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Microalgae II: Cell Structure, Nutrition and Metabolism
Published in Arun Kumar, Jay Shankar Singh, Microalgae in Waste Water Remediation, 2021
Microalgae including cyanobacteria obtain their carbon requirement through reducing atmospheric CO2 into organic matter that are needed for cell growth. The pathway of the Calvin cycle or reductive pentose phosphate cycle is used for this reductive biosynthesis of organic matter (Pelroy and Bassham 1972, Jansz and Maclean 1973). In the Calvin cycle, the first step involves the carboxylation of ribulose 1,5-bisphosphate (RuBP) into a 6-carbon carboxylated intermediate (2-carboxy-3-keto-Dribitol 1,5-bisphosphate) (Siegel and Lane 1973, Sjodin and Vestermark 1973); then it subsequently breaks down into two molecules of 3-phosphoglyceric acid. This phosphoglyceric acid then reduces to produce glyceraldehydes-3-phosphate which is later transported to cytosol for glucose synthesis (Fig. 2.1).
Current research and perspectives on microalgae-derived biodiesel
Published in Biofuels, 2020
Kartik Singh, Deeksha Kaloni, Sakshi Gaur, Shipra Kushwaha, Garima Mathur
Microalgae are free-living microorganisms belonging to the Kingdom Protista and are found in a variety of aquatic habitats. They are often small in size (mostly 5–50 µm) and are generally unicellular; however, a few exceptions are multicellular – e.g. seaweed and filamentous algae. Microalgal cells are photoautotrophic since they have chlorophyll. The pigment content in microalgae is a specific feature of each species [8]. A rigid cell wall with a polysaccharide composition unlike that of animal cells, and a cell membrane whose biochemical composition makes it a selective barrier, surround the microalgal cell. Microalgae possess lipid bodies that serve as energy reserves. Algal photosynthesis is mainly based on the Calvin cycle wherein ribulose-1,5- biphosphate reacts with CO2 to synthesize 3-phosphoglyceric acid (3-PGA), which is used up during production of glucose and other metabolites [9]. Microalgae have much better photoconversion efficiency than most of the terrestrial plants and can produce larger quantities of carbohydrate biomass [10]. Unlike plants, most algae reproduce asexually or by means of cell separation; they devote more energy to photosynthesis and subsequent production of biomass as they do not need to generate large reproductive or support structures.
Toxicity, monitoring and biodegradation of organophosphate pesticides: A review
Published in Critical Reviews in Environmental Science and Technology, 2019
Gurpreet Kaur Sidhu, Simranjeet Singh, Vijay Kumar, Daljeet Singh Dhanjal, Shivika Datta, Joginder Singh
Organophosphate pesticides have been shown to adversely affect the photosynthesis (Zobiole, Kremer, de Oliveira, & Constantin, 2012; Kielak, Sempruch, Mioduszewska, Klocek, & Leszczyński, 2011) plant mineral nutrition (Zobiole et al., 2010; Zobiole, Kremer, Oliveira, & Constantin, 2011), carbon metabolism (Ding, Reddy, Zablotowicz, Bellaloui, & Bruns, 2011; Zobiole et al., 2011), photochemical reactions (Vivancos et al., 2011), chlorophyl biosynthesis (Serra et al., 2013), fatty acids synthesis, amino acids synthesis, nitrogen metabolism (Zobiole et al., 2010), and oxidative stress (Vagi, Petsas, Pavlaki, Smaragdaki, & Kostopoulou, 2018; Stauber, Chariton, & Apte, 2016; Filimonova, Gonçalves, Marques, De Troch, & Goncalves, 2016; Yanniccari, Tambussi, Istilart, & Castro, 2012). OPs prevent the biosynthesis of catalase, perioxidase and δ-aminolevulinic acids (ALA) which are the major component of chlorophyl biosynthetic pathway by inducing Fe deficiency in plants (Barcelos et al., 2012). However, it affects ALA production by competing with the major product of the ALA synthetase active site or leading to deprivation of glumate content by competing with glycine in the photorespiration process as depicted in soybean (Vivancos et al., 2011). They also reduce the availability of amino acids and metal ions which are associated with PSI and PSII to transfer photon (light energy) into the electron transport chain system (Cakmak, Yazici, Tutus, & Ozturk, 2009). Foliar spray of glyphosate and its metabolites decreases the net stomatal conductance and carbon exchange in plants thus reducing the CO2 assimilation capacity (Zobiole et al., 2011; Ding et al., 2011). Exposure of organophosphate pesticide, glyphosate also lower down the levels of 3-phosphoglyceric acid (PGA) and ribulose-1,5-biphosphate (RuBP) affecting ribulose 1,5-biphosphate carboxylase oxygenase activity (Rubisco) in plants (de María et al., 2006).