Combination of trace elements and salt stress in different cultivation modes improves the lipid productivity of Scenedesmus spp

Cell rupture of Tetradesmus obliquus using high-pressure homogenization at the pilot scale and recovery of pigments and lipids

Microalgae are promising sources of intracellular metabolites such as proteins, polysaccharides, pigments, and lipids. Thus, this study applied high-pressure homogenization (HPH) techniques on a pilot scale to disrupt the cells of Tetradesmus obliquus. The effects of pressure (P; 150, 250, and 350 bar), suspension concentration (Cs; 1.0, 1.5, and 2.0 % w/v), and number of cycles (Nc; 5, 15, and 25) were evaluated in HPH via a Box-Behnken experimental design. Response surface methodology was applied to optimize the recovery rate (dTr) of pigments and lipids. The specific energy consumption (SEC) and color change gradient (ΔE) of the biomass during HPH were also assessed. The optimal HPH conditions for pigment extraction with 1.5 % Cs (w/v) were as follows: P = 312 bar and Nc = 22 for chlorophyll-a (0.83 g/100 g; dTr = 69 %; SEC = 47.50 kJ/g dry matter); P = 345 bar and Nc = 24 for chlorophyll-b (0.63 g/100 g; dTr = 80 %; SEC = 57.30 kJ/g dry matter); P = 345 bar and Nc = 24 for total carotenoids (0.53 g/100 g; dTr = 79 %; SEC = 54.12 kJ/g dry matter); and P = 350 bar and Nc = 25 for β-carotene (299 µg/g; dTr = 58 %; SEC = 62.08 kJ/g dry matter). The optimal HPH conditions for lipid extraction were P = 350 bar and Nc = 23, with a lipid recovery rate of ≥28 %. Cell disruption during HPH caused a change in the color of the biomass (ΔE) due to the release of intracellular biocompounds. Increasing P and Nc led to higher SECs, ΔE gradients, and pigment and lipid contents. Thus, the levels of recovered pigments and lipids can be indicators of cell disruption in T. obliquus.

Extraction methods of algae oils for the production of third generation biofuels - A review

Microalgae are the main source of third-generation biofuels because they have a lipid content of 20-70%, can be abundantly produced and do not compete in the food market besides other benefits. Biofuel production from microalgae is a promising option to contribute for the resolution of the eminent crisis of fossil energy and environmental pollution specially in the transporting sector. The choice of lipid extraction method is of relevance and associated to the algae morphology (i.e., rigid cells). Therefore, it is essential to develop suitable extraction technologies for economically viable and environment-friendly lipid recovery processes with the aim of achieving a commercial production of biofuels from this biomass. This review presents an exhaustive analysis and discussion of different methods and processes of lipid extraction from microalgae for the subsequent conversion to biodiesel. Physical methods based on the use of supercritical fluids, ultrasound and microwaves were reviewed. Chemical methods using solvents with different polarities, aside from mechanical techniques such as mechanical pressure and enzymatic methods, were also analyzed. The advantages, drawbacks, challenges and future prospects of lipid extraction methods from microalgae have been summarized to provide a wide panorama of this relevant topic for the production of economic and sustainable energy worldwide.

Current advances for omics-guided process optimization of microbial manufacturing

Currently, microbial manufacturing is widely used in various fields, such as food, medicine and energy, for its advantages of greenness and sustainable development. Process optimization is the committed step enabling the commercialization of microbial manufacturing products. However, the present optimization processes mainly rely on experience or trial-and-error method ignoring the intrinsic connection between cellular physiological requirement and production performance, so in many cases the productivity of microbial manufacturing could not been fully exploited at economically feasible cost. Recently, the rapid development of omics technologies facilitates the comprehensive analysis of microbial metabolism and fermentation performance from multi-levels of molecules, cells and microenvironment. The use of omics technologies makes the process optimization more explicit, boosting microbial manufacturing performance and bringing significant economic benefits and social value. In this paper, the traditional and omics technologies-guided process optimization of microbial manufacturing are systematically reviewed, and the future trend of process optimization is prospected.

Recent advances in CO2 fixation by microalgae and its potential contribution to carbon neutrality

Many countries and regions have set their schedules to achieve the carbon neutrality between 2030 and 2070. Microalgae are capable of efficiently fixing CO₂ and simultaneously producing biomass for multiple applications, which is considered one of the most promising pathways for carbon capture and utilization. This work reviews the current research on microalgae CO₂ fixation technologies and the challenges faced by the related industries and government agencies. The technoeconomic analysis indicates that cultivation is the major cost factor. Use of waste resources such as wastewater and flue gas can significantly reduce the costs and carbon footprints. The life cycle assessment has identified fossil-based electricity use as the major contributor to the global warming potential of microalgae-based CO₂ fixation approach. Substantial efforts and investments are needed to identify and bridge the gaps among the microalgae strain development, cultivation conditions and systems, and use of renewable resources and energy.

Effects of high-strength landfill leachate effluent on stress-induced microalgae lipid production and post-treatment micropollutant degradation

This research investigates the effects of landfill leachate effluent concentrations from moving bed biofilm reactor (MBBR) on stress-induced Chlorella vulgaris and Scenedesmus armatus lipid production and post-treatment micropollutant degradation. The effluent concentrations were varied between 25%, 50%, 75%, and 100% (v/v). The landfill leachate influent was treated using two-stage moving bed biofilm reactor under 24 h and 18 h hydraulic retention time (HRT). The results indicated that the effluent concentration was positively correlated with the stress-induced microalgae lipid production in the post-treatment of residual micropollutants. C. vulgaris and S. armatus completely remove residual micropollutants in the effluent. The superoxide dismutase and peroxidase activity were positively correlated with the cellular lipid content. The lipid content of C. vulgaris and S. armatus cultivated in the 18 h HRT effluent were 31-51% and 51-64%, while those in the 24 h HRT effluent were 15-16% and 5-19%. The optimal condition of microalgae cultivation for the post-treatment of residual micropollutants was 50-75% (v/v) effluent concentrations under 18 h HRT, achieving the highest lipid production of 113-116 mg/L for C. vulgaris and 74-75 mg/L for S. armatus. Essentially, the MBBR landfill leachate effluent holds promising potential as a substrate for microalgae lipid production.

Improving the content of high value compounds in Nordic Desmodesmus microalgal strains

Nordic Desmodesmus microalgal strains (2-6) and (RUC-2) were exposed to abiotic stress (light and salt) to enhance lipids and carotenoids. The biomass output of both strains increased by more than 50% during light stress of 800 μmol m^-2 s^-1 compared to control light. The biomass of Desmodesmus sp. (2-6) contained most lipids (15% of dry weight) and total carotenoids (16.6 mg g^-1) when grown at moderate light stress (400 μmol m^-2 s^-1), which further could be enhanced up to 2.5-fold by salinity stress. Desmodesmus sp. (RUC-2) exhibited maximal lipid (26.5%) and carotenoid (43.8 mg L^-1) content at light intensities of 400 and 100 μmol m^-2 s^-1, respectively. Salinity stress stimulated lipid accumulation by 39%. Nordic Desmodesmus strains therefore are not only able to tolerate stress conditions, but their biomass considerably improves under stress. These strains have high potential to be used in algal bio-factories on low-cost medium like Baltic seawater.

Biochemical and morphological characterization of freshwater microalga Tetradesmus obliquus (Chlorophyta: Chlorophyceae)

Tetradesmus is a microalgal genus with biotechnological potential due to its rapid production of biomass, which is plenty in proteins, carbohydrates, lipids, and bioactives. However, its morphology and physiology need to be determined to guide better research to optimize the species cultivation and biocompounds processing. Thus, this study describes the biochemistry and morphology of the strain Tetradesmus obliquus BR003, isolated from a sample of freshwater reservoirs in a Brazilian municipality. In the T. obliquus BR003 dry biomass, we identified 61.6% unsaturated fatty acids, and 3.4% saturated fatty acids. Regarding other compounds, 28.50 ± 1.47 g soluble proteins/100 g, 0.14 ± 0.009 g carotenoids/100 g, 0.76 ± 0.013 g chlorophyll a/100 g, and 0.42 ± 0.015 g chlorophyll b/100 g with a chlorophyll a/b ratio of 1.8 were detected. The main chemical elements found were S, Mg, and P. The cells of BR003 were elliptically curved at the ends and without appendages. Histochemical tests showed carbohydrates distributed in the cytoplasm and pyrenoids, some lipid droplets, and proteins. The cytoplasm is rich in vacuoles, rough endoplasmic reticulum, mitochondria, and chloroplasts. The nucleus has a predominance of decondensed chromatin, and the cell wall has three layers. Chloroplasts have many starch granules and may be associated with a spherical central pyrenoid. To the best of our knowledge, this was the first biochemical description combined with ultrastructural morphological characterization of the strain T. obliquus BR003, grown under standard conditions, to demonstrate specific characteristics of the species.

Aeroterrestrial and Extremophilic Microalgae as Promising Sources for Lipids and Lipid Nanoparticles in Dermal Cosmetics

Microscopic prokaryotic and eukaryotic algae (microalgae), which can be effectively grown in mass cultures, are gaining increasing interest in cosmetics. Up to now, the main attention was on aquatic algae, while species from aeroterrestrial and extreme environments remained underestimated. In these habitats, algae accumulate high amounts of some chemical substances or develop specific compounds, which cause them to thrive in inimical conditions. Among such biologically active molecules is a large family of lipids, which are significant constituents in living organisms and valuable ingredients in cosmetic formulations. Therefore, natural sources of lipids are increasingly in demand in the modern cosmetic industry and its innovative technologies. Among novelties in skin care products is the use of lipid nanoparticles as carriers of dermatologically active ingredients, which enhance their penetration and release in the skin strata. This review is an attempt to comprehensively cover the available literature on the high-value lipids from microalgae, which inhabit aeroterrestrial and extreme habitats (AEM). Data on different compounds of 87 species, subspecies and varieties from 53 genera (represented by more than 141 strains) from five phyla are provided and, despite some gaps in the current knowledge, demonstrate the promising potential of AEM as sources of valuable lipids for novel skin care products.

Microalgae as Contributors to Produce Biopolymers

Biopolymers are very favorable materials produced by living organisms, with interesting properties such as biodegradability, renewability, and biocompatibility. Biopolymers have been recently considered to compete with fossil-based polymeric materials, which rase several environmental concerns. Biobased plastics are receiving growing interest for many applications including electronics, medical devices, food packaging, and energy. Biopolymers can be produced from biological sources such as plants, animals, agricultural wastes, and microbes. Studies suggest that microalgae and cyanobacteria are two of the promising sources of polyhydroxyalkanoates (PHAs), cellulose, carbohydrates (particularly starch), and proteins, as the major components of microalgae (and of certain cyanobacteria) for producing bioplastics. This review aims to summarize the potential of microalgal PHAs, polysaccharides, and proteins for bioplastic production. The findings of this review give insight into current knowledge and future direction in microalgal-based bioplastic production considering a circular economy approach. The current review is divided into three main topics, namely (i) the analysis of the main types and properties of bioplastic monomers, blends, and composites; (ii) the cultivation process to optimize the microalgae growth and accumulation of important biobased compounds to produce bioplastics; and (iii) a critical analysis of the future perspectives on the field.

Green coagulants recovering Scenedesmus obliquus: An optimization study

The recovery of microalgae by means of coagulation-flocculation is efficient, simple and low operating costs. The addition of coagulants makes it possible to destabilize the microalgae surface loads and recover their biomass. Chemical coagulants can contaminate the environment and negatively affect human health. Thus, the exploration of natural coagulants, such as Moringa oleifera and Guazuma ulmifolia, are innovative. Thus, this study aimed to evaluate the efficiency of biomass separation from the microalgae Scenedesmus obliquuos by means of coagulation-flocculation. M. oleifera and G. ulmifolia were used in order to optimize the variables dose, pH and settling time, through a central composite rotational design, which presented recovery efficiencies above 80.0% and 60.0%, respectively. In relation to M. oleifera, optimum regions were obtained for biomass recovery at both pH 4.0 with a dose of 40.0 mg L^-1 and pH 9.0 with a dose of 80.0 mg L^-1, both in 30 min of settling times. For G. ulmifolia, an optimum dose of 30.0 mg L^-1 at pH 4.0 with a 3 min settling time demonstrated that this new coagulant for microalgae recovery has potential for application. Thus, these natural coagulants are promising and can be used in coagulation-flocculation to recover biomass from Scenedesmus obliquuos and, thus, minimize the use of synthetic or metallic products.

NaCl Improves Suaeda salsa Aniline Tolerance in Wastewater

Halophytes have been studied as a model for morphological traits of adaptation to saline environments. However, little information has been given on plant growth, chlorophyll fluorescence responses, and change of ion content in halophytes grown in an aniline–salinity coexistent environment. This study hypothesized that aniline could induce alterations in plant growth, chlorophyll fluorescence, and ion content in Suaeda salsa, but salinity could promote the tolerance of halophytes to aniline. A 6 (aniline) × 3 (NaCl) factorial experiment (for a total of 18 treatments) was conducted to test the above hypothesis. After 30 d of cultivation, roots and shoots were harvested separately to analyze the effects of salinity on the seedling growth under aniline stress. Biomass accumulation was inhibited by aniline treatment, and the inhibition was significantly alleviated by 200 mM NaCl. The change in chlorophyll fluorescence in leaves with aniline stress was moderated by the addition of NaCl. The removal efficiency of aniline was significantly enhanced by moderate salinity. Aniline stress decreased the accumulation of Mg2+, but various concentrations of NaCl increased the accumulation of Mg2+, especially with 200 mM NaCl in both roots and shoots. Both aniline and salinity decreased the content of Ca2+. There was a negative correlation between the K+ and NaCl concentrations and between the Cl− and aniline concentrations. Our results indicated that Suaeda salsa may be suitable for the remediation of salinity and aniline-enriched wastewater.

Extraction of proteins from the microalga Scenedesmus obliquus BR003 followed by lipid extraction of the wet deproteinized biomass using hexane and ethyl acetate

A current problem of the lipid extraction from wet biomass is the formation of emulsions during the mixing of the microalgal biomass and organic solvents. It has been suggested that microalgal proteins play an important role in the formation and stability of such emulsions. Herein, the extraction of proteins of the freshwater microalga Scenedesmus obliquus BR003 was optimized for further extraction of lipids from the wet deproteinized biomass. The optimal (pH 12 at 60 °C for 3 h) and moderate (pH 10.5 at 50 °C for 2 h) conditions of protein extraction resulted in protein yields of 20.6% and 15.4%, respectively. Wet lipid extraction of deproteinized biomass resulted in a less stable emulsion that released twice the solvent than the control biomass. However, the faster separation of phases that occurred during the wet lipid extraction of the deproteinized biomass resulted in a lipid yield twice lower than the control biomass.

Microalgae proteins: production, separation, isolation, quantification, and application in food and feed

Many countries have been experienced an increase in protein consumption due to the population growth and adoption of protein-rich dietaries. Unfortunately, conventional-based protein agroindustry is associated with environmental impacts that might aggravate as the humankind increase. Thus, it is important to screen for novel protein sources that are environmentally friendly. Microalgae farming is a promising alternative to couple the anthropic emissions with the production of food and feed. Some microalgae show protein contents two times higher than conventional protein sources. The use of whole microalgae biomass as a protein source in food and feed is simple and well-established. Conversely, the production of microalgae protein supplements and isolates requires the development of feasible and robust processes able to fractionate the microalgae biomass in different value-added products. Since most of the proteins are inside the microalgae cells, several techniques of disruption have been proposed to increase the efficiency to extract them. After the disruption of the microalgae cells, the proteins can be extracted, concentrated, isolated or purified allowing the development of different products. This critical review addresses the current state of the production of microalgae proteins for multifarious applications, and possibilities to concatenate the production of proteins and advanced biofuels.

Alternative fertilizer-based growth media support high lipid contents without growth impairment in Scenedesmus obliquus BR003

Nitrogen (N) sources have been target in microalgae cultivation studies, considering their nutritional impact on growth and high costs. Here, we have evaluated the growth of Scenedesmus obliquus BR003, applying alternative low-cost culture media containing ammonium and urea, or combinations of both N sources. The culture media were applied for indoor and outdoor cultivation, followed by growth analyses and metabolic characterization. The alternative culture media B4 and L4 supported higher biomass production (1.4 g L^-1) compared to BG11 (nitrate-based medium). In addition, the lipid percentage was higher for B4 (ammonium-based culture medium), reaching up to 25% DW. High contents of carbohydrates (60%) and proteins (40%) were also obtained in media with ammonium and urea, respectively. Considering the lower costs of alternative fertilizer-based media, using ammonium and/or urea as N sources, and the high lipid content observed, we suggest these media as viable for large-scale production of S. obliquus.