Browsing by Author "Nitesh Prasad"

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An exploration of lipid remodeling by microalga Chlamydomonas reinhardtii in autotrophic and mixotrophic cultivation for bioenergy prospects
(Elsevier Ltd, 2025) Avinash K. Singh; Savita S. Singh; Nitesh Prasad; Sakshi Singh; Abhishek Mohanta; Arvind Mohan Kayastha; Ravi Kumar Asthana
Optimizing microalgal biomass production is pivotal for advancing sustainable bioenergy production, yet the inherent trade-off between growth and lipid accumulation under nutrient stress remains a significant hurdle. This study utilized C. reinhardtii to examine the effects of acetate supplementation on enhancing biomass under nitrogen sufficiency (Stage I) and lipid synthesis under nitrogen deficiency (Stage II) through growth kinetics, key enzymatic activities, and metabolomic profiling. Results displayed that at Stage I, optimum acetate supplementation increased the biomass concentration (4 fold), Chl a (∼3 fold), Fv/Fm (0.71) reflected in simultaneous increment in the enzymatic activities of isocitrate lyase (12.5 folds), malate synthase (20 folds), citrate synthase (9.75-fold) and RuBisCO (1.72-fold) against the control. However, acetate spiked culture (50 mM) led to a significant increase in the lipid content (44 % DCW) with enhanced activities of antioxidant enzymes (SOD, CAT, and APX) at Stage II. In addition, the increased ACCase and GPAT enzymatic activities substantiated the elevated fatty acid biosynthesis. Furthermore, high-resolution mass spectrometry (HR-MS)-based untargeted metabolomic analysis revealed a pronounced decline in polyunsaturated fatty acids and carbohydrates, concomitant with a substantial increase in saturated and monounsaturated fatty acids. This shift underscores a strategic metabolic reprogramming of the cellular carbon flux toward the biosynthesis of vehicular-grade lipids at Stage II cultivation. Collectively, these findings elucidate the intricate metabolic adjustments induced by acetate assimilation, presenting innovative strategies to enhance sustainable and economically viable microalgal biofuel production. © 2025 Elsevier Ltd
Harnessing bioenergy potential of Chlamydomonas reinhardtii: A comprehensive characterization and valorization of biomass towards energy conversion under circular bioeconomy
(Elsevier Ltd, 2025) Avinash K. Singh; Savita S. Singh; Sakshi Singh; Nitesh Prasad; Ravi Kumar Asthana
Despite the immense potential of microalgal bioenergy, limitations in biofuel precursors and ineffective zero-waste management hinder economic scalability. This study explores the response of Chlamydomonas reinhardtii to bicarbonate supplementation under nitrogen-sufficient (Stage I) and deficient (Stage II) conditions within a circular bioeconomy framework aimed at maximizing bioenergy potential. Optimal bicarbonate supplementation resulted enhancement in 3.35-fold biomass, 5.38-fold GS activity, NH₄⁺ removal (90.45 %), and a reduced zeta potential (−33.27 mV). Elevated ACCase and GPAT activities under bicarbonate supplementation boosted lipid accumulation (49.61 %) while enhancing antioxidant enzyme activities (SOD, CAT, APX) at Stage II. The increase in lipids was further validated by distinct FTIR peaks (2968 cm⁻1, 2855 cm⁻1, and 1744 cm⁻1) and 1H NMR signals (1.0–1.4 ppm, 4.1–4.25 ppm), indicating the metabolic rewiring of C. reinhardtii towards neutral lipid accumulation. Enhanced biofuel precursors contributed to improved thermochemical conversion efficiency, as revealed by TGA/DTG analyses. P-XRD confirmed the increased amorphous nature of the biomass. CHNS and SEM/EDX analyses revealed a marked increase in carbon content with a reduction in oxygen levels reflected in the HHV (21.52 MJ kg⁻1) and an elevated H/C ratio under nitrogen-starved conditions, further highlighting the biomass's enhanced suitability for efficient energy conversion. In addition, a 1.76-fold theoretical biomethane yield (TMP) was recorded against the control. Interestingly, lipid-extracted algal biomass (LEAB) yielded 0.158 g ethanol/g LEA. Thus, the study presents the potential of bicarbonate supplementation in C. reinhardtii for bioenergy precursors, advancing sustainable biofuel production and biomass valorization within a circular bioeconomy framework under nitrogen starvation. © 2024 Elsevier Ltd
Hydrogenation of biomass-derived fatty acid esters and Dunaliella salina catalyzed by Pd on V2O5
(Springer Science and Business Media Deutschland GmbH, 2025) Manisha Pandey; Akanksha Rai; Nitesh Prasad; Abhishek Mohanta; Ravi Kumar Asthana; Kalluri Venkata Sri Ranganath
The hydrogenation of methyl oleate (C18:1) over vanadium-supported Pd was studied in the liquid phase under hydrogen pressure (1.0 atm). The hydrogenated product methyl stearate (C18:0) was obtained in good yields which are well-known precursors for the synthesis of long-chain alkanes (jet fuels). The catalytic activity of Pd/V2O5 is independent of the nature of the alkyl chain, the presence of a number of double bonds, and the source of fatty acids of methyl esters. The potentiality of Pd/V2O5 catalyst has been also studied in the hydrogenation of poly-unsaturated fatty acid esters from methyl linoleate, micro alga, soybean oil, and olive oil resulting in complete hydrogenation without effecting ester groups in excellent yields. During the process of hydrogenation of methyl oleate, isomerization of cis–trans was negligible, (1.56% of cis–trans) even at 70 ℃ in hexane. Both oxidation states of support vanadium (V5+, V4+) and noble metals Pd2+ and Pd0 play a key role in this reaction under heterogeneous conditions. © The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature 2025.
IAA induced biomass and lipid overproduction in microalga via two-stage cultivation strategy: Characterization using FTIR/CHNS/TGA/DTG and 1H- NMR for bioenergy potential
(Elsevier Ltd, 2024) Savita Singh; Avinash Singh; Sakshi Singh; Nitesh Prasad; Laxmi; Prabhakar Singh; Ravi Kumar Asthana
Microalgae are an excellent carbon concentrators with substantial lipid content. However, biomass production vis-à-vis lipid hyperaccumulation is a major constraint in the biofuel economy. In this regard, Dunaliella salina, an oleaginous, wall less microalga, was grown in graded concentration of indole-3-acetic acid (IAA). There was a significant increase in biomass (1.57-fold), photosynthetic efficiency (Fv/Fm = 0.72), and chlorophyll a content in 0.25 mg/L IAA supplemented cultures over the control (stage I). However, supplementation of IAA under nitrogen deprivation (stage II) led to a significant rise in the lipid content (47 % DCW), carbohydrate (18.37 %) and simultaneous reduction in the oxidative status (MDA, H2O2, O2·−, OH·) over the control. Further, 0.25 mg/L IAA supplemented cultures under nitrogen starvation were undertaken for biomass and lipid characterization. Nile red based flow cytometric analysis revealed an apparent increase in the neutral lipid fluorescence, also validated by 1H- NMR based lipidome, revealing the presence of triacylglycerol (TAG, 4.12–4.31 ppm). FTIR spectra revealed the increased absorbance at 2926 cm−1, 1740 cm−1 and 1025 cm−1, validating the increased carbohydrate and lipid, while biomass pyrolysis showed 81.42 % decomposition in the active pyrolytic zone as recorded by the TGA/DTG analysis. Interestingly, elemental analysis (CHNS) of the biomass showed an increased carbon and hydrogen %, HHV (19.94 MJ kg−1), H/C ratio (1.78), and CO2 fixation rate. Thus, the present study opens new avenues for the economic feasibility of bioenergy/biofuel production from microalgal biomass at commercial scale. © 2024 Elsevier Ltd
Optimizing light regimes for neutral lipid accumulation in Dunaliella salina MCC 43: a study on physiological status and carbon allocation
(Springer Science and Business Media B.V., 2024) Abhishek Mohanta; Nitesh Prasad; Sk Riyazat Khadim; Prabhakar Singh; Savita Singh; Avinash Singh; A.M. Kayastha; R.K. Asthana
Dunaliella salina is a favourable source of high lipid feedstock for biofuel and medicinal chemicals. Low biomass output from microalgae is a significant barrier to industrial-scale commercialisation. The current study aimed to determine how photosynthetic efficiency, carbon fixation, macromolecular synthesis, accumulation of neutral lipids, and antioxidative defence (ROS scavenging enzyme activities) of D. salina cells were affected by different light intensities (LI) (50, 100, 200, and 400 µmol m−2 s−1). The cells when exposed to strong light (400 µmol m−2 s−1) led to reduction in chlorophyll a but the carotenoid content increased by 19% in comparison to the control (LI 100). The amount of carbohydrate changed significantly under high light and in spite of stress inflicted on the cells by high irradiation, a considerable increase in activity of carbonic anhydrase and fixation rate of CO2 were recorded, thus, preserving the biomass content. The high light exposed biomass when subjected to nitrogen-deficient medium led to increase in lipid content (59.92% of the dry cell weight). However, neutral lipid made up 78.26% of the total lipid while other lipids like phospholipid and glycolipid content decreased, showing that the lipid was redistributed in these cells under nitrogen deprivation, making the organism more appropriate for biodiesel/jet fuel use. Although D. salina cells had a relatively longer generation time (3.5 d) than other microalgal cells, an economic analysis concluded that the amount of carotenoid they produced and the quality of their lipids made them more suited for commercialization. Graphical abstract: [Figure not available: see fulltext.] © 2024, The Author(s), under exclusive licence to Springer Nature B.V.
Photoautotrophic Growth and the Transcriptome of the Halotolerant Model Microalga Dunaliella salina MCC43 Under Salt Stress
(John Wiley and Sons Inc, 2025) Sakshi Singh; Prabhakar Singh; Nitesh Prasad; Savita S. Singh; Avinash K. Singh; Pankaj Kumar Singh; Arvindkumar Kumar Singh; Devashish Rath; Ravi Kumar Asthana
Dunaliella salina is a geographically distinct, green alga without a rigid cell wall recognized as a model system for halotolerance. In this study, D. salina strains of the Indian origin isolated from the Sambhar Lake, Rajasthan, were initially cultured optimally at a 0.5 M NaCl level, and these cultures were exposed to 1–2 M NaCl for up to 2 h for transcriptomic analyses. The cells did not accumulate substantial levels of intracellular Na+. Reduced photosynthetic efficiency was observed at 2 h with an Fv/Fm ratio (~0.2) and thereafter reached a maximum on the 10th day. Concurrently, elevated levels of proline and malondialdehyde (MDA) were also detected at higher salt concentrations, suggesting the initiation of a stress response. The transcriptomic study revealed that amino acid biosynthesis pathways, along with pyruvate and carbohydrate metabolism-related genes, were significantly enriched in 0.5 M versus 2 M NaCl-grown D. salina cells at 2 h. Downregulated genes were mainly related to cytoskeletal and microtubule proteins as owing to the loss of flagellar structures at 2 h. There was a change in the carbon flux because of the upregulation of key genes concerned with glyoxylate and TCA cycles, along with fatty acid metabolism, contributing to the remodeling of membrane lipids, thereby supporting membrane integrity. The upregulated differentially expressed genes (DEGs) were validated through qRT-PCR for the photosynthetic apparatus, antioxidative defense, ion homeostasis, and protein translocation and folding. The metabolomic profile under long-term (10th day) acclimation showed the upregulation of secondary metabolites and sterols. Therefore, the altered expression of genes indicated that D. salina strains tolerated elevated salt levels in a specified adaptive process to attain metabolic readjustments. © 2025 Scandinavian Plant Physiology Society.
Phytohormone augmented biomass and lipid production in Dunaliella salina under two-stage cultivation strategy: A comprehensive characterization of biomass and lipid using DLS, FTIR, CHNS and NMR for bioenergy prospects
(Elsevier Ltd, 2024) Savita Singh; Avinash Singh; Nitesh Prasad; Sakshi Singh; Ravi Kumar Asthana
Increasing population, climatic shifts, and decreasing fossil-fuels worldwide led scientists to explore microalgae as a renewable energy resource. The present study unravels the impact of gibberellic acid (GA3) on biomass production, enzymatic activities, macromolecular synthesis, and metabolome analysis of Dunaliella salina using two-stage cultivation strategy. The results indicated a marked increase in biomass (1.44-fold), photosynthetic yield (Fv/Fm 0.68), along with RuBisCO activity (1.66-fold), with an increased in absolute value of zeta potential(ζ) in cultures treated with 10 µM GA3 compared to controls (Stage I). Interestingly, 15 µM GA3-treated cells significantly enhanced lipid content (42.36 %), and carbohydrates (16.56 %) with elevated antioxidative enzymes (SOD, CAT, and APX) activities (Stage II). Enhanced lipid content was further confirmed through FTIR spectra (2928 cm-1, and 1740 cm-1) and 1H NMR signals (1.0– 2, 3.5–4.5 ppm), indicating an increase in both saturated (SFA) and polyunsaturated fatty acids (PUFAs). Elemental analysis demonstrated higher carbon and hydrogen percentages, reflected in higher heating value (HHV) and H/C ratio at 15 µM GA3. The increased lipid content was found to be significantly correlated with ACCase and GPAT activities, suggesting the allocation of carbon flux toward lipid biosynthesis pathways. To substantiate the carbon flux, HR-MS-based metabolomic analysis was performed, indicating a reduction in TCA and Calvin cycle intermediates with a significant rise in carotenoid biosynthesis, as well as metabolic shift towards fatty acid biosynthesis reflecting in the enhanced SFA and PUFAs. Thus, these findings highlighted GA3 significant role in the carbon flux allocation towards the neutral lipid biosynthesis for bioenergy prospects. © 2024 Elsevier Ltd
Surface-modified NiFe2O4 nanoparticles for the production of biodiesel from fatty acids and microalgae lipids Dunaliella salina
(John Wiley and Sons Ltd, 2024) Manisha Pandey; Neeraj Kumar; Nitesh Prasad; Ravi Kumar Asthana; Kalluri V. S. Ranganath
Development of a new and sustainable catalyst is necessary to the society for providing economical technology. Surface modification of nanometal oxides is one of the rapidly growing methods for developing a sustainable catalyst with attractive properties than their parent oxide. In this work, surface-modified nickel ferrites have been carried out using 4,4′-biphenyldisulfonic acid (BPDSA) as the linker. Thus, obtained modified material has been characterized using different techniques such as DLS, FT-IR, TGA, XRD, VSM, and XPS. This well-characterized, stable, robust, recyclable material offers a good conversion in the fatty acid, that is, oleic acid esterification in the presence of methanol in a short period of time (3.0 h). Based on the kinetic study in the oleic acid esterification, it fits in the pseudo first-order kinetics, and activation energy was found to be 60.0 kJ/mol. Further, the potentiality of our catalyst was also tested in the transesterification of various raw materials like mustard oil, olive oil, almond oil, and neem oil. In addition, it provides an excellent conversion with microalgae lipid extraction for the production of biodiesel. The kinematic viscosity of the methyl oleate (biodiesel) has been found to be 5.0426 mm2/s at 25°C whereas the dynamic viscosity is 6.0511 mPa, which is nearly the same as biodiesel obtained from Dunaliella salina, microalgae lipid. © 2024 John Wiley & Sons Ltd.