Browsing by Author "Laxmi"

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A Study on Mixotrophic Approach for Maximizing Lipid Production in a Hypersaline Microalga, Dunaliella salina
(Springer, 2023) Abhishek Mohanta; Sk Riyazat Khadim; Prabhakar Singh; Laxmi; R.K. Asthana
The microalga, Dunaliella salina, is a treasure of fine chemicals, carotenoids, and lipids of industrial importance. The present investigation focused on the maximization of lipid content in the context of biofuel. Mixotrophic cultures growing in different combinations of sodium bicarbonate (NaHCO3) and glucose (Glu) or sodium acetate (Na-Ace) were monitored for essential growth parameters such as photosynthesis, dry biomass, and Chl a content. The maximum photosynthetic quantum yield (Fv/Fm) of all the screened mixotrophic cultures along with control ranged between 0.63 and 0.72, indicating the cells were in a good physiological state. The highest biomass productivity (33.46 ± 0.58 mg/L/d) was recorded in 1.0 mM NaHCO3 + 1.0 mM Glu-containing cultures. However, the highest lipid content (56% DCW) was recorded in 1.0 mM NaHCO3 + 0.5 mM Na-Ace-containing cultures. Interestingly, a 1.7-fold higher starch content (72.3 μg/mL) was recorded in 0.25 mM NaHCO3 + 0.5 mM Na-Ace over 1.0 mM NaHCO3 + 0.5 mM Na-Ace-containing cultures. Thus, data indicated that the higher concentration of NaHCO3 along with Na-Ace favoured lipid biosynthesis, while the lower concentration of NaHCO3 with Na-Ace favoured starch synthesis. Thus, substrate provision determined the desired products. Lipids obtained from D. salina at stage II (nitrogen-deficient condition) possessed ideal fuel properties according to international standards of EN 14214 and ASTM D6751. Therefore, the present work explored the threshold level of bicarbonate along with Na-Ace which was able to maintain good physiological status and produced higher lipids with better biodiesel properties. Graphical Abstract: [Figure not available: see fulltext.] © 2023, The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.
Bioactive molecules from microalgae and constraints in commercialization
(Elsevier, 2020) Urmilesh Singh; Laxmi; Ankit K. Singh; Ravi K. Asthana
Increasing drug resistance in pathogenic microorganisms especially fungi and bacteria, menace caused by AIDS in modern society, spread of dreaded cancer disease worldwide, especially in third-world countries led the scientists to look at nature and little explored microalgae which seem to be a bioresource for biomolecules. Microalgae, in general, involve all microscopic algae including cyanobacteria which have originated on earth ~2.8 billion years ago. Modern knowledge of genomics, proteomics and understanding of the strategy of survival of such microalgal strains inhabiting various environments including extreme habitats must be endowed with specific metabolic pathways, producing specific biomolecules of synthetic biochemist’s interest. Bioassays of microalgal extracts clearly demonstrate their potential to kill fungi and bacteria and to inhibit growth of viral and cancer cells. The identification of target biomolecules is a difficult task. Modern instruments including chromatography and high-resolution mass spectrometry led to the isolation and identification of biomolecules. However, small quantities of biomolecules (µg/g dry weight) made it difficult to produce at large scale. This chapter reviews the state of the art in extraction, purification and extent of nanotechnology for its impact on microbial system as well as cancer cells. Constraints in commercialization of biomolecules and drug production and its overcoming strategies are also discussed. © 2021 Elsevier Inc.
Green synthesis of gold nanoparticles from Dunaliella salina, its characterization and in vitro anticancer activity on breast cancer cell line
(Editions de Sante, 2019) Ankit Kumar Singh; Ratnakar Tiwari; Vikas Kumar Singh; Prabhakar Singh; Sk Riyazat Khadim; Urmilesh Singh; Laxmi; Vikas Srivastava; S.H. Hasan; R.K. Asthana
An ecofriendly and efficient method (photoinduced) has been used for green synthesis of stable gold nanoparticles (AuNPs) using aqueous extract as a reducing and stabilizing agent, derived from halotolerant microalga Dunaliella salina. Synthesis of AuNPs was confirmed by UV–Vis spectroscopy showing sharp SPR band at 560 nm after 30 min exposure of sunlight. The synthesis was optimized further as exposure(75min) to sunlight, aqueous extract of Dunaliella (AED) inoculum dose(30%) and HAuCl 4 .xH 2 O (1 mM). The presence of nearly spherical shape of AuNPs with average size of 22.4 nm and crystalline nature were confirmed by TEM, SAED and XRD analysis. The XPS analysis of AuNPs showed presence of two individual peaks at 85.17 and 88.94eV that attributed to Au 4f7/2 and Au 4f5/2 respectively. Phycochemical analysis of AED demonstrated presence of phenolics, flavonoids, tannin and proteins. AED when subjected to SDS-PAGE showed protein bands of 92 and 66 KDa. AuNPs were tested for anticancer activity on MCF7 (cancer) and MCF 10A (normal) cell lines, keeping commercial drug cisplatin as positive control. AuNPs selectively killed cancer cells and were not detrimental to the normal cell line whereas cisplatin killed normal cells also at 48 h exposure, therefore, such AuNPs may be used as an anticancer agent. © 2019 Elsevier B.V.
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
Identification of antifungal and antibacterial biomolecules from a cyanobacterium, Arthrospira platensis
(Elsevier B.V., 2021) Urmilesh Singh; Prabhakar Singh; Ankit K. Singh; Laxmi; Deepak Kumar; Ragini Tilak; Sushant K. Shrivastava; Ravi K. Asthana
Arachidonoyl dopamine and fluocinolone were identified as ‘active compounds’ from the methanolic extract of a species of cyanobacterium, Arthrospira platensis, isolated from a hypersaline lake in Rajasthan, India. In vitro testing of these compounds has shown potential antifungal activity as well as antibacterial activity against strains with multidrug resistance. A. platensis-derived methanolic crude extract and purified fractions were assayed against bacterial and fungal target pathogens prioritized by the World Health Organization (WHO). The active fractions were subjected to high-resolution liquid chromatography/mass spectrometry (HR-LC/MS). Molecular docking analysis of the screened compounds revealed that arachidonoyl dopamine showed a significant interaction with the enzyme sterol-14-alpha demethylase targeted by other antifungal drugs; likewise, fluocinolone interacted with the OMP-F porin protein present in the outer membranes of the bacteria. However, neither molecule has yet been reported from any cyanobacterial system until now. In vitro activity of both compounds clearly indicates their potential for the development and/or repurposing of antifungal and antibacterial drugs. © 2021 Elsevier B.V.
In silico and in vitro evaluation of extract derived from Dunaliella salina, a halotolerant microalga for its antifungal and antibacterial activity
(Taylor and Francis Ltd., 2023) Urmilesh Singh; Laxmi; Prabhakar Singh; Ankit Kumar Singh; Sweksha Singh; Deepak Kumar; Sushant Kumar Shrivastava; Ravi Kumar Asthana
In the present study little explored halotolerant wall-less green alga Dunaliella salina was found to be a potent source of antibacterial and antifungal biomolecules. Both the target pathogens, bacteria (Escherischia coli, Klebsiella pneumoniae, and Acinetobacter baumannii) and fungi (Candida albicans, C. tropicalis, and Cryptococus sp.) were WHO prioritized. The bioassay guided approach led us to evaluate antibacterial and antifungal lead molecule(s) from an array of compounds using spectroscopic and in silico studies. The methanol derived crude extract was purified via thin layer chromatography (TLC) using solvent system methanol: chloroform (1:19). Maximum antimicrobial activity was observed in fractions D5, D6 and D7, the components of which were then recognized using high resolution-liquid chromatography/mass spectroscopy (Orbitrap) (HR-LC/MS). The screened compounds were then docked with target enzymes sterol-14-alpha demethylase and OmpF porin protein. The energy scores revealed that amongst all, lariciresinol-4-O-glucoside showed better binding affinity, in silico, using the Schrödinger Maestro 2018-1 platform. The 3-dimensional crystal structures of both the proteins were retrieved from the protein data bank (PDB), and showed binding energies of −14.35 kcal/mol, and −11.0 kcal/mol against respective drug targets. The molecular dynamics (MD) simulations were performed for 100 ns, using Desmond package, Schrödinger to evaluate the conformational stability and alteration of protein-ligand complexes during the simulation. Thus, our findings confirmed that lariciresinol-4-O-glucoside, a lignan derivative and known strong antioxidant, may be used as an important “lead” molecule to be developed as antibacterial and antifungal drugs in the future. Communicated by Ramaswamy H. Sarma. © 2022 Informa UK Limited, trading as Taylor & Francis Group.