Nutrient-rich Environment Research Articles

The gut microbiome of farmed Arctic char (Salvelinus alpinus) is shaped by feeding stage and nutrient presence.

The gut microbiome plays an important role in maintaining health and productivity of farmed fish. However, the functional role of most gut microorganisms remains unknown. Identifying the stable members of the gut microbiota and understanding their functional roles could aid in the selection of positive traits or act as a proxy for fish health in aquaculture. Here, we analyse the gut microbial community of farmed juvenile Arctic char (Salvelinus alpinus) and reconstruct the metabolic potential of its main symbionts. The gut microbiota of Arctic char undergoes a succession in community composition during the first weeks post-hatch, with a decrease in Shannon diversity and the establishment of three dominant bacterial taxa. The genome of the most abundant bacterium, a Mycoplasma sp., shows adaptation to rapid growth in the nutrient-rich gut environment. The second most abundant taxon, a Brevinema sp., has versatile metabolic potential, including genes involved in host mucin degradation and utilization. However, during periods of absent gut content, a Ruminococcaceae bacterium becomes dominant, possibly outgrowing all other bacteria through the production of secondary metabolites involved in quorum sensing and cross-inhibition while benefiting the host through short-chain fatty acid production. Whereas Mycoplasma is often present as a symbiont in farmed salmonids, we show that the Ruminococcaceae species is also detected in wild Arctic char, suggesting a close evolutionary relationship between the host and this symbiotic bacterium.

Advancements in Biological Strategies for Controlling Harmful Algal Blooms (HABs)

Harmful algal blooms (HABs) are a primary environmental concern, threatening freshwater ecosystems and public health and causing economic damages in the billions of dollars annually. These blooms, predominantly driven by phytoplankton species like cyanobacteria, thrive in nutrient-rich, warm, and low-wind environments. Because of the adverse impacts of HABs, this review examines various control methods, focusing on biological strategies as sustainable solutions. While effective in disrupting algal populations, traditional chemical and physical interventions carry ecological risks and can be resource-intensive. Biological control methods, including biomanipulation and using algicidal microorganisms such as Streptococcus thermophiles, Myxobacteria, and Lopharia spadicea, emerge as eco-friendly alternatives offering long-term benefits. Additionally, barley and rice straw application has demonstrated efficacy in curbing HAB growth. These biological approaches work by inhibiting algal proliferation, disrupting cellular structures, and fostering algal cell aggregation. Despite their advantages over conventional methods, biological controls face challenges, including intricate ecological interactions. This article delves into the latest biological techniques aimed at eradicating HABs, intending to diminish their frequency and reduce toxin levels in aquatic environments. While most research to date has been confined to laboratory settings, scaling these methods to field applications presents hurdles due to the variability and complexity of natural ecosystems. The review underscores the need for further research and development in this critical area of environmental science.

Emerging technologies are revolutionizing the rootstock rooting process in agricultural engineering through in vitro techniques

This article endeavors to showcase the seamless integration of cutting-edge technologies into the agricultural sector, with a specific emphasis on their application within biotechnology laboratories specializing in in vitro cultivation. The pioneering technology at the heart of this project centers on the automated detection of viral symptoms in micro-cut rootstocks grown in nutrient-rich substrates. Furthermore, we will delve into a comparative analysis, contrasting laboratories equipped with automated processes against those devoid of such advancements, specifically in the context of in vitro cultivation of subject-rooted plants in identical nutrient-rich environments. The anticipated annual financial gains stemming from the incorporation of an automated system into the in vitro laboratory are projected to reach an impressive 1.8 million Russian rubles.

Direct and higher‐order interactions in plant communities under increasing weather persistence

Climate change is increasing the weather persistence in the mid‐latitudes, prolonging both dry and wet spells compared to historic averages. These newly emerging environmental conditions destabilize plant communities, but the role of species interactions in this process is unknown. Here, we tested how direct and higher‐order interactions (HOIs) between species may change in synthesized grassland communities along an experimental gradient of increasing persistence in precipitation regimes. Our results indicate that species interactions (including HOIs) are an important determinant of plant performance under increasing weather persistence. Out of the 12 most parsimonious models predicting species productivity, 75% contained significant direct interactions and 92% significant HOIs. Inclusion of direct interactions or HOIs respectively tripled or quadrupled the explained variance of target species biomass compared to null models only including the precipitation treatment. Drought was the main driver of plant responses, with longer droughts increasing direct competition but also HOI‐driven facilitation. Despite these counteracting changes, drought intensified net competition. Grasses were generally more involved in competitive interactions whereas legumes were more involved in facilitative interactions. Under longer drought, species affinity for nutrient rich or wet environments resulted in more negative direct interactions or HOIs, respectively. We conclude that HOIs, crucially depending on species identity, only partially stabilize community dynamics under increasing weather persistence.Keywords: drought, facilitation and competition, grasslands, higher‐order interactions, increasing weather persistence, species interactions

Cascading effects from soil to maize functional traits explain maize response to microplastics disturbance in multi-nutrient soil environment

Microplastics (MPs) is a major threat to agroecosystems. Their accumulation and impacts should be evaluated to advance our understanding of soil function and health. Uncovering the role of cascade effects in regulating crop growth is crucial to understanding the link between MPs disturbance and environmental functions. Therefore, we aimed to assess how the cascade changes between (non-) biological factors and functional traits of maize regulate the response of maize growth to MPs in different nutrient soil environments. We found that soil dehydration induced by MPs may disrupt the balance of the physiological status of maize, negatively affect photosynthetic performance, and enhance competition among organisms for limited nutrients. However, root-responsive nutrient cues with a high degree of tectonic freedom allowed adaptive phenotypic plasticity to occur, masking the negative effects of MPs. In nutrient-rich soil environments, moderate and high intensity (>0.5 %) MPs disturbances initiated root nutrient foraging activities, and maize tended to decrease its cost of investing in root construction, i.e., increasing specific root length (SRL) to promote its own growth. The growth of maize was mainly characterized by increases in the belowground biomass (BGB, 7.11 to 20.81 g) and aboveground biomass (AGB, 61.11 to 118.26 g). Our study suggests that a cascade effect between environmental factors initiated by MPs and the functional architecture of the maize root system drives maize to regulate its growth by responding to nutrient cues. These findings will help to ensure food security, formulate environmental risk management policies and protect soil health, especially in the context of future agriculture.

Stem Cells Derived from Human Exfoliated Deciduous Teeth Functional Assessment: Exploring the Changes of Free Fatty Acids Composition during Cultivation.

The metabolic regulation of stemness is widely recognized as a crucial factor in determining the fate of stem cells. When transferred to a stimulating and nutrient-rich environment, mesenchymal stem cells (MSCs) undergo rapid proliferation, accompanied by a change in protein expression and a significant reconfiguration of central energy metabolism. This metabolic shift, from quiescence to metabolically active cells, can lead to an increase in the proportion of senescent cells and limit their regenerative potential. In this study, MSCs from human exfoliated deciduous teeth (SHEDs) were isolated and expanded in vitro for up to 10 passages. Immunophenotypic analysis, growth kinetics, in vitro plasticity, fatty acid content, and autophagic capacity were assessed throughout cultivation to evaluate the functional characteristics of SHEDs. Our findings revealed that SHEDs exhibit distinctive patterns of cell surface marker expression, possess high self-renewal capacity, and have a unique potential for neurogenic differentiation. Aged SHEDs exhibited lower proliferation rates, reduced potential for chondrogenic and osteogenic differentiation, an increasing capacity for adipogenic differentiation, and decreased autophagic potential. Prolonged cultivation of SHEDs resulted in changes in fatty acid composition, signaling a transition from anti-inflammatory to proinflammatory pathways. This underscores the intricate connection between metabolic regulation, stemness, and aging, crucial for optimizing therapeutic applications.

Geographic Variation in Progeny: Climatic and Soil Changes in Offspring Size and Colour in Four Sorbus spp. (Rosaceae)

To investigate resource allocation and adaptation strategies of Sorbus spp. under different environment and soil conditions, four Sorbus L. species (Sorbus hupehensis C. K. Schneid, Sorbus pohuashanensis (Hance) Hedl, Sorbus discolor (Maxim.) Maxim, Sorbus koehneana C. K. Schneid) were selected as the study materials. Phenotypic traits including seed mass, fruit mass, and fruit colour were measured and analyzed. Linear Mixed-Effects Models were employed to analyze the associations between phenotypic traits and the environment, and the Maxent model was used to predict the potential distribution areas. Our study reveals that Sorbus spp. tend to prioritize seed production to increase their survival ability in nutrient-poor environments, while they tend to lean towards fruit production in nutrient-rich environments. Specifically, S. pohuashanensis has fruit skin rich in carotenoids and anthocyanins, with the degree of fruit colouration being positively correlated with the environmental suitability. However, the other three spp. demonstrate the opposite pattern. S. pohuashanensis is found to be most suitable for growth in mountainous areas around 40° N, and it is adapted to low temperatures. S. hupehensis prefers warm regions and is distributed in southern Shanxi, while S. discolor has a wider range of adaptability. These results provide a scientific basis for the protection and rational utilization of Sorbus spp. by elucidating their ecological adaptation abilities.

Irradiated animal bedding material derived from cattail leaves and rice straw with orthophosphoric acid activation for amplified ammonia absorption

This scientific study investigates the suitability of cattail leaves and rice straw as biomass materials for animal bedding. Cattail, an invasive plant species known for its ability to thrive in nutrient-rich environments, offers high cellulose content for absorption. In combination with rice straw, which is readily available and cost-effective, the aim is to achieve optimal carbon-to-nitrogen ratios that suppress the growth of microorganisms. To resist bacterial growth, the mixed cattail leaves and rice straw samples undergo treatment with orthophosphoric acid at concentration of 25%, 30%, and 35% v/v, followed by gamma irradiation at 25 kGy. A comprehensive evaluation of the materials, focusing on surface morphology, water absorption, ammonia absorption, and bacterial resistance was conducted. SEM images provide evidence of dramatic surface restructuring. Samples treated with 30% v/v orthophosphoric acid exhibit enhanced water absorption capacities, and can absorb water equivalent to 2.2 times their own weight. Also, samples containing a 1:1 ratio of cattail leaves and rice straw demonstrate superior ammonia absorptions as evidenced by gas chromatography (GC) measurements compared to other samples. After sample irradiation, less bacterial growth was observed by optical density measurements. These findings support the potential utilization of a 1:1 ratio of cattail leaves and rice straw, treated with orthophosphoric acid of 30% v/v and irradiated with gamma radiation, as an effective animal bedding material. This combination offers advantages in terms of waste absorption and microbial control, making it a promising option for use in animal husbandry and laboratory settings.

Characterization of an aspartate aminotransferase encoded by YPO0623 with frequent nonsense mutations in Yersinia pestis.

Yersinia pestis, the causative agent of plague, is a genetically monomorphic bacterial pathogen that evolved from Yersinia pseudotuberculosis approximately 7,400 years ago. We observed unusually frequent mutations in Y. pestis YPO0623, mostly resulting in protein translation termination, which implies a strong natural selection. These mutations were found in all phylogenetic lineages of Y. pestis, and there was no apparent pattern in the spatial distribution of the mutant strains. Based on these findings, we aimed to investigate the biological function of YPO0623 and the reasons for its frequent mutation in Y. pestis. Our in vitro and in vivo assays revealed that the deletion of YPO0623 enhanced the growth of Y. pestis in nutrient-rich environments and led to increased tolerance to heat and cold shocks. With RNA-seq analysis, we also discovered that the deletion of YPO0623 resulted in the upregulation of genes associated with the type VI secretion system (T6SS) at 26°C, which probably plays a crucial role in the response of Y. pestis to environment fluctuations. Furthermore, bioinformatic analysis showed that YPO0623 has high homology with a PLP-dependent aspartate aminotransferase in Salmonella enterica, and the enzyme activity assays confirmed its aspartate aminotransferase activity. However, the enzyme activity of YPO0623 was significantly lower than that in other bacteria. These observations provide some insights into the underlying reasons for the high-frequency nonsense mutations in YPO0623, and further investigations are needed to determine the exact mechanism.

The Composition and Diversity of the Rhizosphere Bacterial Community of Ammodendron bifolium Growing in the Takeermohuer Desert Are Different from Those in the Nonrhizosphere.

Soil microorganisms play important roles in vegetation establishment and soil biogeochemical cycling. Ammodendron bifolium is a dominant sand-fixing (i.e., stabilizing sand dunes) and endangered plant in the Takeermohuer Desert, and the bacterial community associated with this plant rhizosphere is still unclear. In this study, we investigated the composition and diversity of the bacterial community from the A. bifolium rhizosphere and bulk soil at different soil depths (i.e., 0-40cm, 40-80cm, 80-120cm) using culture and high-throughput sequencing methods. We preliminarily analyzed the edaphic factors influencing the structure of bacterial communities. The results showed that the high-salinity Takeermohuer Desert has an oligotrophic environment, while the A. bifolium rhizosphere exhibited a relatively nutrient-rich environment due to higher contents of soil organic matter (SOM) and soil alkaline nitrogen (SAN) than bulk soil. The dominant bacterial groups in the desert were Actinobacteria (39.8%), Proteobacteria (17.4%), Acidobacteria (10.2%), Bacteroidetes (6.3%), Firmicutes (6.3%), Chloroflexi (5.6%), and Planctomycetes (5.0%) at the phylum level. However, the relative abundances of Proteobacteria (20.2%) and Planctomycetes (6.1%) were higher in the rhizosphere, and those of Firmicutes (9.8%) and Chloroflexi (6.9%) were relatively higher in barren bulk soil. A large number of Actinobacteria were detected in all soil samples, of which the most abundant genera were Streptomyces (5.4%) and Actinomadura (8.2%) in the bulk soil and rhizosphere, respectively. The Chao1 and PD_whole_tree indices in the rhizosphere soil were significantly higher than those in the bulk soil at the same soil depth and tended to decrease with increasing soil depth. Co-occurrence network analyses showed that the keystone species in the Takeermohuer Desert were the phyla Actinobacteria, Acidobacteria, Proteobacteria, and Chloroflexi. Furthermore, the major edaphic factors affecting the rhizosphere bacterial community were electrical conductivity (EC), SOM, soil total nitrogen (STN), SAN, and soil available potassium (SAK), while the major edaphic factors affecting the bacterial community in bulk soil were distance and ratio of carbon to nitrogen (C/N). We concluded that the A. bifolium rhizosphere bacterial community is different from that of the nonrhizosphere in composition, structure, diversity, and driving factors, which may improve our understanding of the relationship between plant and bacterial communities and lay a theoretical foundation for A. bifolium species conservation in desert ecosystems.

Typology of planktonic food webs and associated emerging properties as indicators of the ecological status of a permanently disturbed Gulf of Gabès

This study highlights the importance of coupling the typology of planktonic food webs and their emerging properties to better describe the ecological status of an ecosystem under permanent disturbance mainly caused by phosphate industry. Linear inverse models were built to describe four stations under various levels of nutrient pressure, using the Markov Chain Monte Carlo method to estimate known and unknown carbon flows, later used to calculate food web typology ratios. Ecological network analysis (ENA) was used to describe the structural and functional properties of each food web. Based on the food web typology ratios, three planktonic trophic pathways (PTP) with different functional indices were distinguished according to nutrient stress. The microbial food web dominated in the least nutrient-rich environment. It mainly relied on phytoplankton production (picophytoplankton <2 μm) that was mainly transferred by the high microbivory of protozooplankton. In contrast, the herbivorous food web developed in the most nutrient-rich environment, where biogenic carbon was mainly produced by large phytoplankton (microphytoplankton >10 μm) and channeled to higher trophic levels by herbivorous protozooplankton and metazooplankton. In the other two stations – moderately nutrient-rich systems – the PTP acted as a multivorous food web. Phytoplankton (small and large size fractions) and non-living components (detritus and dissolved organic carbon) played a significant role in carbon production, and competed with protozooplankton and metazooplankton for its transport. ENA indices revealed that the herbivorous food web, with the highest total system throughput and lowest relative Ascendency and cycling, was the most active but the least organized and stable system. In contrast, the microbial food web, with the lowest total system flux and highest Ascendency, was least active but more organized than the herbivorous food web. The multivorous food web displayed the most recycling and most organized system, with high values of the detritivory-to-herbivory ratio, cycling and Ascendency. In addition to ENA indices, which are considered effective tools for studying the structural and functional properties of food webs, marine ecosystem management efforts heavily focus on using the “marine food web” as a descriptor of the system's ecological status. However, we suggest that the combination of food web typology and ecological indices could be used as an effective tool for the management and assessment of ecosystem health wherever possible, as well as for the study of anthropogenic pressures.

Phytoplankton metabolism in a stratified nearshore ecosystem with recurrent harmful algal blooms (HABs)

Abstract The coastal ocean is experiencing changes in its physical and chemical properties that strongly affect planktonic metabolism assemblages and, in some cases, favor the occurrence of harmful algal blooms (HABs). Here we analyze the variations in phytoplankton biomass, gross and net primary production (NCP) as well as community respiration (CR) at two nearshore sampling sites (P1 and P2) located at a Mediterranean beach where high biomass HABs are recurrent. At P1, the most exposed site, phytoplankton chlorophyll was generally low, whereas dinoflagellates outbreaks of the genus Gymnodinium and Alexandrium were recurrent during summer at P2 spanning for 10–20 days. During bloom episodes, NCP increased up to 10-fold (&amp;gt;80 mmol O2 m−3 day−1). Contrastingly, variation in CR only reached an average of 1.8-fold the rates of non-bloom conditions. Remarkably, although the enhanced NCP:CR ratio suggests net autotrophic population growth, production per unit biomass at P1 and P2 was not significantly different. Our results indicate that although summer conditions favor the necessary primary production enhancement leading to HAB occurrences, the short-term dynamics driving high biomass episodes are not driven by metabolic variations but instead are governed by subtle accumulative processes of some flagellate species in the nutrient-rich nearshore environment.

The repair mechanism of sublethal Salmonella by intense pulsed light treatment

Recently, intense pulsed light (IPL) technology, as a novel non-thermal sterilization method, has been increasingly applied to the inactivation of microorganisms, such as Salmonella, in food processing industry. Simultaneously, an emerging concern arises from the sublethal injuries of microorganisms caused by these non-thermal sterilization techniques. In this study, IPL (0.98 J/cm2/pulse luminous flux) showed different bactericidal capacity for Salmonella in water, LB broth, and on the surface of chicken, respectively reducing by approximately 5, 2.11 and 1.77 log CFU/mL after one application performed at a 3 cm distance. These differences were attributed to the induction of sublethal injury in Salmonella by IPL treatment, which can subsequently be repaired within nutrient-rich environments, such as foods or broths. To elucidate the repair mechanism, several intracellular oxidative damage enzymes were measured in sublethal Salmonella with IPL treatment, and then the differentially expressed genes of the sublethal cells were examined by RNA-seq. In the results, the levels of TrxR, NOX, and endogenous H2S were significantly increased (27, 2 and 5 fold, respectively); and 264 of 793 identified differentially expressed genes were functionally associated with responding to the IPL stimulus, which were enriched in DNA replication, DNA repair, cell membrane protein, oxidative response, amino acid synthesis and metabolism, and ABC transporters. Therefore, the study identified two key repair mechanisms: repairing membrane proteins and addressing DNA damage. In conclusion, the repair mechanism of Salmonella under IPL stimulus explored in this study provides a new idea for reducing and controlling pathogenic bacteria in the food industry.

Competitive Mn(II) removal occurs in Lysinibacillus sp. MHQ-1 through microbially-induced carbonate precipitation (MICP) and indirect Mn(II) oxidation

Biological Mn(II) removal usually involves adsorption and precipitation of Mn(II) in the form of various minerals. Manganese oxides (MnOx) formation through the activity of Mn(II) oxidation bacteria (MnOB) contributes to the majority of Mn(II) removal. However, whether other bacterial-mediated pathway could couple or competitive with Mn(II) oxidation during Mn(II) removal is scarcely reported. In this study, we reported a competitive Mn(II) removal occurred in nutrient-rich condition during the indirect Mn(II) oxidation of Lysinibacillus sp. MHQ-1, i.e., microbially-induced carbonate precipitation (MICP). In the presence of 1 mM Mn(II), 39.4% of free Mn(II) converted to MnCO3(s) quickly within 100 h, and then 11.6% of initial Mn(II) slowly oxidized to MnOx within 442 h. The urease activity assay and the genome sequencing confirmed the existence of urease and the absence of Mn(II)-oxidizing enzymes in the genome of strain MHQ-1. The urease catalyzed the formation of carbonate ion that reacts with Mn(II) and the formed ammonia raises the pH to initiate indirect Mn(II) oxidation. Genome survey suggests the urease widely exists in various Mn(II)-oxidizing bacteria (MnOB), emphasizing the importance to reconsider the composition, stability and environmental effects of biological Mn(II) removal products in nutrient-rich environment.

Mutational hotspots lead to robust but suboptimal adaptive outcomes in certain environments.

The observed mutational spectrum of adaptive outcomes can be constrained by many factors. For example, mutational biases can narrow the observed spectrum by increasing the rate of mutation at isolated sites in the genome. In contrast, complex environments can shift the observed spectrum by defining fitness consequences of mutational routes. We investigate the impact of different nutrient environments on the evolution of motility in Pseudomonas fluorescens Pf0-2x (an engineered non-motile derivative of Pf0-1) in the presence and absence of a strong mutational hotspot. Previous work has shown that this mutational hotspot can be built and broken via six silent mutations, which provide rapid access to a mutation that rescues swimming motility and confers the strongest swimming phenotype in specific environments. Here, we evolved a hotspot and non-hotspot variant strain of Pf0-2x for motility under nutrient-rich (LB) and nutrient-limiting (M9) environmental conditions. We observed the hotspot strain consistently evolved faster across all environmental conditions and its mutational spectrum was robust to environmental differences. However, the non-hotspot strain had a distinct mutational spectrum that changed depending on the nutrient environment. Interestingly, while alternative adaptive mutations in nutrient-rich environments were equal to, or less effective than, the hotspot mutation, the majority of these mutations in nutrient-limited conditions produced superior swimmers. Our competition experiments mirrored these findings, underscoring the role of environment in defining both the mutational spectrum and the associated phenotype strength. This indicates that while mutational hotspots working in concert with natural selection can speed up access to robust adaptive mutations (which can provide a competitive advantage in evolving populations), they can limit exploration of the mutational landscape, restricting access to potentially stronger phenotypes in specific environments.

Alteration of the embryonic microenvironment and sex-specific responses of the preimplantation embryo related to a maternal high-fat diet in the rabbit model.

The maternal metabolic environment can be detrimental to the health of the offspring. In a previous work, we showed that maternal high-fat (HH) feeding in rabbit induced sex-dependent metabolic adaptation in the fetus and led to metabolic syndrome in adult offspring. As early development representing a critical window of susceptibility, in the present work we aimed to explore the effects of the HH diet on the oocyte, preimplantation embryo and its microenvironment. In oocytes from females on HH diet, transcriptomic analysis revealed a weak modification in the content of transcripts mainly involved in meiosis and translational control. The effect of maternal HH diet on the embryonic microenvironment was investigated by identifying the metabolite composition of uterine and embryonic fluids collected in vivo by biomicroscopy. Metabolomic analysis revealed differences in the HH uterine fluid surrounding the embryo, with increased pyruvate concentration. Within the blastocoelic fluid, metabolomic profiles showed decreased glucose and alanine concentrations. In addition, the blastocyst transcriptome showed under-expression of genes and pathways involved in lipid, glucose and amino acid transport and metabolism, most pronounced in female embryos. This work demonstrates that the maternal HH diet disrupts the in vivo composition of the embryonic microenvironment, where the presence of nutrients is increased. In contrast to this nutrient-rich environment, the embryo presents a decrease in nutrient sensing and metabolism suggesting a potential protective process. In addition, this work identifies a very early sex-specific response to the maternal HH diet, from the blastocyst stage.

Changes in bivalve assemblages at the onset of the OAE2 event in the Peri-Tethyan area (Bohemian Cretaceous Basin)

The Ocean Anoxic Event (OAE2) at the Cenomanian-Turonian boundary presents a unique record of gradual global warming and its effects on benthic organisms. The present research considers a palaeoecological, systematical and statistical evaluation of bivalve assemblages from the Pecínov Member in the Bohemian Cretaceous Basin. The well-exposed succession of Cenomanian through lower Turonian strata contains one of the most complex records of the OAE2 in central Europe. In total, 392 specimens have been studied and assigned to 24 genera within 21 families and 9 orders. The bivalve association prior to the positive shift of the δ13Corg (peak “a” sensu global carbon curve; lower part of the Metoicoceras geslinianum Zone) is strongly dominated by infaunal suspension feeders, followed by semi-infaunal suspension feeders. The near-absence of free-living epifaunal bivalves may be linked to a very fine, muddy substrate and water turbidity, a limiting factor for many epifaunal species. Infaunal deposit feeders are also present but comparatively rare, indicating a nutrient-rich environment with energy levels sufficiently high to keep organic matter in suspension. The Cucullaea glabra – Pseudoptera anomala assemblage of this level is considered to have formed during normal, shallow (15–20 m, supported by abundant material of Pinna) marine conditions. The association inhabiting the area above this level (upper part of the M. geslinianum Zone, S. gracile/E. septemseriatum Subzone) is characterized by the Panopea gurgitis – Rhynchostreon suborbiculatum assemblage suggesting considerably shallower depths and higher energy. Clusters of Modiolus and small oysters characterize the upper parts directly prior to the prominent positive δ13Corg peak “b” (the major peak of OAE2 CIE; ? base/lower part of the N. juddii Zone). No benthic fauna occurs above this level.

Nutrient condition modulates the antibiotic tolerance of Pseudomonas aeruginosa

The variation in nutrient content across diverse environments has a significant impact on the survival and metabolism of microorganisms. In this study, we examined the influence of nutrients on the antibiotic tolerance of the PAO1 strain of Pseudomonas aeruginosa. Our findings indicate that under nutrient-rich conditions, this strain exhibited relatively high tolerance to ceftazidime, chloramphenicol, and tetracycline, but not aminoglycosides and fluoroquinolones. Transcriptome analysis revealed that genes associated with antibiotic tolerance were expressed more efficiently in nutrient-rich media, including ribosomal protein genes and multidrug efflux pump genes, which conferred higher tetracycline tolerance to the strain. Furthermore, the genes responsible for translation, biosynthesis, and oxidative phosphorylation were suppressed when nutrients were limited, resulting in decreased metabolic activity and lower sensitivity to ciprofloxacin. Artificial interference with ATP synthesis utilizing arsenate confirmed that the curtailment of energy provision bolstered the observed tolerance to ciprofloxacin. In general, our results indicate that this strain of P. aeruginosa tends to activate its intrinsic resistance mechanisms in nutrient-rich environments, thereby enhancing resistance to certain antibiotics. Conversely, in nutrient-limited environments, the strain is more likely to enter a dormant state, which enables it to tolerate antibiotics to which it would otherwise be sensitive. These findings further suggest that antibiotics released in environments with varying eutrophication levels may have divergent effects on the development of bacterial antibiotic resistance.

Morphological instability of solid tumors in a nutrient-deficient environment.

A phenomenological reaction-diffusion model that includes a nutrient-regulated growth rate of tumor cells is proposed to investigate the morphological instability of solid tumors during the avascular growth. We find that the surface instability could be induced more easily when tumor cells are placed in a harsher nutrient-deficient environment, while the instability is suppressed for tumor cells in a nutrient-rich environment due to the nutrient-regulated proliferation. In addition, the surface instability is shown to be influenced by the growth moving speed of tumor rims. Our analysis reveals that a larger growth movement of the tumor front results in a closer proximity of tumor cells to a nutrient-rich region, which tends to inhibit the surface instability. A nourished length that represents the proximity is defined to illustrate its close relation to the surface instability.

Hiding in the yolk: A unique feature of Legionella pneumophila infection of zebrafish.

The zebrafish has become a powerful model organism to study host-pathogen interactions. Here, we developed a zebrafish model to dissect the innate immune response to Legionella pneumophila during infection. We show that L. pneumophila cause zebrafish larvae death in a dose dependent manner. Additionally, we show that macrophages are the first line of defence and cooperate with neutrophils to clear the infection. Immunocompromised humans have an increased propensity to develop pneumonia, similarly, when either macrophages or neutrophils are depleted, these "immunocompromised" larvae become lethally sensitive to L. pneumophila. Also, as observed in human infections, the adaptor signalling molecule Myd88 is not required to control disease in the larvae. Furthermore, proinflammatory cytokine genes il1β and tnf-α were upregulated during infection, recapitulating key immune responses seen in human infection. Strikingly, we uncovered a previously undescribed infection phenotype in zebrafish larvae, whereby bloodborne, wild type L. pneumophila invade and grow in the larval yolk region, a phenotype not observed with a type IV secretion system deficient mutant that cannot translocate effectors into its host cell. Thus, zebrafish larva represents an innovative L. pneumophila infection model that mimics important aspects of the human immune response to L. pneumophila infection and will allow the elucidation of mechanisms by which type IV secretion effectors allow L. pneumophila to cross host cell membranes and obtain nutrients from nutrient rich environments.