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Biofuel and Biochemical Production by Photosynthetic Organisms
Published in Kazuyuki Shimizu, Metabolic Regulation and Metabolic Engineering for Biofuel and Biochemical Production, 2017
Cyanobacteria have sophisticated mechanisms to cope with nitrogen limitation, where the primary step is the capture of nitrogen-containing compounds with high affinity, where ammonia, nitrate, and nitrite are the typical nitrogen sources with preference for ammonium (Flores and Herrero 2005). Some strains can fix dinitrogen gas, and may use also urea, cyanate, and amino acids as additional nitrogen sources (Flores and Herrero 2005, Valladares et al. 2002, Garcia-Fernandez et al. 2004). Nitrogen compounds are eventually converted to ammonium and utilized for biosynthesis via the glutamin synthetase (GS)-glutamine oxoglutarate aminotransferase or glutamate synthase (GOGAT) cycle, where glutamate dehydrogenase (GDH) pathway does not function, probably due to low affinity to ammonium.
Exogenous Hemin alleviates cadmium stress in maize by enhancing sucrose and nitrogen metabolism and regulating endogenous hormones
Published in International Journal of Phytoremediation, 2023
Meng Zhao, Yao Meng, Yong Wang, Guangyan Sun, Xiaoming Liu, Jing Li, Shi Wei, Wanrong Gu
NH4+ can be assimilated to glutamine through GS/GOGAT pathway or glutamate through GDH pathway. The excessive accumulation of NH4+ in plant tissues will aggravate the harm of cadmium stress. NH4+ content increased under cadmium stress and the range of Tiannong 9 is low. The results indicated that cadmium stress had little toxicity of Tiannong 9. NR activity decreased significantly. NH4+ accumulation leads to a large of NH4+ released by photorespiration and the inhibition of GS/GOGAT pathway. Hemin could keep photosynthetic system stability and reduce NH4+ content. Reducing NH4+ accumulation in plant tissues can improve the stress resistance. The results indicated that exogenous Hemin could significantly reduce the NH4+ content in maize leaves under cadmium stress.
Enhancement of growth and biomolecules (carbohydrates, proteins, and chlorophylls) of isolated Chlorella thermophila using optimization tools
Published in Preparative Biochemistry & Biotechnology, 2022
Sambit Sarkar, Jaivik Mankad, Nitin Padhihar, Mriganka Sekhar Manna, Tridib Kumar Bhowmick, Kalyan Gayen
In this study, nitrate was found to impart a negative effect on biomass synthesis. This result is similar to another study conducted with Asterarcys sp. where 0.375 g/L of nitrate concentration in the media provided higher biomass concentration than other concentrations of nitrates.[16] Similar results were obtained in another study where an increase in nitrate concentration decreased the biomass production and the highest biomass was obtained at the lowest nitrate concentration used in that study (1.5 g/L).[44] However, nitrogen in a form of urea was shown to boost the growth in Chlorella spp.[19] Microalgae cells necessitate nitrogen in a higher amount owing to its role as the critical constituent of proteins, peptides, chlorophylls, enzymes, ATP, RNA, DNA, and other cellular constituents.[45] Nitrogen in form of nitrate, nitrite, and ammonium are directly assimilable in the metabolic activity of microalgae. However, nitrate is comparatively stable thermodynamically than other forms of nitrogen that get oxidized in the aqueous medium. Nitrate after being translocated across plasmalemma requires to be chemically reduced to ammonium for being assimilated into the cell. Chemical reduction of nitrate is governed by two enzymes which are nitrate reductase and nitrite reductase.[46] Nitrate reductase catalyzes the bi-electron transfer in the cytosol with the aid of NADPH. The enzyme nitrate reductase is attached with the pyridine nucleotide oxidation in microalgae.[44] Nitrite reductase reduces nitrite in a reaction of six-election transfer. Nitrite reductase localized in the chloroplast uses ferredoxin which is sourced from the photosynthetic electron flow in microalgae. Ammonium is mostly incorporated into amino acids by the chronological act of glutamine synthetase (GS) and glutamine 2 oxoglutarate aminotransferase (GOGAT). Ammonium is assimilated by GS in an irreversible reaction utilizing glutamate as substrate. GS and GOGAT are usually located in the chloroplast. However, their isoenzymes may also be found in the cytosol. Glutamate synthase facilitates the synthesis of amino acids through transamination after being transported to cytosol from chloroplast.[44]
Wastewater treatment for nutrient removal with Ecuadorian native microalgae
Published in Environmental Technology, 2019
María Belén Benítez, Pascale Champagne, Ana Ramos, Andres F. Torres, Valeria Ochoa-Herrera
Figure 2(a and b) represent the changes in concentration in the agitation and aeration PBRs, respectively. The removal rates were calculated from the slope of the concentration as a function of time during the first 96 h, and were computed to be 0.37 and 0.5 mg for agitation and aeration nutrient removal photobioreactors (NR PBRs), respectively. However, the removal efficiencies were very similar, 52.6 ± 5.9 and 55.6 ± 7.4% in agitation and aeration NR PBRs (Table 2), respectively. The efficiencies achieved in this study were comparable to those obtained in other studies. For example, a 50% removal was observed when the media concentration ranged from 41.8 to 92.8 mg L−1 in agitation batch photobioreactors [17]. Similarly, removal efficiencies for Chlorella sp. were 82.4% from a wastewater collected before primary settling and 74.7% from a wastewater collected after primary settling [32]. Aeration did not appear to influence overall removal efficiency, but was noted to increase removal rates. The elimination of ammonium was influenced by the pH of the culture medium, the NR PBRs exhibited ammonia (NH3) volatilization, since the initial pH was 8.45 ± 0.1 and 8.7 ± 0.2 in agitation and aeration essays, respectively. The acid/base equilibrium of the ammonium/ammonia reaction involved in this system has a small Kb value of 1.8 × 10−5, meaning that NH3 is a weak base. Since the pH is >7 in the PBRs and the pKb of the reaction is 4.74, the reaction will shift to the production of the base, in this case NH3 [36]. In this study, some of the ammonium elimination occurred by desorption as ammonia, indeed after 72 h the pH of the NR aeration PBR decreased to 6.3 (Fig. S2); the decrease of the pH was caused by the elimination of OH− [36,37]. The control PBRs (AC and NVC) (Figure 2(a and b)), show some variations in ammonium concentrations, which can likely be attributed to experimental error associated with the analytical methods. Thus, when comparing the NR PBRs with the controls, it was found that no appreciable ammonium removals could be noted in the controls, suggesting that biological assimilation was a likely nitrogen removal source during this study. Assimilation is the process by which microalgae converts inorganic nitrogen to its organic form; however, algae require inorganic nitrogen in the form of nitrate, nitrite and ammonium [35]. In this study, the decrease in concentration could likely be attributed to the metabolic utilization of ammonium ion as a nitrogen source by microalgae. The primary product of ammonium assimilation is glutamine (Gln); which is important in all subsequent nitrogen metabolisms because it acts as an amine donor to organic acids. Ammonium assimilation by microalgae can be achieved via one of two glutamine sythetase/glutamine (GS) pathways: 2-oxoglutayate aminotransferase (GS-GOGAT) or by the action of GS and glutamate dehydrogenase [34].