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Abstract Euglena gracilis (E. gracilis), pivotal in the study of photosynthesis, endosymbiosis, and chloroplast development, is also an industrial microalga for paramylon production. Despite its importance, E. gracilis genome exploration faces challenges due to its intricate nature. In this study, we achieved a chromosome-level de novo assembly (2.37 Gb) using Illumina, PacBio, Bionano, and Hi-C data. The assembly exhibited a contig N50 of 619 Kb and scaffold N50 of 1.12 Mb, indicating superior continuity. Approximately 99.83% of the genome was anchored to 46 chromosomes, revealing structural insights. Repetitive elements constituted 58.84% of the sequences. Functional annotations were assigned to 39,362 proteins, enhancing interpretative power. BUSCO analysis confirmed assembly completeness at 80.39%. This first high-quality E. gracilis genome offers insights for genetics and genomics studies, overcoming previous limitations. The impact extends to academic and industrial research, providing a foundational resource.

Relying on the middle line of south-to-north water diversion project ning storage reservoir has built the construction load impact assessment project, the study through the analysis of field conditions select reasonable monitoring section and monitoring scheme, the late monitoring, the results can reflect the overall deformation of the wall and stress, and use in advance in the wall, monitoring instruments, to the typical section of field deformation, pressure, strain and stress, automatic oblique monitoring results to introduce the stress strain of the whole wall. Research results: The soil pressure showed the larger on the outside and the slightly smaller on the inside; Concrete strain relative to the initial state in the direction of vertical wall and vertical strain increment is larger, The strain increment along the wall direction is small; The data of the reinforcement stress gauge are all negative, And the quantity value of the inner steel bar gauge continues to increase, The monitoring value of the outer steel bar gauge has a tendency to decrease gradually; Small displacement of the plastic concrete walls, Large displacement of reinforced concrete walls, And the value along the wall for the small law; The inclination displacement value of monitoring section 2-2 and 3-3 gradually decreases with the continuous construction, The displacement value of monitoring 1–1 section also becomes smaller in the first and middle stages of construction, But in the late construction, This shows that the horizontal displacement of the monitoring 1–1 section in the later construction period has a recovery trend; The top settlement value is larger at the 1st-3rd wall, About 6 mm–10mm, The 4–6 pin is smaller, About 4 mm–5mm, Article 7–10, the pin is directly crushed by the vehicle, Its value is approximately 6 mm–8mm.

Abstract Background Microalgae can absorb CO2 during photosynthesis, which causes the aquatic environmental pH to rise. However, the pH is reduced when microalga Euglena gracilis (EG) is cultivated under photoautotrophic conditions. The mechanism behind this unique phenomenon is not yet elucidated. Results The present study evaluated the growth of EG, compared to Chlorella vulgaris (CV), as the control group; analyzed the dissolved organic matter (DOM) in the aquatic environment; finally revealed the mechanism of the decrease in the aquatic environmental pH via comparative metabolomics analysis. Although the CV cell density was 28.3-fold that of EG, the secreted-DOM content from EG cell was 49.8-fold that of CV (p-value

Abstract Background Microalgae can contribute to more than 40% of global primary biomass production and are suitable candidates for various biotechnology applications such as food, feed products, drugs, fuels, and wastewater treatment. However, the primary limitation for large-scale algae production is the fact that algae requires large amounts of fresh water for cultivation. To address this issue, scientists around the world are working on ways to reuse the water to grow microalgae so that it can be grown in successive cycles without the need for fresh water. Results In this study, we present the results when we cultivate microalgae with cultivation water that is purified and reused. Specifically, we purify the cultivation water using an ultrafiltration membrane (UFM) treatment and investigate how this treatment affects: the biomass and biochemical components of the microalgae; characteristics of microalgae growth inhibitors; the mechanism whereby potential growth inhibitors are secreted (followed using metabolomics analysis); the effect of activated carbon (AC) treatment and advanced oxidation processes (AOPs) on the removal of growth inhibitors of Euglena gracilis. Firstly, the results show that E. gracilis can be only cultivated through two growth cycles with water that has been filtered and reused, and the growth of E. gracilis is significantly inhibited when the water is used a third time. Secondly, as the number of reused water cycles increases, the Cl− concentration gradually increases in the cultivation water. When the Cl− concentration accumulates to a level of fivefold higher than that of the control, growth of E. gracilis is inhibited as the osmolality tolerance range is exceeded. Interestingly, the osmolality of the reused water can be reduced by replacing NH4Cl with urea as the source of nitrogen in the cultivation water. Thirdly, E. gracilis secretes humic acid (HA)—which is produced by the metabolic pathways for valine, leucine, and isoleucine biosynthesis and by linoleic acid metabolism—into the cultivation water. Because HA contains large fluorescent functional groups, specifically extended π(pi)-systems containing C=C and C=O groups and aromatic rings, we were able to observe a positive correlation between HA concentration and the rate of inhibition of E. gracilis growth using fluorescence spectroscopy. Moreover, photosynthetic efficiency is adversely interfered by HA, thereby reductions in the synthetic efficiency of paramylon and lipid in E. gracilis. In this way, we are able to confirm that HA is the main growth inhibitor of E. gracilis. Finally, we verify that all the HA is removed or converted into nutrients efficiently by AC or UV/H2O2/O3 treatments, respectively. As a result of these treatments, growth of E. gracilis is restored (AC treatment) and the amount of biomass is promoted (UV/H2O2/O3 treatment). Conclusions These studies have important practical and theoretical significance for the cyclic cultivation of E. gracilis and for saving water resources. Our work may also provide a useful reference for other microalgae cultivation.

Life cycle assessment (LCA) is a powerful tool to evaluate environmentally sustainable production or consumption of various goods or services. Microalgae are single-celled green factories and good resources of biofuels, bioactive products, food ingredients, and degradable biomaterials. Currently, microalgae are also valuable for mitigating elevated greenhouse gases like CO2 levels and treatment of wastewater. LCA evaluation was limited and separated, majorly in microalgal biofuels and heterotrophic cultivation. Comparative LCA for different final algal products such as algal powder, bio-oil, total fatty acid, and residue recycling is still limited, especially autotrophic algal cultivation for products other than bio-oils and biofuels. Thus, we chose several autotrophic cultivated microalgae and made a comparative LCA among these selected species and a detailed step-by-step production in Chlorella sp. Results indicated that we could significantly reduce the production cost and lower environmental impacts by selecting algal species and final products, optimizing methods for algal cultivation, biomass separation, and drying process, and land selection plus electricity renewable energy, together with thermal power plants nearby for CO2 or flu gas. It shed light on the insight of microalgal consumption selection under current international requirements and challenges for carbon sequestration.

With the continuous growth of the world’s population and the increasing development of industrialization, the demand for energy by human beings has been expanding, resulting in an increasingly severe energy crisis. Microalgae are considered the most potential alternatives to traditional fossil fuels due to their many advantages, like fast growth rate, strong carbon sequestration capacity, and low growth environment requirements. Euglena can use carbon sources such as glucose, ethanol, and others for heterotrophic growth. Moreover, Euglena is highly adaptable to the environment and has a high tolerance to various environmental stresses, such as salinity, heavy metals, antibiotics, etc. Different treatments of Euglena cells could affect their growth and the accumulation of bioactive substances, especially fatty acids. To expand the industrial application of Euglena as a potential biodiesel candidate, we determine the physiological responses of Euglena against environmental stresses (antibiotics, heavy metals, salinity) or carbon resources (glucose and ethanol), and evaluate the potential for higher quality and yield of fatty acid with a high growth rate. Adding glucose into the culture media increases cell biomass and fatty acid production with high-quality biodiesel characters. The transcriptome analysis helped explore the possible regulation and biosynthesis of fatty acids under different treatments and exploited in the improvement of biodiesel production. This study provides insights for further improvement and various culture treatments for Euglena-based biodiesel and jet fuels.

Euglena gracilis, a single-celled microalga with various trophic growth styles under different cultivation conditions, contains nutrients, such as ß-1,3-glucans, essential amino acids, fatty acids, vitamins, and minerals. It has recently attracted attention as a new health food. Among them, ß-1,3-glucans, paramylon of Euglena, is an insoluble dietary fiber and is well known as an immune booster, attenuator of obesity and diabetes, reducer of acute liver injury, and suppressor of atopic dermatitis, and other chronic inflammatory disorders. Recently, evidence has appeared for the positive health effects of foods, food ingredients, or biochemical compounds derived from several other microalgae, such as Chlorella, Spirulina, Dunaliella, Phaeodactylum, and Pavlova. Until most recently, the prebiotic activity of Euglena and paramylon was reported. Emerging prospects of microalgae as prebiotics were well summarized, but the mechanisms behind the bacterial growth promotion by microalgae are not elucidated yet. Thus, we evaluated the prebiotic prospects of both autotrophic and heterotrophic Euglena on six different Lactobacillus. What’s more, the stimulated mechanism was revealed by bacterial culture medium metabolomic analysis. This study could widen the knowledge about the prebiotic activity of Euglena as a next-generation prebiotic and other microalgae-derived compounds as potential health foods.

Abstract Purpose Under different abiotic-stress conditions, the unicellular green microalga Dunaliella salina accumulates large amounts of carotenoids which are accompanied by fatty acid biosynthesis. Carotenoids and fatty acids both possess long carbon backbones; however, the relationship between carotenoid and fatty acid metabolism is controversial and remains poorly understood in microalgae. Methods In this study, we investigated the growth curves and the β-carotene, lutein, lipid, and fatty acid contents of D. salina Y6 grown under different abiotic-stress conditions, including high light, nitrogen depletion, and high salinity. Results Both high-salinity and nitrogen-depleted conditions significantly inhibited cell growth. Nitrogen depletion significantly induced β-carotene accumulation, whereas lutein production was promoted by high light. The accumulation of lipids did not directly positive correlate with β-carotene and lutein accumulation under the three tested abiotic-stress conditions, and levels of only a few fatty acids were increased under specific conditions. Conclusion Our data indicate that cellular β-carotene accumulation in D. salina Y6 positive correlates with accumulation of specific fatty acids (C16:0, C18:3n3, C14:0, and C15:0) rather than with total fatty acid content under different abiotic stress conditions.

Abstract Background Euglena is a new super health food resource that is rich in the natural polysaccharide paramylon, a linear β-1,3-glucan with various biological activities including activity on the immune system in different cell lines and animals. Despite these reports, the immune regulation mechanism of paramylon is still unclear. Results We investigate the signaling pathways paramylon impacts in immune macrophages. In RAW264.7 macrophages, sonicated and alkalized paramylon oligomers up-regulated inducible nitric oxide synthase (iNOS) and increased secretion of nitric oxide (NO), interleukin (IL)-6 and tumor necrosis factor (TNF)-α, in a concentration-dependent manner. In addition, paramylon activated the nuclear factor-κB(NF-κB) and mitogen-activated protein kinase (MAPK) signaling pathways and inhibiting these pathways attenuated the paramylon-induced secretion of the above immune-mediators. Conclusions These results demonstrate that Euglena gracilis paramylon modulates the immune system via activation of the NF-κB and MAPK signaling pathways and thus has potential therapeutic benefits.

Abstract Background Microalgae are widely be used in carbon sequestration, food supplements, natural pigments, polyunsaturated fatty acids, biofuel applications, and wastewater treatment. However, the difficulties incurred in algae cell separation and harvesting, and the exorbitant cost required to overcome these challenges, are the primary limitations to large-scale industrial application of microalgae technology. Results Herein, we explore the potential of inducing flocculation by adjusting the pH for pre-concentrating Euglena gracilis. Our results demonstrate that flocculation can be induced by increasing the medium pH to 8.5; however, most of the algae cells were broken by increasing the pH > 10. Magnesium phosphate, calcium phosphate, and their derivatives precipitation jointly led to flocculation, although calcium phosphate and its derivatives precipitation had a greater effect. Conclusions This study demonstrates that pH treatment-induced flocculation is efficient and feasible for the pre-concentration of E. gracilis under a pilot-scale culture system. Moreover, it also maintained the microalgae cells’ integrity, chlorophyll production, and increased paramylon production. These findings provide a theoretical basis for reducing the cost of large-scale E. gracilis harvesting; as well as provide a reference for harvesting other microalgae.

Euglena is a genus of single-celled eukaryotes that show both plant- and animal-like characteristics. Euglena gracilis, a model species, is of great academic interest for studying endosymbiosis and chloroplast development. As an industrial species, E. gracilis is also of primary biotechnological and economic importance as high value-added food, medicine, and cosmetic and high-quality feedstock for jet-fuel production because of its cells containing many high-value products, such as vitamins, amino acids, pigments, unsaturated fatty acids, and carbohydrate paramylon, as metabolites. For more than half a century, E. gracilis has been used as an industrial biotechnology platform for fundamental biology research, mainly exploring relevant physiological and biochemical method studies. Although many researchers focused on genetic engineering tools for E. gracilis in recent years, little progress has been achieved because of the lack of high-quality genome information and efficient techniques for genetic operation. This article reviewed the progress of the genetic transformation of E. gracilis, including methods for the delivery of exogenous materials and other advanced biotechnological tools for E. gracilis, such as CRISPR and RNA interference. We hope to provide a reference to improve the research in functional genomics and synthetic biology of Euglena.

Euglena gracilis (E. gracilis) has secondary endosymbiotic chloroplasts derived from ancient green algae. Its chloroplasts are easily lost under numerous conditions to become permanently bleached mutants. Green cells adapted in the dark contain undeveloped proplastids and they will develop into mature chloroplasts after 3 days of light exposure. Thus, E. gracilis is an ideal model species for a chloroplast development study. Previous studies about chloroplast development in E. gracilis focused on morphology and physiology, whereas few studies have addressed the regulatory processes induced by light in the proteome. In this study, the whole-genome proteome of dark-adapted E. gracilis (WT) and permanently ofloxacin-bleached mutant (B2) was compared under the light exposure after 0, 12, and 72 h. The results showed that the photosynthesis-related proteins were up-regulated over time in both WT and B2. The B2 strain, with losing functional chloroplasts, seemed to possess a complete photosynthetic function system. Both WT and B2 exhibited significant light responses with similar alternation patterns, suggesting the sensitive responses to light in proteomic levels. The main metabolic activities for the utilization of carbon and energy in WT were up-regulated, while the proteins with calcium ion binding, cell cycle, and non-photosynthetic carbon fixation were down-regulated in B2. This study confirmed light-induced chloroplast development in WT from dark, and also for the first time investigates the light responses of a bleached mutant B2, providing more information about the unknown functions of residual plastids in Euglena bleached mutants.

Euglena comprises over 200 species, of which Euglena gracilis is a model organism with a relatively high fatty acid content, making it an excellent potential source of biodiesel. This study isolated and characterized a new strain named E. gracilis 815. E. gracilis 815 cells were cultivated under light and dark conditions, with either ethanol or glucose as an external carbon source and an autotrophic medium as control. To achieve maximum active substances within a short period i.e., 6 days, the effects of the light condition and carbon source on the accumulation of bioactive ingredients of E. gracilis 815 were explored, especially fatty acids. In comparison with the industrially used E. gracilis Z strain, E. gracilis 815 exhibited high adaptability to different carbon sources and light conditions, with a comparable biomass and lipid yield. The content and composition of fatty acids of E. gracilis 815 were further determined to assess its potential for biodiesel use. Results suggested that E. gracilis 815 has biodiesel potential under glucose addition in dark culture conditions and could be a promising source for producing unsaturated fatty acids. Therefore, E. gracilis 815 is a candidate for short-chain jet fuel, with prospects for a wide variety of applications.

Bentonite, a supplementary cementitious material for Portland cement, has greatly contributed to environmental sustainability. However, few studies have investigated mortar samples produced by substituting bentonite for cement, and cement strength may be adversely affected when cement is replaced with bentonite in larger proportions. Therefore, this paper investigates and discusses the effect of microbially induced calcium carbonate precipitation (MICP) on improving the strength of bentonite-amended cement. The bio-mineralization process of MICP was characterized by SEM-EDS, while the biominerals formed in bentonite-amended mortar were identified by FIIR and XRD analysis. The results showed that: at bentonite concentrations of 0%, 10%, 20%, 30%, and 40% in cement, the bacterial suspension and reaction solution enhanced the compressive strength of bentonite-amended cement by 17%, 20%, 79%, 78%, and 38%, respectively, after 28 days, compared to control specimens; With the increased bacterial concentration in the presence of the reaction solution, the strength of the bentonite-amended cement (20% bentonite) increased remarkably compared to the control specimen (without bacteria). When the bacterial concentration was OD600 2.0, the compressive strength of bentonite-amended cement (20% bentonite) increased by 80% after 28 days; MICP process has a great effect on improving the strength of bentonite-amended cement. It is a green and economical choice to use MICP to improve the strength of bentonite-amended cement.

Euglena gracilis, a green microalga known as a potential candidate for jet fuel producers and new functional food resources, is highly tolerant to antibiotics, heavy metals, and other environmental stresses. Its cells contain many high-value products, including vitamins, amino acids, pigments, unsaturated fatty acids, and carbohydrate paramylon as metabolites, which change contents in response to various extracellular environments. However, mechanism insights into the cellular metabolic response of Euglena to different toxic chemicals and adverse environmental stresses were very limited. We extensively investigated the changes of cell biomass, pigments, lipids, and paramylon of E. gracilis under several environmental stresses, such as heavy metal CdCl2, antibiotics paromomycin, and nutrient deprivation. In addition, global metabolomics by Ultra-high-performance liquid chromatography tandem mass spectrometry (UHPLC–MS/MS) was applied to study other metabolites and potential regulatory mechanisms behind the differential accumulation of major high-valued metabolites. This study collects a comprehensive update on the biology of E. gracilis for various metabolic responses to stress conditions, and it will be of great value for Euglena cultivation and high-value [154mm][10mm]Q7metabolite production.

The microalga Euglena gracilis is utilized in the food, medicinal, and supplement industries. However, its mass production is currently limited by its low production efficiency and high risk of microbial contamination. In this study, physiological and biochemical parameters of E. gracilis co-cultivated with the bacteria Vibrio natriegens were investigated. A previous study reports the benefits of E. gracilis and V. natriegens co-cultivation; however, no bacterium growth and molecular mechanisms were further investigated. Our results show that this co-cultivation positively increased total chlorophyll, microalgal growth, dry weight, and storage sugar paramylon content of E. gracilis compared to the pure culture without V. natriegens. This analysis represents the first comprehensive metabolomic study of microalgae-bacterial co-cultivation, with 339 metabolites identified. This co-cultivation system was shown to have synergistic metabolic interactions between microalgal and bacterial cells, with a significant increase in methyl carbamate, ectoine, choline, methyl N-methylanthranilate, gentiatibetine, 4R-aminopentanoic acid, and glu-val compared to the cultivation of E. gracilis alone. Taken together, these results fill significant gaps in the current understanding of microalgae-bacteria co-cultivation systems and provide novel insights into potential improvements for mass production and industrial applications of E. gracilis.

Abstract Background Individual nutrient depletion is widely used to induce lipid accumulation in microalgae, which also causes cell growth inhibition and decreases the total biomass. Thus, improving the lipid accumulation without biomass loss in the nutrient deficiency cells becomes a potential cost-effective treatment for cheaper biofuels. Methods In this study, the effects of different nutritional conditions on the growth and contents of lipids in Chlamydomonas reinhardtii were compared, and the metabolic profiles under different nutritional conditions were also investigated. Results We showed that similar to other microalgae, nitrogen or phosphorus deficiency inhibited the growth of Chlamydomonas and combined nutrition deficiency reduced biomass by up to 31.7%, though lipid contents in cells (g/g dry weight [DW]) were significantly increased. The addition of sodium acetate countered this growth inhibition that resulted from nitrogen and phosphorus deficiency, with significantly increased biomass. Furthermore, the combination of 4 g/L sodium acetate supplementation with nitrogen and phosphorous deficiency increased total fatty acid yield (mg/L) by 93.0 and 150.1% compared to nutrient-depleted and normal culture conditions, respectively. Metabolite content was affected by the different nutritional conditions, especially metabolites that are involved in lipid metabolism, amino acid metabolism and metabolism of external substances. Conclusion Further research into these metabolites could shed light onto the relationship between cell growth inhibition and fatty acid accumulation in Chlamydomonas.

Abstract Background Microalgae have been demonstrated to be among the most promising phototrophic species for producing renewable biofuels and chemicals. Ethanol and butanol are clean energy sources with good chemical and physical properties as alternatives to gasoline. However, biosynthesis of these two biofuels has not been achieved due to low tolerance of algal cells to ethanol or butanol. Results With an eye to circumventing these problems in the future and engineering the robust alcohol-producing microalgal hosts, we investigated the metabolic responses of the model green alga Chlamydomonas reinhardtii to ethanol and butanol. Using a quantitative proteomics approach with iTRAQ-LC–MS/MS technologies, we detected the levels of 3077 proteins; 827 and 730 of which were differentially regulated by ethanol and butanol, respectively, at three time points. In particular, 41 and 59 proteins were consistently regulated during at least two sampling times. Multiple metabolic processes were affected by ethanol or butanol, and various stress-related proteins, transporters, cytoskeletal proteins, and regulators were induced as the major protection mechanisms against toxicity of the organic solvents. The most highly upregulated butanol response protein was Cre.770 peroxidase. Conclusions The study is the first comprehensive view of the metabolic mechanisms employed by C. reinhardtii to defend against ethanol or butanol toxicity. Moreover, the proteomic analysis provides a resource for investigating potential gene targets for engineering microalgae to achieve efficient biofuel production.

Euglena, a new superfood on the market, is a nutrient-rich, green single-celled microorganism that features the characteristics of both plant and animal. When cultivated under different conditions, Euglena produces different bioactive nutrients. Interestingly, Euglena is the only known microorganism whose chloroplasts are easy to lose under stress and become permanently bleached. We applied gas chromatography-mass spectrometry (GC-MS) to determine the metabolomes of wild-type (WT) Euglena gracilis and its bleached mutant OflB2 under light stimulation. We found a significant metabolic difference between WT and OflB2 cells in response to light. An increase of membrane components (phospholipids and acylamides) was observed in WT, while a decrease of some stimulant metabolites was detected in OflB2. These metabolomic changes after light stimulation are of great significance to the development of Euglena chloroplasts and their communications with the nucleus.

Epigenetic modifications such as DNA methylation are well known as connected with many important biological processes. Rapid accumulating evidence shows environmental stress can generate particular defense epigenetic changes across generations in eukaryotes. This transgenerational epigenetic inheritance in animals and plants has gained interest over the last years. Cyanobacteria play very crucial role in the earth, and as the primary producer they can adapt to nearly all diverse environments. However, few knowledge about the genome wide epigenetic information such as methylome information in cyanobacteria, especially under any environment stress, was reported so far. In this study we profiled the genome-wide cytosine methylation from a model cyanobacterium Synechocystis sp. PCC 6803, and explored the possibility of transgenerational epigenetic process in this ancient single-celled prokaryote by comparing the DNA methylomes among normal nitrogen medium cultivation, nitrogen starvation for 72 h and nitrogen recovery for about 12 generations. Our results shows that DNA methylation patterns in nitrogen starvation and nitrogen recovery are much more similar with each other, significantly different from that of the normal nitrogen. This study reveals the difference in global DNA methylation pattern of cyanobacteria between normal and nutrient stress conditions and reports the evidence of transgenerational epigenetic process in cyanobacteria. The results of this study may contribute to a better understanding of epigenetic regulation in prokaryotic adaptation to and survive in the ever changing environment.

Macroalgae has bloomed in the brackish lake of Shenzhen Bay, China continuously from 2010 to 2014. Gracilaria tenuistipitata was identified as the causative macroalgal species. The aim of this study was to explore the outbreak mechanism of G. tenuistipitata, by studying the effects of salinity and nitrogen sources on growth, and the different nitrogen sources uptake characteristic. Our experimental design was based on environmental conditions observed in the bloom areas, and these main factors were simulated in the laboratory. Results showed that salinity 12 to 20 ‰ was suitable for G. tenuistipitata growth. When the nitrogen sources' (NH4+, NO3-) concentrations reached 40 µM or above, the growth rate of G. tenuistipitata was significantly higher. Algal biomass was higher (approximately 1.4 times) when cultured with NH4+ than that with NO3- addition. Coincidentally, macroalgal bloom formed during times of moderate salinity (∼12 ‰) and high nitrogen conditions. The NH4+ and NO3- uptake characteristic was studied to understand the potential mechanism of G. tenuistipitata bloom. NH4+ uptake was best described by a linear, rate-unsaturated response, with the slope decreasing with time intervals. In contrast, NO3- uptake followed a rate-saturating mechanism best described by the Michaelis-Menten model, with kinetic parameters Vmax = 37.2 µM g-1 DM h-1 and Ks = 61.5 µM. Further, based on the isotope 15N tracer method, we found that 15N from NH4+ accumulated faster and reached an atom% twice than that of 15N from NO3-, suggesting when both NH4+ and NO3- were available, NH4+ was assimilated more rapidly. The results of the present study indicate that in the estuarine environment, the combination of moderate salinity with high ammonium may stimulate bloom formation.