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Carbon nanotubes (CNTs), α-Fe 2 O 3 nanoparticles (nano Fe 2 O 3 ) and MgO nanoparticles (nano MgO) were evaluated for the effects on algae growth and lipid production. Nano Fe 2 O 3 promoted cell growth in the range of 0–20 mg·L −1 . CNTs, nano Fe 2 O 3 and nano MgO inhibited cell growth of Scenedesmus obliquus at 10, 40 and 0.8 mg·L −1 respectively. Neutral lipid and total lipid content increased with the increasing concentration of all tested nanoparticles. The maximum lipid productivity of cultures exposed to CNTs, nano Fe 2 O 3 and nano MgO was observed at 5 mg·L −1 , 5 mg·L −1 and 40 mg·L −1 , with the improvement by 8.9%, 39.6% and 18.5%. High dose exposure to nanoparticles limited increase in lipid productivity, possibly due to the repression on cell growth caused by nanoparticles-catalyzed reactive oxygen species (ROS) generation, finally leading to reduction in biomass and lipid production. Reduced accumulation of fatty acids of C18:3n3, C18:3n6 and C20:2 was observed in cells exposed to nanoparticles.

Biodiesel from microalgae seems to be the only renewable biofuel that has the potential to completely replace the petroleum-derived transport fuels. Therefore, improving lipid content of microalgal strains could be a cost-effective second generation feedstock for biodiesel production. Lipid accumulation in Scenedesmus obliquus was studied under various culture conditions. The most significant increase in lipid reached 43% of dry cell weight (dcw), which was recorded under N-deficiency (against 12.7% under control condition). Under P-deficiency and thiosulphate supplementation the lipid content also increased up to 30% (dcw). Application of response surface methodology in combination with central composite rotary design (CCRD) resulted in a lipid yield of 61.3% (against 58.3% obtained experimentally) at 0.04, 0.03, and 1.0 g l⁻¹ of nitrate, phosphate, and sodium thiosulphate, respectively for time culture of 8 days. Scenedesmus cells pre-grown in glucose (1.5%)-supplemented N 11 medium when subjected to the above optimized condition, the lipid accumulation was boosted up to 2.16 g l⁻¹, the value ~40-fold higher with respect to the control condition. The presence of palmitate and oleate as the major constituents makes S. obliquus biomass a suitable feedstock for biodiesel production.

Small-scale photobioreactors (PBRs) in the inoculum stage were designed with internal (red or green) and external white LED light as an initial step of a larger-scale installation aimed at fulfilling the integral biorefinery concept for maximum utilization of microalgal biomass in a multifunctional laboratory. The specific growth rate of Scenedesmus obliquus (Turpin) Kützing biomass for given cultural conditions was analyzed by using MAPLE software. For the determination of total polyphenols, flavonoids, chlorophyll “a” and “b”, carotenoids and lipids, UHPLC-HRMS, ISO-20776/1, ISO-10993-5 and CUPRAC tests were carried out. Under red light growing, a higher content of polyphenols was found, while the green light favoured the flavonoid accumulation in the biomass. Chlorophylls, carotenoids and lipids were in the same order of magnitude in both samples. The dichloromethane extracts obtained from the biomass of each PBR synergistically potentiated at low concentrations (0.01–0.05 mg/mL) the antibacterial activity of penicillin, fluoroquinolones or oregano essential oil against the selected food-borne pathogens (Staphylococcus aureus, Escherichia coli and Salmonella typhimurium) without showing any in vitro cytotoxicity. Both extracts exhibited good cupric ion-reducing antioxidant capacity at concentrations above 0.042–0.08 mg/mL. The UHPLC-HRMS analysis revealed that both extracts contained long chain fatty acids and carotenoids thus explaining their antibacterial and antioxidant potential. The applied engineering approach showed a great potential to modify microalgae metabolism for the synthesis of target compounds by S. obliquus with capacity for the development of health-promoting nutraceuticals for poultry farming.

In this paper, the influence of culture conditions (irradiance, temperature, pH, and dissolved oxygen) on the photosynthesis rate of Scenedesmus almeriensis cultures is analyzed. Short-run experiments were performed to study cell response to variations in culture conditions, which take place in changing environments such as outdoor photobioreactors. Experiments were performed by subjecting diluted samples of cells to different levels of irradiance, temperature, pH, and dissolved oxygen concentration. Results demonstrate the existence of photoinhibition phenomena at irradiances higher than 1,000 μE/m 2  s; in addition to reduced photosynthesis rates at inadequate temperatures or pH—the optimal values being 35 °C and 8, respectively. Moreover, photosynthesis rate reduction at dissolved oxygen concentrations above 20 mg/l is demonstrated. Data have been used to develop an integrated model based on considering the simultaneous influence of irradiance, temperature, pH, and dissolved oxygen. The model fits the experimental results in the range of culture conditions tested, and it was validated using data obtained by the simultaneous variation of two of the modified variables. Furthermore, the model fits experimental results obtained from an outdoor culture of S. almeriensis performed in an open raceway reactor. Results demonstrate that photosynthetic efficiency is modified as a function of culture conditions, and can be used to determine the proximity of culture conditions to optimal values. Optimal conditions found ( T  = 35 °C, pH = 8, dissolved oxygen concentration <20 mg/l) allows to maximize the use of light by the cells. The developed model is a powerful tool for the optimal design and management of microalgae-based processes, especially outdoors, where the cultures are subject to daily culture condition variations.

Mass culture of algae for the production of biofuels is a developing technology designed to offset the depletion of fossil fuel reserves. However, large scale culture of algae in open ponds can be challenging because of incidences of infestation with algal parasites. Without knowledge of the identity of the specific parasite and how to control these pests, algal-based biofuel production will be limited. We have characterized a eukaryotic parasite of Scenedesmus dimorphus growing in outdoor ponds used for biofuel production. We demonstrated that as the genomic DNA of parasite FD01 increases, the concentration of S. dimorphus cells decreases; consequently, this is a highly destructive pathogen. Techniques for culture of the parasite and host were developed, and the endoparasite was identified as the Aphelidea, Amoeboaphelidium protococcarum. Phylogenetic analysis of ribosomal sequences revealed that parasite FD01 placed within the recently described Cryptomycota, a poorly known phylum based on two species of Rozella and environmental samples. Transmission electron microscopy demonstrated that aplanospores of the parasite produced filose pseudopodia, which contained fine fibers the diameter of actin microfilaments. Multiple lipid globules clustered and were associated with microbodies, mitochondria and a membrane cisternae, an arrangement characteristic of the microbody-lipid globule complex of chytrid zoospores. After encystment and attachment to the host cells, the parasite injected its protoplast into the host between the host cell wall and plasma membrane. At maturity the unwalled parasite occupied the entire host cell. After cleavage of the protoplast into aplanospores, a vacuole and lipids remained in the host cell. Amoeboaphelidium protococcarum isolate FD01 is characteristic of the original description of this species and is different from strain X-5 recently characterized. Our results help put a face on the Cryptomycota, revealing that the phylum is more diverse than previously understood and include some of the Aphelidea as well as Rozella species and potentially Microsporidia.

In current study isolates of two native microalgae species were screened on the basis of growth kinetics and lipid accumulation potential. On the basis of data obtained on growth parameters and lipid accumulation, it is concluded that Scenedesmus dimorphus has better potential as biofuel feedstock. Two of the isolates of Scenedesmus dimorphus performed better than other isolates with respect to important growth parameters with lipid content of ~30% of dry biomass. Scenedesmus dimorphus was found to be more suitable as biodiesel feedstock candidate on the basis of cumulative occurrence of five important biodiesel fatty acids, relative occurrence of SFA (53.04%), MUFA (23.81%) and PUFA (19.69%), and more importantly that of oleic acid in its total lipids. The morphological observations using light and Scanning Electron Microscope and molecular characterization using amplified 18S rRNA gene sequences of microalgae species under study were also performed. Amplified 18S rRNA gene fragments of the microalgae species were sequenced, annotated at the NCBI website and phylogenetic analysis was done. We have published eight 18S rRNA gene sequences of microalgae species in NCBI GenBank.

Microalgae like Scenedesmus sp. are promising alternatives for sustainable food and animal feed due to their high protein content and adaptability to different light intensities. Optimal light enhances growth and nutrient accumulation, while excessive light can reduce productivity. This study investigates the effects of different light intensities (100–300 µmol m⁻ 2  s⁻ 1 ) on the growth performance and nutritional composition of Scenedesmus sp., aiming to improve microalgae production efficiency and contribute to commercial standards for sustainable protein sources. Results show that dry biomass concentration (0.975 g L −1 ) and cell count (2.96) peaked at a light intensity of 200 μmol m −2  s −1 ( P  <  0.0001 ), while dry biomass decreased at 300 μmol m⁻ 2  s⁻ 1 . Scenedesmus sp. grown at 200 and 300 µmol m −2  s −1 had higher carbohydrate contents (50.1% and 54%, P  <  0.001 ), while the highest lipid content (42.3%) was observed at 100 µmol m −2  s −1 . The highest crude protein was recorded at 200 µmol m −2  s −1 (15.6%, P  <  0.0001 ). Regarding amino acid composition, leucine was the most abundant essential amino acid (1.20 mg/100 mg dry weight), while glutamic acid was the most abundant non-essential amino acid (1.73 mg/100 mg). For color characteristics, biomass produced at 300 µmol m −2  s −1 exhibited a darker color, with the lowest L* value (21.66), and a more yellowish hue compared to 200 µmol m −2  s −1 . These findings highlight the importance of optimizing light conditions to enhance Scenedesmus sp. productivity for sustainable animal feed applications. This study indicates that the productivity of Scenedesmus sp. could be enhanced for biomass and protein production by maintaining an optimal light regime. By maximizing biomass yield and nutrient composition, this study supports the development of microalgae-based protein sources that can serve as a viable alternative to conventional feed ingredients, contributing to more sustainable and efficient feed production systems.

Microalgae cultivation on tannery wastewater (TWW) has been examined in some studies as a possible biological application to reduce contamination load and discharge effluents safely. However, Growth aspects, different tolerate strains and enriching the medium were not well investigated. In our study we applied Scenedesmus sp., Chlorella variabilis and Chlorella sorokiniana with different TWW concentrations. C. sorokiniana and C. variabilis cell density, chlorophyll, and sugar content grew substantially as compared to control. C. sorokiniana biomass and total lipids folded three and two times in 25% and 40% TWW, respectively as compared to control. Scenedesmus sp. showed longer lag phase and lower performance compared to the other two strains. Kelp waste extract (KWE) was added to balance the nutrients supply for C. sorokiniana , of which growth and effluents indicators were then greatly promoted in all concentrations. As the lag phase was shortened from 8 to 4 days in 60% concentration, subsequently, chlorophyll, carbohydrates, biomass and total lipids appreciated by 184%, 400%, 162% and 135%, respectively. Furthermore, the COD and ammonium removals improved by 51% and 45%, respectively. These outcomes emphasize the suitability of using TWW for microalgae cultivation with the suitable concentration while adding kelp waste extract for further enhancement.

One of the main parameters influencing microalgae production is light, which provides energy to support metabolism but, if present in excess, can lead to oxidative stress and growth inhibition. In this work, the influence of illumination on Scenedesmus obliquus growth was assessed by cultivating cells at different light intensities in a flat plate photobioreactor. S. obliquus showed a maximum growth rate at 150 μmol photons m⁻² s⁻¹. Below this value, light was limiting for growth, while with more intense illumination photosaturation effects were observed, although cells still showed the ability to duplicate. Looking at the biochemical composition, light affected the pigment contents only while carbohydrate, lipid, and protein contents remained stable. By considering that in industrial photobioreactors microalgae cells are subjected to light–dark cycles due to mixing, algae were also grown under pulsed illumination (5, 10, and 15 Hz). Interestingly, the ability to exploit pulsed light with good efficiency required a pre-acclimation to the same conditions, suggesting the presence of a biological response to these conditions.

Phosphorus is one of the crucial elements required for the proper functioning of metabolic processes in microalgae. Despite the crucial role of phosphate (P), the dynamics of polyphosphate accumulation with respect to nutrient availability remain unknown in freshwater microalgae. We have investigated three freshwater microalgal strains – Chlorella pyrenoidosa , Scenedesmus obliquus , and Chlamydomonas reinhardtii under varied phosphate treatments to understand the phosphate metabolic responses and polyphosphate dynamics. Our results show that the accumulation of polyP in microalgae is very dynamic and mainly depends on the availability of extracellular phosphate. Reduced P availability showed algal species-specific reduction in the polyphosphate storage with a decline in growth and total chlorophyll content. Further, an increase in lipid and carbohydrate content with a substantial decrease in protein was observed under P stress, suggesting preferential utilization of stored polyP to support cell survival. Species-specific differences in the fatty acid profiles were also observed in the GC analysis among all three algal strains, indicating varied mechanisms happening among the species to adapt and protect themselves against cellular damage under P stress. Our results suggest the existence of natural variability among the selected algal strains in their ability to accumulate polyP and metabolites with respect to P-varied conditions. Among the three microalgal species, Scenedesmus obliquus showed notably enhanced accumulation of polyphosphate, highlighting its potential application as P-rich biofertilizer.