Nitrogen Recycling Research Articles

Different characteristics of sediment nitrogen and phosphorus recycling during cyanobacterial growth and their succession

Different characteristics of sediment nitrogen and phosphorus recycling during cyanobacterial growth and their succession

Alteration enrichment of nitrogen in the gabbroic oceanic crust: Implications for global subducting nitrogen budget and subduction-zone nitrogen recycling

Uptake of nitrogen (N) during hydrothermal alteration of oceanic crust makes the altered oceanic crust (AOC) a significant N reservoir in parallel to seafloor sediments. While N enrichment in the upper (basaltic) oceanic crust during low-temperature alteration has been widely observed, the N characteristics of moderate- to high-temperature altered gabbroic oceanic crust, which accounts for ∼70 vol% of the crustal material in subducting slabs, have been rarely studied. The lack of these data resulted in large uncertainties in calculating the N input flux of global subducting slabs and modeling the N quantities released through the arc and subducted into the deep mantle. To fill this gap, we examined the N concentrations and isotope compositions of 38 altered gabbroic rocks recovered by ODP/IODP drillings from three oceans, i.e., Hole 735B at the Atlantis Bank in the Southwest Indian Ridge, Hole 1309D at the Atlantis massif in the Mid-Atlantic Ridge, and Hole 1415P at the Hess Deep in the East Pacific Rise. All the gabbroic samples show significant N enrichment with mostly positive δ15N values (in average: 7.4±3.8 ppm and +0.6±2.0‰ for Hole 735B, 5.3±2.1 ppm and +1.4±1.3‰ for Hole 1309D and 7.9±1.9 ppm and +2.0±1.8‰ for Hole 1415P), which are comparable to those of altered basalts from global oceanic crust. The N concentrations and δ15N values of these gabbroic rocks can be readily explained by mixing between minor inherited mantle N and mainly secondary N derived from seawater. The secondary N-hosting minerals in altered gabbroic rocks are likely plagioclase, amphibole and chlorite formed during moderate- to high-temperature alteration stages. Using these new data, we obtained a global nitrogen input flux of 20.6-1.3+0.9 × 109 mol·yr−1 to 29.9±2.2 × 109 mol·yr−1 for subducting AOC, in which 50% – 64% is contributed by the altered gabbroic oceanic crust. Integrating with previous estimate of N input flux from seafloor sediments, a total N input flux of 74.9-1.3+0.9 – 84.2±2.2 mol·yr−1 was estimated for global subducting slabs. Mass balance between this input N flux and various estimates of N output flux in global arcs gave a large range (from 47% – 53% to 10% – 20%) for the fraction of slab N to be subducted beyond the sub-arc depth to the deeper mantle. The upper end (47% – 53%) of this range is more consistent with the results from other constraints, such as thermal structural control and comparison between altered gabbros and meta-gabbros.

Cuticle supplementation and nitrogen recycling by a dual bacterial symbiosis in a family of xylophagous beetles

Many insects engage in stable nutritional symbioses with bacteria that supplement limiting essential nutrients to their host. While several plant sap-feeding Hemipteran lineages are known to be simultaneously associated with two or more endosymbionts with complementary biosynthetic pathways to synthesize amino acids or vitamins, such co-obligate symbioses have not been functionally characterized in other insect orders. Here, we report on the characterization of a dual co-obligate, bacteriome-localized symbiosis in a family of xylophagous beetles using comparative genomics, fluorescence microscopy, and phylogenetic analyses. Across the beetle family Bostrichidae, most investigated species harbored the Bacteroidota symbiont Shikimatogenerans bostrichidophilus that encodes the shikimate pathway to produce tyrosine precursors in its severely reduced genome, likely supplementing the beetles’ cuticle biosynthesis, sclerotisation, and melanisation. One clade of Bostrichid beetles additionally housed the co-obligate symbiont Bostrichicola ureolyticus that is inferred to complement the function of Shikimatogenerans by recycling urea and provisioning the essential amino acid lysine, thereby providing additional benefits on nitrogen-poor diets. Both symbionts represent ancient associations within the Bostrichidae that have subsequently experienced genome erosion and co-speciation with their hosts. While Bostrichicola was repeatedly lost, Shikimatogenerans has been retained throughout the family and exhibits a perfect pattern of co-speciation. Our results reveal that co-obligate symbioses with complementary metabolic capabilities occur beyond the well-known sap-feeding Hemiptera and highlight the importance of symbiont-mediated cuticle supplementation and nitrogen recycling for herbivorous beetles.

Abstract 3680: Multiomics analysis of triple negative breast cancer identifies potential metabolic vulnerability for overcoming the resistance of neoadjuvant therapy

Abstract Triple-negative breast cancer (TNBC) is a heterogeneous disease that remains currently medically incurable. We comprehensively analyzed clinical, proteomic, and metabolomic data of a cohort of 12 highly selected primary TNBCs. Among them, 7 patients after neoadjuvant chemotherapy had residual disease and micro- or macro-metastases that were non-pathologically complete response (non-pCR); 5 patients had pathologically complete response (pCR). Interestingly, both proteomic and metabolic profiling results revealed dramatically different molecular signatures in non-pCR relative to pCR. Non-pCR were enriched in metabolites involving aspartic acid, fumarate, nicotinamide, and adenosine that are critical intermediates for nitrogen recycling and tricarboxylic acid (TCA) cycle, which are essential fuels for tumor biomass. Moreover, non-pCR were enriched in urea cycle, oxidative phosphorylation, glycolysis, sirtuin signaling, nucleotide De Novo biosynthesis, which are resistance-associated. Putative therapeutic targets were identified in non-pCR patients. Collectively, our multiomics analysis demonstrated the heterogeneity of TNBCs at multi-levels and enabled the development of personalized therapies targeting unique tumor metabolic profiles. Citation Format: Zuen Ren, Kiran Kurmi, Robert Morris, Shakchhi Joshi, Eric Zaniewski, Johannes Kreuzer, Gabrielle Elena Gioia, Wilhelm Haas, Marcia C. Haigis, Leif W. Ellisen. Multiomics analysis of triple negative breast cancer identifies potential metabolic vulnerability for overcoming the resistance of neoadjuvant therapy. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 3680.

SLC14A1 is a new biomarker in renal cancer.

Renal cancer is one of the common malignant tumors of the urinary tract, prone to distant metastasis and drug resistance, with a poor clinical prognosis. SLC14A1 belongs to the solute transporter family, which plays a role in urinary concentration and urea nitrogen recycling in the renal, and is closely associated with the development of a variety of tumors. Transcription data for renal clear cell carcinoma (KIRC) were obtained from the public databases Gene Expression Omnibus database (GEO) and The Cancer Genome Atlas (TCGA), and we investigated the differences in SLC14A1 expression in cancerous and normal tissues of renal cancer, its correlation with the clinicopathological features of renal cancer patients. Then, we verified the expression levels of SLC14A1 in renal cancer tissues and their Paracancerous tissues using RT-PCR, Western-blotting and immunohistochemistry. Finally, we used renal endothelial cell line HEK-293 and renal cancer cell lines 786-O and ACHN to explore the effects of SLC14A1 on the biological behaviors of renal cancer cell proliferation, invasion and metastasis using EDU, MTT proliferation assay, Transwell invasion assay and scratch healing assay. SLC14A1 was lowly expressed in renal cancer tissues and this was further validated by RT-PCR, Western blotting, and immunohistochemistry in our clinical samples. Analysis of KIRC single-cell data suggested that SLC14A1 was mainly expressed in endothelial cells. Survival analysis showed that low levels of SLC14A1 expression were associated with a better clinical prognosis. In biological behavioral studies, we found that upregulation of SLC14A1 expression levels inhibited the proliferation, invasion, and metastatic ability of renal cancer cells. SLC14A1 plays an important role in the progression of renal cancer and has the potential to become a new biomarker for renal cancer.

Estimation of the Potential Global Nitrogen Flow in a Nitrogen Recycling System with Industrial Countermeasures

This study proposes a nitrogen recycling system that collects and recycles nitrogen compounds from waste gases in the industrial sector, such as those from stationary sources, from industrially processed wastewater containing livestock effluent, and from household wastewater. Multiple scenarios are set, and the potential global flows of anthropogenic nitrogen in 2050 are estimated and compared to assess the effects on the largest planetary boundary problem. In contrast to the business-as-usual (BAU) scenario, in which environmental conditions are worsened through a 47% increase in nitrogen emissions by 2050 above the 2010 levels, the agricultural countermeasures scenario produced a reduction in emissions which was less than the 2010 levels. The industrial countermeasures scenario proposed in this study achieved comfortable reductions in nitrogen production by constructing a nitrogen recycling system that installs the nitrogen compounds to ammonia (NTA) technologies. Combining the agricultural and industrial countermeasures achieves a 66% reduction in nitrogen emissions compared with the BAU scenario in 2050. The combination of both countermeasures with a high installation rate of NTA technologies can achieve the reduction of nitrogen emissions beneath the planetary boundary.

An efficient diazotroph‐derived nitrogen transfer pathway in coral reef system

AbstractThe underlying mechanism for sustaining the high productivity of coral reefs in nutrient deplete water, known as the Darwin Paradox, has long been debated. The input of new nitrogen, for example, derived from N2 fixation, and efficient nitrogen recycling are hypothesized as two critical factors in resolving the paradox. However, the source of new nitrogen and its connection to nitrogen recycling in the coral reef system remain poorly understood. We measured N2 fixation rates and investigated the diazotroph community in different components of a tropical coral reef system. Our results show that the reef‐building crustose coralline algae demonstrate a significantly higher N2 fixation rate than the overlying water or the coral holobiont, representing a large source of N2 fixation to the system. The associated diazotroph community was dominated by the non‐cyanobacterial Rhizobiales. 15N2‐based pulse‐chase incubation experiments revealed ~ 50% of the diazotroph‐derived nitrogen was released from the crustose coralline algae holobiont to the overlying water and coral holobiont within 48 h, which was five fold higher than the fraction of nitrogen released from nitrate‐based assimilation by crustose coralline algae. Furthermore, the released diazotroph‐derived nitrogen was rapidly transferred to the coral holobiont through grazing and was subsequently released back to the overlying water as dissolved organic nitrogen, revealing an efficient pathway that connects the new nitrogen input with the nitrogen recycling in the coral reef ecosystem. Our results provide new insights into the sources and fates of new nitrogen in the coral reefs, helping to resolve the Darwin Paradox in this unique ecosystem.

Molecular insights into the Darwin paradox of coral reefs from the sea anemone Aiptasia

Symbiotic cnidarians such as corals and anemones form highly productive and biodiverse coral reef ecosystems in nutrient-poor ocean environments, a phenomenon known as Darwin's paradox. Resolving this paradox requires elucidating the molecular bases of efficient nutrient distribution and recycling in the cnidarian-dinoflagellate symbiosis. Using the sea anemone Aiptasia, we show that during symbiosis, the increased availability of glucose and the presence of the algae jointly induce the coordinated up-regulation and relocalization of glucose and ammonium transporters. These molecular responses are critical to support symbiont functioning and organism-wide nitrogen assimilation through glutamine synthetase/glutamate synthase-mediated amino acid biosynthesis. Our results reveal crucial aspects of the molecular mechanisms underlying nitrogen conservation and recycling in these organisms that allow them to thrive in the nitrogen-poor ocean environments.

Trophic Path of Marked Exuviae Within Colonies ofCoptotermes gestroi(Blattodea: Rhinotermitidae)

Nitrogen, a limiting growth factor in wood-feeding insects, was hypothesized to play a role in the recently discovered behavior of subterranean termites returning to the nest to molt. Coptotermes gestroi (Wasmann) exuviae is approximately 11% N by dry weight, and therefore a potentially rich source of recyclable nitrogen. Exuviae from a C. gestroi colony were marked with immunoglobulin G (IgG) and were fed to two-year-old C. gestroi colonies. IgG-marked exuviae were detected with an enzyme-linked immunosorbent assay. The IgG marker was later detected in every caste and life stage except first-instar larvae (L1). The proportion of individuals positive for the marker varied by caste, with the queens always being positive for the marker. The queens and second-or-higher-instar workers (W2+) had significantly higher concentrations of the marker than the eggs and L1. The trophic path of exuviae includes individuals that directly fed on marked exuviae (workers and possibly second-instar larvae) and individuals that secondarily received marked exuviae through trophallaxis (queens, kings, and soldiers). This study described the trophic path of consumed exuviae and demonstrated its role in the recycling of nitrogen in a subterranean termite. Molting at the central nest may be an efficient means to transfer nitrogen from shed exuviae to recipients and may be a nitrogen recycling behavior conserved from a termite ancestor.

Exuviae Recycling Can Enhance Queen Oviposition and Colony Growth in Subterranean Termites (Blattodea: Rhinotermitidae: Coptotermes).

Wood-feeding termites have a nitrogen-poor diet and have therefore evolved nitrogen conservation strategies. However, termite workers molt periodically, and throughout the lifetime of a colony, millions of exuviae, a nitrogen-rich resource, are produced by the colony. In Coptotermes Wasmann, workers foraging at remote feeding sites must return to the central part of the nest to molt, where the queen, king, eggs, and larvae are located. It was hypothesized that this molting-site fidelity is an efficient way to recycle nitrogen for reproduction and colony growth, as nestmates involved in exuviae consumption can directly transfer such resources to individuals engaged in reproduction (the queen) or growth (larvae). This study investigates whether incipient colonies of C. gestroi (Wasmann) can gain additional biomass when they are fed supplementary exuviae. Incipient colonies were reared in nitrogen-poor or nitrogen-rich conditions, and 0, 1, 5, or 10 exuviae were added to 3-month-old colonies. After 6.5 months, colonies reared in nitrogen-poor environments gained significantly more biomass when exuviae were added than colonies with no added exuviae. However, the addition of exuviae had no effect on colony growth for colonies reared in nitrogen-rich environments. In a second experiment, queens from colonies in which exuviae were effectively removed laid fewer eggs than queens from colonies in which exuviae were not removed. Therefore, consumption of exuviae from molting individuals by nestmates is an important part of the nitrogen recycling strategy in Coptotermes colonies, as it facilitates queen oviposition and colony growth, especially when such colonies have limited access to nitrogen-rich soils.

Nitrogen impacts on structural stability of feldspar: Constraints from high temperature and high pressure spectroscopy and machine learning

The nitrogen cycling between the surficial and deep Earth is vital for the evolution of atmosphere and life. Silicate minerals are the main nitrogen carriers and their stabilities dictate the recycling efficiency of nitrogen to the deep Earth. Although extensive studies have explored silicate stabilities, the impacts of nitrogen on the stability of silicate minerals have received very few attentions. Feldspar is one of the most important nitrogen carriers and nitrogen is mainly incorporated as ammonium. Here, we reveal nitrogen impacts on the structural stability of feldspar, using in situ high temperature and high pressure spectroscopy and machine learning. The results show that the thermal expansion coefficient of the feldspar with 0.12 wt% ammonium is 14.9 ± 0.5 K−1, smaller than 18.3 ± 1.83 K−1 of the nitrogen-free feldspar with similar other elemental compositions. The nitrogen-bearing feldspar experiences a structural transition near 15.3 GPa, while the reported structural transition pressures of nitrogen-free feldspars were generally lower than 13 GPa. By comparing with previous studies, we also reveal that ammonium reduces the thermal stability of tectosilicates when the ammonium content is high enough while it enhances the thermal stability of phyllosilicates regardless of content. These findings provide crucial constraints on the densities and phase stabilities of nitrogen-bearing silicates. The nitrogen-bearing feldspar has a higher density than those nitrogen-free counterparts, and can survive in polymorph modifications to greater depths. The role of nitrogen-bearing silicates is thus highlighted for not only deep nitrogen recycling, but also potential contribution to physical properties of the subducting slab.

Variations in ecosystem service provision of two functionally similar bivalve habitats

ABSTRACT The quantification of ecosystem services (ES) remains challenging and can result in biases towards data-rich ES in management. For infaunal bivalves, little quantitative in situ data are available on the ES they provide, and differences between functionally similar species in different habitats are rarely considered. Here, we aimed to measure and compare the ecosystem functions (primary production, nutrient processing, water clearance rates) underpinning water quality regulation in an estuarine intertidal and subtidal bivalve habitat (dominated by Austrovenus stutchburyi and Paphies australis respectively). In situ benthic chambers were used to measure sediment–water column solute fluxes (NH4 +, N2, O2) and clearance rates which were scaled up (accounting for habitat differences; e.g. inundation period) to daily estimates of ES potential. Higher hourly microphytobenthic productivity, nitrogen recycling and water filtration were observed for the intertidal bivalve habitat. These differences were attributed to environmental differences rather than differences in bivalve biomass. However, scaling these rates to daily ES estimates showed that inundation period will restrict water quality regulating services in the intertidal. Measuring multiple ecosystem functions in situ provides an important step forward in ES quantification and accounts for ecological complexity, feedbacks and highlights habitat-specific differences in how functionally similar species contribute to ES.

HEAT SHOCK PROTEIN 90.6 interacts with carbon and nitrogen metabolism components during seed development.

Carbon and nitrogen are the two main nutrients in maize (Zea mays L.) kernels, and kernel filling and metabolism determine seed formation and germination. However, the molecular mechanisms underlying the relationship between kernel filling and corresponding carbon and nitrogen metabolism remain largely unknown. Here, we found that HEAT SHOCK PROTEIN 90.6 (HSP90.6) is involved in both seed filling and the metabolism processes of carbon and nitrogen. A single-amino acid mutation within the HATPase_c domain of HSP90.6 led to small kernels. Transcriptome profiling showed that the expression of amino acid biosynthesis- and carbon metabolism-related genes was significantly downregulated in the hsp90.6 mutant. Further molecular evidence showed strong interactions between HSP90.6 and the 26S proteasome subunits REGULATORY PARTICLE NON-ATPASE6 (RPN6) and PROTEASOME BETA SUBUNITD2 (PBD2). The mutation of hsp90.6 significantly reduced the activity of the 26S proteasome, resulting in the accumulation of ubiquitinated proteins and defects in nitrogen recycling. Moreover, we verified that HSP90.6 is involved in carbon metabolism through interacting with the 14-3-3 protein GENERAL REGULATORY FACTOR14-4 (GF14-4). Collectively, our findings revealed that HSP90.6 is involved in seed filling and development by interacting with the components controlling carbon and nitrogen metabolism.

Quantifying seaweed and seagrass beach deposits using high-resolution UAV imagery

Macroalgae and seagrass wash ashore by tidal waters and episodic events and create an ocean-to-land transport of carbon and nutrients. On land, these deposits (beach wrack) are consumed by macrofauna, remineralized by microorganisms, or washed back to the sea, during which recycling of carbon and nitrogen affect the biochemical cycles in coastal zones. Manual quantification of beach wracks is time-consuming and often difficult due to complex topography and remote locations. Here, we present a novel method using Unoccupied Aerial Vehicle (UAV) photogrammetry combined with in situ measurements of carbon and nitrogen contents of wrack to quantify marine carbon and nutrient deposits in beach zones. The UAV method was tested against placed cubes ranging from 125 to 88,218 cm3 and demonstrated a high accuracy (R2 > 0.99) for volume acquisition when compared to manual measurements. Also, the UAV-based assessments of the cross-sectional area of beach deposits demonstrated a high accuracy when compared to manual and high-precision GNSS (Global Navigation Satellite System) measurements without significant differences between the methods. This demonstrated that UAVs can provide detailed spatial maps, three-dimensional (3D) surface models, and accurate volumetric assessments of beach wrack deposits. In three case studies, combined with carbon and nitrogen measures, total organic carbon and nitrogen deposits in beach wracks were quantified ranging from 4.3 to 9.7 and from 0.3 to 0.5 kg per meter coastline, respectively. In conclusion, this UAV method demonstrated an effective tool to quantify ecosystem carbon and nitrogen deposits relevant to ecosystem assessments and quantification of blue carbon stocks. The method is optimal when the terrain below beach wrack deposits is known, as in the case with before-and-after or repeated surveys. Further, UAVs display strong time- and cost-effective advantages over manual methods which is amplified with increasing project scale. We propose it as a valuable method for multiple scientific and commercial applications related to environmental monitoring and management, including marine resource exploration and exploitation.

Physiological and transcriptome analysis of Dendrobium officinale under low nitrogen stress.

Nitrogen (N) is the main nutrient of plants, and low nitrogen usually affects plant growth and crop yield. The traditional Chinese herbal medicine Dendrobium officinale Kimura et. Migo is a typical low nitrogen-tolerant plant, and its mechanism in response to low nitrogen stress has not previously been reported. In this study, physiological measurements and RNA-Seq analysis were used to analyse the physiological changes and molecular responses of D. officinale under different nitrogen concentrations. The results showed that under low nitrogen levels, the growth, photosynthesis and superoxide dismutase activity were found to be significantly inhibited, while the activities of peroxidase and catalase, the content of polysaccharides and flavonoids significantly increased. Differentially expressed genes (DEGs) analysis showed that nitrogen and carbon metabolisms, transcriptional regulation, antioxidative stress, secondary metabolite synthesis and signal transduction all made a big difference in low nitrogen stress. Therefore, copious polysaccharide accumulation, efficient assimilation and recycling of nitrogen, as well as rich antioxidant components play critical roles. This study is helpful for understanding the response mechanism of D. officinale to low nitrogen levels, which might provide good guidance for practical production of high quality D. officinale .

Binding asymmetry and conformational studies of the AtGSDA dimer

Guanosine deaminase (GSDA) is an important deaminase that converts guanosine to xanthosine, a key intermediate in nitrogen recycling in plants. We previously solved complex structures of Arabidopsis thaliana GSDA bound by various ligands and examined its catalytic mechanism. Here, we report cocrystal structures of AtGSDA bound by inactive guanosine derivatives, which bind relatively weakly to the enzyme and mostly have poor binding geometries. The two protomers display unequal binding performances, and molecular dynamics simulation identified diverse conformations during the enzyme-ligand interactions. Moreover, intersubunit, tripartite salt bridges show conformational differences between the two protomers, possibly acting as “gating” systems for substrate binding and product release. Our structural and biochemical studies provide a comprehensive understanding of the enzymatic behavior of this intriguing enzyme.

Metabolites of extracellular organic matter from Microcystis and Dolichospermum drive distinct modes of carbon, nitrogen, and phosphorus recycling

Algal extracellular organic matter (EOM) metabolites exert considerable impact on the carbon (C), nitrogen (N), and phosphorus (P) cycles mediated by attached bacteria. Field investigations were conducted in two ponds to explore the relationship among EOM metabolites from Microcystis and Dolichospermum, co-occurring microbes, and nutrient recycling from April 2021 to December 2021. Microcystis blooms primarily produced more complex bound EOM (bEOM) metabolites with many amino acid components, which facilitated bacterial colonization and provided sufficient substrates for ammonification. Meanwhile, high abundances of dissimilatory nitrate reduction to ammonium genes from co-occurring microbes such as Rhodobacter have demonstrated their strong N retention ability. Metabolic products of bEOM from Microcystis comprise a large number of organic acids that can solubilize non-bioavailable P. All these factors have collectively resulted in the increase of all fractions of N and P, except for nitrate (NO3−-N) in the water column. In contrast, the EOM metabolite from Dolichospermum was simple, coupled with high abundance of functional genes of α-glucosidase, and produced small molecular substances fueling denitrification. The metabolic products of EOM from Dolichospermum include abundant N-containing substances dominated by heterocyclic substances, suggesting that the metabolic products of Dolichospermum are not conducive to N regeneration and retention. Therefore, the metabolic products of EOM from Microcystis triggered a shift in the attached microbial community and function toward C, N, and P recycling with close mutual coupling. Acquisition of N and P in Dolichospermum is dependent on itself based on N fixation and organic P hydrolysis capacity. This study provides a new understanding of the contribution of algal EOM to the nutrient cycle.

Hydrothermal Regeneration of Ammonium as a Basin-Scale Driver of Primary Productivity.

Hydrothermal vents are important targets in the search for life on other planets due to their potential to generate key catalytic surfaces and organic compounds for biogenesis. Less well studied, however, is the role of hydrothermal circulation in maintaining a biosphere beyond its origin. In this study, we explored this question with analyses of organic carbon, nitrogen abundances, and isotopic ratios from the Paleoproterozoic Zaonega Formation (2.0 Ga), NW Russia, which is composed of interbedded sedimentary and mafic igneous rocks. Previous studies have documented mobilization of hydrocarbons, likely associated with magmatic intrusions into unconsolidated sediments. The igneous bodies are extensively hydrothermally altered. Our data reveal strong nitrogen enrichments of up to 0.6 wt % in these altered igneous rocks, suggesting that the hydrothermal fluids carried ammonium concentrations in the millimolar range, which is consistent with some modern hydrothermal vents. Furthermore, large isotopic offsets of ∼10‰ between organic-bound and silicate-bound nitrogen are most parsimoniously explained by partial biological uptake of ammonium from the vent fluid. Our results, therefore, show that hydrothermal activity in ancient marine basins could provide a locally high flux of recycled nitrogen. Hydrothermal nutrient recycling may thus be an important mechanism for maintaining a large biosphere on anoxic worlds.

Nitrogen enrichment in the altered upper oceanic crust: A new perspective on constraining the global subducting nitrogen budget and implications for subduction-zone nitrogen recycling

Studies of alteration enrichment of nitrogen (N) in seafloor basalts clearly indicate that the upper oceanic crust is an important reservoir to transfer crustal N into Earth's interior. However, since previous studies have focused on relatively few DSDP/ODP/IODP drill cores, the factors controlling N enrichment in the altered upper oceanic crust at a global scale have not been revealed. Here we report N concentrations and isotope compositions of altered basalts from four additional DSDP/ODP Holes (556, 1224F, 417A and 543A). These new data, together with the published data from Holes 801C, 1149D, 1256D and 504B, enable systematic assessment of the potential affecting factors such as alteration degree, crustal age, spreading rate and sediment type, on N enrichment in the upper oceanic crust. The new data demonstrate ubiquitous N enrichment (1.3 – 48.4 ppm) in global seafloor basalts. The results indicate that, (i) the secondary N (in the form of ammonium) in altered basalts was sourced from sediment/seawater with δ15N values of 0‰ to +8‰, with a minor source from abiotic N2 reduction with δ15N values of -12‰ to -21‰; (ii) N enrichments in the upper oceanic crust do not correlate with crustal age, suggesting that the N uptake should mainly occur over early ages (likely within ∼20 Myr of crustal formation); (iii) the magnitude of N enrichment in the upper oceanic crust is primarily controlled by the N availability in the surrounding environment, which is ultimately related to the N abundance of basal sediments and/or seawater. The highest degree of N enrichment occurs in the upper oceanic crust overlain by N-rich basal sediments (claystone), i.e., at Hole 543A (N = 24.9±8.3 ppm; 1σ). In contrast, the lowest degree of N enrichment occurs in the upper oceanic crust overlain by N-poor basal sediments (chert), i.e., at Hole 1149D (N = 2.0±0.5 ppm; 1σ). With the consideration of this primary controlling factor, a global N input flux of 3.7±0.3 ×109 mol⋅yr−1 for the 300 – 600 m upper oceanic crust is calculated. These new data also demonstrate that N concentrations are relatively low in global altered basalts (average: 10.1±7.8 pm; 1σ). In comparison to their metamorphic equivalents, blueschists have much higher N concentrations (up to ∼122 ppm) whereas eclogites have N concentrations comparable to altered basalts. This implies further N enrichment in basaltic oceanic crust during early subduction and N devolatilization during deep subduction (by eclogite facies).

Interactions between Entodinium caudatum and an amino acid-fermenting bacterial consortium: fermentation characteristics and protozoal population in vitro.

Ruminal protozoa, especially entodiniomorphs, engulf other members of the rumen microbiome in large numbers; and they release oligopeptides and amino acids, which can be fermented to ammonia and volatile fatty acids (VFAs) by amino acid-fermenting bacteria (AAFB). Studies using defaunated (protozoa-free) sheep have demonstrated that ruminal protozoa considerably increase intraruminal nitrogen recycling but decrease nitrogen utilization efficiency in ruminants. However, direct interactions between ruminal protozoa and AAFB have not been demonstrated because of their inability to establish axenic cultures of any ruminal protozoan. Thus, this study was performed to evaluate the interaction between Entodinium caudatum, which is the most predominant rumen ciliate species, and an AAFB consortium in terms of feed degradation and ammonia production along with the microbial population shift of select bacterial species (Prevotella ruminicola, Clostridium aminophilum, and Peptostreptococcus anaerobius). From an Ent. caudatum culture that had been maintained by daily feeding and transfers every 3 or 4 days, the bacteria and methanogens loosely associated with Ent. caudatum cells were removed by filtration and washing. An AAFB consortium was established by repeated transfers and enrichment with casamino acids as the sole substrate. The cultures of Ent. caudatum alone (Ec) and AAFB alone (AAFB) and the co-culture of Ent. caudatum and AAFB (Ec + AAFB) were set up in three replicates and incubated at 39°C for 72 h. The digestibility of dry matter (DM) and fiber (NDF), VFA profiles, ammonia concentrations, pH, and microscopic counts of Ent. caudatum were compared among the three cultures. The co-culture of AAFB and Ent. caudatum enhanced DM degradation, VFA production, and Ent. caudatum cell counts; conversely, it decreased acetate: propionate ratio although the total bacterial abundance was similar between Ec and the Ec + AAFB co-culture after 24 h incubation. The ammonia production and relative abundance of C. aminophilum and P. anaerobius did not differ between AAFB alone and the Ec + AAFB co-culture. Our results indicate that Ent. caudatum and AAFB could have a mutualistic interaction that benefited each other, but their interactions were complex and might not increase ammoniagenesis. Further research should examine how such interactions affect the population dynamics of AAFB.