Nitrate or ammonium: Influences of nitrogen source on the physiology of a green alga

Mechanistic characterization of dissolved inorganic phosphorus in water during the red tide

The eutrophication of water, such as excessive nitrogen and phosphorus, are closely associated with the outbreak of red tide. However, the response of dissolved inorganic phosphorus (DIP) to red tide remained unclear in water. In this study, three species of diatoms capable of causing red tides were cultured in simulated seawater with different concentrations of DIP. The changes of biomass, chlorophyll a concentration and the carbon stable isotope composition of microalgae, the DIP concentration and pH of the culture medium were compared among the experimental groups. In addition, correlation verification was used to test the correlation between the change of DIP concentration and other indicators. The results showed that in the experimental period, the DIP concentration of each experimental group decreased significantly first, and the concentration dropped to less than 40% of the initial level. After that, the pH of the medium, the biomass, chlorophyll a concentration and carbon stable isotope composition of the microalgae showed varying degrees of increase, and then stabilized or decreased. These also marked the outbreak of red tide. Moreover, the correlation test showed that there was a correlation between them and the change of DIP concentration. Therefore, by exploring the relationship between the change of DIP concentration in water and the occurrence of red tide, this study provides a possible direction for the current prediction of red tide, and provides a basis for further investigation of the occurrence mechanism of red tide.

Co-bioaugmentation with microalgae and probiotic bacteria: Sustainable solutions for upcycling of aquaculture wastewater and agricultural residues into microbial-rice bran complexes

Aquaculture farming generates a significant amount of wastewater, which has prompted the development of creative bioprocesses to improve wastewater treatment and bioresource recovery. One promising method of achieving these aims is to directly recycle pollutants into microbe-rice bran complexes, which is an economical and efficient technique for wastewater treatment that uses synergetic interactions between algae and bacteria. This study explores novel bioaugmentation as a promising strategy for efficiently forming microbial-rice bran complexes in unsterilized aquaculture wastewater enriched with agricultural residues (molasses and rice bran). Results found that rice bran serves a dual role, acting as both an alternative nutrient source and a biomass support for microalgae and bacteria. Co-bioaugmentation, involving the addition of probiotic bacteria (Bacillus syntrophic consortia) and microalgae consortiums (Tetradesmus dimorphus and Chlorella sp.) to an existing microbial community, led to a remarkable 5-fold increase in microbial-rice bran complex yields compared to the non-bioaugmentation approach. This method provided the most compact biofloc structure (0.50 g/L) and a large particle diameter (404 μm). Co-bioaugmentation significantly boosts the synthesis of extracellular polymeric substances, comprising proteins at 6.5 g/L and polysaccharides at 0.28 g/L. Chlorophyta, comprising 80% of the total algal phylum, and Proteobacteria, comprising 51% of the total bacterial phylum, are emerging as dominant species. These microorganisms play a crucial role in waste and wastewater treatment, as well as in the formation of microbial-rice bran complexes that could serve as an alternative aquaculture feed. This approach prompted changes in both microbial community structure and nutrient cycling processes, as well as water quality. These findings provide valuable insights into the transformative effects of bioaugmentation on the development of microbial-rice bran complexes, offering potential applications in bioprocesses for waste and wastewater management.

Stress Responses and Ammonia Nitrogen Removal Efficiency of Oocystis lacustris in Saline Ammonium-Contaminated Wastewater Treatment

The increasing concern over climate change has spurred significant interest in exploring the potential of microalgae for wastewater treatment. Among the various types of industrial wastewaters, high-salinity NH4+-N wastewater stands out as a common challenge. Investigating microalgae's resilience to NH4+-N under high-salinity conditions and their efficacy in NH4+-N utilization is crucial for advancing industrial wastewater microalgae treatment technologies. This study evaluated the effectiveness of employing nitrogen-efficient microalgae, specifically Oocystis lacustris, for NH4+-N removal from saline wastewater. The results revealed Oocystis lacustris's tolerance to a Na2SO4 concentration of 5 g/L. When the Na2SO4 concentration reached 10 g/L, the growth inhibition experienced by Oocystis lacustris began to decrease on the 6th day of cultivation, with significant alleviation observed by the 7th day. Additionally, the toxic mechanism of saline NH4+-N wastewater on Oocystis lacustris was analyzed through various parameters, including chlorophyll-a, soluble protein, oxidative stress indicators, key nitrogen metabolism enzymes, and microscopic observations of algal cells. The results demonstrated that when the Oocystis lacustris was in the stationary growth phase with an initial density of 2 × 107 cells/L, NH4+-N concentrations of 1, 5, and 10 mg/L achieved almost 100% removal of the microalgae on the 1st, 2nd, and 4th days of treatment, respectively. On the other hand, saline NH4+-N wastewater minimally impacted photosynthesis, protein synthesis, and antioxidant systems within algal cells. Additionally, NH4+-N within the cells was assimilated into glutamic acid through glutamate dehydrogenase-mediated pathways besides the conventional pathway involving NH4+-N conversion into glutamine and assimilation amino acids.

Features of the microalga Raphidocelis subcapitata: physiology and applications

The microalga Raphidocelis subcapitata was isolated from the Nitelva River (Norway) and subsequently deposited in the collection of the Norwegian Institute of Water Research as "Selenastrum capricornutum Printz". This freshwater microalga, also known as Pseudokirchneriella subcapitata, acquired much of its notoriety due to its high sensitivity to different chemical species, which makes it recommended by different international organizations for the assessment of ecotoxicity. However, outside this scope, R. subcapitata continues to be little explored. This review aims to shed light on a microalga that, despite its popularity, continues to be an "illustrious" unknown in many ways. Therefore, R. subcapitata taxonomy, phylogeny, shape, size/biovolume, cell ultra-structure, and reproduction are reviewed. The nutritional and cultural conditions, chronological aging, and maintenance and preservation of the alga are summarized and critically discussed. Applications of R. subcapitata, such as its use in aquatic toxicology (ecotoxicity assessment and elucidation of adverse toxic outcome pathways) are presented. Furthermore, the latest advances in the use of this alga in biotechnology, namely in the bioremediation of effluents and the production of value-added biomolecules and biofuels, are highlighted. To end, a perspective regarding the future exploitation of R. subcapitata potentialities, in a modern concept of biorefinery, is outlined. KEY POINTS: • An overview of alga phylogeny and physiology is critically reviewed. • Advances in alga nutrition, cultural conditions, and chronological aging are presented. • Its use in aquatic toxicology and biotechnology is highlighted.

Growth of microalgae and cyanobacteria consortium in a photobioreactor treating liquid anaerobic digestate from vegetable waste

This research examines the biological treatment of undiluted vegetable waste digestate conducted in a bubble column photobioreactor. Initially, the bioreactor containing 3N-BBM medium was inoculated with Microglena sp., Tetradesmus obliquus, and Desmodesmus subspicatus mixture with a density of 1.0 × 104 cells/mL and the consortium was cultivated for 30 days. Then, the bioreactor was semi-continuously fed with liquid digestate with hydraulic retention time (HRT) of 30 days, and the treatment process was continued for the next 15 weeks. The change in the microalgal and cyanobacterial species domination was measured in regular intervals using cell counting with droplet method on a microscope slide. At the end of the experiment, Desmonostoc sp. cyanobacteria (identified with 16S ribosomal RNA genetical analysis) as well as Tetradesmus obliquus green algae along with Rhodanobacteraceae and Planococcaceae bacteria (determined with V3-V4 16sRNA metagenomic studies) dominated the microbial community in the photobioreactor. The experiment demonstrated high treatment efficiency, since nitrogen and soluble COD were removed by 89.3 ± 0.5% and 91.2 ± 1.6%, respectively, whereas for phosphates, 72.8 ± 2.1% removal rate was achieved.

Nitrogen and phosphorus stress as a tool to induce lipid production in microalgae

Microalgae, capable of accumulating large amounts of lipids, are of great value for biodiesel production. The high cost of such production stimulates the search for cultivation conditions that ensure their highest productivity. Reducing the content of nitrogen and phosphorus in the culture medium is widely used to change the content and productivity of lipids in microalgae. Achieving the right balance between maximum growth and maximum lipid content and productivity is the primary goal of many experimental works to ensure cost-effective biodiesel production from microalgae. The content of nitrogen and phosphorus in nutrient media for algal cultivation after converted to nitrogen (-N) and phosphorus (-P) lies in an extensive range: from 0.007 g L- 1 to 0.417 g L- 1 and from 0.0003 g L- 1 to 0.227 g L- 1 and N:P ratio from 0.12:1 to 823.33:1. When studying nutritional stress in microalgae, no single approach is used to determine the experimental concentrations of nitrogen and phosphorus. This precludes the possibility of correct interpretation of the data and may lead to erroneous conclusions. This work results from the systematisation of information on using nitrogen and phosphorus restriction to increase the lipid productivity of microalgae of different taxonomic and ecological groups to identify future research directions. The results of 301 experiments were included in the analysis using the principal components method. The investigation considered various divisions and classes: Cyanobacteria, Rhodophyta, Dinophyta, Haptophyta, Cryptophyta, Heterokontophyta/Ochrophyta (Bacillariophyceae, Eustigmatophyceae, Xanthophyceae), Chlorophyta, and also the ratio N:P, the time of the experiment, the light intensity during cultivation. Based on the concentrations of nitrogen and phosphorus existing in various nutrient media, a general scheme for designating the supply of nutrient media for nitrogen (as NO3- or NH4+, N g L- 1) and phosphorus (as РO4-, P g L- 1) has been proposed: replete -N (˃0.4 g L- 1), moderate -N (0.4-0.2), moderate N-limitation (0.19-0.1), strong N-limitation (˂0.1), without nitrogen (0), replete -Р (˃0.2), moderate -P (0.2-0.02), moderate P-limitation (0.019-0.01), strong P-limitation (˂0.01), without phosphorus (0).

Transcriptional and metabolomic responses of Methylococcus capsulatus Bath to nitrogen source and temperature downshift

Methanotrophs play a significant role in methane oxidation, because they are the only biological methane sink present in nature. The methane monooxygenase enzyme oxidizes methane or ammonia into methanol or hydroxylamine, respectively. While much is known about central carbon metabolism in methanotrophs, far less is known about nitrogen metabolism. In this study, we investigated how Methylococcus capsulatus Bath, a methane-oxidizing bacterium, responds to nitrogen source and temperature. Batch culture experiments were conducted using nitrate or ammonium as nitrogen sources at both 37°C and 42°C. While growth rates with nitrate and ammonium were comparable at 42°C, a significant growth advantage was observed with ammonium at 37°C. Utilization of nitrate was higher at 42°C than at 37°C, especially in the first 24 h. Use of ammonium remained constant between 42°C and 37°C; however, nitrite buildup and conversion to ammonia were found to be temperature-dependent processes. We performed RNA-seq to understand the underlying molecular mechanisms, and the results revealed complex transcriptional changes in response to varying conditions. Different gene expression patterns connected to respiration, nitrate and ammonia metabolism, methane oxidation, and amino acid biosynthesis were identified using gene ontology analysis. Notably, key pathways with variable expression profiles included oxidative phosphorylation and methane and methanol oxidation. Additionally, there were transcription levels that varied for genes related to nitrogen metabolism, particularly for ammonia oxidation, nitrate reduction, and transporters. Quantitative PCR was used to validate these transcriptional changes. Analyses of intracellular metabolites revealed changes in fatty acids, amino acids, central carbon intermediates, and nitrogen bases in response to various nitrogen sources and temperatures. Overall, our results offer improved understanding of the intricate interactions between nitrogen availability, temperature, and gene expression in M. capsulatus Bath. This study enhances our understanding of microbial adaptation strategies, offering potential applications in biotechnological and environmental contexts.

Synergistic promoting effect of increasing aquatic ammonium and CO2 on Microcystis aeruginosa

Owing to climate change and intensive agricultural development, freshwater bodies have been affected by increases in both CO₂ levels and chemically-reduced forms of N. However, little is known about how these changes affect cyanobacterial growth and blooms. This study explored a range of light conditions (30, 80, 130, or 200 μmol photons/m²/s) wherein Microcystis aeruginosa, a widespread bloom-forming species, was exposed to different concentrations of CO₂ (400 parts per million (ppm) and 1000 ppm) in a medium containing NH₄⁺ or NO₃－. The interactive effects of N sources and CO₂ levels on the C/N metabolic balance and energy balance were examined to assess changes in the growth of M. aeruginosa. When the light intensity was 80 μmol photons/m²/s, elevated CO₂ could reduce intracellular reactive oxygen species (ROS) in NH₄⁺-grown M. aeruginosa. Meanwhile, cell density and chlorophyll a (Chl a) increased with increasing CO₂ levels, and the increase in Chl a was significantly greater in NH₄⁺-grown M. aeruginosa than in NO₃－-grown M. aeruginosa. Under light conditions of 200 μmol photons/m²/s, elevated CO₂ concentration caused NO₃－-grown M. aeruginosa to be affected by a large amount of ROS, and the growth of NO₃－-grown M. aeruginosa was finally suppressed. However, NH₄⁺-grown M. aeruginosa had a smaller amount of ROS and showed improved growth as CO₂ was elevated. This difference can be attributed to the faster metabolic pathways in the NH₄⁺ environment, which manifested in a lower accumulation of 2-oxoglutarate and fatty acids as CO₂ was elevated. These findings suggest that the simultaneous increase in ammonium and CO₂ in aquatic ecosystems confers cyanobacteria with greater advantages than the combination of nitrate and CO₂, which may aggravate cyanobacterial blooms.

Impact of Nitrate and Ammonium Concentrations on Co-Culturing of Tetradesmus obliquus IS2 with Variovorax paradoxus IS1 as Revealed by Phenotypic Responses

Mutual interactions in co-cultures of microalgae and bacteria are well known for establishing consortia and nutrient uptake in aquatic habitats, but the phenotypic changes in terms of morphological, physiological, and biochemical attributes that drive these interactions have not been clearly understood. In this novel study, we demonstrated the phenotypic response in a co-culture involving a microalga, Tetradesmus obliquus IS2, and a bacterium, Variovorax paradoxus IS1, grown with varying concentrations of two inorganic nitrogen sources. Modified Bold's basal medium was supplemented with five ratios (%) of NO₃-N:NH₄-N (100:0, 75:25, 50:50, 25:75, and 0:100), and by maintaining N:P Redfield ratio of 16:1. The observed morphological changes in microalga included an increase in granularity and a broad range of cell sizes under the influence of increased ammonium levels. Co-culturing in presence of NO₃-N alone or combination with NH₄-N up to equimolar concentrations resulted in complete nitrogen uptake, increased growth in both the microbial strains, and enhanced accumulation of carbohydrates, proteins, and lipids. Total chlorophyll content in microalga was also significantly higher when it was grown as a co-culture with NO₃-N and NH₄-N up to a ratio of 50:50. Significant upregulation in the synthesis of amino acids and sugars and downregulation of organic acids were evident with higher ammonium uptake in the co-culture, indicating the regulation of carbon and nitrogen assimilation pathways and energy synthesis. Our data suggest that the co-culture of strains IS1 and IS2 could be exploited for effluent treatment by considering the concentrations of inorganic sources, particularly ammonium, in the wastewaters.

Growth Characteristics of Chlorella sorokiniana in a Photobioreactor during the Utilization of Different Forms of Nitrogen at Various Temperatures

The cultivation of microalgae requires the selection of optimal parameters. In this work, the effect of various forms of nitrogen on the growth and productivity of Chlorella sorokiniana AM-02 when cultivated at different temperatures was evaluated. Regardless of the temperature conditions, the highest specific growth rate of 1.26 day^-1 was observed in modified Bold's basal medium (BBM) with NH₄⁺ as a nitrogen source, while the highest specific growth rate in BBM with NO₃^- as a nitrogen source achieved only 1.07 day^-1. Moreover, C. sorokiniana grew well in medium based on anaerobic digester effluent (ADE; after anaerobic digestion of chicken/cow manure) with the highest growth rate being 0.92 day^-1. The accumulation of proteins in algal cells was comparable in all experiments and reached a maximum of 42% of dry weight. The biomass productivity reached 0.41-0.50 g L^-1 day^-1 when cultivated in BBM, whereas biomass productivity of 0.32-0.35 g L^-1 day^-1 was obtained in ADE-based medium. The results, based on a bacterial 16S rRNA gene sequencing approach, revealed the growth of various bacterial species in ADE-based medium in the presence of algal cells (their abundance varied depending on the temperature regimen). The results indicate that biomass from C. sorokiniana AM-02 may be sustainable for animal feed production considering the high protein yields.

Interactive effects of acidification and copper exposure on the reproduction and metabolism of coral endosymbiont Cladocopium goreaui

Ocean acidification resulting from increased CO₂ and pollution from land-sourced toxicants such as copper have been linked to coral cover declines in coastal reef ecosystems. The impacts of ocean acidification and copper pollution on corals have been intensively investigated, whereas research on their effects on coral endosymbiont Symbiodiniaceae is limited. In this study, reproduction, photosynthetic parameters, nutrient accumulation and metabolome of Symbiodiniaceae Cladocopium goreaui were investigated after a weeklong treatment with acute CO₂-induced acidification and copper ion. Acidification promoted algal reproduction through increased nutrients assimilation, upregulated citrate cycle and biomolecular biosynthesis pathway, while copper exposure repressed algal reproduction through toxic effects. The combined acidification and copper exposure caused the same decline in algal reproduction as copper exposure alone, but the upregulation of pentose phosphate pathway and the downregulation of aromatic amino acid biosynthesis. These results suggest that copper pollution could override the positive effects of acidification on the symbiodiniacean reproduction.

Aquaculture waste nutrients removal using microalgae with floating permeable nutrient uptake system (FPNUS)

Large area requirements and huge energy consumption restrict the applications of microalgae in wastewater treatment. In this study, in-situ nutrient removal was tested using a floating permeable nutrients uptake system with pore sizes of 1, 5, 10, and 40 µm, and Chlorella sorokiniana and Scenedesmus acuminatus. Results showed that N transfer rate across FPNUS varied with membrane pore size and N-type. Average transfer rate of NH₄⁺-N, NO₃^--N, and NO₂^--N across 1 µm membrane was 2.6, 14.6, and 2.3 mg m^-2h^-1, respectively, sufficient to support microalgal growth. The NH₄⁺-N and NO₃^--N removal rate in shrimp wastewater reached 1.32 and 1.88 mg L^-1d^-1, comparable to some BNR processes used in RAS. According to the developed area ratio prediction model, FPNUS to pond area ratio of 21% is sufficient to balance N loading of 0.05 mg L^-1d^-1. These results indicate extraordinary potential of in-situ nutrient removal from wastewaters using FPNUS.

Assessment of Nutrients Recovery Capacity and Biomass Growth of Four Microalgae Species in Anaerobic Digestion Effluent

Four microalgae species were evaluated for their bioremediation capacity of anaerobic digestion effluent (ADE) rich in ammonium nitrogen, derived from a biogas plant. Chlorella vulgaris, Chlorella sorokiniana, Desmodesmus communis and Stichococcus sp. were examined for their nutrient assimilation efficiency, biomass production and composition through their cultivation in 3.7% v/v ADE; their performance was compared with standard cultivation media which consisted in different nitrogen sources, i.e., BG-11NO3 and BG-11ΝH4 where N-NO3 was replaced by N-NH4. The results justified ammonium as the most preferable source of nitrogen for microalgae growth. Although Stichococcus sp. outperformed the other 3 species in N-NH4 removal efficiency both in BG-11NH4 and in 3.7% ADE (reaching up to 90.79% and 69.69% respectively), it exhibited a moderate biomass production when it was cultivated in diluted ADE corresponding to 0.59 g/L, compared to 0.89 g/L recorded by C. vulgaris and 0.7 g/L by C. sorokiniana and D. communis. Phosphorus contained in the effluent and in the control media was successfully consumed by all of the species, although its removal rate was found to be affected by the type of nitrogen source used and the particular microalgae species. The use of ADE as cultivation medium resulted in a significant increase in carbohydrates content in all investigated species.

Salinity-induced microalgal-based mariculture wastewater treatment combined with biodiesel production

Mariculture wastewater has drawn growing attention due to associated threats for coastal environment. However, most biological techniques exhibit unfavorable performance due to saline inhibition. Furthermore, only NaCl was used in most studies causing clumsy evaluation, undermining the potential of microalgal mariculture wastewater treatment. Herein, various concentrations of NaCl and sea salt are comprehensively examined and compared for their efficiencies of mariculture wastewater treatment and biodiesel conversion. The results indicate sea salt is a better trigger for treating wastewater (nearly 100% total nitrogen and total phosphorus removal) and producing high-quality biodiesel (330 mg/L•d). Structure equation model (SEM) further demonstrates the correlation of wastewater treatment performance and microalgal status is gradually weakened with increment of sea salt concentrations. Furthermore, metabolic analysis reveals enhanced photosynthesis might be the pivotal motivator for preferable outcomes under sea salt stimulation. This study provides new insights into microalgae-based approach integrating mariculture wastewater treatment and biodiesel production.

Immobilized Tetraselmis sp. for reducing nitrogenous and phosphorous compounds from aquaculture wastewater

Removal of nitrogenous and phosphorus compounds from aquaculture wastewater by green microalgae (Tetraselmis sp.) was investigated using a novel method of algal cell immobilization. Immobilized microalgae removed nitrogenous and phosphorous compounds efficiently from aquaculture wastewater. Results showed that Tetraselmis beads reduced significantly (p < 0.05) the total ammonia nitrogen, nitrite nitrogen and soluble reactive phosphorous concentration (0.08; 0.10 and 0.17 mg/L, respectively) from the initial concentration of 7.7, 3.1 and 2.0 mg/L respectively within 48 h compared to other treatments. Removal rate of total ammonia nitrogen, nitrite nitrogen and soluble reactive phosphorous were 99.2, 99.2 and 94.3% respectively, for the artificial wastewater within 24 h. For the shrimp pond wastewater, total ammonia nitrogen, nitrite nitrogen and soluble reactive phosphorous were reduced 98.9, 97.7 and 91.1% respectively within 48 h. It is concluded that Tetraselmis sp. beads is an effective means to reduce nitrogen and phosphorus levels in aquaculture wastewater.

Revisiting carbon, nitrogen, and phosphorus metabolisms in microalgae for wastewater treatment

Threats posed to humans - including environmental pollution, water scarcity, food shortages, and resource crises drive a new concept to think about wastewater and its treatment. Wastewater is not only a waste but also a source of energy, renewable and/or non-renewable resources, including water itself. The nutrient in wastewater should not only be removed but also need to be upcycled. Microalgae based wastewater treatment has attracted considerable interests because algae have the potential to efficiently redirect nutrients from wastewater to the accumulated algal biomass. Additionally, microalgae are commercialized in human consumption and animal feed owing to their high content of essential amino and fatty acids, vitamins, and pigments. The whole process establishes a circular economy, totally relying on the ability of microalgae to uptake and store nutrients in wastewater, such as carbon (C), nitrogen (N), and phosphorus (P). It makes the study of the mechanisms underlying the uptake and storage of nutrients in microalgae of great interest. This review specifically aims to summarize C, N, and P metabolisms in microalgae for a better understanding of the microalgae-based wastewater treatment from the nutrient uptake pathway, and examine the key physiological factors or the operating conditions related to nutrient metabolisms that may affect the treatment efficiency. At last, I discuss the potential approaches to enhance the overall treatment performance by adjusting the critical parameters for C, N, and P metabolisms.

Ammonium Utilization in Microalgae: A Sustainable Method for Wastewater Treatment

In plant cells, ammonium is considered the most convenient nitrogen source for cell metabolism. However, despite ammonium being the preferred N form for microalgae, at higher concentrations, it can be toxic, and can cause growth inhibition. Microalgae’s tolerance to ammonium depends on the species, with various taxa showing different thresholds of tolerability and symptoms of toxicity. In the environment, ammonium at high concentrations represents a dangerous pollutant. It can affect water quality, causing numerous environmental problems, including eutrophication of downstream waters. For this reason, it is important to treat wastewater and remove nutrients before discharging it into rivers, lakes, or seas. A valid and sustainable alternative to conventional treatments could be provided by microalgae, coupling the nutrient removal from wastewater with the production of valuable biomass. This review is focused on ammonium and its importance in algal nutrition, but also on its problematic presence in aquatic systems such as wastewaters. The aim of this work is to provide recent information on the exploitation of microalgae in ammonium removal and the role of ammonium in microalgae metabolism.

Effects of different phosphorus concentrations on growth and biochemical composition of Desmodesmus communis (E.Hegewald) E.Hegewald

The members of the family Scenedesmaceae has the most widely used microalgae species in algal biotechnology studies because of their fast growth rate, quality of nutrition content and lipid accumulation under nutrient-limiting conditions. However, the biochemical responses of the species under phosphorus (P) limiting conditions are still unknown. The growth and biochemical composition of Desmodesmus communis in response to different phosphorus concentrations were investigated in this research. Five different phosphorus conditions were used: control (BG11); excess treatments (50% P+, 75% P+) and limited treatments (50% P-, 75% P-The highest cell concentration was observed in 75% P+ (725.6 × 104 cells/mL), whereas the highest dry weight concentration (1.81 mg/L) was found in 50% P- medium. The highest total lipid (4.94%) accumulation was found in the 50% P + medium and the maximum protein (49.5%) content was detected in 50% P- medium. Fatty acid and amino acid compositions change according to P concentration. PUFAs concentrations are higher than SFAs and MUFAs. Therefore the microalgae biomass obtained from this study cannot be used for biodiesel production although it is more suitable for nutritional supplement productions.

Coral Productivity Is Co-Limited by Bicarbonate and Ammonium Availability

The nitrogen environment and nitrogen status of reef-building coral endosymbionts is one of the important factors determining the optimal assimilation of phototrophic carbon and hence the growth of the holobiont. However, the impact of inorganic nutrient availability on the photosynthesis and physiological state of the coral holobiont is partly understood. This study aimed to determine if photosynthesis of the endosymbionts associated with the coral Stylophora pistillata and the overall growth of the holobiont were limited by the availability of dissolved inorganic carbon and nitrogen in seawater. For this purpose, colonies were incubated in absence or presence of 4 µM ammonium and/or 6 mM bicarbonate. Photosynthetic performances, pigments content, endosymbionts density and growth rate of the coral colonies were monitored for 3 weeks. Positive effects were observed on coral physiology with the supplementation of one or the other nutrient, but the most important changes were observed when both nutrients were provided. The increased availability of DIC and NH₄⁺ significantly improved the photosynthetic efficiency and capacity of endosymbionts, in turn enhancing the host calcification rate. Overall, these results suggest that in hospite symbionts are co-limited by nitrogen and carbon availability for an optimal photosynthesis.

Isolation, screening and comprehensive characterization of candidate microalgae for biofuel feedstock production and dairy effluent treatment: A sustainable approach

In this study, the indigenous native microalgae were isolated from domestic and dairy effluent (DE) and further screened for DE treatment and lipid accumulation. All the isolated microalgae were examined for their growth adaptability in DE. The growth parameters of 15 isolates were determined and the following six isolates further selected for comprehensive analysis and identified as Desmodesmus sp. ASK01, Chlorella sp. ASK14, Scenedesmus sp. ASK16, Scenedesmus sp. ASK22, Chlorella sp. ASK25 and Chlorella sp. ASK27. The nutrient remediation capacity of six isolates as well as its lipid accumulation potential and biomass composition were determined. The Scenedesmus sp. ASK22 showed the best combined results and promising strain for the DE treatment and biofuel production. Biomass composition of Scenedesmus sp. ASK22 showed an oil accumulation of 30.7% (w/w) and biomass yield 1.22 g L^-1. The fatty acid methyl ester (FAME) mainly composed of C15:0, C16:0, C18:0, C18:1 and C18:3.