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Nanobiotechnology Advances in Bioreactors for Biodiesel Production
Published in Madan L. Verma, Nanobiotechnology for Sustainable Bioenergy and Biofuel Production, 2020
Bhaskar Birru, P. Shalini, Madan L. Verma
The lower greenhouse gas emission is achievable with the use of biodiesel as a renewable energy resource and it is derived from fatty acids and oil. To increase the yield of biodiesel, fatty acid, lipid synthesis and metabolic engineering approach are inevitable. The initial step in the fat synthesis is the conversion of actyl-CoA into Malonyl-CoA, catalyzed by acetyl-CoA carboxylase. The soxidation of NADPH requires fat synthesis, which occurs in the cytosol. The pyruvate dehydrogenase (PDH) and fatty acid oxidation pathways generate acetyl-CoA in mitochondria; it cannot be transported into the cytosol. Kerb’s cycle produces citrate in mitochondria, which is transported into the cytoplasm. Citrate breaks down into acetyl-CoA and oxalo acetate (OAA); this is catalyzed by ATP citrate lyase. The OAA converts into malate by malate dehydrogenase enzyme and NAD+. Subsequently, pyruvate is synthesized from malate and then it enters into mitochondria. This pyruvate is also produced through the glycolytic pathway. Transesterification of triacyl glycerol (TAG) produces biodiesel. TAG serves as energy storage in all cells and easily catabolized to provide metabolic energy. TAG contains three fatty acids and the glycerol molecule (Vuppaladadiyam et al. 2018).
Potential of Oleaginous Microorganisms in Green Diesel Production
Published in V. Sivasubramanian, Bioprocess Engineering for a Green Environment, 2018
R. Selvaraj, I. Ganesh Moorthy, V. Sivasubramanian, R. Vinoth Kumar, R. Shyam Kumar
The ATP citrate lyase enzyme is present in oleaginous yeasts. The citrate is catalyzed to give oxaloacetate and acetyl Co-A by ATP citrate lyase (Beopoulos et al. 2009). The concentration of lipid synthesis depends on ATP citrate lyase activity in oleaginous microorganisms (Certik et al. 1999; Ratledge 2002). Citrate lyase activity is needed for triacylglycerols synthesis. () Citrate+ATP+CoA→acetyl CoA + oxaloacetate + ADP+
Utilization of Agro-Industrial Wastes for Biofuel Generation
Published in Anil Kumar Anal, Parmjit S. Panesar, Valorization of Agro-Industrial Byproducts, 2023
Rajeev K. Sukumaran, Meera Christopher, AthiraRaj Sreeja-Raju, Meena Sankar, Prajeesh Kooloth-Valappil, Valan Rebinro Gnanaraj, Anoop Puthiyamadam, Reshma M. Mathew, Velayudhan Pillai-Prasannakumari Adarsh
More common approaches towards generating oil from agro-residues include fermentation processes where oleaginous micro-organisms can be grown on biomass hydrolysates to produce oil. Oil-producing fermentative micro-organisms (known as single-cell oils) are attractive feedstock for biodiesel production because of several desirable features such as the ability to produce under all seasons and climatic conditions, a lesser requirement of space, an easiness in scale-up, minimal labour requirements, etc. (Mhlongo et al., 2021). Oleaginous micro-organisms, which can sometimes accumulate 20% or more of their weight as triacylglycerols, have multiple advantages like (i) high growth rate; (ii) high lipid accumulation; (iii) lipid composition similar to vegetable oils; (iv) having lipids with rare fatty acid structure; and (v) negligible resorption of the stored lipids for cellular metabolism (Carvalho et al., 2015; Uthandi et al., 2021). These organisms are able to attain an enhanced synthesis of fatty acids due to the presence of the enzyme ATP: citrate lyase (ACL), which provides a continuous supply of the precursor of lipid biosynthesis, acetyl-CoA (Boulton and Ratledge, 1981). In the presence of excess carbon sources, when another nutrient like nitrogen or phosphorous becomes limited, the utilization of carbohydrates through glycolysis results in an accumulation of citrate in the mitochondria due to rapid depletion of Adenosine monophosphate (AMP) as it is diverted for an alternate nitrogen supply mechanism in the organism. The excess citrate transported to the cytoplasm is converted by the ACL to acetyl-CoA, which in turn is routed to fatty acid synthesis (Ratledge and Wynn, 2002). Many microbes have been reported for the production of single-cell oils for biofuel applications, and some of them are able to grow on LCB hydrolysates and other agro-industrial residues. These include Rhodosporidium toruloides, Cryptococcus sp., Trichosporon fermentans, Fusarium oxysporum, Rhodococcus opacus, etc. (Patel et al., 2020). Studies on the cultivation of oleaginous organisms in biomass hydrolysates for the production of microbial oils/single-cell oils are reviewed in Diwan et al. (2018), Patel et al. (2020), Chintagunta et al. (2021), and Mhlongo et al. (2021). While the production of high-value lipids from oleaginous micro-organisms has been commercialized, the same is not true for biofuels because the high cost of production impairs commercial viability (Ochsenreither et al., 2016). Improvements in production conditions, recovery of lipids, and efficiency of organisms themselves are currently being explored for viability.
Biodiesel from oleaginous microbes: opportunities and challenges
Published in Biofuels, 2019
Lohit K. S. Gujjala, S. P. Jeevan Kumar, Bitasta Talukdar, Archana Dash, Sanjeev Kumar, Knawang Ch. Sherpa, Rintu Banerjee
In fungi, initiation of the fatty acid synthesis is done by the fatty acid synthetase (FAS) complex within the cytosol, for which a continuous supply of acetyl-Coenzyme A is required. This demand for acetyl-CoA is mainly met by the cleavage of citrate which takes place due to the nitrogen-limiting conditions [79]. Along with the supply of acetyl-CoA, nitrogen limitation also triggers the supply of ammonium ions to the nitrogen-starved cells since it activates Adenosine monophosphate deaminase (AMP-deaminase) [80]. Due to the activation of AMP-deaminase, the concentration of AMP decreases in mitochondria, as a result of which the Tricarboxylic acid (TCA) cycle is blocked. Thus, the excess citrate which is accumulated due to the blocked TCA cycle is removed from the mitochondria and ultimately gets cleaved into oxaloacetate and acetyl-CoA in the cytosol by the action of Adenosine triphosphate ATP-citrate lyase (ACL). As far as acyl chain elongation steps are concerned, NADPH is required within the cytosol and its major contributor is the pentose phosphate pathway in which three enzymes, viz. pyruvate carboxylase (PC), malate dehydrogenase (MDH) and malic enzyme (ME), catalyze the conversion of Nicotinamide adenine dinucleotide (NADH) into NADPH (Figure 2).
Effects of organic and inorganic salts on docosahexaenoic acid (DHA) production by a locally isolated strain of Thraustochytrium sp. T01
Published in Preparative Biochemistry and Biotechnology, 2018
Kabilan Chandrasekaran, Muthu Dhanraj, Anju Chadha
Thraustochytrium sp. T01 can accumulate lipid up to 50% of the total dry biomass. To increase the lipid content, it is important to study the precursor and the key enzymes in fatty acid synthesis. Two distinct DHA biosynthetic pathways have been reported in the thraustochytrids family i.e. FAS pathway and PKS pathway.[10] Acetyl-CoA, the precursor for fatty acid synthesis is produced inside the cell from various organic acids such as pyruvate, citrate and malate which are formed in the TCA cycle. Pyruvate is converted to acetyl-CoA by the enzyme pyruvate dehydrogenase. Citrate is converted to acetyl-CoA by ATP citrate lyase (ACL). Malic acid is first converted to pyruvate by malic enzyme (ME) and then converted to acetyl-CoA.[21] This group of organic acids plays a crucial role in the formation of the lipid precursor, acetyl-CoA. The enhancement in the level of acetyl-CoA can be achieved by the addition of any organic acid mentioned above to the culture media. The time of the addition of these salts in the culture media is critical to accelerate the lipid synthesis in the cell and thus, was considered as an important parameter. In addition, NADPH cofactor is also an important requirement for DHA biosynthesis. NADPH is required for fatty acid desaturation by desaturases in the FAS pathway. DHA biosynthesis via FAS pathway consists of many desaturases (Δ9, Δ12, Δ15, Δ6, Δ5 and Δ4) which are NADPH and oxygen dependent.[22] Replenishing NADPH inside the cell by the addition of organic acids would increase the DHA content in T01. These organic acids were added as salts in the culture media individually in various concentrations (2–8 gL−1). The dry biomass, lipid content and DHA content were measured separately with respect to various organic salt concentrations and plotted against the obtained yield in one liter of culture media (Figure 2).