Marine Microalgae Contribution to Sustainable Development

Commercial paper as a promising carrier for biofilm cultivation of Chlorella sp. for the treatment of anaerobic digestate food effluent (ADFE): Effect on the photosynthetic efficiency

Microalgal technology is still economically unattractive due to the high cost associated with microalgal cultivation and biomass recovery from conventional suspension cultures. Biofilm-based cultivation is a promising alternative for higher biomass yield and cheap/easy biomass harvesting opportunities. Additionally, using anaerobic digestate food effluent (ADFE) as a nutrient source reduces the cultivation cost and achieves ADFE treatment as an added value. However, the search for locally available, inexpensive, and efficient support materials is still open to research. This study evaluates the potential of commercially available, low-cost papers as support material for biofilm cultivation of Chlorella sp. and treatment of ADFE. Among the four papers screened for microalgal attachment, quill board paper performed better in higher biomass yield and stability throughout the study period. The attached growth study was done in a modular food container vessel, using anaerobic digestate food effluent (ADFE) as a nutrient source and a basal medium as a control. The microalgae grew well on the support material with higher biomass yield and productivity of 108.64 g(DW) m-2 and 9.96 g (DW) m-2 d-1, respectively, in the ADFE medium compared with 85.87 g (DW) m-2 and 4.99 g (DW) m-2 d-1, respectively in the basal medium. Chlorophyll, a fluorescence (ChlF) probe, showed that cell density in the biofilm significantly changes the photosynthetic apparatus of the algae, with evidence of stress observed as the culture progressed. Also, efficient nutrient removal from the ADFE medium was achieved in the 100 %, 85 %, and 40.2 % ratios for ammoniacal nitrogen, phosphate, and chemical oxygen demand (COD). Therefore, using quill board paper as carrier material for microalgal cultivation offers promising advantages, including high biomass production, easy biomass harvesting (by scrapping or rolling the biomass with the paper), and efficient effluent treatment.

Cultivation of the polyextremophile Cyanidioschyzon merolae 10D during summer conditions on the coast of the Red Sea and its adaptation to hypersaline sea water

The west coast of the Arabian Peninsula borders the Red Sea, a water body which maintains high average temperatures and increased salinity compared to other seas or oceans. This geography has many resources which could be used to support algal biotechnology efforts in bio-resource circularity. However, summer conditions in this region may exceed the temperature tolerance of most currently cultivated microalgae. The Cyanidiophyceae are a class of polyextremophilic red algae that natively inhabit acidic hot springs. C. merolae 10D has recently emerged as an interesting model organism capable of high-cell density cultivation on pure CO₂ with optimal growth at elevated temperatures and acidic pH. C. merolae biomass has an interesting macromolecular composition, is protein rich, and contains valuable bio-products like heat-stable phycocyanin, carotenoids, β-glucan, and starch. Here, photobioreactors were used to model C. merolae 10D growth performance in simulated environmental conditions of the mid-Red Sea coast across four seasons, it was then grown at various scales outdoors in Thuwal, Saudi Arabia during the Summer of 2022. We show that C. merolae 10D is amenable to cultivation with industrial-grade nutrient and CO₂ inputs outdoors in this location and that its biomass is relatively constant in biochemical composition across culture conditions. We also show the adaptation of C. merolae 10D to high salinity levels of those found in Red Sea waters and conducted further modeled cultivations in nutrient enriched local sea water. It was determined that salt-water adapted C. merolae 10D could be cultivated with reduced nutrient inputs in local conditions. The results presented here indicate this may be a promising alternative species for algal bioprocesses in outdoor conditions in extreme coastal desert summer environments.

Responses and tolerance mechanisms of microalgae to heavy metal stress: A review

Microalgae, the primary producers in water ecosystems, are the main food of fish and shrimp. Microalgae have a great capacity to absorb heavy metals, and low concentrations of heavy metals can promote the growth of them. But high concentrations have a strong influence on the physiological and biochemical processes in algae, such as growth, photosynthesis, cell ultrastructure, protein content and fatty acid composition. Heavy metals may also induce the formation of reactive oxygen species (ROS), which causes the oxidation damage of protein, lipid and thiol peptides, and activates the antioxidant system. Heavy metals can be removed or converted into another state by biosorption of cell surface, accumulation in cells, combining with antioxidant enzymes and so on. This review summarized the responses of microalgae to heavy metals and comprehensively described the removal and tolerance mechanisms by extracellular adsorption and intracellular accumulation, which are helpful to treat pollution and improve the culture of microalgae.

Role of microalgae in achieving sustainable development goals and circular economy

In 2015, the United Nations General Assembly (UNGA) set out 17 Sustainable Development Goals (SDGs) to be achieved by 2030. These goals highlight key objectives that must be addressed. Each target focuses on a unique perspective crucial to meeting these goals. Social, political, and economic issues are addressed to comprehensively review the main issues combating climate change and creating sustainable and environmentally friendly industries, jobs, and communities. Several mechanisms that involve judicious use of biological entities are among instruments that are being explored to achieve the targets of SDGs. Microalgae have an increasing interest in various sectors, including; renewable energy, food, environmental management, water purification, and the production of chemicals such as biofertilizers, cosmetics, and healthcare products. The significance of microalgae also arises from their tendency to consume CO2, which is the main greenhouse gas and the major contributor to the climate change. This work discusses the roles of microalgae in achieving the various SDGs. Moreover, this work elaborates on the contribution of microalgae to the circular economy. It was found that the microalgae contribute to all the 17th SDGs, where they directly contribute to 9th of the SDGs and indirectly contribute to the rest. The major contribution of the Microalgae is clear in SDG-6 "Clean water and sanitation", SDG-7 "Affordable and clean energy", and SDG-13 "Climate action". Furthermore, it was found that Microalgae have a significant contribution to the circular economy.

Could Chlorella pyrenoidosa be exploited as an alternative nutrition source in aquaculture feed? A study on the nutritional values and anti-nutritional factors

This work attempted to identify if microalgal biomass can be utilized as an alternative nutrition source in aquaculture feed by analyzing its nutritional value and the anti-nutritional factors (ANFs). The results showed that Chlorella pyrenoidosa contained high-value nutrients, including essential amino acids and unsaturated fatty acids. The protein content in C. pyrenoidosa reached 52.4%, suggesting that microalgal biomass can be a good protein source for aquatic animals. We also discovered that C. pyrenoidosa contained some ANFs, including saponin, phytic acid, and tannins, which may negatively impact fish productivity. The high-molecular-weight proteins in microalgae may not be effectively digested by aquatic animals. Therefore, based on the findings of this study, proper measures should be taken to pretreat microalgal biomass to improve the nutritional value of a microalgae-based fish diet.

Year-round sustainable biomass production potential of Nannochloris sp. in outdoor raceway pond enabled through strategic photobiological screening

Microalgae cultivation utilizes the energy of sunlight to reduce carbon dioxide (CO₂) for producing renewable energy feedstock. The commercial success of the biological fixation of carbon in a consistent manner depends upon the availability of a robust microalgae strain. In the present work, we report the identification of a novel marine Nannochloris sp. through multiparametric photosynthetic evaluation. Detailed photobiological analysis of this strain has revealed a smaller functional antenna, faster relaxation kinetics of non-photochemical quenching, and a high photosynthetic rate with increasing light and temperatures. Furthermore, laboratory scale growth assessment demonstrated a broad range halotolerance of 10-70 parts per thousand (PPT) and high-temperature tolerance up to 45 °C. Such traits led to the translation of biomass productivity potential from the laboratory scale (0.2-3.0 L) to the outdoor 50,000 L raceway pond scale (500-m²) without any pond crashes. The current investigation revealed outdoor single-day peak areal biomass productivity of 43 g m^-2 d^-1 in summer with an annual (March 2019-February 2020) average productivity of 20 g m^-2 d^-1 in seawater. From a sustainability perspective, this is the first report of successful round-the-year (> 347 days) multi-season (summer, monsoon, and winter) outdoor cultivation of Nannochloris sp. in broad seawater salinity (1-57 PPT), wide temperature ranges (15-40 °C), and in fluctuating light conditions. Concurrently, outdoor cultivation of this strain demonstrated conducive fatty acid distribution, including increased unsaturated fatty acids in winter. This inherent characteristic might play a role in protecting photosynthesis machinery at low temperatures and in high light stress. Altogether, our marine Nannochloris sp. showed tremendous potential for commercial scale cultivation to produce biofuels, food ingredients, and a sustainable source for vegetarian protein.

Extraction and purification of phycobiliproteins from algae and their applications

Microalgae, macroalgae and cyanobacteria are photosynthetic microorganisms, prokaryotic or eukaryotic, living in saline or freshwater environments. These have been recognized as valuable carbon sources, able to be used for food, feed, chemicals, and biopharmaceuticals. From the range of valuable compounds produced by these cells, some of the most interesting are the pigments, including chlorophylls, carotenoids, and phycobiliproteins. Phycobiliproteins are photosynthetic light-harvesting and water-soluble proteins. In this work, the downstream processes being applied to recover fluorescent proteins from marine and freshwater biomass are reviewed. The various types of biomasses, namely macroalgae, microalgae, and cyanobacteria, are highlighted and the solvents and techniques applied in the extraction and purification of the fluorescent proteins, as well as their main applications while being fluorescent/luminescent are discussed. In the end, a critical perspective on how the phycobiliproteins business may benefit from the development of cost-effective downstream processes and their integration with the final application demands, namely regarding their stability, will be provided.

Centrate as a sustainable growth medium: Impact on microalgal inocula and bacterial communities in tubular photobioreactor cultivation systems

Centrate is a low-cost alternative to synthetic fertilizers for microalgal cultivation, reducing environmental burdens and remediation costs. Adapted microalgae need to be selected and characterised to maximise biomass production and depuration efficiency. Here, the performance and composition of six microalgal communities cultivated both on synthetic media and centrate within semi-open tubular photobioreactors were investigated through Illumina sequencing. Biomass grown on centrate, exposed to a high concentration of ammonium, showed a higher quantity of nitrogen (5.6% dry weight) than the biomass grown on the synthetic media nitrate (3.9% dry weight). Eukaryotic inocula were replaced by other microalgae while cyanobacterial inocula were maintained. Communities were generally similar for the same inoculum between media, however, inoculation with cyanobacteria led to variability within the eukaryotic community. Where communities differed, centrate resulted in a higher richness and diversity. The higher nitrogen of centrate possibly led to higher abundance of genes coding for N metabolism enzymes.

An overview on microalgae as renewable resources for meeting sustainable development goals

The increased demands and dependence on depleted oil reserves, accompanied by global warming and climate change have driven the world to explore and develop new strategies for global sustainable development. Among sustainable biomass sources, microalgae represent a promising alternative to fossil fuel and can contribute to the achievement of important Sustainable Development Goals (SDGs). This article has reviewed the various applications of microalgal biomass that includes (i) the use in aquaculture and its sustainability; (ii) commercial value and emerging extraction strategies of carotenoids; (iii) biofuels from microalgae and their application in internal combustion engines; (iv) the use and reuse of water in microalgae cultivation; and (v) microalgae biotechnology as a key factor to assist SDGs. The future prospects and challenges on the microalgae circular bio economy, issues with regard to the scale-up and water demand in microalgae cultivation are also highlighted.

Fucoxanthin Production of Microalgae under Different Culture Factors: A Systematic Review

Fucoxanthin is one of the light-harvesting pigments in brown microalgae, which is increasingly gaining attention due to its numerous health-promoting properties. Currently, the production of microalgal fucoxanthin is not yet feasible from an economic perspective. However, the cultivation of microalgae at favourable conditions holds great potential to increase the viability of this fucoxanthin source. Hence, this study aimed to review the fucoxanthin production of microalgae under different conditions systematically. A literature search was performed using the Web of Science, Scopus and PubMed databases. A total of 188 articles were downloaded and 28 articles were selected for the current review by two independent authors. Microalgae appeared to be a more reliable fucoxanthin source compared to macroalgae. Overall, a consensus fucoxanthin production condition was obtained and proposed: light intensity ranging from 10 to 100 µmol/m²/s could achieve a higher fucoxanthin content. However, the optimal light condition in producing fucoxanthin is species-specific. The current review serves as an antecedent by offering insights into the fucoxanthin-producing microalgae response to different culture factors via a systematic analysis. With the current findings and recommendations, the feasibility of producing fucoxanthin commercially could be enhanced and possibly achieve practical and sustainable fucoxanthin production.

Algae in wastewater treatment, mechanism, and application of biomass for production of value-added product

The pollutants can enter water bodies at various point and non-point sources, and wastewater discharge remains a major pathway. Wastewater treatment effectively reduces contaminants, it is expensive and requires an eco-friendly and sustainable alternative approach to reduce treatment costs. Algae have recently emerged as a potentially cost-effective method to remediate toxic pollutants through the mechanism of biosorption, bioaccumulation, and intracellular degradation. Hence, before discharging the wastewater into the natural environment better solutions for environmental resource recovery and sustainable developments can be applied. More importantly, algae are a potential feedstock material for various industrial applications such as biofuel production. Currently, researchers are developing algae as a source for pharmaceuticals, biofuels, food additives, and bio-fertilizers. This review mainly focused on the potential of algae and their specific mechanisms involved in wastewater treatment and energy recovery systems leading to important industrial precursors. The review is highly beneficial for scientists, wastewater treatment plant operators, freshwater managers, and industrial communities to support the sustainable development of natural resources.

Bioactive Compounds for Quorum Sensing Signal-Response Systems in Marine Phycosphere

Quorum sensing in the phycosphere refers to a sensor system in which bacteria secrete bioactive compounds to coordinate group behavior relying on cell density. It is an important way for algae and bacteria to communicate with each other and achieve interactions. It has been determined that quorum sensing is widely presented in the marine phycosphere, which involves a variety of bioactive compounds. Focused on these compounds in marine phycosphere, this review summarizes the types and structures of the compounds, describes the methods in detection and functional evaluation, discusses the ecological functions regulated by the compounds, such as modulating microbial colonization, achieving algae–bacteria mutualism or competition and contributing to marine biogeochemical cycles. Meanwhile, the application prospects of the compounds are also proposed, including controlling harmful algal blooms and producing biofuel. Future research should focus on improving detection techniques, developing more model systems and investigating the effects of climate change on the quorum-sensing pathway to further understand the mechanism and application potential of quorum sensing compounds. This review aims to present an overview of current research carried out in order to provide the reader with perspective on bioactive compounds involved in quorum sensing.

Bioprospecting of Microalgae Isolated from the Adriatic Sea: Characterization of Biomass, Pigment, Lipid and Fatty Acid Composition, and Antioxidant and Antimicrobial Activity

Marine microalgae and cyanobacteria are sources of diverse bioactive compounds with potential biotechnological applications in food, feed, nutraceutical, pharmaceutical, cosmetic and biofuel industries. In this study, five microalgae, Nitzschia sp. S5, Nanofrustulum shiloi D1, Picochlorum sp. D3, Tetraselmis sp. Z3 and Tetraselmis sp. C6, and the cyanobacterium Euhalothece sp. C1 were isolated from the Adriatic Sea and characterized regarding their growth kinetics, biomass composition and specific products content (fatty acids, pigments, antioxidants, neutral and polar lipids). The strain Picochlorum sp. D3, showing the highest specific growth rate (0.009 h⁻¹), had biomass productivity of 33.98 ± 0.02 mg L⁻¹ day⁻¹. Proteins were the most abundant macromolecule in the biomass (32.83–57.94%, g g⁻¹). Nanofrustulum shiloi D1 contained significant amounts of neutral lipids (68.36%), while the biomass of Picochlorum sp. D3, Tetraselmis sp. Z3, Tetraselmis sp. C6 and Euhalothece sp. C1 was rich in glycolipids and phospholipids (75%). The lipids of all studied microalgae predominantly contained unsaturated fatty acids. Carotenoids were the most abundant pigments with the highest content of lutein and neoxanthin in representatives of Chlorophyta and fucoxanthin in strains belonging to the Bacillariophyta. All microalgal extracts showed antioxidant activity and antimicrobial activity against Gram-negative E. coli and S. typhimurium and Gram-positive S. aureus.

Algae biotechnology for industrial wastewater treatment, bioenergy production, and high-value bioproducts

A growing world population is causing hazardous compounds to form at an increasingly rapid rate, calling for ecological action. Wastewater management and treatment is an expensive process that requires appropriate integration technology to make it more feasible and cost-effective. Algae are of great interest as potential feedstocks for various applications, including environmental sustainability, biofuel production, and the manufacture of high-value bioproducts. Bioremediation with microalgae is a potential approach to reduce wastewater pollution. The need for effective nutrient recovery, greenhouse gas reduction, wastewater treatment, and biomass reuse has led to a wide interest in the use of microalgae for wastewater treatment. Furthermore, algae biomass can be used to produce bioenergy and high-value bioproducts. The use of microalgae as medicine (production of bioactive and medicinal compounds), biofuels, biofertilizers, and food additives has been explored by researchers around the world. Technological and economic barriers currently prevent the commercial use of algae, and optimal downstream processes are needed to reduce production costs. Therefore, the simultaneous use of microalgae for wastewater treatment and biofuel production could be an economical approach to address these issues. This article provides an overview of algae and their application in bioremediation, bioenergy production, and bioactive compound production. It also highlights the current problems and opportunities in the algae-based sector, which has recently become quite promising.

Tocochromanol Profiles in Chlorella sorokiniana, Nannochloropsis limnetica and Tetraselmis suecica Confirm the Presence of 11′-α-Tocomonoenol in Cultured Microalgae Independently of Species and Origin

11′-α-Tocomonoenol (11′-αT1) is structurally related to vitamin E and has been quantified in the microalgae Tetraselmis sp. and Nannochloropsis oceanica. However, it is not known whether 11′-αT1 is present in other microalgae independent of species and origin. The aim of this study was to analyze the tocochromanol profiles of Chlorella sorokiniana, Nannochloropsis limnetica, and Tetraselmis suecica and to determine if 11′-αT1 is present in these microalgae. Cultured microalgae were freeze-dried and the presence and identity of α-tocomonoenols were confirmed by LC-MSn (liquid chromatography coupled to mass spectroscopy) and GC-MS (gas chromatography coupled to mass spectroscopy). Tocochromanol profiles were determined by HPLC-FLD (liquid chromatography with fluorescence detection) and fatty acid profiles (as fatty acid methyl esters; FAME) by GC-MS. As confirmed by LC-MSn and GC-MS, 11′-αT1 was the dominant αT1 isomer in cultured microalgae instead of 12′-αT1, the isomer also known as marine-derived tocopherol. αT1 represented less than 1% of total tocochromanols in all analyzed samples and tended to be more abundant in microalgae with higher proportions of polyunsaturated fatty acids. In conclusion, our findings confirm that αT1 is not restricted to terrestrial photosynthetic organisms, but can also accumulate in microalgae of different species, with 11′-αT1—and not the marine-derived tocopherol (12′-αT1)—as the predominant αT1 isomer.

Metabolic systems biology and multi-omics of cyanobacteria: Perspectives and future directions

Cyanobacteria are oxygenic photoautotrophs whose metabolism contains key biochemical pathways to fix atmospheric CO₂ and synthesize various metabolites. The development of bioengineering tools has enabled the manipulation of cyanobacterial chassis to produce various valuable bioproducts photosynthetically. However, effective utilization of cyanobacteria as photosynthetic cell factories needs a detailed understanding of their metabolism and its interaction with other cellular processes. Implementing systems and synthetic biology tools has generated a wealth of information on various metabolic pathways. However, to design effective engineering strategies for further improvement in growth, photosynthetic efficiency, and enhanced production of target biochemicals, in-depth knowledge of their carbon/nitrogen metabolism, pathway fluxe distribution, genetic regulation and integrative analyses are necessary. In this review, we discuss the recent advances in the development of genome-scale metabolic models (GSMMs), omics analyses (metabolomics, transcriptomics, proteomics, fluxomics), and integrative modeling approaches to showcase the current understanding of cyanobacterial metabolism.

Arthrospira platensis as a Feasible Feedstock for Bioethanol Production

In recent decades and to deal with the scarcity of fossil fuels, many studies have been developed in order to set up a sustainable biofuel production sector. This new sector must be efficient (high productivity), economically profitable (low production costs and therefore acceptable fuel prices), and ethical (low carbon balance, no competition with food resources). The production of bioethanol is based on the fermentation of reserve sugars, accumulated in the form of starch in microalgae and glycogen in cyanobacteria. The advantage of this bioenergy production route lies in the fact that the post-crop fermentation process is at the industrial stage since it has already been tested for many years for the production of bioethanol from agricultural resources. One of the most cultivated cyanobacteria is Arthrospira (“Spirulina”) and its production is also already at industrial scale. Depending on the cultivation conditions, this cyanobacteria is able to accumulate up to 65% DW (dry weight) of glycogen, making it a feasible feedstock for bioethanol production. The aim of this review is to provide a clear overview of these operating conditions for glycogen accumulation.