Plasticity and remodelling of lipids support acclimation potential in two species of low-intertidal macroalgae, Fucus serratus (Phaeophyceae) and Palmaria palmata (Rhodophyta)

Biochemical profiling and antioxidant activity analysis of commercially relevant seaweeds from northwest Europe

BACKGROUND

The drive towards ensuring the sustainability of bioresources has been linked with better valorising primary materials and developing biorefinery pipelines. Seaweeds constitute valuable coastal resources with applications in the bioenergy, biofertiliser, nutrition, pharmaceutical and cosmetic sectors. Owing to the various sought-after metabolites they possess, several seaweed species are commercially exploited throughout Western Europe, including Ireland. Here, four commercially relevant brown (Fucus serratus and Fucus vesiculosus) and red (Chondrus crispus and Mastocarpus stellatus) seaweed species were sampled during a spring tide in July 2021 on moderately exposed shores across three coastal regions in the west of Ireland.

RESULTS

Significant regional differences were identified when specimens were analysed for carbohydrates (max. 80.3 μg glucose eq mg-1 DW), proteins (max. 431.3 μg BSA eq. mg-1 DW), lipids (max. 158.6 mg g-1 DW), pigment signature and antioxidant potential. Protein content for F. serratus recorded a twofold difference between northern and southern specimens. The antioxidant potential of F. vesiculosus and M. stellatus returned greater activity compared to F. serratus and C. crispus, respectively. Multivariate analysis showed a clear latitudinal pattern across the three western coastal regions (north, west and south) for both F. vesiculosus and F. serratus.

CONCLUSION

F. vesiculosus thalli from the northwest were richer in pigment content while the F. serratus thalli from the northwest were richer in antioxidants. Such biogeographic patterns in the biochemical make-up of seaweeds need consideration for the development of regional integrated aquaculture systems and the optimisation of the biomass content for targeted downstream applications. © 2024 Society of Chemical Industry.

Revealing the polar lipidome, pigment profiles, and antioxidant activity of the giant unicellular green alga, Acetabularia acetabulum

Marine algae are one of the most important sources of high-value compounds such as polar lipids, omega-3 fatty acids, photosynthetic pigments, or secondary metabolites with interesting features for different niche markets. Acetabularia acetabulum is a macroscopic green single-celled alga, with a single nucleus hosted in the rhizoid. This alga is one of the most studied dasycladalean species and represents an important model system in cell biology studies. However, its lipidome and pigment profile have been overlooked. Total lipid extracts were analyzed using hydrophilic interaction liquid chromatography-high resolution mass spectrometry (HILIC-HRMS), tandem mass spectrometry (MS/MS), and high-performance liquid chromatography (HPLC). The antioxidant capacity of lipid extracts was tested using DPPH and ABTS assays. Lipidomics identified 16 polar lipid classes, corresponding to glycolipids, betaine lipids, phospholipids, and sphingolipids, with a total of 191 lipid species, some of them recognized by their bioactivities. The most abundant polar lipids were glycolipids. Lipid classes less studied in algae were identified, such as diacylglyceryl-carboxyhydroxymethylcholine (DGCC) or hexosylceramide (HexCer). The pigment profile of A. acetabulum comprised carotenoids (17.19%), namely cis-neoxanthin, violaxanthin, lutein and β,β-carotene, and chlorophylls a and b (82.81%). A. acetabulum lipid extracts showed high antioxidant activity promoting a 50% inhibition (IC50 ) with concentrations of 57.91 ± 1.20 μg · mL-1 (438.18 ± 8.95 μmol Trolox · g-1 lipid) in DPPH and 20.55 ± 0.60 μg · mL-1 in ABTS assays (918.56 ± 27.55 μmol Trolox · g-1 lipid). This study demonstrates the potential of A. acetabulum as a source of natural bioactive molecules and antioxidant compounds.

Estudio de la variabilidad en el tiempo y espacio de la actividad antioxidante y composición bioquímica de Kappaphycus alvarezii en diferentes densidades de siembra

Kappaphycus alvarezii es una de las especies de algas más cultivadas en el mundo, debido a su alto contenido de compuestos bioactivos con reportes antioxidantes y bioestimulantes. El presente estudio evaluó el efecto de las densidades de plantación sobre la composición bioquímica y antioxidante de K. alvarezii cultivada en un sistema de línea larga durante las estaciones seca y húmeda, con el fin de proporcionar una base científica para una cosecha óptima. Se midieron el contenido de humedad, cenizas, grasa, fibra, auxinas, fenoles, flavonoides, DPPH y ABTS. Los datos se analizaron mediante pruebas t, Wilcoxon, Kruskal-Wallis y ANOVA unidireccional. Los resultados mostraron un mayor contenido de grasa (2,01 % P.s), fibra bruta (5,21% P.s), contenido total de fenoles (324,09 μg GAE/g P.s) y ABTS (9,32 μg GAE/g P.s) durante la estación seca. Con respecto a la densidad de plantación, se produjo un aumento significativo del contenido en cenizas, fenoles totales y ABTS con una densidad de 10 líneas.célula-1 al mismo tiempo. Los contenidos de flavonoides, DPPH y auxina mostraron una tendencia estacional opuesta, alcanzando los niveles máximos en la estación húmeda. Este estudio aporta nueva información sobre las condiciones ambientales que pueden provocar cambios en la actividad antioxidante y la composición bioquímica de esta especie con vistas al desarrollo de bioproductos para diferentes sectores industriales como el alimentario, el farmacéutico y el de los fertilizantes en Ecuador. Palabras claves: Alga roja; Fenoles; Flavonoides; Antioxidante; Composición bioquímica; Variación estacional; densidad de siembra.

Low light acclimation strategy of the brown macroalga Undaria pinnatifida: Significance of lipid and fatty acid remodeling for photosynthetic competence

Brown macroalgae, being important components of benthic communities in temperate regions, are frequently subjected to light limitation. To extend our understanding of their low light acclimation strategies to the regulation of membrane lipid environment, photosynthetic characteristics, lipid class, fatty acid profiles and chloroplast ultrastructure were compared in Undaria pinnatifida (Phaeophyceae, Ochrophyta) after long-term exposure to low and moderate light intensities (LL, 100 and ML, 280 µmol photons · m-2 · s-1 ). We show that light limitation significantly increased PSII quantum efficiency and photosynthetic electron transport rate, enhanced pigment contents and concentration of thylakoid membranes in chloroplasts but decreased the distance between the thylakoid stacks. These physiological alterations at LL were accompanied by a selective remodeling of thylakoid membrane lipids driven by increases in monogalactosyldiacylglycerol (MGDG) and phosphatidylglycerol (PG) contents. Light limitation also induced active production of PG specific trans-Δ3 -hexadecenoic acid and accumulation of n-3 polyunsaturated fatty acids (PUFA) mostly in PG and MGDG at the expense of the rise in 18:3n-3 and 20:5n-3, 18:4n-3, respectively. These changes in lipid and FA profiles are apparently responsible for supporting thylakoid biogenesis and efficient photosynthesis at light limitation, thus contributing to photoacclimation strategies in brown algae. The content of triacylglycerols (TAG) and the level of their PUFA were decreased at LL, suggesting the consumption of TAG as a source of PUFA and energy reserves. Thus, U. pinnatifida is able to successfully overcome periods of low irradiance through the effective light harvesting and utilization that are provided by high flexibility of lipid biosynthesis.

Seagrass fatty acid profiles as a sensitive indicator of climate settings across seasons and latitudes

Zostera marina is a dominant meadow-forming seagrass in temperate regions in the northern hemisphere. Here, fatty acid content and composition, and pigmentation, in leaves were evaluated across temporal (April, July, November -2015 and January-2016) and latitudinal (Greenland to southern Spain) environmental gradients. Content of total fatty acids (TFA) in samples collected in Ireland during warmer periods (summer) was 2-3 times lower than in winter and exhibited a lower proportion of polyunsaturated fatty acids (PUFAs), which have high high-nutritional value relative to saturated fatty acids (SAFA). The latitudinal comparison (Greenland to southern Spain) revealed a clear reduction in the proportion n-3 PUFAs and an increase in n-6 PUFA and SAFA, which correlated with the rise in temperature towards southern locations, which correlated with the rise in temperature towards south. Results indicate that future warming may negatively affect its lipid nutritional value. These results demonstrate the capacity of seagrasses to adjust their lipid composition to achieve optimal membrane functionality, suggesting the potential use of FA as an eco-physiological indicator of global change conditions. The results also suggest that future warming may negatively affect the lipid nutritional value of seagrasses.

Valuing Bioactive Lipids from Green, Red and Brown Macroalgae from Aquaculture, to Foster Functionality and Biotechnological Applications

Marine edible macroalgae have functional proprieties that might improve human health and wellbeing. Lipids represent a minor fraction of macroalgae, yet with major interest as main carriers of omega 3 polyunsaturated fatty acids and intrinsic bioactive properties. In this study, we used lipid extracts from the green macroalgae Ulva rigida and Codium tomentosum; the red Gracilaria gracilis,Palmaria palmata and Porphyra dioica; and the brown Fucus vesiculosus, produced in a land-based integrated multitrophic aquaculture (IMTA) system. We determined the lipid quality indices based on their fatty acid profiles and their bioactivities as putative antioxidant, anti-inflammatory and antiproliferative agents. The results reveal to be species-specific, namely U. rigida displayed the lowest atherogenicity and thrombogenicity indices. Palmaria palmata and F. vesiculosus lipid extracts displayed the lowest inhibitory concentration in the free radical scavenging antioxidant assays. Ulva rigida, C. tomentosum, P. palmata and P. dioica inhibited COX-2 activity by up to 80%, while P. dioica and P. palmata extracts showed the highest cytotoxic potential in the MDA-MB-231 breast cancer cells. This work enhances the valorization of macroalgae as functional foods and promising ingredients for sustainable and healthy diets and fosters new applications of high-valued algal biomass, in a species-specific context.

Domesticated Populations of Codium tomentosum Display Lipid Extracts with Lower Seasonal Shifts than Conspecifics from the Wild-Relevance for Biotechnological Applications of this Green Seaweed

In the last decades, the use of algae in biotechnology and food industries has experienced an exponential growth. Codium tomentosum is a green macroalgae with high biotechnological potential, due to its rich lipidome, although few studies have addressed it. This study aimed to investigate the seasonal changes in lipid and pigment profiles of C. tomentosum, as well as to screen its antioxidant activity, in order to evaluate its natural plasticity. Samples of C. tomentosum were collected in two different seasons, early-autumn (September/October) and spring (May), in the Portuguese coast (wild samples), and in a land-based integrated multitrophic aquaculture (IMTA) system (IMTA samples). Total lipid extracts were analysed by LC-MS, GC-MS, and HPLC, and antioxidant activity was screened through free radical scavenging potential against DPPH and 2,20-azino-bis-3-ethylbenzothiazoline-6-sulfonic acid (ABTS) radicals. Wild samples showed a high seasonal variability, modifying their lipidome and pigment profiles according to environmental shifts, while IMTA samples showed a relatively stable composition due to early-stage culturing in controlled conditions. The lipids that contributed the most to seasonal discrimination were glycolipids (monogalactosyl diacylglycerol - MGDG and digalactosyl diacylglycerol - DGDG) and the lyso forms of phospholipids and glycolipids. Lipid extracts showed antioxidant activity ranging from 61 ± 2 to 115 ± 35 µmol Trolox g^-1 of lipid extract in DPPH assay and from 532 ± 73 to 927 ± 92 µmol Trolox g^-1 of lipid extract in ABTS assay, with a more intense antioxidant activity in wild spring samples. This study revealed that wild specimens of C. tomentosum presented a higher plasticity to cope with seasonal environmental changes, adjusting their lipid, pigment, and bioactivity profiles, while IMTA samples, cultured under controlled conditions, displayed more stable lipidome and pigment compositions.

Site-Specific Lipidomic Signatures of Sea Lettuce (Ulva spp., Chlorophyta) Hold the Potential to Trace Their Geographic Origin

The wild harvest and aquaculture of Ulva spp. has deserved growing attention in Europe. However, the impact of geographical origin on the biochemical composition of different species and/or strains is yet to be described in detail. Hence, the present study aimed to detect the variability of the lipidome of different species and/or strains of Ulva originating from different geographic locations. We hypothesized that lipidomic signatures can be used to trace the geographic origin post-harvesting of these valuable green seaweeds. Ulva spp. was sampled from eight distinct ecosystems along the Atlantic Iberian coast and Ulva rigida was sourced from an aquaculture farm operating a land-based integrated production site. Results showed significant differences in the lipidomic profile displayed by Ulva spp. originating from different locations, namely, due to different levels of polyunsaturated betaine lipids and galactolipids; saturated betaine lipids and sulfolipids; and some phospholipid species. Overall, a set of 25 site-specific molecular lipid species provide a unique lipidomic signature for authentication and geographic origin certification of Ulva species. Present findings highlight the potential of lipidome plasticity as a proxy to fight fraudulent practices, but also to ensure quality control and prospect biomass for target bioactive compounds.

Nitrogen sufficiency enhances thermal tolerance in habitat-forming kelp: implications for acclimation under thermal stress

Local and global changes associated with anthropogenic activities are impacting marine and terrestrial ecosystems. Macroalgae, especially habitat-forming species like kelp, play critical roles in temperate coastal ecosystems. However, their abundance and distribution patterns have been negatively affected by warming in many regions around the globe. Along with global change, coastal ecosystems are also impacted by local drivers such as eutrophication. The interaction between global and local drivers might modulate kelp responses to environmental change. This study examines the regulatory effect of NO₃⁻ on the thermal plasticity of the giant kelp Macrocystis pyrifera. To do this, thermal performance curves (TPCs) of key temperature-dependant traits–growth, photosynthesis, NO₃⁻ assimilation and chlorophyll a fluorescence–were examined under nitrate replete and deplete conditions in a short-term incubation. We found that thermal plasticity was modulated by NO₃⁻ but different thermal responses were observed among traits. Our study reveals that nitrogen, a local driver, modulates kelp responses to high seawater temperatures, ameliorating the negative impacts on physiological performance (i.e. growth and photosynthesis). However, this effect might be species-specific and vary among biogeographic regions – thus, further work is needed to determine the generality of our findings to other key temperate macroalgae that are experiencing temperatures close to their thermal tolerance due to climate change.

Lipidomic Signatures Reveal Seasonal Shifts on the Relative Abundance of High-Valued Lipids from the Brown Algae Fucus vesiculosus

Fucus vesiculosus is an edible brown macroalga, with health benefits associated with its consumption and also a source of bioactive molecules. It is acknowledged that the biochemical composition of macroalgae changes when exposed to different environmental conditions occurring on different habitats, such as the water temperature, and light intensity. In the present study, the polar lipidome of Fucus vesiculosus was characterized for the first time using modern high-resolution HILIC-MS, and MS/MS approaches, to evaluate the phenotypic variability in two seasons of the year, e.g., winter and spring. A total of 187 molecular species were identified over eighteen classes of glycolipids, phospholipids and betaine lipids. Principal component analysis (PCA) multivariate statistical analysis and cluster analysis of polar lipid classes, polar lipid species and total fatty acids (FA) datasets, showed clustering according to the seasonal groups. While the lipid profile of Fucus vesiculosus harvested in the winter and spring yielded the same molecular species, the relative abundance of these species was significantly different. In the winter, changes were mainly due to the increased relative abundance of some molecular species of glycolipids and phospholipids, bearing octadeca(poly)enoic (18:3, 18:4) and eicosa(poly)enoic (20:4, 20:5) FA and betaine lipids species with short saturated FA (14:0) and polyunsaturated FA (PUFA). Importantly, glycolipids with n-3 PUFA and sulfolipids, have been reported to have important biological activities and therapeutic value. Overall, Fucus vesiculosus is a promising source of bioactive compounds that can be used as functional food or ingredients for human nutrition, feed, pharma, and cosmetic formulations. In this study, samples harvested in the winter season maximized yields of these bioactive components, when compared with samples harvested in the spring.

Responses of macroalgae to CO2 enrichment cannot be inferred solely from their inorganic carbon uptake strategy

Increased plant biomass is observed in terrestrial systems due to rising levels of atmospheric CO2, but responses of marine macroalgae to CO2 enrichment are unclear. The 200% increase in CO2 by 2100 is predicted to enhance the productivity of fleshy macroalgae that acquire inorganic carbon solely as CO2 (non-carbon dioxide-concentrating mechanism [CCM] species-i.e., species without a carbon dioxide-concentrating mechanism), whereas those that additionally uptake bicarbonate (CCM species) are predicted to respond neutrally or positively depending on their affinity for bicarbonate. Previous studies, however, show that fleshy macroalgae exhibit a broad variety of responses to CO2 enrichment and the underlying mechanisms are largely unknown. This physiological study compared the responses of a CCM species (Lomentaria australis) with a non-CCM species (Craspedocarpus ramentaceus) to CO2 enrichment with regards to growth, net photosynthesis, and biochemistry. Contrary to expectations, there was no enrichment effect for the non-CCM species, whereas the CCM species had a twofold greater growth rate, likely driven by a downregulation of the energetically costly CCM(s). This saved energy was invested into new growth rather than storage lipids and fatty acids. In addition, we conducted a comprehensive literature synthesis to examine the extent to which the growth and photosynthetic responses of fleshy macroalgae to elevated CO2 are related to their carbon acquisition strategies. Findings highlight that the responses of macroalgae to CO2 enrichment cannot be inferred solely from their carbon uptake strategy, and targeted physiological experiments on a wider range of species are needed to better predict responses of macroalgae to future oceanic change.

Effects of an experimental heat wave on fatty acid composition in two Mediterranean seagrass species

Global warming is emerging as one of the most critical threats to terrestrial and marine species worldwide. This study assessed the effects of simulated warming events in culture on two seagrass species, Posidonia oceanica and Cymodocea nodosa, which play a key role in coastal ecosystems of the Mediterranean Sea. Changes in fatty acids as key metabolic indicators were assessed in specimens from two geographical populations of each species adapted to different in situ temperature regimes. Total fatty acid (TFA) content and composition were compared in C. nodosa and P. oceanica from natural populations and following exposure to heat stress in culture. After heat exposure, individuals of C. nodosa and P. oceanica adapted to colder temperatures in situ accumulated significantly more TFA than controls. For both species, the proportion of polyunsaturated fatty acids (PUFA) decreased, and the percentage of saturated fatty acids (SFA) increased significantly after the heat treatment. These results highlight that populations of both species living at warmest temperatures in situ were more thermo-tolerant and exhibited a greater capacity to cope with heat stress by readjusting their lipid composition faster. Finally, exposure of seagrasses to warmer conditions may induce a decrease in PUFA/SFA ratio which could negatively affect their nutritional value and generate important consequences in the healthy state of next trophic levels.

Seasonal Variability of the Biochemical Composition and Antioxidant Properties of Fucus spiralis at Two Azorean Islands

This study evaluates, for the first time, the seasonal (winter and summer) and geographical (São Miguel⁻SMG and Santa Maria⁻SMA Islands) variability of Fucus spiralis (Fs) biochemical composition (dry weight basis) and antioxidant properties. Protein and carbohydrates presented higher values in Fs-SMGwinter, lipids, total dietary fiber, and energy value in Fs-SMAsummer, and ash and soluble dietary fiber/insoluble dietary fiber ratio in Fs-SMAwinter. The fatty acid (FA) profiles showed a lower SFA in Fs-SMGsummer, whereas MUFA and PUFA presented higher values in Fs-SMGsummer and Fs-SMGwinter, respectively. Excellent dietary ratios of n6/n3 PUFA and hypocholesterolemic/hypercholesterolemic FA were found, with lower values in Fs-SMAwinter and higher in Fs-SMGsummer, respectively. The highest total phenolics was found in Fs-SMAsummer acetone:water extract and total flavonoids showed the higher value in Fs-SMGwinter methanol extract. The best free radical-scavenging activity was observed in the Fs-SMAwinter methanol (EC50 = 0.045 mg/mL) and acetone:water (EC50 = 0.059 mg/mL) extracts. The ferric-reducing antioxidant power showed the best results in Fs-SMAwinter methanol extract (EC50 = 0.016 mg/mL) and Fs-SMAsummer acetone:water extract (EC50 = 0.017 mg/mL). The best ferrous ion-chelating activity was found in Fs-SMGwinter acetone:water extract. Overall, results revealed that F. spiralis nutritional and functional bioactivity values have geographical and seasonal variations and that its regular consumption may add benefits to human health.

Southern Australian seaweeds: A promising resource for omega-3 fatty acids

To assess the suitability of southern-Australian macroalgae as potential marine resources for fatty acids (FA), and in particular polyunsaturated fatty acids (PUFA), analysis of 61 species, comprising of 11 Chlorophyta, 17 Phaeophyceae (Ochrophyta) and 33 Rhodophyta, was conducted. Total fatty acid (TFA) concentrations varied considerably (between 0.6 and 7.8 in % of dry weight (DW)) between species, with on average the highest concentrations being in the Phaeophyceae, then the Chlorophyta, and with the Rhodophyta recording the lowest average concentrations. Results revealed significant differences in the fatty acid profiles of the three algal groups. Most species exhibit high proportions of PUFA in their fatty acid profile and a low ratio of n-6/n-3 PUFA. These properties highlight the potential for southern-Australian macroalgae to be used for these FA in food, animal feed and nutraceutical applications.