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![The schematic diagram illustrates the metabolic reactions and enzymes (highlighted in red color) that are involved in the response to abiotic stresses in the biosynthetic pathways of lipids in microalgae; modified from [235]. It depicts the synthesis of free fatty acids (FFAs) and triacylglycerols (TAGs) in both the endoplasmic reticulum and chloroplast. The conversion of TAGs into biofuels, bioproducts, and bioenergy was also outlined. 3-phosphoglyceric acid (3-PGA), glyceraldehyde 3-phosphate (G3P), pyruvate kinase (PK), pyruvate dehydrogenase (PDH), acetyl-CoA carboxylase (ACCase), malonyl-CoA-ACP transacylase (MAT), 3-ketoacyl-ACP synthase (KAS), 3- ketoacyl-ACP reductase (KAR), 3-hydroxyacyl-ACP dehydratase (HAD), enoyl-ACP reductase (ENR), fatty acyl-ACP thioesterase (TE), dihydroxyacetone phosphate (DHAP), gycerol-3-phosphate dehydrogenase (G3PDH), glycerol 3-phosphate dehydrogenase (GPAT), lysophosphatidic acid (LPA), lysophosphatidic acid acyltransferase (LPAAT), phosphatidic acid (PA), phosphatidic acid phosphatase (PAP), diacylglycerol (DAG), diacyglyceryl acyl transferase (DGAT), triacylglycerol (TAG).](profile/Rahul-Singh-260/publication/373891680/figure/fig4/AS:11431281188428761@1694612751662/The-schematic-diagram-illustrates-the-metabolic-reactions-and-enzymes-highlighted-in-red.png)
The schematic diagram illustrates the metabolic reactions and enzymes (highlighted in red color) that are involved in the response to abiotic stresses in the biosynthetic pathways of lipids in microalgae; modified from [235]. It depicts the synthesis of free fatty acids (FFAs) and triacylglycerols (TAGs) in both the endoplasmic reticulum and chloroplast. The conversion of TAGs into biofuels, bioproducts, and bioenergy was also outlined. 3-phosphoglyceric acid (3-PGA), glyceraldehyde 3-phosphate (G3P), pyruvate kinase (PK), pyruvate dehydrogenase (PDH), acetyl-CoA carboxylase (ACCase), malonyl-CoA-ACP transacylase (MAT), 3-ketoacyl-ACP synthase (KAS), 3- ketoacyl-ACP reductase (KAR), 3-hydroxyacyl-ACP dehydratase (HAD), enoyl-ACP reductase (ENR), fatty acyl-ACP thioesterase (TE), dihydroxyacetone phosphate (DHAP), gycerol-3-phosphate dehydrogenase (G3PDH), glycerol 3-phosphate dehydrogenase (GPAT), lysophosphatidic acid (LPA), lysophosphatidic acid acyltransferase (LPAAT), phosphatidic acid (PA), phosphatidic acid phosphatase (PAP), diacylglycerol (DAG), diacyglyceryl acyl transferase (DGAT), triacylglycerol (TAG).
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The world is currently facing global energy crises and escalating environmental pollution, which are caused by the extensive exploitation of conventional energy sources. The limited availability of conventional energy sources has opened the door to the search for alternative energy sources. In this regard, microalgae have emerged as a promising sub...
Citations
... These challenges underscore the urgent need for renewable and sustainable energy alternatives (Narayanan, 2024). Microalgae have gained attention as potential biofuel feedstocks because they have high photosynthetic productivity and CO 2 conversion rates, require less land, may not compete with food sources, and can generate various value-added products (Kumar et al., 2023;Sun et al., 2023;Liu et al., 2024;Praveena et al., 2024). ...
... This interest intensified following the discovery of starchless mutants in C. reinhardtii, which, unlike their wild type (WT) counterparts, accumulate significant amounts of lipids, primarily triacylglycerols (TAGs), instead of starch. In addition, it has been found that microalgae produce lots of lipids under various stress conditions, such as nutrient depletion or osmotic stress (Maltsev et al., 2023;Polat and Altinbas, 2023;Singh et al., 2023). Based on these results, there has been a growing interest in metabolic and cultivation engineering to enhance carbon flux towards lipids from CO 2 (Dasan et al., 2023). ...
Microalgae, valued for their sustainability and CO2 fixation capabilities, are emerging as promising sources of biofuels and high-value compounds. This study aimed to boost lipid production in C. reinhardtii by overexpressing chloroplast glyceraldehyde-3-phosphate dehydrogenase (GAPDH), a key enzyme in the Calvin cycle and glycolysis, under the control of a nitrogen-inducible NIT1 promoter, to positively impact overall carbon metabolism. The standout transformant, PNG#7, exhibited significantly increased lipid production under nitrogen starvation, with biomass rising by 44% and 76% on days 4 and 16, respectively. Fatty acid methyl ester (FAME) content in PNG#7 surged by 2.4-fold and 2.1-fold, notably surpassing the wild type (WT) in lipid productivity by 3.4 and 3.7 times on days 4 and 16, respectively. Transcriptome analysis revealed a tenfold increase in transgenic GAPDH expression and significant upregulation of genes involved in fatty acid and triacylglycerol synthesis, especially the gene encoding acyl-carrier protein gene (ACP, Cre13. g577100. t1.2). In contrast, genes related to cellulose synthesis were downregulated. Single Nucleotide Polymorphism (SNP)/Indel analysis indicated substantial DNA modifications, which likely contributed to the observed extensive transcriptomic and phenotypic changes. These findings suggest that overexpressing chloroplast GAPDH, coupled with genetic modifications, effectively enhances lipid synthesis in C. reinhardtii. This study not only underscores the potential of chloroplast GAPDH overexpression in microalgal lipid synthesis but also highlights the expansive potential of metabolic engineering in microalgae for biofuel production.
... When microalgae face a deficiency in nitrogen, they reduce the production of numerous proteins engaged in various cellular functions. This reduction in protein synthesis during nitrogen limitation serves to conserve energy and enables the microalgae to allocate more resources toward the synthesis of lipids [22]. This suggests that a lower nitrogen concentration at lower EC levels may result in increased lipid contents in microalgae. ...
In recent years, researchers have turned their attention to the co-cultivation of microalgae and plants as a means to enhance the growth of hydroponically cultivated plants while concurrently producing microalgal biomass. However, the techniques used require precise calibration based on plant growth responses and their interactions with the environment and cultivation conditions. This study initially focused on examining the impact of hydroponic nutrient concentrations on the growth of the microalga Chlorella sp. AARL G049. The findings revealed that hydroponic nutrient solutions with electrical conductivities (EC) of 450 µS/cm and 900 µS/cm elicited a positive response in microalgae growth, resulting in high-quality biomass characterized by an elevated lipid content and favorable properties for renewable biodiesel. The biomass also exhibited high levels of polyunsaturated fatty acids (PUFAs), indicating excellent nutritional indices. The microalgae culture and microalgae-free culture, along with inoculation-free lettuce (Lactuca sativa L. var. longifolia) and lettuce that was inoculated with plant growth actinobacteria, specifically the actinomycete Streptomyces thermocarboxydus S3, were subsequently integrated into a hydroponic deep-water culture system. The results indicated that several growth parameters of lettuce cultivated in treatments incorporating microalgae experienced a reduction of approximately 50% compared to treatments without microalgae, and lowering EC levels in the nutrient solution from 900 µS/cm to 450 µS/cm resulted in a similar approximately 50% reduction in lettuce growth. Nevertheless, the adverse impacts of microalgae and nutrient stress were alleviated through the inoculation with actinomycetes. Even though the co-cultivation system leads to reduced lettuce growth, the system enables the production of high-value microalgal biomass with exceptional biodiesel fuel properties, including superior oxidative stability (>13 h), a commendable cetane number (>62), and a high heating value (>40 MJ/kg). This biomass, with its potential as a renewable biodiesel feedstock, has the capacity to augment the overall profitability of the process. Hence, the co-cultivation of microalgae and actinomycete-inoculated lettuce appears to be a viable approach not only for hydroponic lettuce cultivation but also for the generation of microalgal biomass with potential applications in renewable energy.
Recent advances in hydrothermal liquefaction (HTL) have established this biomass conversion technology as a potent tool for the effective valorization and energy densification of varied feedstocks, ranging from lignocelluloses to microalgae and organic wastes. Emphasizing its application across biomass types, this exploration delves into the evolving landscape of HTL. Microalgae, recognized as a promising feedstock, offer a rich source of biomolecules, including lipids, carbohydrates, and proteins, making them particularly attractive for biofuel production. The comprehensive review explores the biofuel products and platform chemicals obtained through HTL of microalgae, delving into biodiesel production, bio-oil composition, characteristics, and to produce high-valued by-products. Challenges and limitations, such as reactor design, scalability issues, and the impact of microalgal composition on yields, are critically analyzed. The future prospects and research directions section envision advancements in HTL technology, integration with biorefinery processes, and the exploration of hybrid approaches for enhanced biofuel production. Overall, the paper emphasizes the promising potential of HTL for wet microalgal biomass and underscores the need for continued research to overcome existing challenges and unlock further opportunities in sustainable biofuel and platform chemical production.
This comprehensive research aims to examine the numerous industrial and agricultural waste streams involved in biodiesel production, providing insights into its potential, problems, and environmental consequences. Applying industrial and agricultural waste products that include high levels of lipids as feedstocks for biodiesel serves the dual purpose of diverting these materials away from landfills and incineration while converting them into lucrative and environmentally sustainable energy sources. This review comprehensively examines many categories of industrial waste feedstocks, including waste oils and greases, residues generated from manufacturing operations, and byproducts derived from agricultural and chemical companies. This review thoroughly investigates many essential components of biodiesel synthesis from industrial and agricultural waste, encompassing the characterisation of feedstock, pre-treatment procedures, transesterification processes, and purification methods. Considerable emphasis is placed on each feedstock’s distinct characteristics and obstacles, fostering a thorough comprehension of the biodiesel manufacturing procedure. The rationale behind implementing this sustainable energy solution is driven by its notable environmental benefits, which include reducing greenhouse gas emissions and facilitating ecological contaminants. Furthermore, this study investigates the economic viability, regulatory considerations, and developing trends within the industry, focusing on the potential of utilising biodiesel created from agricultural and industrial waste to foster a circular economy and optimise resource utilisation.
The development of algae is seen as a potential and ecologically sound approach to address the increasing demands in multiple sectors. However, successful implementation of processes is highly dependent on effective growing and harvesting methods. The present study provides a complete examination of contemporary techniques employed in the production and harvesting of algae, with a particular emphasis on their sustainability. The review begins by examining several culture strategies, encompassing open ponds, closed photobioreactors, and raceway ponds. The analysis of each method is conducted in a systematic manner, with a particular focus on highlighting their advantages, limitations, and potential for expansion. This approach ensures that the conversation is in line with the objectives of sustainability. Moreover, this study explores essential elements of algae harvesting, including the processes of cell separation, dewatering, and biomass extraction. Traditional methods such as centrifugation, filtration, and sedimentation are examined in conjunction with novel, environmentally concerned strategies including flocculation, electro-coagulation, and membrane filtration. It evaluates the impacts on the environment that are caused by the cultivation process, including the usage of water and land, the use of energy, the production of carbon dioxide, and the runoff of nutrients. Furthermore, this study presents a thorough examination of the current body of research pertaining to Life Cycle Analysis (LCA) studies, presenting a perspective that emphasizes sustainability in the context of algae harvesting systems. In conclusion, the analysis ends up with an examination ahead at potential areas for future study in the cultivation and harvesting of algae. This review is an essential guide for scientists, policymakers, and industry experts associated with the advancement and implementation of algae-based technologies.
