Chapter 3 - Nitrogen Assimilation and its Regulation
Publisher Summary
This chapter presents nitrogen assimilation in the context of genome analysis and gene function, with particular emphasis on inorganic nitrogen transporters, molybdenum cofactor (Moco) metabolism, and regulation of the nitrate assimilation pathway. In a comparative view, if considering only nitrate assimilation genes, Chlamydomonas and Arabidopsis show similar complexity whereas Ostreococcus, another unicellular alga, is much simpler. Understanding the bases of these differences will provide important perspectives into the biology of this pathway. Little information apart from that reviewed previously has been generated on the assimilation of organic nitrogen compounds in Chlamydomonas. A general view of the pathways is presented here, along with the putative genes involved. Glutamate is a key molecule that couples the metabolic pathways of amino acids with those of carbohydrates and lipids, with transamination reactions playing an important role in the control of internal amino acid pools. The properties and regulation of the GS/GOGAT cycle enzymes have been previously reviewed, and are outlined and updated here. These findings show that negative signaling by ammonium and its derivatives in the nitrate assimilation pathway are part of a complex network. Further efforts will likely uncover the precise roles of those genes in nitrate assimilation and their connection with other pathways.
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Effect of light intensity on nitrogen transformation, enzymatic activity, antioxidant system and transcriptional response of Chlorella pyrenoidosa during treating mariculture wastewater
2024, Bioresource TechnologyThe nitrogen transformation, enzymatic activity, antioxidant ability and transcriptional response of Chlorella pyrenoidosa (C. pyrenoidosa) treating mariculture wastewater were compared under different light intensities. The microalgal growth, chlorophyll synthesis and nitrogen removal ability of C. pyrenoidosa increased with the light intensity from 3000 to 7000 Lux, whereas they slightly decreased under 9000 and 11,000 Lux. The nitrogen metabolism enzymatic activities displayed obvious differences under different light intensities and affected the nitrogen transformation process. The reactive oxygen species (ROS) production increased with the increase of operational time, whereas it had distinct differences under different light intensities. The changes of antioxidant enzymatic activities were positively correlated with the ROS production. The transcriptional response of C. pyrenoidosa was in accordance with the variation of the photosynthesis, nitrogen assimilation and antioxidant system under different light intensities. This study provides theoretical basis and technical support to select suitable light intensity for algae treating mariculture wastewater.
Immobilized microalgal system: An achievable idea for upgrading current microalgal wastewater treatment
2023, Environmental Science and EcotechnologyEfficient wastewater treatment accompanied by sustainable “nutrients/pollutants waste-wastewater-resources/energy nexus” management is acting as a prominent and urgent global issue since severe pollution has occurred increasingly. Diverting wastes from wastewater into the value-added microalgal-biomass stream is a promising goal using biological wastewater treatment technologies. This review proposed an idea of upgrading the current microalgal wastewater treatment by using immobilized microalgal system. Firstly, a systematic analysis of microalgal immobilization technology is displayed through an in-depth discussion on why using immobilized microalgae for wastewater treatment. Subsequently, the main technical approaches employed for microalgal immobilization and pollutant removal mechanisms by immobilized microalgae are summarized. Furthermore, from high-tech technologies to promote large-scale production and application potentials in diverse wastewater and bioreactors to downstream applications lead upgradation closer, the feasibility of upgrading existing microalgal wastewater treatment into immobilized microalgal systems is thoroughly discussed. Eventually, several research directions are proposed toward the future immobilized microalgal system for microalgal wastewater treatment upgrading. Together, it appears that using immobilization for further upgrading the microalgae-based wastewater treatment can be recognized as an achievable alternative to make microalgal wastewater treatment more realistic. The information and perspectives provided in this review also offer a feasible reference for upgrading conventional microalgae-based wastewater treatment.
Nitrogen metabolism in Chlamydomonas
2023, The Chlamydomonas Sourcebook: Volume 2: Organellar and Metabolic ProcessesNitrogen (N) is a major limiting nutrient for plant and algal growth. Its assimilation enables cells to synthesize amino acids, the building blocks of proteins, and other essential N-containing macromolecules such as nucleic acids. Different forms of N may be available in the environment and thus, organisms have developed preferences for specific N sources through fine-tuned regulatory responses that integrate external cues for optimizing cell metabolism and ensuring survival. Because not all N imported into cells can be assimilated, some N compounds such as nitrate can be released as the volatile compounds nitric oxide and nitrous oxide, a scavenger of ozone and long-lived greenhouse gas. In this chapter, we describe the various N compounds used by the microalga Chlamydomonas reinhardtii, its N assimilation and regulatory pathways, and the possible mechanisms by which this alga dissimilates nitrate/nitrite to nitrous oxide. We also discuss the interaction with growth-promoting bacteria that can foster the use of amino acids and peptides by Chlamydomonas.
A natural microalgae consortium for the biological nutrient removal in a upflow photobioreactor as tertiary wastewater treatment
2022, Bioresource Technology ReportsA natural microalgae consortium from a eutrophic lagoon was used and evaluated for the tertiary treatment in a upflow photobioreactor. The photobioreactor was continuously fed with the effluent of a UASB high-rate reactor. The photobioreactor average concentration of the inflow pre-treated wastewater in terms of chemical oxygen demand (COD), nitrogen (N), and phosphorus (P) was 125 mg/L, 49 mg/L, and 8 mg/L, respectively. The operation variables of the photobioreactor include a hydraulic retention time (HRT) of 1 day and 2 days of solids retention time (SRT). The photoperiod in the photobioreactor was 24 h at a light illuminance of 5000 lx. The highest nutrient uptake rates in the photobioreactor were 14 mg TN/L·d and 2 mg TP/L·d. Environmental conditions in the photobioreactor favour the cyanobacteria dominance over the microalgae taxonomic groups. In addition, the outcomes established CO2:N ratios of 9:1 to ensure the N removal in wastewater microalgae treatment systems.
Capabilities and mechanisms of microalgae on nutrients and florfenicol removing from marine aquaculture wastewater
2022, Journal of Environmental ManagementThe regulations governing the discharge of marine aquaculture wastewater are becoming increasingly stringent, and the problems of nitrogen and phosphorus pollution and antibiotic residues in wastewater are serious. Microalgae-based treatment with the dual benefits of wastewater purification and microalgae resource recycling was regarded as the most promising technology in aquaculture wastewater treatment. Isochrysis galbana and Chlorella sp. were chosen to investigate antibiotic and nutrient removal mechanisms from aquaculture wastewater. FLO addition stimulated microalgae growth at low FLO concentrations (0.1 and 1 mg/L) but inhibited growth at 10 mg/L. The removal efficiency of DIN by Chlorella sp. and I. galbana after 7 days of cultivation was 66.4% and 25.8%, respectively. Linear curves were obtained between DIN concentration and cultivation duration, remove constant (k) increased as FLO concentration increased from 0 to 10 mg/L, and the highest value of k was obtained in both the Chlorella sp. and I. galbana groups at 10 mg/L. DIP concentrations in FLO-contained simulated aquaculture wastewater decreased sharply with the cultivation of Chlorella sp. and I. galbana, and DIP removal rate increased as FLO concentration increased. When the initial concentration of FLO was 0.1 mg/L, biodegradation by I. galbana accounted for 86.67% of FLO removal. In contrast, FLO removal with biodegradation and biosorption by Chlorella sp. was 89.74% and 3.72%, respectively. Furthermore, Chlorella sp. grown in MPBR demonstrated superior capability for antibiotic-containing marine aquaculture wastewater purification, with average removal rates of DIN and DIP of 81.2% and 100%, respectively. The high removal rate is related to membranes which can improve microalgae performance by decoupling SRT and HRT. For microalgae-based aquaculture wastewater, ammonia was the most crucial nitrogen source, followed by nitrate. These findings serve as a theoretical foundation for developing microalgae-based aquaculture wastewater treatment technology and eliminating antibiotics in aquaculture.
Integrating photobioreactor with conventional activated sludge treatment for nitrogen removal from sidestream digestate: Current challenges and opportunities
2021, Journal of Environmental Chemical EngineeringSidestream digestate is a liquid effluent stream generated from the anaerobic sludge digestion process in a wastewater treatment plant (WWTP). It is rich in inorganic nutrients, mainly nitrogen and phosphorus, and it requires further treatment in order to meet the stringent discharge/regulatory standards. It is usually treated through conventional activated sludge process (ASP) in the WWTPs. However, its direct recirculation to the WWTP imparts burden of excess nutrient removal on the biological treatment, i.e. in terms of the increased energy costs for aeration and it can pose a higher risk of eutrophication in the receiving water body. One alternative is the integration of photobioreactor (PBR) with ASP treatment for enhanced nitrogen removal from sidestream digestate. This paper critically reviewed the techno-economic feasibility of integrating a PBR with the ASP of a WWTP for sidestream digestate treatment. It is estimated that the integrated PBR-ASP process requires small land area and can achieve high nitrogen removal. Microalgae, owing to its high ability in nutrient cycling and biomass production, can effectively be used as biocatalysts for the treatment of sidestream digestate. Microalgae can assimilate nitrogen resulting in oxygen production by photosynthesis. The heterotrophic bacteria mineralise the pollutants present in wastewater, i.e. in the presence of oxygen, releasing carbon dioxide through bacterial respiration. The carbon dioxide is utilised by the microalgae to complete the photosynthetic cycle for wastewater treatment, thus decreasing the greenhouse emissions. The microalgae-bacterial treatment as compared to ASP can reduce more than 50% of the energy costs.