, thereby also enhancing the covering fraction of OVI above a given column density threshold. The fossil effect tends to increase with increasing AGN luminosity, and towards shorter AGN lifetimes and larger AGN duty cycle fractions. In the limit of short AGN lifetimes, the effect converges to that of a continuous AGN with a luminosity of $(f_{\rm duty}/100\%)$ times the AGN luminosity. We also find significant fossil effects for other metal ions, where low-ionization state ions are decreased (SiIV, CIV at $z=3$) and high-ionization state ions are increased (CIV at $z=0.1$, NeVIII, MgX). Using observationally motivated AGN parameters, we predict AGN proximity zone fossils to be ubiquitous around $M_{\ast} \sim 10^{10-11}$ M$_{\odot}$ galaxies, and to affect observations of metals in the circumgalactic medium at both low and high redshifts.Comment: 17 pages, 11 figures (not including appendix), accepted for publication in MNRA

Clinical and electrophysiological markers of primary progressive aphasia : a systematic review

Primary Progressive Aphasia (PPA) refers to a group of clinical syndromes characterized by the progressive loss of language functions with initial preservation of the other cognitive functions. Despite the availability of international guidelines for diagnosing PPA and its variants (Gorno-Tempini et al., 2011), the differential diagnosis and clinical distinction between variants in the early disease stage remains complex and challenging. Consequently, the aim of this systematic review was to establish language, speech and electrophysiological markers to identify PPA and its variants. To provide clinical markers, studies in which the initial symptoms were reported by the patients or their family and studies in which the quantitative and qualitative results of the speech and language assessments performed at initial specialty referral were described, were included. Furthermore, studies in which an electrophysiological measurement technique was used in patients with PPA were included in the systematic review. An overview of the initial symptoms, the initial speech and language assessments and electrophysiological techniques to improve an early-stage diagnosis of PPA is provided in this poster. However, research on the electrophysiological processes in PPA is still limited, only seven electrophysiological studies were included in this review. Further research is required to investigate the applicability of electrophysiological measurement techniques for diagnosing PPA