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We recently demonstrated the monthly variation and antioxidant activity of mycosporine-like amino acids (MAAs) from red alga dulse in Japan. The antioxidant activity of MAAs in acidic conditions was low compared to that in neutral and alkali conditions, but we found strong antioxidant activity from the heated crude MAA fraction in acidic conditions. In this study, we identified and characterized the key compounds involved in the antioxidant activity of this fraction. We first isolated two MAAs, palythine, and porphyra-334, from the fraction and evaluated the activities of the two MAAs when heated. MAAs possess absorption maxima at around 330 nm, while the heated MAAs lost this absorption. The heated MAAs showed a high ABTS radical scavenging activity at pH 5.8–8.0. We then determined the structure of heated palythine via ESI-MS and NMR analyses and speculated about the putative antioxidant mechanism. Finally, a suitable production condition of the heated compounds was determined at 120 °C for 30 min at pH 8.0. We revealed compounds from red algae with antioxidant activities at a wide range of pH values, and this information will be useful for the functional processing of food.

Atopic dermatitis (AD) is a chronic, relapsing inflammatory skin disease driven by immune dysregulation and epidermal barrier dysfunction. Current therapeutic options are often limited by safety concerns or suboptimal tolerability. In this study, we isolated and structurally characterized GRB-H—a λ-carrageenan-enriched sulfated hybrid galactan from the marine red alga Gigartina radula—as a complex polysaccharide containing κ-, ι-, μ-, ν-, and λ-carrageenan structural units, and systematically evaluated its anti-AD potential using both in vitro and in vivo models. In vitro, GRB-H significantly suppressed lipopolysaccharide (LPS)-induced nitric oxide (NO), tumor necrosis factor-α (TNF-α), and interleukin-6 (IL-6) in RAW 264.7 macrophages, and reduced 2,4-dinitrochlorobenzene (DNCB)-evoked TNF-α and IL-1β expression in HaCaT keratinocytes. In a DNCB-induced murine model of AD, topical application of GRB-H markedly ameliorated skin inflammation, epidermal hyperplasia, and dermal immune cell infiltration. GRB-H treatment lowered total serum immunoglobulin E (IgE) levels, restored the imbalanced Th1/Th2 cell ratio in the spleen, and downregulated the mRNA expression of key inflammatory cytokines—including TNF-α, IL-4, IL-5, IL-31, and interferon-γ (IFN-γ)—in lesional skin. Collectively, these findings demonstrate that GRB-H alleviates AD symptoms through coordinated local anti-inflammatory and systemic immunomodulatory actions, highlighting its promise as a marine-derived candidate for the topical management of AD.

Background The translocation of photoassimilates is a critical process that links the source and sink in plants, playing an irreplaceable role in maintaining source-sink balance, ensuring plant growth and development, and the formation of yield. Nevertheless, the mechanisms underlying the translocation of photosynthetic products in macroalgae are yet to be fully understood. The purpose of this study is to reveal the role of endocytosis in the translocation of photosynthetic products in the marine red alga Gracilariopsis lemaneiformis by investigating the uptake of photosynthetic products by endocytosis and the impact of endocytic activity on cellular ultrastructure, photosynthesis, and growth. Results This study discovered that the endocytic activity in non-epidermal cells (NEC, sink cells) of G. lemaneiformis is significantly higher than that in epidermal cells (EC, source cells). NEC is capable of internalizing a greater amount of extracellular carbohydrates, such as sucrose, via endocytosis compared to EC. Further inhibition of endocytic activity in G. lemaneiformis using EIPA resulted in a significant reduction in the content of floridean starch within NEC, whereas the decrease in floridean starch content in EC was not statistically significant. Inhibition of endocytic activity led to an initial decline in photosynthetic efficiency of algal thalli within a few hours, which was followed by an increase as inhibition duration extended, yet the growth rate of the thalli remained substantially suppressed. Conclusions These findings indicate that endocytosis in G. lemaneiformis plays a role in regulating the cellular uptake of extracellular photoassimilates, which in turn influences the storage substances in sink cells and the overall growth and development of the algae. This study sheds new light on the regulatory mechanisms governing photoassimilate translocation in macroalgae.

Background The genus Virescentia is a significant member of the Batrachospermaceae, exhibiting distinctive life history characteristics defined by alternating generations. This group of taxa has specific environmental requirements for growth. This paper investigates Virescentia , which primarily thrives in freshwater environments, such as streams and springs, characterized by low light, low temperatures, and high dissolved oxygen levels. Currently, no laboratory simulations of their growth conditions have been reported in culture studies. Additionally, previous studies indicate that comparisons of photosynthetic strength across different life-history stages of the same species have not been conducted, mainly due to the challenges of simultaneously collecting algal strains at both life-history stages. Results During the gametophyte stage, the chloroplast and mitochondrial genomes were measured at 184,899 bp and 26,867 bp, respectively. In the chantransia stage, the lengths of these genomes were 184,887 bp and 27,014 bp, respectively. A comparison of organellar genome covariation and phylogenetic reconstruction revealed that the chloroplast and mitochondrial genomes across different life history stages were highly conserved, with genetic distances of 0 and nucleotide variants of only 9–15 bp. The mitochondrial genome of gametophyte SXU-YN24005 was found to lack two tRNA-Leu (tag) genes compared to that of the chantransia strain. Additionally, a comparative analysis of KEGG pathway transcriptome data from the two life history stages showed that 33 genes related to the ribosomal pathway and 53 genes associated with the photosynthesis pathway exhibited a significant decline in expression during the gametophyte stage compared to the chantransia stage. Conclusion In this study, two samples of the same species at different life-history stages were collected from the same location for the first time. The analysis revealed a high degree of conservation between their organelle genomes. Additionally, transcriptome sequencing results indicated substantial differences in gene expression patterns between the two life-history stages. This research will provide reliable data to support the future histological database of freshwater red algae and will establish a theoretical basis for conserving rare and endangered species.

In recent years, studies on the more efficient use of natural materials in adsorption processes have increased significantly. Thus, obtaining new adsorbents from marine algae biomass with higher adsorptive performance will ensure a better use of these renewable resources. In this study, the adsorption of Cu(II) ions from aqueous solution was done using three types of adsorbent materials obtained from marine red algae biomass (Callithamnion corymbosum sp.), namely: alginate (Alg), algae waste biomass resulted after alginate extraction (AWB) and iron nanoparticles functionalized with alginate (Fe-NPs-Alg), compared to raw marine red algae biomass (RAB). FTIR spectra and SEM images recorded for each type of adsorbent indicate a porous structure and the presence of various superficial functional groups who may be involved in the retention of Cu(II) ions. The biosorption experiments were performed in a batch system, at different initial Cu(II) ion concentrations and contact times, maintaining a constant initial solution pH (4.4), adsorbent dose (2.0 g/L), and temperature (25 ± 1 °C). The obtained results indicate that the retention of Cu(II) ions requires a maximum of 60 min to reach equilibrium, and the maximum adsorption capacity increases in order: RAB (47.62 mg/g) < Fe-NPs-Alg (52.63 mg/g) < AWB (83.33 mg/g) < Alg (166.66 mg/g). The quantitative removal of Cu(II) ions from aqueous effluents can be done in two successive adsorption stages, using AWB (in the first stage) and Fe-NPs-Alg (in the second stage), when the treated solution has a Cu(II) ions concentration below the maximum permissible limit. The quantitative recovery of retained Cu(II) ions (over 97%) can be done by treating these exhausted adsorbent materials with 0.1 N HNO3 solution. Therefore, the extraction of alginate from marine red algae biomass could be a viable solution to obtain efficient adsorbent materials for Cu(II) ions removal from aqueous media, and allow for a better valorisation of marine red algae biomass.

Background The unicellular red alga Cyanidioschyzon merolae exhibits a very simple cellular and genomic architecture. In addition, procedures for genetic modifications, such as gene targeting by homologous recombination and inducible/repressible gene expression, have been developed. However, only two markers for selecting transformants, uracil synthase ( URA ) and chloramphenicol acetyltransferase ( CAT ), are available in this alga. Therefore, manipulation of two or more different chromosomal loci in the same strain in C. merolae is limited. Results This study developed a nuclear targeting and transformant selection system using an antibiotics blasticidin S (BS) and the BS deaminase ( BSD ) selectable marker by homologous recombination in C. merolae . In addition, this study has succeeded in simultaneously modifying two different chromosomal loci by a single-step cotransformation based on the combination of BSD and CAT selectable markers. A C. merolae strain that expresses mitochondrion-targeted mSCARLET (with the BSD marker) and mVENUS (with the CAT marker) from different chromosomal loci was generated with this procedure. Conclusions The newly developed BSD selectable marker enables an additional genetic modification to the already generated C. merolae transformants based on the URA or CAT system. Furthermore, the cotransformation system facilitates multiple genetic modifications . These methods and the simple nature of the C. merolae cellular and genomic architecture will facilitate studies on several phenomena common to photosynthetic eukaryotes.

We examined the inhibitory activity of angiotensin I converting enzyme (ACE) in protein hydrolysates from dulse, Palmaria palmata. The proteins extracted from dulse were mainly composed of phycoerythrin (PE) followed by phycocyanin (PC) and allophycocyanin (APC). The dulse proteins showed slight ACE inhibitory activity, whereas the inhibitory activity was extremely enhanced by thermolysin hydrolysis. The ACE inhibitory activity of hydrolysates was hardly affected by additional pepsin, trypsin and chymotrypsin treatments. Nine ACE inhibitory peptides (YRD, AGGEY, VYRT, VDHY, IKGHY, LKNPG, LDY, LRY, FEQDWAS) were isolated from the hydrolysates by reversed-phase high-performance liquid chromatography (HPLC), and it was demonstrated that the synthetic peptide LRY (IC50: 0.044 μmol) has remarkably high ACE inhibitory activity. Then, we investigated the structural properties of dulse phycobiliproteins to discuss the origin of dulse ACE inhibitory peptides. Each dulse phycobiliprotein possesses α-subunit (Mw: 17,477–17,638) and β-subunit (Mw: 17,455–18,407). The sequences of YRD, AGGEY, VYRT, VDHY, LKNPG and LDY were detected in the primary structure of PE α-subunit, and the LDY also exists in the APC α- and β-subunits. In addition, the LRY sequence was found in the β-subunits of PE, PC and APC. From these results, it was suggested that the dulse ACE inhibitory peptides were derived from phycobiliproteins, especially PE. To make sure the deduction, we carried out additional experiment by using recombinant PE. We expressed the recombinant α- and β-subunits of PE (rPEα and rPEβ, respectively), and then prepared their peptides by thermolysin hydrolysis. As a result, these peptides showed high ACE inhibitory activities (rPEα: 94.4%; rPEβ: 87.0%). Therefore, we concluded that the original proteins of dulse ACE inhibitory peptides were phycobiliproteins.

This review presents an analysis of works devoted to the anti-human immunodeficiency virus (HIV) activity of algae metabolites—sulfated polysaccharides (fucoidans, carrageenans), lectins, laminarans, and polyphenols. Despite the presence of a significant number of antiretroviral drugs, the development of new therapeutic and prophylactic agents against this infection remains very urgent problem. This is due to the variability of HIV, the absence of an animal model (except monkeys) and natural immunity to this virus and the toxicity of therapeutic agents and their high cost. In this regard, the need for new therapeutic approaches and broad-spectrum drugs, which in addition to antiviral effects can have anti-inflammatory, antioxidant, and immunomodulatory effects, and to which the minimum resistance of HIV strains would be formed. These requirements meet the biologically active substances of marine algae. The results of experimental and clinical studies conducted in vitro and in vivo are presented, and the issues of the anti-HIV activity of these compounds are considered depending on their structural features. On the whole, the presented data prove the high efficiency of seaweed metabolites and justify the possibility of their use as a potential basis for the development of new drugs with a wide spectrum of activity.

The red alga Asparagopsis armata is a species with a haplodiplophasic life cycle alternating between morphologically distinct stages. The species is known for its various biological activities linked to the production of halogenated compounds, which are described as having several roles for the algae such as the control of epiphytic bacterial communities. Several studies have reported differences in targeted halogenated compounds (using gas chromatography–mass spectrometry analysis (GC-MS)) and antibacterial activities between the tetrasporophyte and the gametophyte stages. To enlarge this picture, we analysed the metabolome (using liquid chromatography–mass spectrometry (LC-MS)), the antibacterial activity and the bacterial communities associated with several stages of the life cycle of A. armata: gametophytes, tetrasporophytes and female gametophytes with developed cystocarps. Our results revealed that the relative abundance of several halogenated molecules including dibromoacetic acid and some more halogenated molecules fluctuated depending on the different stages of the algae. The antibacterial activity of the tetrasporophyte extract was significantly higher than that of the extracts of the other two stages. Several highly halogenated compounds, which discriminate algal stages, were identified as candidate molecules responsible for the observed variation in antibacterial activity. The tetrasporophyte also harboured a significantly higher specific bacterial diversity, which is associated with a different bacterial community composition than the other two stages. This study provides elements that could help in understanding the processes that take place throughout the life cycle of A. armata with different potential energy investments between the development of reproductive elements, the production of halogenated molecules and the dynamics of bacterial communities.

A separation process was established to sequentially fractionate and recover three anti-inflammatory components derived from sugars, phycobiliprotein, and chlorophyll from the hot-air-dried thalli of the red alga dulse (Palmaria palmata). The developed process consisted of three steps, without the use of organic solvents. In Step I, the sugars were separated by disrupting the cell wall of the dried thalli with a polysaccharide-degrading enzyme, and a sugar-rich extract (E1) was obtained by precipitating the other components, which were simultaneously eluted by acid precipitation. In Step II, the residue suspension from Step I was digested with thermolysin to obtain phycobiliprotein-derived peptides (PPs), and a PP-rich extract (E2) was obtained by separating the other extracts using acid precipitation. In Step III, solubilized chlorophyll was obtained by heating the residue, which was acid-precipitated, neutralized, and re-dissolved to concentrate the chlorophyll-related components (Chls)-rich extract (E3). These three extracts suppressed inflammatory-cytokine secretion by lipopolysaccharide (LPS)-stimulated macrophages, confirming that the sequential procedure had no negative effects on the activities of any of the extracts. The E1, E2, and E3 were rich in sugars, PPs, and Chls, respectively, indicating that the anti-inflammatory components were effectively fractionated and recovered through the separation protocol.