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Modern life is intimately linked to the availability of fossil fuels, which continue to meet the world's growing energy needs even though their use drives climate change, exhausts finite reserves and contributes to global political strife. Biofuels made from renewable resources could be a more sustainable alternative, particularly if sourced from organisms, such as algae, that can be farmed without using valuable arable land. Strain development and process engineering are needed to make algal biofuels practical and economically viable.

This study aimed at investigating the potential of microalgae species grown on industrial waste water as a new source of natural antioxidants. Six microalgae from different classes, including Phaeodactylum sp. (Bacillariophyceae), Nannochloropsis sp. (Eustigmatophyceae), Chlorella sp., Dunaniella sp., and Desmodesmus sp. (Chlorophyta), were screened for their antioxidant properties using different in vitro assays. Natural antioxidants, including pigments, phenolics, and tocopherols, were measured in methanolic extracts of microalgae biomass. Highest and lowest concentrations of pigments, phenolic compounds, and tocopherols were found in Desmodesmus sp. and Phaeodactylum tricornuotom microalgae species, respectively. The results of each assay were correlated to the content of natural antioxidants in microalgae biomass. Phenolic compounds were found as major contributors to the antioxidant activity in all antioxidant tests while carotenoids were found to contribute to the 1,1-diphenyl-2-picryl-hydrazil (DPPH) radical scavenging activity, ferrous reduction power (FRAP), and ABTS-radical scavenging capacity activity. Desmodesmus sp. biomass represented a potentially rich source of natural antioxidants, such as carotenoids (lutein), tocopherols, and phenolic compounds when cultivated on industrial waste water as the main nutrient source.

Extremophilic environments are rich reservoirs for discovering microorganisms with vast biotechnological potential. Among these, microalgae stand out for their pivotal role in sustainable wastewater treatment and nutrient recycling. This study introduces Coelastrella thermophile D14, a microalga isolated from a solar panel, identified through morphological studies and genomic sequencing. The genus Coelastrella has been characterized and classified as highly productive strains valuable for biofuel and bioproduct generation as well as for their ability to produce significant amounts of carotenoids. Experiments revealed the extraordinary resilience of this strain to prolonged desiccation and high-strength piggery wastewater. Notably, D14 cultivated in 10% pig effluent exhibited biostimulant properties, achieving a germination index 23% higher than the control on Lepidium sativum . In a groundbreaking development, we have successfully established an Agrobacterium -mediated transformation protocol for C. thermophila D14, optimizing key parameters for effective T-DNA transfer. This marks a pioneering achievement within the genus Coelastrella . These findings highlight the significant potential of D14 as a robust platform for future biotechnological applications, opening new opportunities for innovative solutions, especially in environmental protection and sustainable agriculture. Graphical Abstract Key points • First microalga from solar panel biofilm: Coelastrella sp. D14 isolated and characterized. • Strain D14 tolerates prolonged desiccation and grows well in piggery wastewater. • Stable Agrobacterium-mediated transformation enables future metabolic engineering.

Microalgae culture collections may contain unexplored strains with great biotechnological potential. Through sampling, identification, characterization, and maintenance of local strains, part of the work described here led to the establishment of the first public Swiss microalgae culture collection, AlgoScope. The potential biotechnological applications of 7 strains from among over 120 native strains were suggested based on growth parameters and biochemical composition. Under standardized growth conditions, Tetradesmus obliquus FAM 27852 and FAM 27855, Chloroidium saccharophilum FAM 27962, Chlorella vulgaris FAM 27965, Stichococcus sp. FAM 27986, Desmodesmus sp. FAM 28090, and Tetranephris brasiliensis FAM 28097 had growth rates of 0.24 d −1 –0.80 d −1 and biomass productivities of 0.24 g L −1 d −1 –0.73 g L −1 d −1 . Proteins, lipids, carbohydrates, and ashes ranged from 32.88 to 53.54%, 9.69–18.08%, 9.32–23.94%, and 3.17–5.51%, respectively. All strains had a similar amino acid composition, containing all essential amino acids. In contrast, the fatty acid composition varied among strains, but, in general, the fatty acids were rich in PUFAs (23.83–53.49% of total fatty acids). Overall, C. saccharophilum FAM 27962 and T. brasiliensis FAM 28097 showed great potential for use in the animal feed sector.

The economic factor of the microalgae harvesting step acts as a barrier to scaling up microalgae-based technology designed for wastewater treatment. In view of that, this study presents an alternative microalgae-bacteria system, which is proposed for eliminating the economic obstacle. Instead of the microalgae-bacteria (activated algae) flocs, the study aimed to develop activated algae granules comprising the microalgae Chlorella sp. as a target species. The presence of the filamentous microalgae ( Phormidium sp.) was necessary for the occurrence of the granulation processes. A progressive decrease in frequency of the free Chlorella sp. cells was achieved once with the development of the activated algae granules as a result of the target microalgae being captured in the dense and tangled network of filaments. The mature activated algae granules ranged between 600 and 2,000 µm, and were characterized by a compact structure and significant settling ability (21.6 ± 0.9 m/h). In relation to the main aim of this study, a microalgae recovery efficiency of higher than 99% was achieved only by fast sedimentation of the granules; this performance highlighted the viability of the granular activated algae system for sustaining a microalgae harvesting procedure with neither cost nor energy inputs.

Biofilm-based algal cultivation has received increased attention as a potential platform for algal production and other applications such as wastewater treatment. Algal biofilm cultivation systems represent an alternative to the suspension-based systems that have yet to become economically viable. One major advantage of algal biofilm systems is that algae can be simply harvested through scraping and thus avoid the expensive harvesting procedures used in suspension-based harvesting such as flocculation and centrifugation. In recent years, an assortment of algal biofilm systems have been developed with various design configurations and biomass production capacities. This review summarizes the state of the art of different algal biofilm systems in terms of their design and operation. Perspectives for future research needs are also discussed to provide guidance for further development of these unique cultivation systems.

Microalgae have been widely reported as a promising source of biofuels, mainly based on their high areal productivity of biomass and lipids as triacylglycerides and the possibility for cultivation on non-arable land. The isolation and selection of suitable strains that are robust and display high growth and lipid accumulation rates is an important prerequisite for their successful cultivation as a bioenergy source, a process that can be compared to the initial selection and domestication of agricultural crops. We developed standard protocols for the isolation and cultivation for a range of marine and brackish microalgae. By comparing growth rates and lipid productivity, we assessed the potential of subtropical coastal and brackish microalgae for the production of biodiesel and other oil-based bioproducts. This study identified Nannochloropsis sp., Dunaniella salina and new isolates of Chlorella sp. and Tetraselmis sp. as suitable candidates for a multiple-product algae crop. We conclude that subtropical coastal microalgae display a variety of fatty acid profiles that offer a wide scope for several oil-based bioproducts, including biodiesel and omega-3 fatty acids. A biorefinery approach for microalgae would make economical production more feasible but challenges remain for efficient harvesting and extraction processes for some species.

Micro-algae synthesize high levels of lipids, carbohydrates and proteins photoautotrophically, thus attracting considerable interest for the biotechnological production of fuels, environmental remediation, functional foods and nutraceuticals. Currently, only a few micro-algae species are grown commercially at large-scale, primarily for “health-foods” and pigments. For a range of potential products (fuel to pharma), high lipid productivity strains are required to mitigate the economic costs of mass culture. Here we present a screen concentrating on marine micro-algal strains, which if suitable for scale-up would minimise competition with agriculture for water. Mass-Spectrophotometric analysis (MS) of nitrogen (N) and carbon (C) was subsequently validated by measurement of total fatty acids (TFA) by Gas-Chromatography (GC). This identified a rapid and accurate screening strategy based on elemental analysis. The screen identified Nannochloropsis oceanica CCAP 849/10 and a marine isolate of Chlorella vulgaris CCAP 211/21A as the best lipid producers. Analysis of C, N, protein, carbohydrate and Fatty Acid (FA) composition identified a suite of strains for further biotechnological applications e.g. Dunaliella polymorpha CCAP 19/14, significantly the most productive for carbohydrates and Cyclotella cryptica CCAP 1070/2, with utility for EPA production and N-assimilation.

The prospects of using produced water (PW), a by-product of oil extraction, as a cultivation medium to not only grow microalgae but also generate value-added by-products has not been much investigated. This study demonstrates the ability of a newly isolated microalga, Asterarcys sp. RA100, for growth in PW and biodiesel production. Although the used PW was slightly alkaline (pH < 10), nutrient deficient and high in boron content, Asterarcys sp. RA100 exhibited good growth with phosphate, and nitrate, reaching optimal growth at 1% salinity, 25°C, 150 rpm, and 4000–8000 Lux LED light intensity. To test for its scalability in a greenhouse, Asterarcys sp. RA100 exhibited areal productivity of 10.3 ± 0.5 g m –2 day –1 . Lipid accumulation in Asterarcys sp. RA100 reached 27.0 ± 5.1% of dry weight when grown in PW. The resulting fatty acids methyl esters (FAME) displayed properties aligning with international biodiesel standards. The FAME profiles showed elevated contents of palmitic acid (C16:0), elaidic acid (C18:1n9t), stearic acid (C18:0) and palmitoleic acid (C16:1n7C). This study demonstrates the immense potential of Asterarcys sp. RA100 to grow in PW and to serve as valuable feedstock for biodiesel production thereby, providing an eco-friendly method to re-use PW and sustain future energy demands.

The marine microbiome arouses an increasing interest, aimed at better understanding coral reef biodiversity, coral resilience, and identifying bioindicators of ecosystem health. The present study is a microbiome mining of three environmentally contrasted sites along the Hermitage fringing reef of La Réunion Island (Western Indian Ocean). This mining aims to identify bioindicators of reef health to assist managers in preserving the fringing reefs of La Réunion. The watersheds of the fringing reefs are small, steeply sloped, and are impacted by human activities with significant land use changes and hydrological modifications along the coast and up to mid-altitudes. Sediment, seawater, and coral rubble were sampled in austral summer and winter at each site. For each compartment, bacterial, fungal, microalgal, and protist communities were characterized by high throughput DNA sequencing methodology. Results show that the reef microbiome composition varied greatly with seasons and reef compartments, but variations were different among targeted markers. No significant variation among sites was observed. Relevant bioindicators were highlighted per taxonomic groups such as the Firmicutes:Bacteroidota ratio (8.4%:7.0%), the genera Vibrio (25.2%) and Photobacterium (12.5%) dominating bacteria; the Ascomycota:Basidiomycota ratio (63.1%:36.1%), the genera Aspergillus (40.9%) and Cladosporium (16.2%) dominating fungi; the genus Ostreobium (81.5%) in Chlorophyta taxon for microalgae; and the groups of Dinoflagellata (63.3%) and Diatomea (22.6%) within the protista comprising two dominant genera: Symbiodinium (41.7%) and Pelagodinium (27.8%). This study highlights that the identified bioindicators, mainly in seawater and sediment reef compartments, could be targeted by reef conservation stakeholders to better monitor La Réunion Island’s reef state of health and to improve management plans.