Nutrient-rich Conditions Research Articles

Non-linear latitudinal cline of egg size and its consequence for larval survival in the rhinoceros beetle

Abstract The egg size of insects often exhibits latitudinal trends, which are attributed to local adaptations to temperature or temperature-related ecological factors. Although increased egg size improves offspring fitness, the relationship between size and fitness is influenced largely by environmental variables. Additionally, there is a trade-off between the size and number of eggs if the quantity of reproductive resources is constant. Despite the key associations among offspring size, number and performance, relatively few studies have jointly considered these traits when studying the genetic differentiation of egg size. Here, we examined the effects of latitude on egg size using 14 populations of the univoltine rhinoceros beetle Trypoxylus dichotomus (Coleoptera, Scarabaeidae, Dynastinae) along a 1200-km latitudinal gradient under common garden laboratory conditions. We found that egg size decreased with increasing latitude in a non-linear manner. Geographical variation in egg size was independent of maternal body size, and there was no difference in female lifetime fecundity between the low-latitude (large eggs) and high-latitude (small eggs) populations. Therefore, low-latitude females invest more resources in reproduction compared with high-latitude females. We further found that the larvae of the high-latitude population showed higher mortality than those of the low-latitude population under both nutrient-poor and nutrient-rich conditions. Although the ecological factors that shape the non-linear cline of egg size were not identified in our study, geographical variation in local environments or in female reproductive strategies could have caused the latitudinal trend.

Characteristics of Phytoplankton Community Structure and Indication to Water Quality in the Lake in Agricultural Areas

In recent years, lakes’ water quality and quantity have been affected and damaged by agricultural activities. The sensitivity of phytoplankton to the hydrological environment can effectively indicate the health of the aquatic ecosystem and the change in water quality. Understanding the changes of phytoplankton communities in lakes contaminated by agriculture may contribute to determining the directions of protection of these water bodies and provide reference cases for wider research. It is found that there are 146 species, 63 genera, and 8 phyla of phytoplankton, including 57 species of Bacillariophyta, 46 species of Chlorophyta, 17 species of Cyanobacteria and Euglenophyta. The total abundance was changed successively with Bacillariophyta (75% in June), Cyanobacteria (50% in July–August), and Chlorophyta (75% in September–October). The total biomass decreased continuously over time. The biomass of Chlorophyta is highest in October (67.4%), and diatoms contribute the most biomass in other months (76.5%). The Redundancy analysis indicated that the main environmental factors affecting phytoplankton’s dynamic change are total salt, water temperature, total phosphorus, and 5-day biochemical oxygen demand. The phytoplankton can be divided into 21 functional groups. The MP group has the highest frequency, mainly distributed in the frequently stirred and turbid shallow water. Representative functional groups indicate the high degree of eutrophication and nutrient-rich conditions and the good associated environment for phytoplankton and slow water flow rate. With the seasonal change of agricultural irrigation and drainage, the water quality of Xinmiao Lake began to deteriorate from medium pollution in July and reached serious pollution in October finally. Furthermore, this research discovered that the risk of cyanobacteria bloom is high in summer, primarily when thermal stratification occurs. This study provides necessary information for understanding and predicting the changes of the phytoplankton community caused by the increase of nutrients, human disturbance, and temperature conditions in eutrophic lakes in agricultural areas.

Dot6/Tod6 degradation fine-tunes the repression of ribosome biogenesis under nutrient-limited conditions

SummaryRibosome biogenesis (Ribi) is a complex and energy-consuming process, and should therefore be repressed under nutrient-limited conditions to minimize unnecessary cellular energy consumption. In yeast, the transcriptional repressors Dot6 and Tod6 are phosphorylated and inactivated by the TORC1 pathway under nutrient-rich conditions, but are activated and repress ∼200 Ribi genes under nutrient-limited conditions. However, we show that in the presence of rapamycin or under nitrogen starvation conditions, Dot6 and Tod6 were readily degraded by the proteasome in a SCFGrr1 and Tom1 ubiquitin ligase-dependent manner, respectively. Moreover, promiscuous accumulation of Dot6 and Tod6 excessively repressed Ribi gene expression as well as translation activity and caused a growth defect in the presence of rapamycin. Thus, we propose that degradation of Dot6 and Tod6 is a novel mechanism to ensure an appropriate level of Ribi gene expression and thereby fine-tune the repression of Ribi and translation activity for cell survival under nutrient-limited conditions.

A lysosomal biogenesis map reveals the cargo spectrum of yeast vacuolar protein targeting pathways.

The lysosome is the major catabolic organelle in the cell that has been established as a key metabolic signaling center. Mutations in many lysosomal proteins have catastrophic effects and cause neurodegeneration, cancer, and age-related diseases. The vacuole is the lysosomal analog of Saccharomyces cerevisiae that harbors many evolutionary conserved proteins. Proteins reach vacuoles via the Vps10-dependent endosomal vacuolar protein sorting pathway, via the alkaline phosphatase (ALP or AP-3) pathway, and via the cytosol-to-vacuole transport (CVT) pathway. A systematic understanding of the cargo spectrum of each pathway is completely lacking. Here, we use quantitative proteomics of purified vacuoles to generate the yeast lysosomal biogenesis map. This dataset harbors information on the cargo-receptor relationship of almost all vacuolar proteins. We map binding motifs of Vps10 and the AP-3 complex and identify a novel cargo of the CVT pathway under nutrient-rich conditions. Our data show how organelle purification and quantitative proteomics can uncover fundamental insights into organelle biogenesis.

Exposure to lysed bacteria can promote or inhibit growth of neighboring live bacteria depending on local abiotic conditions.

Microbial death is extremely common in nature, yet the ecological role of dead bacteria is unclear. Dead cells are assumed to provide nutrients to surrounding microbes, but may also affect them in other ways. We found that adding lysate prepared from dead bacteria to cultures of Escherichia coli in nutrient-rich conditions suppressed their final population density. This is in stark contrast with the notion that the primary role of dead cells is nutritional, although we also observed this type of effect when we added dead bacteria to cultures that were not supplied with other nutrients. We only observed the growth-suppressive effect of our dead-bacteria treatment after they had undergone significant lysis, suggesting a key role for cellular contents released during lysis. Transcriptomic analysis indicated changes in gene expression in response to dead cells in growing populations, particularly in genes involved in motility. This was supported by experiments with genetic knockouts and copy-number manipulation. Because lysis is commonplace in natural and clinical settings, the growth-suppressive effect of dead cells we describe here may be a widespread and previously unrecognized constraint on bacterial population growth.

Cascading effects of predators on algal size structure

The presence of edible and inedible prey species in a food web can influence the strength that nutrients (bottom-up) or herbivores (top-down) have on primary production. In boreal peatlands, wetter more nutrient-rich conditions associated with ongoing climate change are expanding consumer access to aquatic habitat and promoting sources of primary production (i.e., algae) that are susceptible to trophic regulation. Here, we used an in situ mesocosm experiment to evaluate the consequences of enhanced nutrient availability and food-web manipulation (herbivore and predator exclusion) on algal assemblage structure in an Alaskan fen. Owing to the potential for herbivores to selectively consume edible algae (small cells) in favor of more resistant forms, we predicted that the proportion of less-edible algae (large cells) would determine the strength of top-down or bottom-up effects. Consistent with these expectations, we observed an increase in algal-cell size in the presence of herbivores (2-tiered food web) that was absent in the presence of a trophic cascade (3-tiered food web), suggesting that predators indirectly prevented morphological changes in the algal assemblage by limiting herbivory. Increases in algal-cell size with herbivory were driven by a greater proportion of filamentous green algae and nitrogen-fixing cyanobacteria, whose size and morphological characteristics mechanically minimize consumption. While consumer-driven shifts in algal assemblage structure were significant, they did not prevent top-down regulation of biofilm development by herbivores. Our findings show that increasing wet periods in northern peatlands will provide new avenues for trophic regulation of algal production, including directly through consumption and indirectly via a trophic cascade.

O1 - Temperature Impacts on Streptococcus Mutans Growth and Substrate Utilization Kinetics

Streptococcus mutans has been studied as a model cariogenic bacterium for decades. In spite of myriad studies, growth and substrate utilization kinetics studies have been largely limited to human body temperature (37 C). This makes it difficult to quantitatively assess the impact of temperature on metabolic kinetics. The objective of this study is to evaluate the effect of temperature, substrate, and nutrient conditions on S. mutans biokinetic parameters to provide comparability between biokinetic studies. S. mutans UA159 from ATCC (700610) was maintained on brain heart infusion (BHI) agar plates. S. mutans was grown in a chemostat fed BHI with either sucrose or glucose to calculate yield, maximal substrate utilization rate, endogenous decay, and half saturation constant from cellmass and substrate data assuming Monod kinetics. Pseudo-first order growth rates were determined in batch culture grown on sucrose or glucose with rich (100% BHI) and diluted (10% BHI) media at different temperatures (20-37 C). An Arrhenius plot was used to assess the impact of temperature on growth. Statistical significance was determined at the 95% confidence interval. Cell yield was statistically significantly greater on sucrose compared to glucose (0.2 g biomass/g sucrose compared to 0.1 g biomass/g glucose) at 37 C. The maximal substrate utilization rate was greater on glucose-amended media compared to sucrose. At lower temperatures, cell growth rate was statistically significantly greater on glucose compared to sucrose, but at 37 C, the growth rate was statistically significantly greater for sucrose-amended diluted media. This indicates that growth on sucrose is more strongly impacted by changes in temperature under nutrient-limited conditions, as confirmed by Arrhenius slope for S. mutans at 65 +/- 15 kJ/mol while growing on glucose and 84 +/- 20 kJ/mol on sucrose. Growth on glucose under nutrient rich conditions had the greatest Arrhenius slope of 132 +/- 8 kJ/mol. These findings enhance the understanding of S. mutans biokinetics and provide useful data for comparing studies under different environmental conditions. S. mutans has a greater cell growth yield on sucrose compared to glucose. Further, growth at lower temperatures is more strongly dependent on having rich media regardless of substrate, as growth rate was approximately double in rich media compared to either sucrose or glucose in diluted media at 20 C. At greater temperatures, these nutritional requirements were less important, as kinetic rates were only 10-20% greater when grown in rich media at human body temperature.

Elucidation of TFEB nuclear translocation dynamics in human cells by means of Quantitative Modelling and Microfluidics

The Transcription Factor EB (TFEB) plays a pivotal role in the transcriptional regulation of lysosomal biogenesis and autophagy in response to starvation. TFEB activity is regulated by the kinase mTOR. In nutrient-rich conditions, mTOR phosphorylates TFEB by sequestering it in the cytoplasm. During starvation, mTOR is inhibited and unphosphorylated TFEB translocates into the nucleus, where it regulates the expression of its target genes. We performed an experiment monitoring in real-time the nuclear localization of TFEB in individual cells growing in a microfluidics device following alternating pulses of starvation and refeeding. The results revealed the presence of an “overshoot” dynamics with TFEB translocating to the nucleus upon starvation but then partially retranslocating to the cytoplasm. To elucidate the mechanism behind its nuclear shuttling dynamics, we first developed a two-compartment dynamical model (nucleus and cytoplasm) with two different species (dephosphorylated and phosphorylated TFEB) for each of the two compartments. The transport and de/phosphorylation kinetics are described with first order kinetics whose parameters depend on the nutrient status, while the total TFEB is kept constant. This model was not capable to recapitulate the observed overshoot dynamics. Consequently, we investigated two alternative models, hypothesizing that upon starvation, a nuclear export channel is activated either by TFEB itself (negative feedback loop - NFL) or as a direct consequence of mTOR inhibition (incoherent feedforward loop -IFFL). The new models were both able to qualitatively recapitulate the observed dynamics. Finally, we propose an experiment able to distinguish between the two alternative models.

Hsp40s play distinct roles during the initial stages of apolipoprotein B biogenesis.

Apolipoprotein B (ApoB) is the primary component of atherogenic lipoproteins, which transport serum fats and cholesterol. Therefore elevated levels of circulating ApoB are a primary risk factor for cardiovascular disease. During ApoB biosynthesis in the liver and small intestine under nutrient-rich conditions, ApoB cotranslationally translocates into the endoplasmic reticulum (ER) and is lipidated and ultimately secreted. Under lipid-poor conditions, ApoB is targeted for ER-associated degradation (ERAD). Although prior work identified select chaperones that regulate ApoB biogenesis, the contributions of cytoplasmic Hsp40s are undefined. To this end, we screened ApoB-expressing yeast and determined that a class A ER-associated Hsp40, Ydj1, associates with and facilitates the ERAD of ApoB. Consistent with these results, a homologous Hsp40, DNAJA1, functioned similarly in rat hepatoma cells. DNAJA1-deficient cells also secreted hyperlipidated lipoproteins in accordance with attenuated ERAD. In contrast to the role of DNAJA1 during ERAD, DNAJB1—a class B Hsp40—helped stabilize ApoB. Depletion of DNAJA1 and DNAJB1 also led to opposing effects on ApoB ubiquitination. These data represent the first example in which different Hsp40s exhibit disparate effects during regulated protein biogenesis in the ER and highlight distinct roles that chaperones can play on a single ERAD substrate.

Dynamic eIF3a O-GlcNAcylation controls translation reinitiation during nutrient stress.

In eukaryotic cells, many messenger RNAs (mRNAs) possess upstream open reading frames (uORFs) in addition to the main coding region. After uORF translation, the ribosome could either recycle at the stop codon or resume scanning for downstream start codons in a process known as reinitiation. Accumulating evidence suggests that some initiation factors, including eukaryotic initiation factor 3 (eIF3), linger on the early elongating ribosome, forming an eIF3-80S complex. Very little is known about how eIF3 is carried along with the 80S during elongation and whether the eIF3-80S association is subject to regulation. Here, we report that eIF3a undergoes dynamic O-linked N-acetylglucosamine (O-GlcNAc) modification in response to nutrient starvation. Stress-induced de-O-GlcNAcylation promotes eIF3 retention on the elongating ribosome and facilitates activating transcription factor 4 (ATF4) reinitiation. Eliminating the modification site from eIF3a via CRISPR genome editing induces ATF4 reinitiation even under the nutrient-rich condition. Our findings illustrate a mechanism in balancing ribosome recycling and reinitiation, thereby linking the nutrient stress response and translational reprogramming.

Mechanisms controlling the transformation of and resistance to mercury(II) for a plant-associated Pseudomonas sp. strain, AN-B15

Bioremediation using mercury (Hg)-volatilizing and immobilizing bacteria is an eco-friendly and cost-effective strategy for Hg-polluted farmland. However, the mechanisms controlling the transformation of and resistance to Hg(II) by these bacteria remain unknown. In this study, a plant-associated Pseudomonas sp. strain, AN-B15 was isolated and determined to effectively remove Hg(II) under both nutrient-poor and nutrient-rich conditions via volatilization by transforming Hg(II) to Hg(0) and immobilization by transforming Hg(II) to mercury sulfide and Hg-sulfhydryl. Genome and transcriptome analyses revealed that the molecular mechanisms involved in Hg(II) resistance in AN-B15 were a collaborative process involving multiple metabolic systems at the transcriptional level. Under Hg(II) stress, AN-B15 upregulated genes involved in the mer operon and producing the reducing power to rapidly volatilize Hg(II), thereby decreasing its toxicity. Hydroponic culture experiments also revealed that inoculation with strain AN-B15 alleviated Hg-induced toxicity and reduced the uptake of Hg(II) in the roots of wheat seedlings, as explained by the volatilization and immobilization of Hg(II) and plant growth-promoting traits of AN-B15. Overall, the results from the in vitro assays provided vital information that are essential for understanding the mechanism of Hg(II) resistance in plant-associated bacteria, which can also be applied for the bioremediation of Hg-contamination in future.

Nutrient Deficiency Affects the Growth and Nitrate Concentration of Hydroponic Radish

In hydroponics, a continuous supply of mineral nutrients is essential for plant growth. However, constitutive nutrient-rich conditions also increase the nitrate content in the plants, which can be harmful to human health. Here, we investigated the effect of nutrient deficiency on the growth and component composition of hydroponic radish by changing the timing of nutrient removal from the hydroponic solution. Radish plants that were 14 days old were transferred to four different nutrient conditions for 14 days: nutrient deficiency for 14 days (WW), full nutrient for 14 days (NN), nutrient deficiency for the last 7 days (NW), and nutrient deficiency for the first 7 days (WN). After the treatments, the NW plants had similar taproot growth to NN plants. In contrast, the WN plants significantly reduced taproot growth. The WW plants reduced the shoot and taproot weight and their water contents. The nitrate content in the taproots was reduced in the NW and WW plants. The WW plants contained lower total phenol and higher ascorbic acid and sugar contents. These results suggest that the uptake of nutrient minerals at the young growth stage is important for the growth of radish taproot. Nutrient deficiency management can be one of the most effective tools for regulating radish growth and composition.

Growth medium- and strain-dependent bactericidal efficacy of blue light against Shiga toxin-producing Escherichia coli on food-grade stainless steel and plastic

Shiga toxin-producing Escherichia coli (STEC) are a major group of human pathogens and may persist on both abiotic and biotic surfaces. In this report, two blue-light prototypes were used to evaluate the antimicrobial efficacy against STEC on food processing surfaces (stainless steel and polyoxymethylene plastic). Investigation using a light-bulb prototype (Prototype 1 at 405 nm, 26 mW/cm2) showed significant antimicrobial effects in nutrient deficient condition but not in nutrient rich condition, demonstrating that the presence of organic matters from rich nutrient medium was thought to be light-absorptive and reduce the bactericidal efficacy of blue light, as evident from the lack of bacterial reduction when suspended in cooked meat broth. An advanced (surface-mounted-diode) light panel, Prototype 2 with high light intensity (405 nm; 50 mW/cm2) was able to inactivate a cocktail of seven STEC strains (from seven major serotypes O26, O45, O103, O111, O121, O145 and O157) on type 304 stainless steel (1.66 log10 CFU) and polyoxymethylene plastic (4.25 log10 CFU) at light dosages of 720 and 45 J/cm2, respectively when cells were illuminated in a nutrient-deficient medium (M9 broth). Post-treatment, no STEC cells were recoverable from plastic, both when tested on plates (agar or petrifilms) and by polymerase chain reaction (PCR). In contrast, surviving colonies were identified on samples taken from stainless steel, albeit only four strains could be detected by PCR analysis – those belonging to serotypes O26, O45, O103 and O157 – which indicated that the susceptibility of STEC to blue light varied across the tested strains.

Investigations on grassland and nature reservation effect of horse grazing in Tapolca and Káli Basins (2008)

Examined areas can be found in the Tapolca and Káli Basins near Köveskál and Nemesgulács. Near Köveskál 2 horses were grazed on a 1 ha grassland, which was on a degraded association of Cynodonti-Poëtum angustifoliae. Control area was found close to the grazed grassland where Salvinio-Festucetum rupicolae association was found. The grassland was grazed formerly by sheep. Near Nemesgulács 4 horses were grazed on a 6 ha pasture under free range grazing system (0.7 horse/ha) on a Cynodonti- Poëtum angustifoliae grassland that is situated on a slope. Sample areas were selected the upper (UTS) and lower (LTS) third of the slope. This area formerly was as vineyard. 5-5 replicates of 2 by 2 m coenological quadrates were monitored on each sample area. Sward composition was investigated by Braun-Blanquet method (1964) in the grazing season of 2008. Ground cover (D) species composition and species number (n) were evaluated as analytical parameters. Relative nitrogen demand (NB), social behavior types (SBT) (Borhidi, 1995) and nature conservation value categories (TVK) (Simon, 2000) were also analyzed. At the LTS of the slope near Nemesgulács we could find species with bigger proportions indicating nutrient rich production sites and N indicating Artemisia vulgaris, characteristic species of manured sites appeared, too. At the UTS their proportion was smaller. The reason for this difference is the nutrient run off the slope and its accumulation at the LTS. The reason for the low nutritive value of the grassland are the lack of valuable Poaceae and pulses species and the low total cover. Valuable plant species were grazed out of the sward and negative effects of trampling could have been observed. Concerning the selective grazing preference of horses, the species composition of this area is not suitable for horse grazing. Instead of horses the area could be more suitable for sheep grazing. Pasture near Köveskál had extremely high proportion of species requiring nutrient rich conditions that can be probably due to frequent depositions of excreta and urine by grazing horses. Both control and pasture areas has the highest (approx. 35% absolute) cover of natural species with disturbance tolerance. The biggest difference in nature conservation value categories was the decrease of association composing species on the pasture. This was mainly caused by the grazing out of Poa angustifolia that was the most valuable species in the association. Overgrazing and grazing method applied caused very low plant cover on the grazed pasture.

Salinity changes may influence dinoflagellate cyst morphometry: data from monsoon-influenced tropical coastal ecosystems

Abstract Generally, dinoflagellate cyst morphology is species specific. Their variability due to environmental factors (temperature and salinity) makes them potential proxies for such factors. However, there is a dearth of information on the variability of cyst morphology from monsoon-influenced coastal ecosystems. This study on distribution and variability in the dinocyst morphometry of Pyrophacus steinii and Protoperidinium pentagonum from estuarine (Cochin port and Zuari estuary) and marine (New Mangalore port) ecosystems along the Indian west coast revealed that both are common and euryhaline species. However, variability in cyst morphometry was observed and correlated salinity values between the ecosystems. Other parameters (i.e. the prevalence of narrow temperature ranges and nutrient-rich conditions) may not be dominant in influencing cysts morphometry. Cyst length, breadth and processes length (only in P. steinii) of both were relatively larger and smaller at salinity ranges higher and lower than 25 psu, respectively. The data presented for different ecosystems are comparable in most parameters except salinity variations. This study extends the ranges of records for both species. Pyrophacus steinii cysts were significantly larger (up to 120 μm in Zuari estuary) than literature reports on cysts from higher salinity systems and salinity-related variability in P. pentagonum cyst size indicates notable potential proxy indicator of salinity.

The Lower Cretaceous “Continental Intercalaire” around Tidikelt (Central Sahara, Algeria): Sedimentology, palaeontology and ichnology

The Lower Cretaceous strata are exposed over a large surface in the northern part of the Ahnet basin. They consist of transgressive, horizontal formations overlying the folded Palaeozoic formations by angular unconformity across the Tidikelt region. The present study addresses the respective lithostratigraphical units of the “Continental Intercalaire” succession and their subsequent palaeo-environment in the Tidikelt area using a trace fossil analysis combined with sedimentological and palaeontologic data. The lithological and sedimentological features of the study sections recognised eleven sub-units organised within four lithological units: the Lower Clay Unit of Barremian-Neocomian age consisting of three Sub-units (Akablie Sandstone, Sidi Mahmoud Clays and Pebbly Sands); the Quartzite Sandstones Unit referred to a Late Barremian-Early Aptian age; the Middle Clay-Sandstone Unit consisting of a thick deposit of Early Aptian-Albian age, divided into five Sub-units (Tit Sandstones, In Salah Sand-Clay, In Salah Sandstone, Foum El Bouib Sandstone, and Sandstone-Clay); and the Upper Clay Unit comprising the Oued Taleh Sand and the El-Golea Clays Sub-units. Vertebrate remains all evidence a Late Albian-Early Cenomanian age for the top part of the Continental Intercalary. Ichnologic data analysis documents lower diversity of the invertebrate trace fossils: only ten ichnotaxa are recorded so far and grouped in five ichnoassemblages. Fuvial-lacustrine ichnoassemblage represents a continental ichnofacies of a fluvial-lacustrine environment: Mermia, Scoyenia and Skolithos ichnofacies. Fluvial Ichnoassemblage of the Quartzite Sandstone Unit is represented by insect trace fossils typical of the Coprinisphaera ichnofacies. Fluvio-marginal ichnoassemblage corresponds to a tidal-influenced, fluvial deposit transgressive on Unit B, represented by Skolithos and Psilonichnus ichnofacies. Lower shoreface ichnoassemblage shows the upper part of Unit C, documented by horizontal trace fossils such as Thalassinoides and vertical root traces, all supporting a lower shoreface environment in a semi-arid climate interlined by well-oxygenated episode with nutrient-rich conditions and vegetation dominance. Near to shoreface ichnoassemblage coincides with the upper unit D of coastal deposits with fluvial-tidal influence at the base (Oued Taleh Sands) associated with Scoyenia and Skolithos trace fossils and lagoon deposit of the El-Golea Clays Sub-units.

Neurotensin Regulates Proliferation and Stem Cell Function in the Small Intestine in a Nutrient-Dependent Manner.

Background & AimsIntestinal stem cells (ISCs) are sensitive to dietary alterations and nutrient availability. Neurotensin (NT), a gut peptide localized predominantly to the small bowel and released by fat ingestion, stimulates the growth of intestinal mucosa under basal conditions and during periods of nutrient deprivation, suggesting a possible role for NT on ISC function.MethodsLeucine-rich repeat-containing G-protein coupled receptor 5-Enhanced Green Fluorescent Protein (Lgr5-EGFP) NT wild type (Nt+/+) and Lgr5-EGFP NT knockout (Nt-/-) mice were fed ad libitum or fasted for 48 hours. Small intestine tissue and crypts were examined by gene expression analyses, fluorescence-activated cell sorting, Western blot, immunohistochemistry, and crypt-derived organoid culture. Drosophila expressing NT in midgut enteroendocrine cells were fed a standard diet or low-energy diet and esg-green fluorescent protein+ ISCs were quantified via immunofluorescence.ResultsLoss of NT impaired crypt cell proliferation and ISC function in a manner dependent on nutrient status. Under nutrient-rich conditions, NT stimulated extracellular signal-regulated kinases 1 and 2 signaling and the expression of genes that promote cell-cycle progression, leading to crypt cell proliferation. Under conditions of nutrient depletion, NT stimulated WNT/β-catenin signaling and promoted an ISC gene signature, leading to enhanced ISC function. NT was required for the induction of WNT/β-catenin signaling and ISC-specific gene expression during nutrient depletion, and loss of NT reduced crypt cell proliferation and impaired ISC function and Lgr5 expression in the intestine during fasting. Conversely, the expression of NT in midgut enteroendocrine cells of Drosophila prevented loss of ISCs during nutrient depletion.ConclusionsCollectively, our findings establish an evolutionarily conserved role for NT in ISC maintenance during nutritional stress. GSE182828

Microbial river-to-sea continuum: gradients in benthic and planktonic diversity, osmoregulation and nutrient cycling

BackgroundCoastal aquatic ecosystems include chemically distinct, but highly interconnected environments. Across a freshwater-to-marine transect, aquatic communities are exposed to large variations in salinity and nutrient availability as tidal cycles create periodic fluctuations in local conditions. These factors are predicted to strongly influence the resident microbial community structure and functioning, and alter the structure of aquatic food webs and biogeochemical cycles. Nevertheless, little is known about the spatial distribution of metabolic properties across salinity gradients, and no study has simultaneously surveyed the sediment and water environments. Here, we determined patterns and drivers of benthic and planktonic prokaryotic and microeukaryotic community assembly across a river and tidal lagoon system by collecting sediments and planktonic biomass at nine shallow subtidal sites in the summer. Genomic and transcriptomic analyses, alongside a suite of complementary geochemical data, were used to determine patterns in the distribution of taxa, mechanisms of salt tolerance, and nutrient cycling.ResultsTaxonomic and metabolic profiles related to salt tolerance and nutrient cycling of the aquatic microbiome were found to decrease in similarity with increasing salinity, and distinct trends in diversity were observed between the water column and sediment. Non-saline and saline communities adopted divergent strategies for osmoregulation, with an increase in osmoregulation-related transcript expression as salinity increased in the water column due to lineage-specific adaptations to salt tolerance. Results indicated a transition from phosphate limitation in freshwater habitats to nutrient-rich conditions in the brackish zone, where distinct carbon, nitrogen and sulfur cycling processes dominated. Phosphorus acquisition-related activity was highest in the freshwater zone, along with dissimilatory nitrate reduction to ammonium in freshwater sediment. Activity associated with denitrification, sulfur metabolism and photosynthesis were instead highest in the brackish zone, where photosynthesis was dominated by distinct microeukaryotes in water (Cryptophyta) and sediment (diatoms). Despite microeukaryotes and archaea being rare relative to bacteria, results indicate that they contributed more to photosynthesis and ammonia oxidation, respectively.ConclusionsOur study demonstrates clear freshwater–saline and sediment–water ecosystem boundaries in an interconnected coastal aquatic system and provides a framework for understanding the relative importance of salinity, planktonic-versus-benthic habitats and nutrient availability in shaping aquatic microbial metabolic processes, particularly in tidal lagoon systems.72ugw57JLuZNUPngo1htqPVideo abstract

The putative elongator complex protein Elp3 is involved in asexual development and pathogenicity by regulating autophagy in the rice blast fungus

Autophagy is responsible for maintaining fundamental cellular homeostasis and is, therefore, essential for diverse development processes. This study reported that PoElp3, the putative catalytic subunit of Elongator complex, is involved in the maintenance of autophagy homeostasis to facilitate asexual development and pathogenicity in the rice blast fungus Pyricularia oryzae. It was found that the ΔPoelp3 strains were defective in vegetative growth, conidiation, stress response, and pathogenicity. The mutants exhibited hyper-activated autophagy in the vegetative hyphae under both nutrient-rich and nutrient-deficient conditions. The hyper-activation of autophagy possibly suppressed the production of vegetative hyphae in the ΔPoelp3 strains. Moreover, the ΔPoelp3 strains were found to be more sensitive to rapamycin during vegetative- and invasive-hyphal growth but have no effect on Target-of-Rapamycin (TOR) signaling inhibition. Taken together, these results demonstrated that PoElp3 is involved in asexual development and pathogenicity by regulating autophagy in the rice blast fungus.

Diphthamide promotes TOR signaling by increasing the translation of proteins in the TORC1 pathway

Diphthamide, a modification found only on translation elongation factor 2 (EF2), was proposed to suppress -1 frameshifting in translation. Although diphthamide is conserved among all eukaryotes, exactly what proteins are affected by diphthamide deletion is not clear in cells. Through genome-wide profiling for a potential -1 frameshifting site, we identified that the target of rapamycin complex 1 (TORC1)/mammalian TORC1 (mTORC1) signaling pathway is affected by deletion of diphthamide. Diphthamide deficiency in yeast suppresses the translation of TORC1-activating proteins Vam6 and Rtc1. Interestingly, TORC1 signaling also promotes diphthamide biosynthesis, suggesting that diphthamide forms a positive feedback loop to promote translation under nutrient-rich conditions. Our results provide an explanation for why diphthamide is evolutionarily conserved and why diphthamide deletion can cause severe developmental defects.