Nitrogen Metabolism Research Articles

Effects of nanoplastics on the growth, transcription, and metabolism of rice (Oryza sativa L.) and synergistic effects in the presence of iron plaque and humic acid

Nanoplastics (NPs) can adversely affect living organisms. However, the uptake of NPs by plants and the physiological and molecular mechanisms underlying NP-mediated plant growth remain unclear, particularly in the presence of iron minerals and humic acid (HA). In this study, we investigated NP accumulation in rice (Oryza sativa L.) and the physiological effects of exposure to polystyrene NPs (0, 20, and 100 mg L−1) in the presence of iron plaque (IP) and HA. NPs were absorbed on the root surface and entered cells, and confocal laser scanning microscopy confirmed NP uptake by the roots. NP treatments decreased root superoxide dismutase (SOD) activity (28.9–44.0%) and protein contents (31.2–38.6%). IP and HA (5 and 20 mg L−1) decreased the root protein content (20.44–58.3% and 44.2–45.2%, respectively) and increased the root lignin content (22.3–27.5% and 19.2–29.6%, respectively) under NP stress. IP inhibited the NP-induced decreasing trend of SOD activity (19.2–29.5%), while HA promoted this trend (48.7–50.3%). Transcriptomic and metabolomic analysis (Control, 100NPs, and IP-100NPs-20HA) showed that NPs inhibited arginine biosynthesis, and alanine, aspartate, and glutamate metabolism and activated phenylpropanoid biosynthesis related to lignin. The coexistence of IP and HA had positive effects on the amino acid metabolism and phenylpropanoid biosynthesis induced by NPs. Regulation of genes and metabolites involved in nitrogen metabolism and secondary metabolism significantly altered the levels of protein and lignin in rice roots. These findings provide a scientific basis for understanding the environmental risk of NPs under real environmental conditions.

Recurrent association between Trichodesmium colonies and calcifying amoebae

Abstract Colonies of the N2-fixing cyanobacterium Trichodesmium spp. constitute a consortium with multiple microorganisms that collectively exert ecosystem-level influence on marine carbon and nitrogen cycling, shunting newly fixed nitrogen to low nitrogen systems, and exporting both carbon and nitrogen to the deep sea. Here we identify a seasonally recurrent association between puff colonies and amoebae through a two-year survey involving over 10 000 Trichodesmium colonies in the Red Sea. This association was most commonly found in near-shore populations during spring. Microscopic observations revealed consistent amoebae morphology throughout the study, and both morphological characteristics and 18S rRNA gene sequencing suggested that these amoebae are likely to belong to the species Trichosphaerium micrum, an amoeba that forms a CaCO3 shell. Co-cultures of Trichosphaerium micrum and Trichodesmium grown in the laboratory suggest that the amoebae feed on heterotrophic bacteria and not Trichodesmium, which adds a consumer dynamic to the complex microbial interactions within these colonies. Sinking experiments with fresh colonies indicated that the presence of the CaCO3-shelled amoebae decreased colony buoyancy. As such, this novel association may accelerate Trichodesmium sinking rates and facilitate carbon and nitrogen export to the deep ocean. Amoebae have previously been identified in Trichodesmium colonies in the western North Atlantic (Bermuda and Barbados), suggesting that this type of association may be widespread. This association may add a new critical facet to the microbial interactions underpinning carbon and nitrogen fixation and fate in the present and future ocean.

Enterobacter-infecting phages in nitrogen-deficient paddy soil impact nitrogen-fixation capacity and rice growth by shaping the soil microbiome

Bacteriophages (“phage”) play important roles in nutrient cycling and ecology in environments by regulating soil microbial community structure. Here, metagenomic sequencing showed that a low relative abundance of nitrogen-fixing bacteria but high abundance of Enterobacter-infecting phages in paddy soil where rice plants showed nitrogen deficiency. From soil in the same field, we also isolated and identified a novel virulent phage (named here as Apdecimavirus NJ2) that infects several species of Enterobacter and characterized its impact on nitrogen fixation in the soil and in plants. It has the morphology of the Autographiviridae family, with a dsDNA genome of 39,605 bp, 47 predicted open reading frames and 52.64 % GC content. Based on genomic characteristics, comparative genomics and phylogenetic analysis, Apdecimavirus NJ2 should be a novel species in the genus Apdecimavirus, subfamily Studiervirinae. After natural or sterilized field soil was potted and inoculated with the phage, soil nitrogen-fixation capacity and rice growth were impaired, the abundance of Enterobacter decreased, along with the bacterial community composition and biodiversity changed compared with that of the unadded control paddy soil. Our work provides strong evidence that phages can affect the soil nitrogen cycle by changing the bacterial community. Controlling phages in the soil could be a useful strategy for improving soil nitrogen fixation.

Desert dust improves the photophysiology of heat-stressed corals beyond iron

Desert dust is an important source of essential metals for marine primary productivity, especially in oligotrophic systems surrounded by deserts, such as the Red Sea. However, there are very few studies on the effects of dust on reef-building corals and none on the response of corals to heat stress. We therefore supplied dust to two coral species (Stylophora pistillata and Turbinaria reniformis) kept under control conditions (26 °C) or heat stress (32 °C). Since dust releases large amounts of iron (Fe) in seawater, among other metals, the direct effect of different forms of Fe enrichment on coral photosynthesis was also tested. First, our results show that the desert dust altered the coral metallome by increasing the content of metals that are important for coral physiology (e.g. lithium (up to 5-fold), manganese (up to 4-fold in S. pistillata), iron (up to 3-fold in S. pistillata), magnesium (up to 1.3-fold), molybdenum (up to 1.5-fold in S. pistillata)). Overall, metal enrichment improved the photosynthetic performance of corals, especially under thermal stress (e.g. Pgross (up to 2-fold), Pnet (up to 10-fold), chlorophyll (up to 1.5-fold), symbionts (up to 1.6-fold)). However, Fe exposure (ferric chloride or ferric citrate) did not directly improve photosynthesis, suggesting that it is the combination of metals released by the dust, the so-called “metal cocktail effect”, that has a positive impact on coral photophysiology. Dust also led to a decrease in Ni uptake (up to 1.4-fold in the symbionts), likely related to the nitrogen metabolism. Finally, we found that the isotopic signature of metals such as iron, zinc and copper is a good indicator of heat stress and dust exposure in corals. In conclusion, desert dust can increase coral resistance to bleaching by supplying corals with essential metals.

Deciphering nitrogen dynamics in aeroponics: physio-biochemical and enzymatic responses influencing nitrogen use efficiency in contrasting potato genotypes

Excessive use of nitrogen (N) in crops, such as potatoes, can lead to economic and environmental repercussions. We hypothesized that potato genotypes with resilient root systems and high genetic capabilities for nitrogen-use efficiency (NUE) could effectively mitigate these challenges. Consequently, we investigated intraspecific variations and characteristics within six distinct potato genotypes exhibiting diverse NUEs in response to varying nitrogen levels in an aeroponic system. The morpho-physiological and biochemical properties showed significant genotypic variations, especially related to the N-assimilating enzyme levels and root characteristics. Notably, the root systems of all genotypes demonstrated greater responsiveness to low nitrogen levels, with genotype C17 showcasing the most substantial root system irrespective of nitrogen concentration. Root morphological traits displayed robust positive correlations with NUtE, primarily influenced by genotype rather than nitrogen concentration. Conversely, nitrogen levels, displaying positive correlations with NUpE, influenced growth and activities of N-assimilating enzymes. Based on their distinct root systems, metabolic activities, and NUE profiles, genotypes C17 and C11 were determined to be N-efficient and N-inefficient, respectively. This study provides novel insights into the physiological and biochemical mechanisms underlying nitrogen use efficiency in potato genotypes under aeroponic conditions, offering potential targets for breeding programs, optimizing fertilizer management and cultivation strategies to improve crop performance under nitrogen-deficient conditions. Future investigations, employing multi-omics approaches, will elucidate key genes and pathways in nitrogen metabolism, potentially offering avenues to enhance root architecture and improve NUE.

Host dependent specialized metabolism of nitrogen export in actinorhizal nodules induced by Frankia cluster-2.

Frankia cluster-2 strains are diazotrophs that engage in root nodule symbiosis with actinorhizal plants of the Cucurbitales and the Rosales. Previous studies have shown that an assimilated nitrogen source, presumably arginine, is exported to the host in nodules of Datisca glomerata (Cucurbitales), while a different metabolite is exported in the nodules of Ceanothus thyrsiflorus (Rosales). To investigate if an assimilated nitrogen form is commonly exported to the host by cluster-2 strains, and which metabolite would be exported in Ceanothus, we analysed gene expression levels, metabolite profiles, and enzyme activities in nodules. We conclude that the export of assimilated nitrogen in symbiosis seems to be a common feature for Frankia cluster-2 strains, but which source is host-dependent. The export of assimilated ammonium to the host suggests that 2-oxoglutarate is drawn from the TCA cycle at a high rate. This specialised metabolism obviates the need for the reductive branch of the TCA cycle. We found several genes encoding enzymes of the central carbon and nitrogen metabolism were lacking in Frankia cluster-2 genomes: the glyoxylate shunt and succinate semialdehyde dehydrogenase. This led to a linearization of the TCA cycle, and we hypothesize this could explain the low saprotrophic potential of Frankia cluster-2.

Effects of Licorice Functional Components Intakes on Blood Pressure: A Systematic Review with Meta-Analysis and NETWORK Toxicology.

To investigate the effects of licorice functional ingredient intake on blood pressure, explore its potential mechanisms of action, and provide safety information for personalized nutritional interventions in special populations and for the application of licorice-derived functional foods. PubMed, Cochrane Library, Medline, Embase, EBSCO, ScienceDirect, and Web of Science databases were searched from inception to 31 August 2024. Randomized controlled trials (RCTs) investigating the intake of licorice or its functional components were included. The range of continuous variables was assessed using the weighted mean difference (WMD) with 95% confidence intervals. Genes associated with hypertension were screened using an online database. Machine learning, receiver operating characteristic(ROC) curve analysis, molecular docking, and gene set enrichment analysis (GSEA) were employed to explore the potential mechanisms underlying licorice-induced blood pressure fluctuations. Eight RCTs (541 participants) were included in the meta-analysis, which indicated interventions containing glycyrrhizic acid (GA) as the main component increased systolic blood pressure (SBP) and diastolic blood pressure (DBP) (SBP: WMD [95% CI] = 3.48 [2.74, 4.21], p < 0.001; DBP: WMD [95% CI] = 1.27 [0.76, 1.78], p < 0.001). However, interventions dominated by licorice flavonoids(LF) had no significant effect on SBP or DBP (SBP: WMD [95% CI] = 0.58 [-1.15, 2.31], p = 0.511; DBP: WMD [95% CI] = 0.17 [-1.53, 1.88], p = 0.843). Three machine learning algorithms identified five biomarkers associated with hypertension: calmodulin 3 (CALM3), cluster of differentiation 9 (CD9), growth factor independence 1B transcriptional repressor (GFI1B), myosin light chain kinase (MYLK), and Ras suppressor-1 (RSU1). After removing biomarkers with lower validity and reliability, GFI1B, MYLK, and RSU1 were selected for subsequent analysis. The network toxicology results suggested that GA and its metabolite glycyrrhetinic acid may act on GFI1B, MYLK, and RSU1, influencing blood pressure fluctuations by modulating nitrogen metabolism signaling pathways. There were distinct differences in the effects of licorice functional components on blood pressure. Functional constituents dominated by GA were shown to increase both SBP and DBP, whereas those dominated by LF did not exhibit significant effects on blood pressure. The hypertensive mechanism of GA may involve the modulation of GFI1B, MYLK, and RSU1 to regulate nitrogen metabolic pathways.

Microbial Ecology of Denitrification Process and Its Application in Wastewater: Treatment, Challenges and Opportunities

Denitrification is a crucial microbial process in the nitrogen cycle, transforming nitrate (NO₃⁻) into nitrogen gas (N₂), thereby mitigating nitrogen pollution in aquatic ecosystems. This microbial activity plays a vital role in wastewater treatment by removing excess nitrogen, which contributes to eutrophication and water contamination. The denitrification process involves various microbial communities, including bacteria such as Pseudomonas, Paracoccus, and Bacillus, which operate under anoxic conditions to achieve nitrogen reduction, an optimizing denitrification in wastewater treatment presents several challenges, such as maintaining ideal environmental conditions (e.g., carbon availability, oxygen levels, pH) and overcoming issues related to incomplete denitrification, which can lead to the production of harmful intermediates like nitrous oxide (N₂O). Despite these hurdles, recent advancements in microbial ecology, such as the use of biofilms, bioreactors, and genetic engineering, offer promising opportunities to enhance denitrification efficiency. This review explores the microbial ecology of the denitrification process, its application in wastewater treatment, and the challenges and opportunities associated with its practical implementation in reducing nitrogen pollution.

Exploring the influence of moisture stress on microbial-driven organic acid synthesis in potato waste fermentation

Anaerobic fermentation of potato leaves and stems for organic acid synthesis, serving as food additives, faces impediments due to misconceptions about the effects of moisture stress on the acid-synthesizing microbiome. An ingenious method, avoiding interference from microbiome and nutrient integrations, was employed in the present study. Results showed that increasing the moisture level from 60 % to 75 % significantly improved lactic acid (182.64 %), acetic acid (163.55 %), propionic acid (1960.43 %), nonprotein nitrogen, free amino acid and ammonia levels but reduced pH value and water-soluble carbohydrate and hemicellulose levels. Microbiologically, the high-moisture groups enriched Lactiplantibacillus, Levilactobacillus and Enterobacter, upregulated glycolysis, nitrogen, pyruvate and propanoate metabolisms, and activated genes for acid-producing and ammonia-forming enzymes. Notably, Lactiplantibacillus and Enterobacter prevailed in glycolysis and nitrogen metabolism, respectively, and Levilactobacillus was more prominent in pyruvate and propanoate metabolism under high-moisture conditions. Collectively, a moisture level of 75 % benefited organic acid synthesis from potato waste via anaerobic fermentation.

Alterations in nitrogen metabolism caused by heavy metals in the acid-tolerant microalga Coccomyxa onubensis

The microalga Coccomyxa onubensis is an extremophile microorganism with a unique ecosystem (Río Tinto, Huelva, Spain) that contains high amounts of contaminants, including heavy metals, sulphates, and nitrates, in acidic environments (pH 2.5). The current work presents an evaluation of the capacity of Coccomyxa onubensis to assimilate different nitrogen sources under Cu2+, Cd2+, AsO33−, AsO43− and Hg2+ stress, and the metabolic implications of these stressors. The results showed that ammonium consumption was less affected than nitrate consumption when microalgae were cultivated with heavy metals (except cadmium). The activities of enzymes involved in nitrogen metabolism, such as nitrite reductase (NiR; EC:1.7.7.1), glutamine synthetase (GS; EC:6.3.2.1) and glutamate dehydrogenase (GDH; EC:1.4.1.2) were characterised to determine the Michaelis-Menten constant (Km) and optimal temperature and pH values, being 45, 40 and 60 °C and pH values of 7.5, 6.0 and 9.0 for NiR, GS, and GDH, respectively. The effects of different heavy metals on these enzymes were assessed at multiple levels, and the results showed that the enzymatic activity of NiR was downregulated, specially under copper stress, maintaining 23 % of control NiR activity at 2 mM Cu2+. The enzymatic activity of GS was upregulated at low concentrations under cadmium and mercury stress (115–120 % of control cultures GS activity at 25 μM Cd2+ and 50 nM Hg2+, respectively) and downregulated at high concentrations of these elements. GDH activity was upregulated in the presence of Cu2+, Cd2+, and Hg2+, with increases up to 192, 155 and 154 % at 1 mM Cu2+, 300 μM Cd2+, and 250 nM Hg2+, respectively. These results provide a better explanation of the effects of heavy metal stress on N metabolism in Coccomyxa onubensis, which may be used as a model eukaryotic organism of the Tinto River acidophilic ecosystem.

Nutrient fluxes, oxygen consumption and fatty acid composition from deep-water demo- and hexactinellid sponges from New Zealand

Sponges are an important component of deep-water ecosystems enhancing eukaryotic biodiversity by hosting diverse endo- and epibiota and providing three dimensional habitats for benthic invertebrates and fishes. As holobionts they are important hosts of microorganisms which are involved in carbon and nitrogen cycling. While increasing exploration of deep-water habitats results in new sponge species being discovered, little is known about their physiology and role in nutrient fluxes. Around New Zealand (Southwest Pacific), the sponge biodiversity is particularly high, and we selected six deep-sea sponge genera (Saccocalyx, Suberites, Tedania, Halichondria/ Dendoricella, Lissodendoryx) and a member of the Sceptrulophora order for in-situ and ex-situ experiments.We investigated the biochemical composition of the sponges, measured oxygen consumption and inorganic nutrient fluxes, as well as bacterial and phospholipid-derived fatty acid (PLFA) compositions. Our aim was to assess differences in fluxes and fatty acid composition among sponges and linking their bacterial communities to nitrogen cycling processes.All sponges excreted nitrite and ammonia. Nitrate and phosphate excretion were independent of phylum affiliation (Demospongiae, Hexactinellida). Nitrate was excreted by Halichondria/ Dendoricella and Lissodendoryx, whereas Suberites, Tedania, and Sceptrulophora consumed it. Phosphate was excreted by Sceptrulophora and Halichondria/ Dendoricella and consumed by all other sponges. Oxygen consumption rates ranged from 0.17 to 3.56±0.60 mmol O2 g C d-1.The PLFA composition was very sponge-genera dependent and consisted mostly of long-chain fatty acids. Most PLFAs were sponge-specific, followed by bacteria-specific PLFAs, and others.All sponges, except for Suberites, were low-microbial abundance (LMA) sponges whose bacterial community composition was dominated by Proteobacteria, Bacteroidota, Planctomycetota, and Nitrospinota. Suberites consisted of high-microbial abundance (HMA) sponges with Proteobacteria, Chloroflexota, Acidobacteriota, and Actinobacteriota as dominant bacteria.Based on the inorganic nitrogen flux measurements, we identified three types of nitrogen cycling in the sponges: In type 1, sponges (Dendoricella spp. indet., Lissodendoryx) respired aerobically and ammonificated organic matter (OM) to ammonium, fixed N2 to ammonium, and nitrified aerobically heterotrophically produced ammonium to nitrate and nitrite. In type 2, sponges (Halichondria sp., Sceptrulophora, Suberites, Tedania) respired OM aerobically and ammonificated it to ammonium. They also reduced nitrate anaerobically to ammonium via dissimilatory nitrate reduction to ammonium. In type 3, ammonium was microbially nitrified to nitrite and afterwards to nitrate presumably by ammonium-oxidizing Bacteria and/ or Archaea.

Metabolism of nitrogen and sulfamethoxazole, performance recovery mechanism, and antibiotic resistance genes (ARGs) behaviors in membrane aerated biofilm reactor (MABR)

The limited information on micro-mechanism of sulfamethoxazole (SMX) metabolism and antibiotics resistance genes (ARGs) behaviors within membrane-aerated biofilm reactor (MABR) blocked the application of MABR in treating antibiotics containing wastewater. In this work, SMX metabolism and the changes of ARGs were investigated in MABR during 0.0-0.7 mg/L SMX. The system achieved a 92.3% SMX removal at 0.7 mg/LSMX, leading to the formation of 17 lower toxic metabolites, which indicated the robust SMX biodegradation capability of MABR. The metabolic pathways of SMX in MABR were first elucidated, revealing key processes including isoxazole ring opening (primarily in anaerobic zones), aniline hydroxylation, and cleavage of the S-N bond in the sulfonyl group. Microbial analysis revealed the involvement of multiple microbes in SMX biodegradation, and among these, sulfate-reducing bacteria (SRB; Desulfovibrio, Desulforhopalus, Desulfomicrobium) facilitated the isoxazole ring opening in the anaerobic zone, while Rhizobium and Chryseobacterium contributed to ipso-hydroxylation and cleavage of the -C-S-N bond in SMX, respectively. Furthermore, the slower accumulation of ARGs under SMX conditions was primarily attributed to the enhanced efflux pump activity, antibiotic target replacement mechanisms, and secretion of extracellular polymeric substances (EPS), suggesting the potential of MABR to inhibit ARG proliferation. Our research filled the knowledge gap in the micro-mechanism of SMX metabolism and ARGs fate within MABR processing SMX-containing wastewater, laying a theoretical foundation for the broader application of MABR in practical engineering.

Heterologous biosynthesis of betanin triggers metabolic reprogramming in tobacco

Engineering of a specialized metabolic pathway in plants is a promising approach to produce high-value bioactive compounds to address the challenges of climate change and population growth. Understanding the interaction between the heterologous pathway and the native metabolic network of the host plant is crucial for optimizing the engineered system and maximizing the yield of the target compound. In this study, we performed transcriptomic, metabolomic and metagenomic analysis of tobacco (Nicotiana tabacum) plants engineered to produce betanin, an alkaloid pigment that is found in Caryophyllaceae plants. Our data reveals that, in a dose-dependent manor, the biosynthesis of betanin promotes carbohydrate metabolism and represses nitrogen metabolism in the leaf, but enhances nitrogen assimilation and metabolism in the root. By supplying nitrate or ammonium, the accumulation of betanin increased by 1.5–3.8-fold in leaves and roots of the transgenic plants, confirming the pivotal role of nitrogen in betanin production. In addition, the rhizosphere microbial community is reshaped to reduce denitrification and increase respiration and oxidation, assistant to suppress nitrogen loss. Our analysis not only provides a framework for evaluating the pleiotropic effects of an engineered metabolic pathway on the host plant, but also facilitates the development of novel strategies to balance the heterologous process and the native metabolic network for the high-yield and nutrient-efficient production of bioactive compounds in plants.

The LysR-type transcriptional factor PacR controls heterocyst differentiation and C/N metabolism in the cyanobacterium Anabaena PCC 7120

PacR (All3953) has previously been identified as a global transcriptional regulator of carbon assimilation in cyanobacteria. In the facultative diazotrophic and filamentous cyanobacterium Anabaena PCC 7120 (Anabaena), inactivation of pacR has been shown to affect cell growth under various conditions. Nitrogen fixation in Anabaena occurs in heterocysts, cells differentiated semiregularly along the filaments following deprivation of combined nitrogen such as nitrate or ammonium. Here, we created a markerless deletion mutant of pacR. In addition to its growth defects observed under different light and nitrogen conditions, the mutant could form a high frequency of heterocysts, including heterocyst doublets, even in the presence of nitrate. Inactivation of pacR led to the upregulation of ntcA, a global regulator of nitrogen metabolism and heterocyst formation, as well as downregulation of genes involved in nitrate uptake and assimilation. These changes led to N-limited cells in the presence of nitrate. PacR also regulates most of the genes encoding bicarbonate transport systems. The promoter regions of ntcA, and several other genes involved in nitrogen or carbon uptake and assimilation, as well as patS and hetN involved in heterocyst patterning can be directly recognized by PacR in vitro. These findings, along with previously reported ChIP-seq data, establish PacR as a crucial transcriptional regulator for balancing carbon and nitrogen metabolism in cyanobacteria.

SALINITY-Induced Changes in Diversity, Stability, and Functional Profiles of Microbial Communities in Different Saline Lakes in Arid Areas

Saline lakes, characterized by high salinity and limited nutrient availability, provide an ideal environment for studying extreme halophiles and their biogeochemical processes. The present study examined prokaryotic microbial communities and their ecological functions in lentic sediments (with the salinity gradient and time series) using 16S rRNA amplicon sequencing and a metagenomic approach. Our findings revealed a negative correlation between microbial diversity and salinity. The notable predominance of Archaea in high-salinity lakes signified a considerable alteration in the composition of the microbial community. The results indicate that elevated salinity promotes homogeneous selection pressures, causing substantial alterations in microbial diversity and community structure, and simultaneously hindering interactions among microorganisms. This results in a notable decrease in the complexity of microbial ecological networks, ultimately influencing the overall ecological functional responses of microbial communities such as carbon fixation, sulfur, and nitrogen metabolism. Overall, our findings reveal salinity drives a notable predominance of Archaea, selects for species adapted to extreme conditions, and decreases microbial community complexity within saline lake ecosystems.

Chitosan nanoparticles alleviate chromium toxicity by modulating metabolic homeostasis and promoting chromium sequestration in Zea mays L.

Chitosan nanoparticles (CSNPs) have been proposed as a potential alternative in alleviating chromium (Cr) toxicity. However, the mechanisms underlying remains poorly understood. This study investigates the effects of CSNPs on carbon/nitrogen metabolism, cell wall Cr binding capacity, and antioxidant activity in Zea mays L. under Cr stress. Cr stress decreased the total dry weight (DW) by 48.5 %. By contrast, the total DW was reduced by only 26.2 % in CSNPs-treated plants. Analysis of transcriptomic, enzyme activity, and metabolite content data, CSNPs-treated plants exhibited a higher level of relatively stable Carbon and Nitrogen metabolism than untreated plants. CSNPs application resulted in a substantial increase in the levels of sucrose and soluble protein by 78.0 % and 19.4 % in the leaves, and 60.0 % and 59.7 % in the roots, respectively. Meanwhile, CSNPs increased the contents of glutathione, phytochelatin, and cell wall polysaccharide. This increase resulted in a higher retention of Cr in vacuole and cell wall. Additionally, CSNPs alleviated the oxidative damage by improving antioxidant activity. Overall, our results suggest that CSNPs alleviates Cr toxicity by modulating metabolic homeostasis and promoting Cr sequestration in maize plants. This study provides new insights into the mechanisms underlying CSNPs-mediated Cr stress response with potential implications for crop production.

The loss-of-function of AtNATA2 enhances AtADC2-dependent putrescine biosynthesis and priming, improving growth and salinity tolerance in Arabidopsis.

Putrescine (Put) is a promising small molecule-based biostimulant to enhance plant growth and resilience, though its mode of action remains unclear. This study investigated the Put priming effect on Arabidopsis mutant lines (Atadc1, Atadc2, Atnata1, and Atnata2) under control conditions and salinity to understand its role in regulating plant growth. The Atadc2 mutant, characterized by reduced endogenous Put levels, showed insensitivity to Put priming without growth enhancement, which was linked to significant imbalances in nitrogen metabolism, including a high Gln/Glu ratio. Contrarily, the Atnata2 mutant exhibited significant growth improvement and upregulated AtADC2 expression, particularly under Put priming, highlighting these genes' involvement in regulating plant development. Put priming enhanced plant growth by inducing the accumulation of specific polyamines (free, acetylated, conjugated, or bound form) and improving light-harvesting efficiency, particularly in the Atnata2 line. Our findings suggest that AtNATA2 may negatively regulate Put synthesis and accumulation via AtADC2 in the chloroplast, impacting light harvesting in photosystem II (PSII). Furthermore, the Atadc2 mutant line exhibited upregulated AtADC1 but reduced AcPut levels, pointing to a cross-regulation among these genes. The regulation by AtNATA2 on AtADC2 and AtADC2 on AtADC1 could be crucial for plant growth and overall stress tolerance by interacting with polyamine catabolism, which shapes the plant metabolic profile under different growth conditions. Understanding the regulatory mechanisms involving crosstalk between AtADC and AtNATA genes in polyamine metabolism and the connection with certain SMBBs like Put can lead to more effective agricultural practices, improving plant growth, nitrogen uptake, and resilience under challenging conditions.

Influence of oxygen transfer performance on nitrogen metabolism and microbial community structure in an aerobic fluidized bed biofilm reactor under different aeration aperture

Influence of oxygen transfer performance on nitrogen metabolism and microbial community structure in an aerobic fluidized bed biofilm reactor under different aeration aperture

Straw return can increase maize yield by regulating soil bacteria and improving soil properties in arid and semi-arid areas

Straw return has been found to benefit soil fertility and crop yield, however, by which it affects microbial communities to mediate soil factors driving crop yields under maize continuous cropping systems in dryland areas is still unclear. To fill this gap, a 6-year field experiment was established with five straw return amounts (T0, T1, T2, T3, and T4, representing 0, 3,000, 6,000, 9,000, and 12,000kgha-1 of straw, respectively), and investigated the effects of on soil properties, enzymes, bacterial community composition and diversity, and crop yields. Our analysis showed that soil organic carbon (SOC), total nitrogen (TN), and total phosphorus (TP) contents significantly increased by 1-8%, 5-25%, and 2-9% under straw return treatments, respectively, compared to the T0, and soil catalase, urease, and alkaline phosphatase activities increased by at least 34.00%. Additionally, crop yield significantly increased by 4.23-12.00% under T1-T4 treatments, and showed highly significant relationships with SOC, TN, and TP. Importantly, we found straw return significantly altered the community of bacteria involved in the carbon and nitrogen cycle, and their abundance of strong responses depending on the amounts of straw return. For example, straw input increased the abundance of Proteobacteria (+2.64–5.57%), Acidobacteria (+3.82–13.83%), and Bacteroidetes (+15.37–30.49%). Similarly, the amount of straw application increased the bacterial diversity indexes (Shannon, 2.65–10.93%; Chao1, 13.47–18.50%), and had significant positive correlations with SOC, TN, and TP contents. Structural equation models (SEM) revealed that straw return management practice had positive and indirect effects on crop yields by influencing soil properties or the bacteria community. In conclusion, our findings revealed common associations and variations of bacterial community diversity with soil factors and crop yields at different straw return rates, and these findings provide insights and options for the development of better straw return strategies and sustainable agriculture in semi-arid regions.

Virus-prokaryote interactions assist pollutant removal in constructed wetlands

As a vital part of microbial communities, viruses in constructed wetlands (CWs) remain poorly explored, yet they could significantly affect pollutant removal. Here, two pilot-scale CWs were built to investigate the viral community under different hydraulic loading rates (HLRs) using in-depth metagenomic analysis. Gene-sharing networks suggested that the CWs were pools of unexplored viruses. A higher abundance of prokaryotic functional genes related to sulfur cycling and denitrification was observed in the higher HLR condition, which was associated with greater removal of total nitrogen and nitrate nitrogen compared to the lower HLR condition. Viruses also affect nitrogen pollutant removal by potentially infecting functional prokaryotes, such as denitrification bacteria and ammonia-oxidizing bacteria, and by providing auxiliary metabolic genes involved in sulfur and nitrogen cycling. These findings reveal the significance of viruses in pollutant removal in CWs and enhance the understanding of the relationship between engineering design parameters and performance from microbial perspectives.