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Recently isolated microalgae Tetraselmis sp. IMP3, Tetraselmis sp. CTP4, and Skeletonema sp. were studied. The three novel strains contained relatively high levels of polyunsaturated fatty acids (PUFA) and n3 PUFA. However, highly unsaturated n3 FA contents were relatively low (5.7–13.0% of the total FA). In general, eicosapentaenoic acid (EPA, 20:5 n3) contents were low (< 6.4% of the total FA). However, in Skeletonema biomass, EPA levels were higher than 10% of the total FA. α-Linolenic acid (ALA, 18:3 n3) and 16:3 n4 were the main PUFA in Tetraselmis strains and Skeletonema, respectively. High contents of myristic (14:0) and palmitoleic (16:1 n7) acids were found in Skeletonema (exceeding 20% of the total FA in both cases), whereas the Tetraselmis strains were rich in palmitic (16:0), 15–27% of the total FA, and oleic (18:1 n9) acids, 12–19% of the total FA. Linoleic acid (18:2 n6) content was low in Skeletonema (< 1% of the total FA). This microalga had the highest total polyphenol content, reaching 300–400 mg/100 g dw. Gentisic acid was the main phenolic compound in the aqueous and ethanolic extracts of this microalga. The highest antioxidant activity was displayed by Skeletonema. The ferric ion reducing antioxidant power (FRAP) and 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) (ABTS) methods showed higher antioxidant power for Skeletonema sp. extracts, reaching an ABTS reduction of more than 80%. Concerning anti-inflammatory activity, ethanolic extracts of Skeletonema sp. exhibited the highest inhibitory capacity of cyclooxygenase-2 (COX-2), 82 ± 2%, which compares to 36 ± 9% in Tetraselmis sp. CTP4 and 45 ± 5% in Tetraselmis sp. IMP3. Aqueous extracts had always a lower anti-inflammatory capacity, 6–30%. Therefore, these microalgae have potential for multiple applications, ranging from bioactive feedstocks to aquaculture and nutraceutical uses.

The accumulation of atmospheric CO sub(2), primarily due to combustion of fossil fuels, has been implicated in potential global climate change. The high rate of CO sub(2) bioremediation by microalgae has emerged as a favourable method for reducing coal-fired power plant emissions. However, coal-fired power station flue gas contains other chemicals such as SO sub(x) which can inhibit microalgal growth. In the current study, the effect of untreated flue gas as a source of inorganic carbon on the growth of Tetraselmis in a 1000 L industrial-scale split-cylinder internal-loop airlift photobioreactor was examined. The culture medium was recycled after each harvest. Tetraselmis suecica grew very well in this airlift photobioreactor during the 7-month experiment using recycled medium from an electroflocculation harvesting unit. Increased medium SO sub(4) super(2-) concentration as high as 870 mg SO sub(4) super(2-)L super(-1) due to flue gas addition and media recycling had no negative effect on the overall growth and productivity of this alga. The potential organic biomass productivity and carbon sequestration using an industrial-scale airlift PBR at International Power Hazelwood, Gippsland, Victoria, Australia, are 178.9 plus or minus 30 mg L super(-1) day super(-1) and 89.15 plus or minus 20 mg'C'L super(-1) day super(-1), respectively. This study clearly indicates the potential of growing Tetraselmis on untreated flue gas and using recycled medium for the purpose of biofuel and CO sub(2) bioremediation.

Microalgae offer a nutritionally robust alternative to fishmeal and fish oil, helping reduce pressure on wild stocks and supporting more sustainable aquafeed production. This study explored the potential of replacing fish oil with Tetraselmis ( Tetraselmis chui ) microalgae biomass in the diet of juvenile rainbow trout (89.0 ± 1.10 g) ( Oncorhynchus mykiss ), assessing its effects on the fish’s health. A control diet containing 53% crude protein and fish oil (FO) was modified by replacing FO with Tetraselmis at three graded inclusion levels: 33% (Tetra33), 66% (Tetra66), and 100% (Tetra100). The 84-day feeding trial evaluated key growth parameters, biochemistry, liver and intestinal histo-architectures, and immune-antioxidant gene expression profiles of the experimental fish. Time-series analyses of growth performance revealed no significant treatment effects from day 14 to day 70, except at the 84-day biomass sampling. The FO (7321.65 ± 60.03g) attained a significantly greater final weight (FW) than Tetra33 (6984.70 ± 86.15g) and Tetra100 (6823.93 ± 160.42g), while remaining statistically similar to Tetra66 (7051.77 ± 107.30g). Likewise, weight gain (WG) of the FO group (5519.65 ± 57.16g) exceeded that of the Tetra100 group (5043.93 ± 142.09g) but did not differ significantly from the Tetra33 (5220.70 ± 73.95g) and Tetra66 (5281.77 ± 110.86g). The feed conversion ratios (FCRs) and specific growth rates (SGRs) of the Tetra groups were comparable to the FO control. Dietary variation did not elicit significant changes in leukocyte distribution, biochemical indices, or gene expression patterns across Tetra groups relative to the FO. Similarly, the histological analysis revealed that Tetraselmis dietary inclusions did not trigger inflammatory reactions in hepatic or intestinal tissues in the Tetra groups compared to the FO. Minor but inconsequential histological modifications were noted, such as moderated sinusoid dilation in the liver and slight changes in intestinal villi of Tetra33 fish. Health biomarker analyses indicated that replacing fish oil with Tetraselmis preserved physiological homeostasis, whereas 66% replacement (Tetra66) yielded the best growth performance compared to FO. However, longer feeding trials are necessary to confirm long-term health and nutritional outcomes.

Oxygenic photosynthetic organisms employ light-harvesting complexes (LHCs) to capture solar energy and regulate excess excitation. Tetraselmis species belong to Chlorodendrophyceae, one of the earliest-diverging lineages within core Chlorophyta. While these organisms exhibit distinctive pigment compositions, their LHC organization and function remain largely uncharacterized. Here, we examined the biochemical and spectral properties of LHC, PSI-LHCI, and PSII-LHCII complexes from Tetraselmis striata NIES-1019. Pigment analysis identified loroxanthin derivatives, loroxanthin decenoate and loroxanthin dodecenoate, in all three complexes. Notably, these carotenoids are absent in Chlamydomonas reinhardtii and Ostreococcus tauri , implying a lineage-specific adaptation. Fluorescence spectra of PSII-LHCII and PSI-LHCI from T. striata exhibited distinct characteristics compared with their counterparts in C. reinhardtii and land plants, indicating differences in pigment organization. In contrast, LHC fluorescence properties closely resembled those of green-lineage organisms, suggesting conservation of chlorophyll-binding arrangements. Phylogenetic analyses revealed that T. striata possesses LHCBM-based LHCII trimers, consistent with other core Chlorophyta, but its PSI antenna composition diverges from that of these algae. Among LHCIs in the PSI outer belt, only LHCA5a was identified, whereas LHCA4a and LHCA6a were absent, implying structural divergence from C. reinhardtii . These findings provide insights into the evolution of LHCs in Chlorophyta and the distinct pigment-protein interactions underlying Tetraselmis light-harvesting strategies.

Cell wall disrupted and dried Microchloropsis gaditana (Mg), Tetraselmis chui (Tc) and Chlorella vulgaris (Cv) microalgae biomasses, with or without ethanol pre‐treatment, were added to wheat bread at a wheat flour substitution level of 12%, to enrich bread protein by 30%. Baking performance, protein quality and basic sensory properties were assessed. Compared to wheat, Mg, Tc and Cv contain higher amounts of essential amino acids and their incorporation markedly improved protein quality in the bread (DIAAS 57–66 vs 46%). The incorporation of microalgae reduced dough strength and bread volume and increased crumb firmness. This was most pronounced for Cv and Tc but could be improved by ethanol treatment. Mg gave adequate dough strength, bread volume and crumb structure without ethanol treatment. To obtain bread of acceptable smell, appearance, and colour, ethanol treatment was necessary also for Mg as it markedly reduced the unpleasant smell and intense colour of all algae breads. Ethanol treatment reduced the relative content of lysine, but no other essential amino acids. However, it also had a negative impact on in vitro protein digestibility. Our results show that Mg had the largest potential for protein fortification of bread, but further work is needed to optimize pre‐processing and assess consumer acceptance.

Abstract Species of the genus Tetraselmis have traditionally been used as a valuable nutritional source in aquaculture for their high fatty acid content (5–10% dry weight). Their use in nutraceutical production for humans is growing worldwide. Among them, Tetraselmis chui is generally reported as rich in polyunsaturated fatty acids (PUFAs), especially eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). We evaluated the potential of three T. chui strains for the production of these nutraceuticals: the model strain CCAP 8/6, which is broadly used in the aquaculture industry due to its high PUFA content, and two strains (TCBG-1 and TCBG-2) isolated from Guanabara Bay (Rio de Janeiro, Brazil). The two Brazilian strains grew faster than CCAP 8/6 with higher percentage of PUFAs (up to 70% of total FA at the exponential growth phase). They also produced unique fatty acids in significant quantities: TCBG-1 produced arachidonic acid (ARA) and EPA during the exponential phase (> 20% of total FA), while TCBG-2 produced these PUFAs in addition to DHA (> 18% of total FA) at the late exponential phase. A two-stage growth system using co-cultures of the two Brazilian strains is proposed as an optimal model for PUFA production, based on their simultaneous scaling cultivation in photobioreactors. Furthermore, both strains are suitable candidates for upscaling in open systems in tropical regions since they are adapted to the environmental conditions in Guanabara Bay, where they form massive blooms by outcompeting other microalgae.

Cosmeceuticals are cosmetic-hybrids intended to enhance health and beauty of the skin. Topical delivery of antioxidants from natural bioresources has gained attention in line with the increasing demand for harmless cosmetics. Tetraselmis tetrathele is a microalgae species, which has high antioxidant contents. In this work, ternary phase analysis with different compositions of oil, surfactant, and water was conducted to evaluate homogeneity and stability of nanoemulsion lotion containing 1% T. tetrathele extract. The three formulations T1, T2, and T3 containing various percentages of the surfactant Tween 80, T1 (20 wt% of Tween 80), T2 (15 wt% of Tween 80), and T3 (10 wt% of Tween 80), were analyzed for size and zeta potential to evaluate stability of the nanoemulsion. All particles were nanosized ranging from 102.3 to 249.5 nm. Zeta potential analysis for all emulsions showed negative values from − 33.2 to − 71.7 mV, which indicates high stability of the nanoemulsion. In order to evaluate the storage stability, a stability test was conducted at different temperature levels (4, 25, and 45 °C) for 10 weeks. At all temperature conditions, T1, T2, and T3 were stable with exception of T3 that precipitated and sedimented after 8 weeks. This study illustrated that T. tetrathele extract can be used as bioactive compound for nanocosmeceutical products, which has high homogeneity and stability.

Microalgae are proposed to have powerful applications for human health in the pharmaceutical and food industries. Tetraselmis species (sp.), which are green microalgae, were identified as a source of broad-spectrum health-promoting biological activities. However, the bioactivity of these species has not been elucidated. We aimed to confirm the antioxidant, antiviral, and anti-inflammatory effects of Tetraselmis sp. extract (TEE). TEE showed 2,2-diphenyl-1-picryl-hydrazyl-hydrate radical and hydrogen peroxide scavenging activities and reduced plaque formation in Vero E6 cells infected with vaccinia virus. TEE treatment also significantly inhibited nitric oxide (NO) production and improved cell viability in lipopolysaccharide (LPS)-induced RAW264.7 cells. These anti-inflammatory effects were further analyzed in LPS-induced RAW 264.7 cells and the zebrafish model. Further, TEE reduced induced NO synthase expression and proinflammatory cytokine release, including tumor necrosis factor-α, interleukin-6, and interleukin-1β, through MAPKs and NF-κB-dependent mechanisms. Further analysis revealed that TEE increased the survival rate and reduced cell death and NO production in an LPS-stimulated zebrafish model. Further, high-performance liquid chromatography revealed a strong presence of the carotenoid lutein in TEE. Overall, the results suggest that lutein-enriched TEE may be a potent antioxidant, antiviral, and anti-inflammatory agent that could be sustainably utilized in industrial applications.

Known as the Roscoff worm or mint-sauce worm, Symsagittifera roscoffensis is an Acoel distinguishable due to the presence of symbiotic alga Tetraselmis convolutae, held beneath the epidermis. Isolated populations of S. roscoffensis span a broad geographical range along the north-eastern Atlantic coast, from Wales to Portugal. The only known population of the worm in the United Kingdom was discovered in Wales decades ago, but very little research has been conducted since. For 13 months, we measured how environmental conditions such as temperature, salinity and light intensity coincided with population size at the Welsh field site. To establish phylogenetic relationships among the different populations and their algal symbionts, we designed new polymerase chain reaction (PCR) oligonucleotides to assess the nucleotide diversity of the mitochondrial cytochrome c oxidase I subunit (COI) gene in gDNA extracted from representative worms across their known range (Wales, France, Portugal, Spain, and Guernsey). We also targeted the 18S rRNA gene of their algal symbiont, Tetraselmis convolutae. We observed temporal shifts in environmental factors coinciding with fluctuating worm colony size, notably temperature. Based on the molecular data, the worm exhibited different ecotypes across locations, while the algal symbiont showed little genetic variation.

The modification of the Tetraselmis sp. algae material (Tetra-Alg) with surfactant Cethyltrimethylammonium Bromide (CTAB) yielded adsorbent Tetra-Alg-CTAB as an adsorbent of methyl orange (MO) and methylene blue (MB) solutions. The characterization of the adsorbent used an infrared (IR) spectrometer to identify functional groups and Scanning Electron Microscopy with Energy Dispersive X-ray (SEM-EDX FEI Inspect-S50, Midland, ON, Canada) to determine the surface morphology and elemental composition. Methyl orange and methylene blue adsorption on the adsorbent Tetra-Alg, Tetraselmis sp. algae-modified Na+ ions (Tetra-Alg-Na), and Tetra-Alg-CTAB were studied, including variations in pH, contact time, concentration, and reuse of adsorbents. The adsorption of MO and MB by Tetra-Alg-CTAB at pH 10, during a contact time of 90 min, and at a concentration of 250 mg L−1 resulted in MO and MB being absorbed in the amounts of 128.369 and 51.013 mg g−1, respectively. The adsorption kinetics and adsorption isotherms of MO and MB and Tetra-Alg, Tetra-Alg-Na, and Tetra-Alg-CTAB tend to follow pseudo-second-order kinetics models and Freundlich adsorption isotherms with each correlation coefficient value (R2) approaching 1. Due to the modification with the cationic surfactant CTAB, anionic dyes can be strongly sorbed in alkaline pH due to strong electrostatic attraction, while MB is more likely to involve cation exchange and hydrogen bonding. The reuse of Tetra-Alg-CTAB was carried out four times with adsorption percent > 70%, and the adsorbent was very effective in the adsorption of anionic dyes such as MO.