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Microalgae, a renewable bio-resource, are considered a potential value-added commodity and a tool to combat climate change. Microalgal research has received worldwide attention recently. Different perspectives have been explored, but cultivation in outdoor photobioreactors (PBRs) is still a less explored field. This review summarizes the studies conducted on the microalgae cultivated in outdoor PBRs only. The locations, algal strains, PBRs, and cultivation media used in these studies were identified and tabulated. Different aspects of outdoor algal cultivation in PBRs, such as temperature control, light intensity control, photosynthetic efficiency (PE), the outdoor adaptation of strains, PBR designs, and algal growth and biochemical composition variation from the weather, were studied and reviewed. A brief review of downstream processes and environmental and economic impacts was also conducted. This review summarizes what has been carried out in this field so far and will help researchers to determine what further work needs to be conducted and in which direction to proceed.

Microalgae, a renewable bio-resource, are considered a potential value-added commodity and a tool to combat climate change. Microalgal research has received worldwide attention recently. Different perspectives have been explored, but cultivation in outdoor photobioreactors (PBRs) is still a less explored field. This review summarizes the studies conducted on the microalgae cultivated in outdoor PBRs only. The locations, algal strains, PBRs, and cultivation media used in these studies were identified and tabulated. Different aspects of outdoor algal cultivation in PBRs, such as temperature control, light intensity control, photosynthetic efficiency (PE), the outdoor adaptation of strains, PBR designs, and algal growth and biochemical composition variation from the weather, were studied and reviewed. A brief review of downstream processes and environmental and economic impacts was also conducted. This review summarizes what has been carried out in this field so far and will help researchers to determine what further work needs to be conducted and in which direction to proceed. [ABSTRACT FROM AUTHOR]

Microalgae-based systems have the potential to remove the nutrients from the sewage that can be reused for agricultural purposes for example. However, there are very few pilot-scale studies conducted in tropical regions. In this study, real anaerobically digested sewage was treated using a native microalgae consortium as inoculum in a lab-scale flat panel photobioreactor operated indoor and a pilot scale flat panel operated outdoors under tropical conditions. The performance was then evaluated by assessing the nutrient removal efficiency and biomass productivity. Both, the indoor and the outdoor photobioreactors were operated in batch mode (seven days each) in southeastern Brazil. This study showed that both bioreactors operated under tropical climatic conditions had a positive performance, however the outdoor flat panel had better performance in terms of nutrient removal (average removals of 85% total nitrogen and 88% total phosphorus) and biomass productivity in terms of total suspended solids (average of 31.3 mg L−1 day−1), mainly because of better light and temperature. Tetradesmus sp. and Mychonastes homosphaera were dominant during the study period in both, indoor and outdoor photobioreactors. [ABSTRACT FROM AUTHOR]

Microalgae are considered the most promising source of renewable fuels, high-value bio-products and nutraceuticals. Potentially, microalgae can satisfy many global demands, but in large-scale cultivation the average productivity of most industrial strains is lower than maximal theoretical estimations, mainly due to sub-optimal growth conditions. Although microalgae have developed complex strategies to cope with environmental stresses, cultivation in outdoor photobioreactors is limited to few species and it is not yet sufficiently remunerative. Indeed, most microalgal species are very sensitive to environmental conditions, and changes in solar irradiation, temperature, and medium composition can drastically decrease biomass yield. Developing new strategies for improving algal tolerance to stress conditions is thus greatly desirable. One of the first responses that occur in both higher plants and microorganisms following the exposure to abiotic stress conditions, is an increased synthesis and accumulation of the amino acid proline. While the role of proline accumulation in stress adaptation is well-recognized in higher plants, in microalgae the implication of proline in stress tolerance still awaits full elucidation. In this review we summarize available data on proline metabolism under environmental stress in eukaryotic microalgae. Possible implications toward optimization of algal growth for biotechnological purposes are also discussed. [ABSTRACT FROM AUTHOR]

Natural astaxanthin has shown its potential value in food, pharmaceuticals and nutraceutical industries. It is found in yeasts, algae, salmons, shrimps etc. but its substantial amounts are biosynthesized in Haematococcus pluvialis. The Haematococcus cells can biosynthesize large amounts of astaxanthin under stress conditions during their red stage to enhance the astaxanthin accumulation and elevation of its productivity. The stress related conditions are best suited in wastewater and can be an economical way of cultivating microalgae for astaxanthin production compared to the artificial media simulated growth in indoor or outdoor photobioreactors. It is well known fact that industrial effluents are rich in various macro and micronutrients which promote algal growth but, in some condition, due to absence of some nutrients the microalgal cells of Haematococcus come in conditions of stress leading to high astaxanthin accumulation. The present review discusses microalgae responsible for producing astaxanthin under stress conditions and valorising the effluents from industrial wastewater. This is further associated with optimizing techniques for culturing microalgae with high biomass and its biocompounds. It also highlights the challenges and knowledge gaps in using wastewater as medium for large scale production of valuable biocompounds like astaxanthin, which paves way towards sustainable environment. [ABSTRACT FROM AUTHOR]

Implementation of outdoor photobioreactors has been challenged by an extremely oversaturated daily peak of solar irradiance. This study aims to understand the role of column size and paranet shading as well as to investigate the most convenient light control in outdoor cyanobacterial culture. The photobioreactor (PBR) consisted of plastic columns with a diameter of 12.74 cm (PBRd-20) and 31.85 cm (PBRd-50) laid outdoors and inclined at 158.22° upwards against solar radiation, while paranet shading was provided at 0%, 50%, 70%, and 90% shading capacity. A semi-continuous culture of cyanobacterium Arthrospira (Spirulina) platensis was conducted for 6 weeks with weekly monitoring of the growth parameter as well as the proximate and pigments content, while the daily irradiance and culture maximum temperature were recorded. The result shows that the column diameter of 12.74 cm had a lethal risk of 44.7% and this decreased to 10.5% by widening the column diameter to 31.85 cm. This lethal risk can be eliminated by the application of a paranet at a 50% reduction level for the column diameter of 31.85 cm and a 70% reduction level for the column diameter of 12.74 cm. The highest culture productivity of 149.03 mg/(L·day) was achieved with a PBRd-20 with 50% shading treatment, but a PBRd-50 with 90% shading treatment led to an increase in the protein and phycocyanin content by 66.7% and 14.91%, respectively. [ABSTRACT FROM AUTHOR]

This article delves into the role of microalgae in advancing a green economy, thereby contributing to the attainment of Sustainable Development Goals (SDGs). Microalgae, as sustainable resources, offer multifaceted benefits across various sectors, including aquaculture, agriculture, food and feed, pharmaceuticals, cosmetics, wastewater treatment, and carbon sequestration. This review highlights the versatility of microalgae in producing biofuels, high-value bioactive compounds, and bioremediation processes. It examines the technical viability and environmental sustainability of microalgae cultivation, emphasizing its low carbon footprint and resource efficiency. This article also explores the integration of microalgae into existing industrial processes, illustrating their potential to mitigate climate change, promote biodiversity, and enhance resource circularity. Challenges such as scalability, cost-effectiveness, and regulatory frameworks are discussed alongside the prospects for technological innovations and policy support to bolster the microalgae industry. By harnessing the potential of microalgae, this article underscores a pathway towards a more sustainable and greener future, aligning with the global agenda for sustainable development. [ABSTRACT FROM AUTHOR]

Amidst the global sanitation challenges of water pollution, waterborne diseases, and the alarming presence of pathogens in disinfected water, microalgal technology has emerged as a viable alternative for wastewater treatment. Recently, the ability of microalgae to remove pathogens from wastewater has been highlighted. However, a critical knowledge gap exists regarding microalgae-mediated pathogen removal mechanisms. The present study uncovers the intricate mechanisms of Chlorella pyrenoidosa-mediated Escherichia coli removal from sewage. Microalgae-induced pH increase was identified as the most crucial mechanism, followed by photooxidation and attachment, mediated by the hydroxyl group. Longer photoperiods or ultraviolet irradiation produced high oxidative stress, promoting microalgal exopolysaccharides' production and increasing pathogen entrapment. The knowledge of crucial removal mechanisms can be harnessed for the development of more efficient, innovative, and scalable microalgal systems. Such improved systems offer a sustainable solution to address water-related issues by improving wastewater treatment, increasing access to clean water, and reducing the transmission risk of waterborne diseases. [ABSTRACT FROM AUTHOR]

Highlights Local algae outdoor production on undiluted anaerobic digestate over 1-year. Dominating eukaryotes transitioned from Coelastrum to Chlorella in warmer season. Culture collapsed when pretreatment on digestate was purposefully stopped. Low cyanobacteria abundance observed in the consortium. Growing algae on anaerobic digestate could decrease the algal production cost while reducing nutrient pollution. In past work, we developed a successful biological pretreatment for digestate that enables rapid algal growth on digestate without dilution. The objective of this work was to test the effectiveness of this pretreatment in outdoor algae cultures over a year-long timeframe. The study was conducted in semi-continuous, replicated bubble column photobioreactors in Auburn, AL, USA. Algae could grow successfully in pretreated digestate during the fall, spring, and summer, achieving average growth rates of 30, 42, and 66 mg L-1 d-1, respectively. Although the cold temperatures in winter suppressed algal growth, external heating was not required to keep the cultures alive. For two weeks during the summer, the system was challenged with 100% digestate that did not undergo pretreatment, and the algal community suffered a culture collapse with a significant (p < 0.001) decrease in productivity compared to the previous batches in which pretreatment was used. Nitrogen, phosphorus, and sulfur removal were observed during robust algal growth. There was no nitrification in the photobioreactors during the initial 200 days, but evidence of nitrification emerged during the summer and persisted into the fall. Nitrospirae were detected by 16S rRNA sequencing, proving that nitrifying bacteria could adapt to high ammonium (462 - 1502 mg/L). The eukaryotic community was dominated by Coelastrum (>90%) in the cold season, and the dominance transitioned to Chlorella in the warm season (>95%) based on 18S rRNA sequencing. The low relative abundance of cyanobacteria showed that green algae were the favored photosynthetic organisms in the system. [ABSTRACT FROM AUTHOR]

Microalgae are excellent sources of biomass containing several important compounds for human and animal nutrition-proteins, lipids, polysaccharides, pigments and antioxidants as well as bioactive secondary metabolites. In addition, they have a great biotechnological potential for nutraceuticals, and pharmaceuticals as well as for CO 2 sequestration, wastewater treatment, and potentially also biofuel and biopolymer production. In this review, the industrial production of the most frequently used microalgae genera-Arthrospira, Chlorella, Dunaliella, Haematococcus, Nannochloropsis, Phaeodactylum, Porphyridium and several other species is discussed as concerns the applicability of the most widely used large-scale systems, solar bioreactors (SBRs)-open ponds, raceways, cascades, sleeves, columns, flat panels, tubular systems and others. Microalgae culturing is a complex process in which bioreactor operating parameters and physiological variables closely interact. The requirements of the biological system-microalgae culture are crucial to select the suitable type of SBR. When designing a cultivation process, the phototrophic production of microalgae biomass, it is necessary to employ SBRs that are adequately designed, built and operated to satisfy the physiological requirements of the selected microalgae species, considering also local climate. Moreover, scaling up microalgae cultures for commercial production requires qualified staff working out a suitable cultivation regime. KEY POINTS: • Large-scale solar bioreactors designed for microalgae culturing. • Most frequently used microalgae genera for commercial production. • Scale-up requires suitable cultivation conditions and well-elaborated protocols., (© 2023. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Adequate mixing is a key factor for microalgal cultivation to achieve high biomass production, so it is essential to clarify the comparative effects of different mixing methods on microalgal productivity, which has rarely been studied previously. This work therefore aimed to investigate the effects of different mixing methods (stirring, aeration, and aeration coupled with stirring) on the growth and metabolite composition of Chlorella sorokiniana SDEC-18, a strain with potential for large-scale application. The results showed that mixing was beneficial for carbohydrate accumulation, while dual mixing (aeration coupled with stirring) promoted growth and achieved the highest dry mass and metabolite productivities (including carbohydrates, proteins, and lipids) through enhancement of light energy capture in the entire system. The stirring speed in the dual mixing approach of aeration coupled with stirring was also considered: the optimal condition was found to be 800 rpm. The maximum biomass was 3.56 g L−1, and the carbohydrate productivity was as high as 119.45 mg L−1 d−1, which was the highest metabolite productivity (higher than proteins or lipids), obtained from aeration coupled with stirring at 800 rpm. Our study suggests that aeration coupled with stirring provides a feasible strategy for microalgal production, due to the optimal availability of CO2 and light achieved through effective mixing. [ABSTRACT FROM AUTHOR]

This research aims to propose management strategies to mitigate eutrophication caused by inefficient wastewater treatment plants in Colombia. The information analyzed was provided by environmental authorities such as IDEAM, CORANTIOQUIA, and CORNARE in Antioquia, where the average concentrations of phosphorus in wastewater from municipal, livestock, and industrial activities are 5.1, 30.6, and 29.1 mg P/L. The total nitrogen concentrations are 77, 143, and 121 mg N/L, respectively, surpassing the limit concentrations stated by the European Union, the United States, and Mexico, among others, while Colombia has not established its own limits. Including limitations for nutrient concentrations will align Colombia with the 2050 Sustainable Development Goals (SDGs), where microalgae species like Chlorella or Scenedesmus could be used in wastewater treatment systems for municipalities and industries. These microalgae can capture organic matter, nutrients, and greenhouse emissions and reduce the concentrations observed in natural water. They could also be an alternative for capturing heavy metals and some pollutants of emerging concern. In addition to the ecological and social benefits, the algal biomass could be valorized by transforming it into biological products such as fuels, fertilizers, and pigments when micropollutants are not present, reducing operational costs for treatment systems. [ABSTRACT FROM AUTHOR]

The recognition and use of algae in the very trend-driven cosmetic industry is progressively increasing. Up to now, the main focus was on large seaweeds and a limited number of microalgae. However, motile microalgae, flagellates, remain underscored in this aspect, although some of them are utilized commercially. Flagellates from different taxonomic groups occupy various habitats and contain bioactive high-value multifunctional compounds, some of which are novel. Moreover, they may simultaneously produce different substances, which together with the development of downstream processing technologies, makes them a promising source for modern biotechnology. The present review covers data on 411 strains, 251 species from 110 genera from 6 phyla, and is oriented generally towards less explored flagellates. It demonstrates their great potential as bearers of interesting novel compounds that can be beneficially applied in modern cosmetics. Safety aspects of both sources and products are also discussed. Considering the gaps in the knowledge, the necessity to expand the research on both well-known and yet unexplored microalgae is shown, encouraging the development of upstreaming processes, including phycoprospecting. Last but not least, this paper outlines the role of living culture collections and of using good taxonomic expertise before running the biochemical tests, cultivation, and bioengineering experiments. [ABSTRACT FROM AUTHOR]

The integration of urban agriculture into cityscapes necessitates a comprehensive understanding of multiple engineering and environmental factors, including urban fabric, building configurations, and dynamic energy and material flows. In contrast to rural settings, urban areas introduce complexities such as hygrothermal fluctuations, variable sunlight exposure and shadow patterns, diverse plant dimensions and shapes, and material interception. To address these challenges, this study presents an open-source Digital Twin model based on the use of a geographical information system (GIS) for near-real-time solar radiation mapping. This methodology aims to optimize crop productivity, enhance resilience, and promote environmental sustainability within urban areas and enables the near-time mapping of the salient features of different portions of the city using available open data. The work is structured into two main parts: (i) definition of the GIS-based Digital Twin model for mapping microclimatic variables (in particular solar radiation) to support sustainable urban agriculture design and (ii) application of the model to the city of Milan to verify its replicability and effectiveness. The key findings are connected to the possibility to integrate open data (solar radiation) with measurements in situ (illuminance and data referred to the specific crops, with related conversion coefficient) to develop a set of maps helpful for urban farmers but also for designers dealing with the synergy between buildings and urban farms. Initially tested on a neighborhood of Milan (Italy), the model will be applied in the Singapore context to verify analogies and differences. This correlation facilitates a more practical and straightforward examination of the relationships between solar irradiation and illuminance values of natural sunlight (involving both incident and diffuse light). The consistency of measurements allows for the precise documentation of these fluctuations, thereby enhancing the understanding of the influence of solar radiation on perceived luminance levels, particularly in urban environments characterized by diverse contextual factors such as vegetation, nearby structures, and geographical positioning. [ABSTRACT FROM AUTHOR]

In the green alga Chlamydomonas reinhardtii, hydrogen production is catalyzed via the [FeFe]-hydrogenases HydA1 and HydA2. The electrons required for the catalysis are transferred from ferredoxin (FDX) towards the hydrogenases. In the light, ferredoxin receives its electrons from photosystem I (PSI) so that H2 production becomes a fully light-driven process. HydA1 and HydA2 are highly O2 sensitive; consequently, the formation of H2 occurs mainly under anoxic conditions. Yet, photo-H2 production is tightly coupled to the efficiency of photosynthetic electron transport and linked to the photosynthetic control via the Cyt b6f complex, the control of electron transfer at the level of photosystem II (PSII) and the structural remodeling of photosystem I (PSI). These processes also determine the efficiency of linear (LEF) and cyclic electron flow (CEF). The latter is competitive with H2 photoproduction. Additionally, the CBB cycle competes with H2 photoproduction. Consequently, an in-depth understanding of light-driven H2 production via photosynthetic electron transfer and its competition with CO2 fixation is essential for improving photo-H2 production. At the same time, the smart design of photo-H2 production schemes and photo-H2 bioreactors are challenges for efficient up-scaling of light-driven photo-H2 production. [ABSTRACT FROM AUTHOR]

Atmospheric CO2 removal (CDR) is a fundamentally endergonic process. Performing CDR or Bioenergy with Carbon Capture and Storage (BECCS) at the gigatonne scale will produce a significant additional burden on the planet’s limited renewable energy resources irrespective of the technology employed. Harnessing photosynthesis to drive industrial-scale CO2 fixation has been of significant interest because of its minimal energy requirements and potential low costs. In this review, we evaluated the thermodynamic considerations of performing atmospheric carbon removal using microalgae and cyanobacteria versus physicochemical processes and explore the implications of these energetic costs on the scalability of each respective solution. We review the biomass productivities of recently discovered fast-growing cyanobacterial strains and discuss the prospects of genetically engineering certain metabolic pathways for channeling the fixed carbon into metabolic ‘carbon sinks’ to further enhance their CO2 capture while concurrently extracting value. We share our perspectives on how new highly productive chassis strains combined with advanced flux balance models, essentially coupling synthetic biology with industrial biotechnology, may unlock more favorable methods for CDR, both from an economic and thermodynamic perspective. [ABSTRACT FROM AUTHOR]

Chlorella vulgaris is of great importance in numerous exploratory or industrial applications (e.g., medicals, food, and feed additives). Rapid quantification of algal biomass is crucial in photobioreactors for the optimization of nutrient management and the estimation of production. The main goal of this study is to provide a simple, rapid, and not-resource-intensive estimation method for determining the algal density of C. vulgaris according to the measured parameters using UV–Vis spectrophotometry. Comparative assessment measurements were conducted with seven different methods (e.g., filtration, evaporation, chlorophyll a extraction, and detection of optical density and fluorescence) to determine algal biomass. By analyzing the entire spectra of diluted algae samples, optimal wavelengths were determined through a stepwise series of linear regression analyses by a novel correlation scanning method, facilitating accurate parameter estimation. Nonlinear formulas for spectrometry-based estimation processes were derived for each parameter. As a result, a general formula for biomass concentration estimation was developed, with recommendations for suitable measuring devices based on algae concentration levels. New values for magnesium content and the average single-cell weight of C. vulgaris were established, in addition to the development of a rapid, semiautomated cell counting method, improving efficiency and accuracy in algae quantification for cultivation and biotechnology applications. [ABSTRACT FROM AUTHOR]

Microalgae harvesting includes conventional methods like centrifugation, sedimentation, and filtration, as well as advanced methods like flocculation, magnetic nanoparticle, and flotation. Biomass recovery using centrifugation is high but high gravitational force can alter the cell structure. Sedimentation is one of the most useful methods in wastewater microalgae harvesting, though it is applicable to large-cell microalgae (>70 μm). Filtration is a low-cost method and easy to process; however, fouling and clogging can result in low yield. Among several techniques, flocculation is one of the most effective and economical approaches for biomass harvesting. Nanomaterial-based flocculants are considered due to their efficiency and reusability. Nanoparticle-based flocculants have gained attention in recent years due to their unique properties, such as high surface area, small size, and enhanced reactivity. These nanoparticles can be engineered to interact with microalgal cells, causing agglomeration and facilitating the separation of biomass from the culture medium. Studies have demonstrated that using nanoparticle-based flocculants can significantly improve the efficiency of microalgae harvesting compared to traditional flocculation methods. This review emphasizes the mechanism of flocculation, types of flocculation, the dosages of flocculants, and the flocculation recovery efficiencies. The role of green routes in synthesizing nanoparticles for the advancement of flocculation technique is especially highlighted in this article for the sustainable biodiesel production from microalgae. Thorough evaluations, encompassing techno-economic and life cycle assessments, play a crucial role in appraising the economic feasibility and environmental ramifications of biofuels derived from microalgae. This article provides an overview of flocculation methods suitable for microalgal harvesting, their mechanisms, advantages, and drawbacks. [ABSTRACT FROM AUTHOR]

The effects of turbulence on phytoplankton growth have received considerable attentions. However, the complexity of turbulence poses a significant challenge to its systematic characterization in the laboratory, resulting in relatively limited data on the effects of turbulence on several algal species. Here, a laboratory turbulence simulation system was set up to systematically investigate the growth of three common diatom species (Thalassiosira pseudonana, Skeletonema costatum, and Phaeodactylum tricornutum) under stationary and turbulent conditions (at 60, 120, 180 rpm), and measurements were taken for the algal biomass, algal photosynthetic activity, and nutrients consumption. By comparing the growth of three algae species under different turbulence exposure intensities, this study found that different algae exhibit varying sensitivities to turbulence, and therefore have different shear thresholds. Meanwhile, cell morphology is the key factor influencing the different shear threshold values observed in the three diatom species. Additionally, turbulence could impact algal aggregation and light availability, and dramatically improve nutrient uptake by phytoplankton. Our study will provides theoretical support for future endeavors in using turbulence to cultivate phytoplankton or combat algal blooms. [ABSTRACT FROM AUTHOR]

Marine microalgae offer a sustainable alternative source for the human diet's essential omega-3-fatty acids, including docosahexaenoic acid (DHA, C22:6) and eicosapentaenoic acid (EPA, C20:5). However, none of them can produce DHA and EPA in a nutritionally balanced ratio of 1:1. As shown recently, the phototrophic co-cultivation of the golden-brown microalgae Tisochrysis lutea (DHA producer) with the green microalgae Microchloropsis salina (EPA producer) can provide microalgae biomass with a balanced DHA-to-EPA ratio with increased productivity compared to monocultures. This study evaluates whether other golden-brown (Isochrysis galbana) and green microalgae (Nannochloropsis oceanica, Microchloropsis gaditana) can enable the phototrophic batch production of omega-3 fatty acids in a nutritionally balanced ratio in co-culture. All co-cultivations applying a physically dynamic climate simulation of a repeated sunny summer day in Australia in LED-illuminated flat-plate gas lift photobioreactors resulted in increased biomass concentrations compared to their respective monocultures, achieving balanced DHA-to-EPA ratios of almost 1:1. Using urea instead of nitrate as a nitrogen source increased the EPA content by up to 80% in all co-cultures. Light spectra measurements on the light-adverted side of the photobioreactor showed that increased biomass concentrations in co-cultures could have been related to enhanced light use due to the utilization of different wavelengths of the two microalgae strains, especially with the use of green light (500–580 nm) primarily by golden-brown microalgae (I. galbana) and orange light (600–620 nm) predominantly used by green microalgae (N. oceanica). Phototrophic co-cultivation processes thus promise higher areal biomass yields if microalgae are combined with complimentary light-harvesting features. [ABSTRACT FROM AUTHOR]

The enormous capability of microalgae for biomass production and co-products has recently been widely researched from a range of research approaches. Microalgae biomass has been discovered as a suitable feedstock for biofuel generation in the third generation. Although they may easily be cultivated in the laboratory, commercial cultivation involves several important considerations, including design, expense, contamination risk, and hygiene. This paper reviews some conventional microalgal cultivation methods along with some harvesting techniques. A short note on the disadvantages of conventional microalgal biofilm cultivation and the need for advanced cultivation techniques are also listed. Further, it highlights some of the modern techniques used for the cultivation of biofilm-based microalgae. It also gives brief information on the various factors affecting the formation of microalgal biofilm. A detailed description of the application of microalgal biofilm concerning biofuel generation is also reviewed. [ABSTRACT FROM AUTHOR]

Growing algae on anaerobic digestate could decrease the algal production cost while reducing nutrient pollution. In past work, we developed a successful biological pretreatment for digestate that enables rapid algal growth on digestate without dilution. The objective of this work was to test the effectiveness of this pretreatment in outdoor algae cultures over a year-long timeframe. The study was conducted in semi-continuous, replicated bubble column photobioreactors in Auburn, AL, USA. Algae could grow successfully in pretreated digestate during the fall, spring, and summer, achieving average growth rates of 30, 42, and 66 mg L-1 d-1, respectively. Although the cold temperatures in winter suppressed algal growth, external heating was not required to keep the cultures alive. For two weeks during the summer, the system was challenged with 100% digestate that did not undergo pretreatment, and the algal community suffered a culture collapse with a significant (p < 0.001) decrease in productivity compared to the previous batches in which pretreatment was used. Nitrogen, phosphorus, and sulfur removal were observed during robust algal growth. There was no nitrification in the photobioreactors during the initial 200 days, but evidence of nitrification emerged during the summer and persisted into the fall. Nitrospirae were detected by 16S rRNA sequencing, proving that nitrifying bacteria could adapt to high ammonium (462 - 1502 mg/L). The eukaryotic community was dominated by Coelastrum (>90%) in the cold season, and the dominance transitioned to Chlorella in the warm season (>95%) based on 18S rRNA sequencing. The low relative abundance of cyanobacteria showed that green algae were the favored photosynthetic organisms in the system. [ABSTRACT FROM AUTHOR]

Astaxanthin is the main natural C40 carotenoid used worldwide in the aquaculture industry. It normally occurs in red yeast Phaffia rhodozyma and green alga Haematococcus pluvialis and a variety of aquatic sea creatures, such as trout, salmon, and shrimp. Numerous biological functions reported its antioxidant and anti-inflammatory activities since astaxanthin possesses the highest oxygen radical absorbance capacity (ORAC) and is considered to be over 500 more times effective than vitamin E and other carotenoids such as lutein and lycopene. Thus, synthetic and natural sources of astaxanthin have a commanding influence on industry trends, causing a wave in the world nutraceutical market of the encapsulated product. In vitro and in vivo studies have associated astaxanthin's unique molecular features with various health benefits, including immunomodulatory, photoprotective, and antioxidant properties, providing its chemotherapeutic potential for improving stress tolerance, disease resistance, growth performance, survival, and improved egg quality in farmed fish and crustaceans without exhibiting any cytotoxic effects. Moreover, the most evident effect is the pigmentation merit, where astaxanthin is supplemented in formulated diets to ameliorate the variegation of aquatic species and eventually product quality. Hence, carotenoid astaxanthin could be used as a curative supplement for farmed fish, since it is regarded as an ecologically friendly functional feed additive in the aquaculture industry. In this review, the currently available scientific literature regarding the most significant benefits of astaxanthin is discussed, with a particular focus on potential mechanisms of action responsible for its biological activities. Highlights: Beneficial use of astaxanthin as a feed supplement in cultured aquatic species. Screening of astaxanthin in pigmentation, growth and immunity enhancement, inflammatory response, and disease resistance of aquatic species. Astaxanthin prevents several diseases associated with oxidative stress in aquatic animals. [ABSTRACT FROM AUTHOR]

Marine macroalgae – next-generation renewable feedstock is a potential solution to the growing need for sustainable future resources, with seaweed protein to cater to the ever-increasing demand of feeding the fast-growing population. The conventional cultivation methods for marine macroalgae are impeded by low productivity, seasonal constraints, and climate change issues, necessitating improved cultivation strategies. The present study demonstrates the use of tank-based (T-PBR) and vertical (V-PBR) outdoor photobioreactors for free-floating substrate-independent land-based cultivation of filamentous green seaweed Enteromorpha prolifera. Optimization of the stocking density (SD) for seasonal variation was carried out to attain maximal biomass productivity. The study demonstrated biomass production with average annual productivity of 480 g fw m−2 d−1 in V-PBR and 413 g fw m−2 d−1 in T-PBR. The season-specific SD, carbon dioxide supplementation (5%), and nutrient supply management ensured a year-round consistent supply of E. prolifera biomass. In spite of seasonal variation in biomass quality and quantity, an annual average content of 24% protein and 51% carbohydrate was observed. The present work substantiates the advancement of land-based seaweed cultivation for sustainable vegan protein production. [Display omitted] • Year-round outdoor cultivation of macroalgae Enteromorpha prolifera biomass. • Tank and vertical photobioreactors for improved land-based cultivation. • Optimized stocking density and CO 2 supplementation improve biomass productivity. • Consistent biomass supply for the macroalgal biorefinery. • Demonstrates the potential for advancing vegan sea protein production. [ABSTRACT FROM AUTHOR]

Ever since agriculture started, plants have been bred to obtain better yields, better fruits, or sustainable products under uncertain biotic and abiotic conditions. However, a new way to obtain products from plant cells emerged with the development of recombinant DNA technologies. This led to the possibility of producing exogenous molecules in plants. Furthermore, plant chemodiversity has been the main source of pharmacological molecules, opening a field of plant biotechnology directed to produce high quality plant metabolites. The need for different products by the pharma, cosmetics agriculture and food industry has pushed again to develop new procedures. These include cell production in bioreactors. While plant tissue and cell culture are an established technology, beginning over a hundred years ago, plant cell cultures have shown little impact in biotechnology projects, compared to bacterial, yeasts or animal cells. In this review we address the different types of bioreactors that are currently used for plant cell production and their usage for quality biomolecule production. We make an overview of Nicotiana tabacum, Nicotiana benthamiana, Oryza sativa, Daucus carota, Vitis vinifera and Physcomitrium patens as well-established models for plant cell culture, and some species used to obtain important metabolites, with an insight into the type of bioreactor and production protocols. [ABSTRACT FROM AUTHOR]

Increasing the volume of untreated and inadequately treated municipal wastewater undermines the circular economy potential of wastewater resources, particularly in low-income regions. This present study focused on and evaluated the performance of native microalgae-activated sludge (MAS) growth for tertiary treatment of anaerobically digested wastewater from an up-flow anaerobic sludge blanket (UASB) in an outdoor lab-scale photobioreactor (2.2 L). Three conditions with distinct MAS inoculum concentrations alongside three controls were operated in batch mode for 5 days hydraulic retention time (HRT) at 11.5:12.5 photo-hours. The MAS inoculum concentration influenced the treatment outcome. The best performance was observed when the MAS concentration was 0.10/0.20 g L−1, and the cell density was 1.60 × 107 cells mL−1, total biomass productivity of 0.10 g TSS L−1 d−1, total phosphorus uptake of 85.1%, and total nitrogen uptake of 66.1%. Logarithmic removal (Log-Re) of bacterial pathogens (water quality indicators) showed Log-Re 3.4 for total coliforms (1.37 × 102 CFU 100 mL−1) and 4.7 for Escherichia coli (0.00 × 100 CFU 100 mL−1). The results revealed optimum remediation performance and nutrient recovery potential with appropriate inoculum concentration, in admiration to advancing the science of circular economy. [ABSTRACT FROM AUTHOR]

Large amounts of astaxanthin (about 4% DW) can be produced under nitrogen starvation of Haematococcus pluvialis in photobioreactors (PBRs) exposed to high light conditions to induce a light stress. However, in PBR, the large biomass concentration usually achieved leads to strong light attenuation conditions, which makes complex the analysis of this "light stress". This study aims to elucidate the role of light transfer in astaxanthin cell content and productivity from the microalga Haematococcus pluvialis during nitrogen starvation. Haematococcus pluvialis was cultivated in a flat-panel PBR in a batch mode with sudden nitrogen starvation conditions and an incident photon flux density (PFD) of 250 µmolhν m−2 s−1. Different initial biomass concentrations ( C x 0 ) were evaluated, 0.21, 0.52, 1.39 and 2.21 kg m−3. As a result, spectral mass absorption cross-sections of Haematococcus pluvialis were measured at different times during nitrogen starvation, and were used to relate the mean rate of photon absorption (MRPA) to the astaxanthin productivity. A minimum initial MRPA of 7000 ± 500 µmolhν kgx−1 s−1 was found necessary to trigger large accumulation of astaxanthin in Haematococcus pluvialis cells (up to 3.21% DW) during nitrogen starvation conditions. The results also demonstrated the link between the MRPA and the daily astaxanthin productivity of Haematococcus pluvialis cultures, introducing then the MRPA as a physical quantity of interest for a rational optimization of the light culture conditions in PBRs. [ABSTRACT FROM AUTHOR]

Microalgae have gained attention as a promising source of chlorophylls and carotenoids in various industries. However, scaling up of conventional bubble columns presents challenges related to cell sedimentation and the presence of non-photosynthetic cells due to non-circulating zones and decreased light accessibility, respectively. Therefore, this study aimed to evaluate the newly developed continuously circulated bioreactor ROSEMAX at both laboratory and pilot scales, compared to a conventional bubble column. There was no significant difference in the biomass production and photosynthetic pigment content of Tetraselmis sp. cultivated at the laboratory scale (p > 0.05). However, at the pilot scale, the biomass cultured in ROSEMAX showed significantly high biomass (1.69 ± 0.11 g/L, dry weight, DW), chlorophyll-a (14.60 ± 0.76 mg/g, DW), and total carotene (5.64 ± 0.81 mg/g, DW) concentrations compared to the conventional bubble column (1.17 ± 0.11 g/L, DW, 10.67 ± 0.72 mg/g, DW, 3.21 ± 0.56 mg/g, DW, respectively) (p ≤ 0.05). Flow cytometric analyses confirmed that the proportion of Tetraselmis sp. live cells in the culture medium of ROSEMAX was 32.90% higher than that in the conventional bubble column, with a photosynthetic efficiency 1.14 times higher. These results support suggestions to use ROSEMAX as a bioreactor for industrial-scale applications. [ABSTRACT FROM AUTHOR]

Climate change and global warming have led to more frequent harmful algal blooms in the last decade. Among these blooms, Heterosigma akashiwo, a golden-brown phytoflagellate, is one of the 40 species with a high potential to form harmful blooms, leading to significant fish mortality. Climate change leads to rising atmospheric and ocean temperatures. These changes, along with altered rainfall patterns and meltwater input, can cause fluctuations in ocean salinity. Elevated atmospheric carbon dioxide (CO 2 ) levels increase water acidity as oceans absorb CO 2 . This study investigated the effects of temperature, salinity, and CO 2 levels on lipid production, hemolytic activity, and toxicity of H. akashiwo using the design of experiment approach, which can be used to investigate the effect of two or more factors on the same response simultaneously in a precise manner with fewer experiments and materials but in a larger region of the factor space. The lipid content was measured using a high-throughput Nile Red method, and the highest level of lipid content was detected at 25°C, a salinity of 30, and a CO 2 concentration of 400 ppm. Hemolytic activity was assessed using rabbit blood erythrocytes in a 96-well plate, and the optimal conditions for achieving the highest hemolytic activity were determined at 15°C, a salinity of 10, and a CO 2 concentration of 400 ppm. As the chemical structure of the toxin is not known, we used the toxicity against the cell line RTgill-W1 as the cell toxicity proxy. The maximum toxicity was identified at 15°C, a salinity of 10, and a CO 2 level of 700 ppm., (© 2024 The Author(s). Journal of Phycology published by Wiley Periodicals LLC on behalf of Phycological Society of America.)

Microalgae are a rich resource of lipids, proteins, carbohydrates and pigments with nutritional and health benefits. They increasingly find use as ingredients in functional foods and feeds as well as in cosmetics and agricultural products including biostimulants. One of their distinct advantages is their ability to grow on wastewaters and other waste streams, and they are considered an environmentally friendly and cheap method to recover nutrients and remove pollutants from the environment. However, there are limits concerning their applications if grown on certain waste streams. Within, we collate an overview of existing algal applications and current market scenarios for microalgal products as foods and feeds along with relevant legislative requirements concerning their use in Europe and the United States. Microalgal compounds of interest and their extraction and processing methodologies are summarized, and the benefits and caveats of microalgae cultivated in various waste streams and their applications are discussed. [ABSTRACT FROM AUTHOR]

Algae have been explored for renewable energy, nutraceuticals, and value‐added products. However, low lipid yield is a significant impediment to its commercial viability. Genetic engineering can improve the fatty acid profile of algae without compromising its growth. This study introduced the diacylglycerol acyltransferase (BnDGAT) gene from Brassica napus into Chlorella sorokiniana‐I, a fast‐growing and thermotolerant natural strain isolated from wastewater, which increased its intracellular lipid accumulation. Hygromycin‐resistant cells were selected, and enhanced green florescence protein fluorescence was used to distinguish pure transgenic cell lines from mixed cultures. Compared to the wild type, BnDGAT expression in transgenic C. sorokiniana‐I caused a threefold increase in non‐polar lipid and a twofold increase in polyunsaturated fatty acids. Nile red staining reaffirmed the presence of higher intracellular lipid bodies in transgenic cells. There was a substantial alteration in the fatty acid profile of transgenic alga expressing BnDGAT. The non‐essential omega 9 (C18: 1) fatty acid decreased (5%–7% from 18%), while alpha‐linolenic acid, an essential omega 3 fatty acid (C18: 3), was increased (23%–24% from 11%). This study substantiates a valuable strategy for enhancing essential omega‐3 fatty acids and neutral lipids to improve its nutritional value for animal feed. The increased lipid productivity should reduce the cost of producing fatty acid methyl esters (FAME). Improved FAME quality should address the clouding issues in cold regions. [ABSTRACT FROM AUTHOR]

Introduction: Nowadays, Spirulina algae is considered as a food supplement and even a healthy and useful food for human and is available in different forms such as powder, tablets, chips, etc. In addition to human consumption, Spirulina is used in aquaculture for feeding the larval stages of crustaceans and some other types of aquatic animals, to prepare livestock and poultry feed, and for cosmetic and industrial purposes. This study was carried out to evaluate the water capacity of the country's first deep aquifer well located in the Seistan region for the cultivation of Spirulina platensis. Materials and methods: Six treatments including deep aquifer well water with high salinity of 25, 12.5, and 5 ppt (Seistan deep aquifer well without changing salinity, deep water diluted with distilled water to 12.5 ppt salinity and 5 ppt) and tap water with high salinity of 25, 12.5 and 5 (prepared from Urmia Lake salt) were prepared. Spirulina algae was cultivated under standard conditions including temperature 30 ± 2 °C, light 37 µmol/m²/s; 16 hours light and 8 hours darkness for 21 days. At the end of the test period, the growth indicators and pigment concentration of the produced algae were measured, and by comparing the data obtained in different treatments, the ability of deep aquifer well water to grow Spirulina algae was determined. Results and discussion: The results showed that the highest biomass was obtained in the treatment of tap water and Urmia salt (2.91 ± 0.14 g/L) and the growth rate in the treatments containing deep aquifer water was lower than the other treatments. Conclusions: The cultivation of Spirulina in the water of deep well (No. 1 Seistan) has a low efficiency compared to tap water, and it is necessary to modify and change its composition in some way so that Spirulina can be cultivated in with proper efficiency. [ABSTRACT FROM AUTHOR]

Microalgae can form renewable feedstock for many sectors. However, most microalgae commercially cultivated are difficult to grow in colder climates. To overcome this problem one could cultivate cold tolerant algae. One such alga is the red marine alga Porphyridium purpureum. It is currently often cultivated in bag systems in limited volumes. In this study we cultivated P. purpureum at pilot-scale in horizontal tubular reactors in a greenhouse. P. purpureum was grown in batch mode in a total volume of either 350, 500, 1000 or 1500 L. A total of 28 batches, spread over two years, were cultivated reaching a maximum dry weight of 1.94 g L−1. The growth was continuously monitored to calculate the productivities and growth rates. The P and N concentrations were measured frequently during four batches to calculate the P and N usage per gram biomass. To calculate CO2 fixation efficiencies the total CO2 consumption was monitored during 6 of the 28 batches. A maximum productivity and growth rate of respectively 0.195 g L−1 day−1 and 0.233 day−1 were achieved while the P and N usage varied from 3.2–6.19 and 14.5–36.6 mg g−1 biomass for P and N, respectively. Growth was supported between 10 °C and 30 °C, while temperatures above 34—35 °C proved to be detrimental. The CO2 efficiencies differed among the 6 tested periods with the highest utilization efficiency being 13.5% and the lowest a mere 1.5%. Further large-scale, continuous, tests would be needed to fully optimize the cultivation of P. purpureum in larger volumes. [ABSTRACT FROM AUTHOR]

The current intensification in agricultural pressure has resulted in the addition of excessive amounts of nutrients. While hydroponic systems have become an agricultural tool to reduce this nutrient addition, the produced nutrient-rich drainage solution, which has a negative effect in water bodies, is still a barrier that needs to be overcome. A promising alternative for nutrient recovery is the cultivation of microalgae, which require a significant quantity of nutrients for their growth. Furthermore, their biostimulant properties enhance the circularity and sustainability approach. This study evaluates microalgae growth with a hydroponic drainage solution and the use of the resulting biomass as a source for biostimulant. Three microalgae strains were tested (Desmodesmus sp., Chlorella vulgaris, and Scenedesmus obliquus) and grown at laboratory scale (0.5 and 2 L) with drainage wastewater taken from hydroponic tomato crops. Measures of OD750 and OD680 revealed Desmodesmus sp. as the strain with the best performance, achieving 1.4 and 1.8, respectively, in the 0.5 L assay and 1.08 and 1.3 in the 2 L assay. These results were confirmed in another assay that compared Desmodesmus sp. growth in drainage wastewater and in control media. Then, Desmodesmus sp. was tested at industrial scale. Results show the columnar PBR reached 1.8 g·L−1 compared to 1.1 g·L−1 achieved with raceways. Finally, the resulting biomass was tested in a biocatalysis process for biostimulant production, suggesting an innovative system to use microalgae biomass cultured in wastewater as a valuable product such as biostimulant. [ABSTRACT FROM AUTHOR]

Astaxanthin is a powerful antioxidant and is used extensively as an animal feed additive and nutraceutical product. Here, we report the use of the β-carotene hydroxylase (CBFD1) and the β-carotene ketolase (HBFD1) from Adonis aestivalis, a flowering plant, to produce astaxanthin in E. coli equipped with the P. agglomerans β-carotene pathway and an over-expressed 4-methylerythritol-phosphate (MEP) pathway or the isopentenol utilization pathway (IUP). Introduction of the over-expressed MEP pathway and the IUP resulted in a 3.2-fold higher carotenoid content in LB media at 36 h post-induction compared to the strain containing only the endogenous MEP. However, in M9 minimal media, the IUP pathway dramatically outperformed the over-expressed MEP pathway with an 11-fold increase in total carotenoids produced. The final construct split the large operon into two smaller operons, both with a T7 promoter. This resulted in slightly lower productivity (70.0 ± 8.1 µg/g·h vs. 53.5 ± 3.8 µg/g·h) compared to the original constructs but resulted in the highest proportion of astaxanthin in the extracted carotenoids (73.5 ± 0.2%). [ABSTRACT FROM AUTHOR]

Microalgal biomass represents a sustainable bioresource for various applications, such as food, nutraceuticals, pharmaceuticals, feed, and other bio-based products. For decades, its mass production has attracted widespread attention and interest. The process of microalgal biomass production involves several techniques, mainly cultivation, harvesting, drying, and pollution control. These techniques are often designed and optimized to meet optimal growth conditions for microalgae and to produce high-quality biomass at acceptable cost. Importantly, mass production techniques are important for producing a commercial product in sufficient amounts. However, it should not be overlooked that microalgal biotechnology still faces challenges, in particular the high cost of production, the lack of knowledge about biological contaminants and the challenge of loss of active ingredients during biomass production. These issues involve the research and development of low-cost, standardized, industrial-scale production equipment and the optimization of production processes, as well as the urgent need to increase the research on biological contaminants and microalgal active ingredients. This review systematically examines the global development of microalgal biotechnology for biomass production, with emphasis on the techniques of cultivation, harvesting, drying and control of biological contaminants, and discusses the challenges and strategies to further improve quality and reduce costs. Moreover, the current status of biomass production of some biotechnologically important species has been summarized, and the importance of improving microalgae-related standards for their commercial applications is noted. [ABSTRACT FROM AUTHOR]

A mathematical model is proposed to describe and simulate microalgae growth from emissions in an outdoor airlift photobioreactor. To this end, the influences of the concentration of total nitrogen, total phosphorus, CO2 present in the exhaust gases, temperature, and light intensity were considered in biomass production. The model was tested under different experimental conditions with biomass concentrations ranging from 2 g L−1 to 4.5 g L−1. Furthermore, the accuracy of the airlift photobioreactor simulations was greater than 90 %. Thus, the developed model was able to satisfactorily describe the experimental data, so that it can be applied in other microalgae systems for optimizing biomass production, both on laboratory and pilot scales. [ABSTRACT FROM AUTHOR]

A symbiotic microalgal-bacterial system may be an optional technology for wastewater treatment. It was composed of microalgae and activated sludge and established in the SBR to explore the effect of different dosing ratios of algae and sludge on the removal of nitrogen and phosphorus from simulated wastewater containing ammonium. It can be seen from the result that varied algae–sludge dosing ratios had a higher removal effect on COD removal, but the difference was not significant. The algal-bacterial symbiosis system had a 100% removal rate for ammonium removal on the 8th day. Relatively speaking, the removal of nutrients and related mechanisms vary with environmental conditions (inoculation rate). In general, when the additive ratio was 5:1 (algae: AS), the removal rate of TN and TP was the highest, reaching 53.85% and 85.13% in the shortest time (14 days), among them, the removal rate of ammonium and COD was 100%, and the reduction rates of Nitrite nitrogen and Nitrate nitrogen were 362.99% and 73.42%, respectively. In addition, 16S rDNA gene analysis results demonstrated that the microbial community in the reactor with algal sludge inoculation ratio of 5:1 had differences in three stages of the initial reaction, the middle reaction and the end of the reaction. Comamonadaceae, Flavobacterium, Paenarthrobacter, Mesorhizobium, Nitrobacter were enriched during the reaction operation. [ABSTRACT FROM AUTHOR]

Cultivation of microalgae and controlling its growth and performance in closed photobioreactors (PBRs) are easier than open pond systems for wastewater treatment. The performance of PBRs is influenced by geometry, hydrodynamic behavior, and mass transfer. Horizontal and vertical configurations as common designs of PBR are reviewed based on their features, advantages, and disadvantages. However, vertically operated PBRs like bubble columns are preferably used for utility-scale applications of microalgae-based processes. Moreover, an appropriate reactor design reduces the inhibitory effect of dissolved oxygen concentration produced by microalgae and consequently increases the level of available CO2 in the medium. Medium properties, superficial gas velocity, gas holdup, bubble sizes, shear stress, mixing time, sparger design, and the ratio of inner diameter to effective height are shown to influence the overall volumetric mass transfer coefficient (KLa) and PBR's performance. The vertical PBRs like bubble columns provide a high mass transfer, a short liquid circulation time, and a long frequency of light/dark cycle for utility application of microalgae. Different flow regimes are obtained in PBRs based on the gas flow rate, inner diameter, and medium properties. Hydraulic retention time as the main operational parameter is determined in a batch mode for continuous wastewater treatment. [ABSTRACT FROM AUTHOR]

Taking into account the worrying scenario of water scarcity, it is essential to enable more efficient technologies for wastewater treatment. Wastewater may be treated by conventional biological processes that remove pathogenic organisms, particulate and soluble organic compounds, and other components. However, secondary effluents from treatment plants may still contain toxic elements or high concentrations of inorganic nutrients (mainly nitrogen and phosphorus), which enable the growth of photosynthetic microorganisms in water bodies, resulting in eutrophication. In this context, cultivation of photosynthetic microorganisms in secondary wastewater from sewage treatment allows the removal of nutrients from such wastewater, reducing the possibility of eutrophication. Moreover, microalgal biomass, produced in this tertiary wastewater treatment, may be harvested by different methods with the potential for different applications, such as fertilizer and biofuel. [ABSTRACT FROM AUTHOR]

Microalgae have recently attracted considerable interest worldwide, due to their extensive application potential in the renewable energy, biopharmaceutical, and nutraceutical industries. For microalgal production, the choice of the photobioreactor, the method of cultivation used, and the harvesting regime adopted (batch, semi-continuous or continuous cultures) are very important. In this work, we examined the growth rate and productivity of a small volume experimental culture in batch and semi-continuous mode. Several microalgae species have been investigated for their potential as valueadded products, thus we have chosen two species: green microalga (Nannochloropsis gaditana) and a cyanobacterium (Arthrospira platensis). This study develops a simple model by which biomass values in semicontinuous operation can be predicted from kinetic growth parameters obtained from a shorter batch experiment. Based on results, biomass concentrations and volumetric productivity in semi-continuous operation were successfully predicted. [ABSTRACT FROM AUTHOR]

Carotenoids are the most abundant lipid-soluble phytochemicals and are used as dietary supplements to protect against diseases caused by oxidative stress. Astaxanthin, a xanthophyll carotenoid, is a very potent antioxidant with numerous beneficial effects on cellular functions and signaling pathways. In this study, using spleen cells from healthy Balb/c mice, we report the bio-functional effects of an astaxanthin-rich extract (EXT) prepared from the microalga Haematococcus pluvialis and its astaxanthin monoesters-rich fraction (ME) and astaxanthin diesters-rich fraction (DE) obtained by fractionation of EXT using countercurrent chromatography (CCC). After incubation under standard culture conditions (humidity, 37 °C, 5% CO2, atmospheric oxygen), the viability of untreated splenocytes, as determined by the trypan blue exclusion assay, the MTT assay, and the neutral red assay, decreases to approximately 75% after 24 h compared with naïve splenocytes. This effect correlated with the decrease in mitochondrial membrane potential and the transition of ~59% of cells to the early stage of apoptosis, as well as with the decreased ROS production, indicating that hyperoxia in cell-culture deteriorates cell functions. They are restored or stimulated by co-cultivation with EXT, ME, and DE up to 10 µg/mL in the order EXT > DE > ME, suggesting that esterification increases bioavailability to cells in vitro. ROS and H2O2 concentrations reflect mRNA transcriptional activity of Nrf2, superoxide dismutase 1 (SOD1), catalase, and glutathione peroxidase 1, as well as SOD-mediated ROS conversion, whereas they inversely correlate with iNOS-mediated NO production. The highest-tested concentration of EXT, ME, and DE (40 µg/mL) is detrimental to cells, probably because of the overwhelming scavenging activity of astaxanthin and its esters for the reactive oxygen/nitrogen species required for cellular functions and signal transduction at low physiological concentrations. In this study, we demonstrate that differential activities of ME and DE contribute to the final antioxidant and cytoprotective effects of astaxanthin extract, which is beneficial in preventing a wide range of ROS-induced adverse effects, with DE being more effective. In addition, the selection of physioxia-like conditions for pharmacological research is highlighted. [ABSTRACT FROM AUTHOR]

In this study, the growth and productivity of five commercially important microalgae, Chroococcus sp., Haematococcus pluvialis, Dunaliella sp., Coelastrella saipanensis, and Chlorella sp., grown in different volume-to-surface area (V/S) ratios (1:1, 1:1.2, 1:1.28, 1:1.3, 1:1.6, 1:2.22, 1:4.16 and 1:6) were assessed based on their cell number, biomass, pigment content, carbohydrate, protein, photosynthetic O2 evolution, and dark respiration. The findings reveal that varied V/S ratios have significant effects on productivity and photosynthesis of each microalga. Hence, for culture system-photobioreactor design, the V/S ratio is to be considered as one of the important parameters. Photobioreactors play a significant role in the production of desired and environmentally benign products from microalgae. It is still challenging to design bioreactors for microalgal production. This study results show that H. pluvialis, Dunaliella sp., and C. saipanensis, potential microalgae for commercial production, have the highest cell number and biomass in the V/S ratio of 1:6, which mimic a tubular bioreactor. The Chroococcus sp. and Chlorella sp. are grown well in 1:4.16 V/S ratio which resemble flat-panel bioreactors. The carbohydrate, protein, and total chlorophyll concentrations also varying according to the V/S ratios. Through this study, it is evident that volume and surface area of culture system have significant effect on algae growth. The productivity of the algae is varying with V/S ratios, suggesting that specific V/S ratio is significant for designing photobioreactor. This laboratory experiment of growing microalgae in different volume to surface area influence the growth and productivity would provide cost effective quick baseline information to work further for selecting suitable bioreactors/culture system for large scale cultivation. [ABSTRACT FROM AUTHOR]