Green Synthesis of Silver Nanoparticles Using the Cell-Free Supernatant of Haematococcus pluvialis Culture

The green synthesis of silver nanoparticles (AgNPs) using the cell-free supernatant of a Haematococcus pluvialis culture (CFS) was implemented in the current study, under illumination conditions. The reduction of Ag+ to AgNPs by the CFS could be described by a pseudo-first-order kinetic equation at the temperature range tested. A high reaction rate during synthesis and stable AgNPs were obtained at 45 °C, while an alkaline pH (pH = 11.0) and a AgNO3 aqueous solution to CFS ratio of 90:10 (v/v) proved to be the most effective conditions in AgNPs synthesis. A metal precursor (AgNO3) at the concentration range tested (1-5 mM) was the limited reactant in the synthesis process. The synthesis of AgNPs was accomplished under static and agitated conditions. Continuous stirring enhanced the rate of reaction but induced aggregation at prolonged incubation times. Zeta potential and polydispersity index measurements indicated stable AgNPs and the majority of AgNPs formation occurred in the monodisperse phase. The X-ray diffraction (XRD) pattern revealed the face-centered cubic structure of the formed AgNPs, while TEM analysis revealed that the AgNPs were of a quasi-spherical shape with a size from 30 to 50 nm. The long-term stability of the AgNPs could be achieved in darkness and at 4 °C. In addition, the synthesized nanoparticles showed antibacterial activity against Escherichia coli.

Extracts from Chlorella vulgaris Protect Mesenchymal Stromal Cells from Oxidative Stress Induced by Hydrogen Peroxide

Microalgae as unicellular eukaryotic organisms demonstrate several advantages for biotechnological and biological applications. Natural derived microalgae products demand has increased in food, cosmetic and nutraceutical applications lately. The natural antioxidants have been used for attenuation of mitochondrial cell damage caused by oxidative stress. This study evaluates the in vitro protective effect of Chlorella vulgaris bioactive extracts against oxidative stress in human mesenchymal stromal/stem cells (MSCs). The classical solid-liquid and the supercritical extraction, using biomass of commercially available and laboratory cultivated C. vulgaris, are employed. Oxidative stress induced by 300 μM H₂O₂ reduces cell viability of MSCs. The addition of C. vulgaris extracts, with increased protein content compared to carbohydrates, to H₂O₂ treated MSCs counteracted the oxidative stress, reducing reactive oxygen species levels without affecting MSC proliferation. The supercritical extraction was the most efficient extraction method for carotenoids resulting in enhanced antioxidant activity. Pre-treatment of MSCs with C. vulgaris extracts mitigates the oxidative damage ensued by H₂O_2. Initial proteomic analysis of secretome from licensed (TNFα-activated) MSCs treated with algal extracts reveals a signature of differentially regulated proteins that fall into clinically relevant pathways such as inflammatory signaling. The enhanced antioxidative and possibly anti-inflammatory capacity could be explored in the context of future cell therapies.

Optimization of Microalga Chlorella vulgaris Magnetic Harvesting

Harvesting of microalgae is a crucial step in microalgae-based mass production of different high value-added products. In the present work, magnetic harvesting of Chlorella vulgaris was investigated using microwave-synthesized naked magnetite (Fe₃O₄) particles with an average crystallite diameter of 20 nm. Optimization of the most important parameters of the magnetic harvesting process, namely pH, mass ratio (m_r) of magnetite particles to biomass (g/g), and agitation speed (rpm) of the C. vulgaris biomass-Fe₃O₄ particles mixture, was performed using the response surface methodology (RSM) statistical tool. Harvesting efficiencies higher than 99% were obtained for pH 3.0 and mixing speed greater or equal to 350 rpm. Recovery of magnetic particles via detachment was shown to be feasible and the recovery particles could be reused at least five times with high harvesting efficiency. Consequently, the described harvesting approach of C. vulgaris cells leads to an efficient, simple, and quick process, that does not impair the quality of the harvested biomass.

A Study on the Effect of Macro- and Micro- Nutrients on Nannochloropsis oceanica Growth, Fatty Acid Composition and Magnetic Harvesting Efficiency

The effect of iron, manganese, phosphorus and nitrogen on growth and lipid synthesis of the microalgae Nannochloropsis oceanica CCMP1779, as well as their impact on the magnetic harvesting efficiency, are examined under their depriving cell culture conditions. Herein, it is demonstrated that nitrogen and manganese depletion primarily reduced cell growth while phosphorus and iron restriction led to higher dry biomass. Subsequently, the role of those nutrients on fatty acids profile was examined. Phosphorus and nitrogen restriction resulted in lower and higher lipid content, respectively. High amounts of polyunsaturated fatty acids like eicosapentaenoic acid are produced under iron and manganese depletion. Phosphorus deprivation favors monounsaturated fatty acids such as C18:1 and C16:1, while nitrogen restriction favors saturated fatty acid production like C14:0, C16:0 and C18:0. Since the presence/absence of macro- and micro-elements may affect the overall electrostatic charges on the outmost microalgae surface, it was also analyzed how these elements affect the magnetic harvesting efficiency. Results showed that phosphorus deprivation led to the best magnetic harvesting efficiency of N. oceanica cells (93%) as compared to other nutrient starvation as well as standard medium.

A Study on Magnetic Removal of Hexavalent Chromium from Aqueous Solutions Using Magnetite/Zeolite-X Composite Particles as Adsorbing Material

Toxic and heavy metals are considered harmful derivatives of industrial activities; they are not biodegradable and their accumulation in living organisms can become lethal. Among other heavy and toxic metals, chromium is considered hazardous, especially in the hexavalent (Cr6+) form. Numerous established studies show that exposure to Cr6+ via drinking water leads to elevated chromium levels in tissues, which may result in various forms of cancer. The purpose of this research is to synthesize magnetite/zeolite-X composite particles for the adsorption and magnetic removal of Cr6+ ions from aqueous solutions. Synthesis and characterization of such composite nanomaterials, along with an initial experimental evaluation of Cr6+ removal from water-based solution, are presented. Results show that zeolite-X is a very promising zeolite form, that when bound to magnetic nanoparticles can be used to trap and magnetically remove toxic ions from aqueous solutions.

Studies on the catalytic behavior of a membrane-bound lipolytic enzyme from the microalgae Nannochloropsis oceanica CCMP1779

The catalytic behavior of a membrane-bound lipolytic enzyme (MBL-Enzyme) from the microalgae Nannochloropsis oceanica CCMP1779 was investigated. The biocatalyst showed maximum activity at 50 °C and pH 7.0, and was stable at pH 7.0 and temperatures from 40 to 60 °C. Half-lives at 60 °C, 70 °C and 80 °C were found 866.38, 150.67 and 85.57 min respectively. Thermal deactivation energy was 68.87 kJ mol^-1. The enzyme's enthalpy (ΔΗ*), entropy (ΔS*) and Gibb's free energy (ΔG*) were in the range of 65.86-66.27 kJ mol^-1, 132.38-140.64 J mol^-1 K^-1 and 107.80-115.81 kJ mol^-1, respectively. Among p-nitrophenyl esters of fatty acids tested, MBL-Enzyme exhibited the highest hydrolytic activity against p-nitrophenyl palmitate (pNPP). The K_m and V_max values were found 0.051 mM and of 0.054 mmole pNP mg protein^-1 min^-1, respectively with pNPP as substrate. The presence of Mn²⁺ increased lipolytic activity by 68.25%, while Fe³⁺ and Cu²⁺ ions had the strongest inhibitory effect. MBL-Enzyme was stable in the presence of water miscible (66% of the initial activity in ethanol) and water immiscible (71% of the initial activity in n-octane) solvents. Myristic acid was found to be the most efficient acyl donor in esterification reactions with ethanol. Methanol was the best acyl acceptor among the primary alcohols tested.