Biochemical characterization of a new ulvan lyase and its applicability in utilization of ulvan and preparation of ulva oligosaccharides

Ulva is globally distributed specie and has a high economic value. Ulvan is one of the main active substances in Ulva, which has a variety of biological properties. Ulvan lyase degrades ulvan through a β-elimination mechanism which cleaves the β-glycosidic bond between Rha3S and GlcA or IdoA. The complex monosaccharide composition of ulvan makes it promising for use in food and pharmaceutical applications. This thesis explores a putative ulvan lyase from Alteromonas sp. KUL_42. We expressed and purified the protein, performed a series of characterizations and signal peptide had been removed. The results showed that the protein molecular weight of ULA-2 was 53.97 kDa, and it had the highest catalytic activity at 45 °C and pH 8.0 in Tris-HCl buffer. The Km and Vmax values were 2.24 mg · mL-1 and 2.048 μmol · min-1 · mL-1, respectively. The activity of ULA-2 was able to maintain more than 80% at 20 ~ 30 °C. ESI-MS analysis showed that the primary end-products were mainly disaccharides to tetrasaccharides. The study of ULA-2 enriches the ulvan lyase library, promotes the development and high-value utilization of Ulva resources, and facilitates further research applications of ulvan lyase in ulva oligosaccharides.

Ulva rigida Valorization into Poly(3-hydroxybutyrate), Organic Acids and Functional Ingredients

Halomonas elongata 1H9T is a moderate halophilic strain able to produce poly(3-hydroxybutyrate) (P(3HB)), a biodegradable plastic, and gluconic acid, a valuable organic acid with wide industrial applications. In this work, the green alga Ulva rigida was used as platform to produce cultivation substrates for microbial conversion as well as functional ingredients, targeting its full valorization. The liquor obtained by autohydrolysis presented the highest concentration of oligosaccharides and protein, being an interesting feedstock to produce functional ingredients. The acid and/or enzymatic hydrolysis liquors are adequate as substrates for microbial processes. Shake flask assays with H. elongata revealed that the N-rich liquor produced after acidic treatment was the best suited for cell growth while the N-poor liquor produced by the enzymatic treatment of acid-pretreated algae residues produced the highest P(3HB) titers of 4.4 g/L. These hydrolysates were used in fed-batch cultivations as carbon and protein sources for the co-production of gluconic acid and polymer achieving titers of 123.2 g/L and 7.2 g/L, respectively. Besides gluconic acid, the Krebs cycle intermediate 2-oxoglutaric acid, also called alpha-ketoglutaric acid (KGA), was produced. Therefore, the co-production of P(3HB) and acids may be of considerable interest as an algal biorefinery valorization strategy.

Activated abscisic acid pathway and C4 pathway, inhibited cell cycle progression, responses of Ulva prolifera to short term high temperature elucidated by multi-omics

The annual outbreak of green tides since 2007 has destroyed coastal waters' ecological environment and caused substantial economic losses. Ulva prolifera, known as the dominant species of green tides, is influenced by temperatures. Omics-based technology was used to analyze U. prolifera under 12 h of treatment at 30 °C in the work. High temperature has the following advantages, e.g., activating the abscisic acid signaling pathway, improving the heat tolerance of U. prolifera, up-regulating metabolites such as glycolipids, glyceroyl, and glutamic acid to maintain the stability and fluidity of cells, and reducing the stimulatory effect of external stress on cells. The key genes and proteins of the tricarboxylic acid cycle, glycolysis, and pentose phosphorylation pathways were inhibited; however, the key enzyme pyruvate phospho-dikinase of the C4 pathway was up-regulated. The C4 pathway was activated in U. prolifera in response to high-temperature stress and may play a key role in photosynthesis. Besides, U. prolifera metabolizing amino acids was active. High temperature inhibited genes and proteins related to DNA replication and cell cycle in the transcriptome and proteome as well as the growth and reproduction of U. prolifera.

Differential responses of bloom-forming Ulva intestinalis and economically important Gracilariopsis lemaneiformis to marine heatwaves under changing nitrate conditions

Marine heatwaves (MHWs) are affecting the survival of macroalgae. However, little is known regarding how the impacts of MHWs are regulated by nitrogen availability. In this study, we investigated the physiological and genetic responses of a green-tide macroalga Ulva intestinalis Linnaeus and a commercially cultivated macroalga Gracilariopsis lemaneiformis (Bory) E.Y. Dawson, Acleto & Foldvik under different nitrate conditions to simulated MHWs. Under nitrogen limited conditions (LN), heatwaves did not significantly affect biomass or Fv/Fm of U. intestinalis although it led to an earlier biomass decline due to more reproduction events, and meanwhile an upregulation in genes related to TCA cycle and oxidative phosphorylation was detected, supporting sporulation. Under nitrogen replete conditions (HN), heatwaves did not change biomass, Fv/Fm or photosynthetic pigments but reduced reproduction rate along with insignificant change of oxidative phosphorylation and TCA cycle related genes. Meanwhile, genes related to photosynthesis and glutathione metabolism were upregulated. Regarding G. lemaneiformis, heatwaves reduced its Fv/Fm and photosynthetic pigments content, leading to bleaching and death, and photosynthesis-related genes were also downregulated at LN. Fv/Fm was improved and photosynthesis-related genes were up-regulated by the combination of nitrogen enrichment and heatwaves, whereas G. lemaneiformis remained bleached and died by day 12. Therefore, U. intestinalis could survive heatwaves through shifting to micropropagules at LN and protecting its photosynthesis at HN. In contrast, G. lemaneiformis died of bleaching when suffering heatwaves regardless of nitrogen availability. These findings suggest that in future oceans with eutrophication and MHWs, the harmful alga U. intestinalis may have more advantages over the economic alga G. lemaneiformis.

Changes in dissolved organic pool and regulation of associated nutrients during green tides: A case study of Ulva prolifera bloom in the southern Yellow Sea

To explore the spatial and temporal distributions of dissolved organic matter (DOM) affected by Ulva prolifera bloom and the regulation of DOM released by the addition of nitrate (NO₃-N) nutrients, the variation in DOM was analyzed by three cruises in the coastal waters of the southern Yellow Sea (SYS) off Qingdao during a 2018 U. prolifera bloom. A mesocosm experiment was conducted during the decay of U. prolifera. The U. prolifera bloom resulted in higher concentrations of the bulk DOM except for total dissolved amino acids (TDAA), compared with levels recorded during non-bloom periods. Three different fluorescent substances of chromophoric dissolved organic matter (CDOM) were identified, which were also affected by the bloom. Concentrations of total dissolved carbohydrates (TCHO), monosaccharides (MCHO), and polysaccharides (PCHO) peaked during the late bloom, with average levels of 49.78 ± 9.73, 14.23 ± 3.32, and 35.55 ± 9.19 μmol C L^-1, respectively, accompanied by an increase of DOC, indicating release of DOM with U. prolifera decay. In contrast, the concentrations of CDOM and TDAA declined during the late bloom, with averages of 0.10 ± 0.10 m^-1 and 1.16 ± 0.82 μmol L^-1, suggesting that the yields of CDOM and TDAA were regulated by the U. prolifera bloom and other mechanism. These findings were confirmed by the mesocosm experiment. DOM production was obviously improved by NO₃-N addition except for TDAA and CDOM. The release of protein-like CDOM was primarily regulated by NO₃-N nutrients, however, it was not obvious with humic-like CDOM. Our findings provide evidence supporting the role of U. prolifera blooms in the coastal DOM pool and its significant effect on the marine carbon cycle.

Metal-free carbocatalysts derived from macroalga biomass (Ulva lactuca) for the activation of peroxymonosulfate toward the remediation of polycyclic aromatic hydrocarbons laden marine sediments and its impacts on microbial community

Potential toxic chemicals, specifically, polycyclic aromatic hydrocarbons (PAHs), are major sediment contaminants. Herein, green seaweed (Ulva lactuca) was used as a feedstock and pyrolyzed at temperature in the range between 300 and 900 °C. The metal-free carbocatalyst (GSBC) for peroxymonosulfate (PMS) activation to degrade PAHs contaminated sediments was studied. The effects of GSBC‒PMS treatment on microbial community abundance was studied as well. The pyrolysis temperature of GSBC preparation affected the PMS activation performance. Results show that GSBC700 exhibited remarkable catalytic characteristics in PAHs degradation by effective activation of PMS. The results also demonstrated that the sulfate radical-carbon-driven advanced oxidation processes (SR-CAOP) reaction achieved 87% and apparent rate constant (k_obs) of 6.3 × 10^-2 h^-1 of total PAHs degradation in 24 h at 3.3 g/L of GSBC, PMS dose of 1 × 10^-4 M, and pH 3.0. The degradation of 2-, 3-, 4-, 5-, and 6-ring PAHs was 84, 83, 83, 80, and 89%, respectively. The synergetic effect established between GSBC and PMS enhanced the formation of ROSs, namely, SO₄^-, HO, and ¹O₂, which were major species contributing to PAHs degradation. The synergistic effect of π‒π stacking structure and graphitization of GSBC formed electron shuttle, which contributed to PAHs degradation performance. Microbial community structure analyses in the GSBC‒PMS treated sediments showed that the relative abundance of Lactobacillus_rhamnosus species, most of which belonged to the Lactobacillus genus and Firmicutes phylum, which aided in continuing PAHs biodegradation post GSBC‒PMS treatment. Therefore, GSBC can be a promising carbocatalyst produced via biomass-to-biochar conversion as biowaste-to-energy source used in the SR-CAOP-mediated process for sediment remediation.

Polyphenols extracted from Enteromorpha clathrata alleviates inflammation in lipopolysaccharide-induced RAW 264.7 cells by inhibiting the MAPKs/NF-κB signaling pathways

ETHNOPHARMACOLOGY RELEVANCE

Enteromorpha has long been recorded in traditional Chinese medicine, with cholesterol-lowering, anti-cancer, anti-inflammatory and antibacterial effects. Recently, we extracted the polyphenol-enriched fraction from Enteromorpha clathrata (E. clathrata) by ethyl acetate (ECPs), and isolated six individual polyphenols from ECPs via high-speed counter-current chromatography (HSCCC) with high-performance liquid chromatography (HPLC).

AIM OF THE STUDY

In this study, we explored the anti-inflammatory activity and underlying mechanism of ECPs in lipopolysaccharide (LPS)-induced RAW 264.7 macrophages.

MATERIALS AND METHODS

ECPs and the six polyphenols were used for nitric oxide (NO) assay to identify the components with potent inflammation inhibitory effect. Enzyme-linked immunosorbent assay (ELISA), quantitative real-time PCR (qPCR), flow cytometry, and Western blot analysis were applied to further investigate their anti-inflammatory effects and underlying mechanism in LPS-stimulated RAW264.7 cells.

RESULTS

ECPs and the three individual polyphenols, including (-)-epicatechin, epigallocatechin-3-O-gallate and (-)-epicatechin-3-O-gallate, showed in vitro immunosuppressive activity by altering the cell biology at the gene, protein and functional levels in a dose- and species-dependent manner. Their anti-inflammatory effects were achieved by inhibiting LPS-induced production of nitric oxide and its upstream enzyme inducible nitric oxide synthase (iNOS), the pro-inflammatory cytokines including interleukin-1 beta (IL-1β), interleukin-6 (IL-6) and tumor necrosis factor-alpha (TNF-α), as well as the phagocytotic capacity, without cytotoxicity. The mechanism study further revealed that these anti-inflammatory properties were, at least partly, attributed to the suppressed activation of nuclear factor-κB (NF-κB) and p38 mitogen-activated protein kinase (MAPK) signaling pathways.

CONCLUSIONS

These findings indicated for the first time the correlation between the anti-inflammatory activity of ECPs and NF-κB and MAPK signaling pathways, suggesting that polyphenol-enriched organic fraction of E. clathrata could be potential candidate as therapeutic agent for treating inflammatory diseases.

Seaweed Extracts: A Promising Source of Antibiofilm Agents with Distinct Mechanisms of Action against Pseudomonas aeruginosa

The organization of bacteria in biofilms is one of the adaptive resistance mechanisms providing increased protection against conventional treatments. Thus, the search for new antibiofilm agents for medical purposes, especially of natural origin, is currently the object of much attention. The objective of the study presented here was to explore the potential of extracts derived from three seaweeds: the green Ulva lactuca, the brown Stypocaulon scoparium, and the red Pterocladiella capillacea, in terms of their antibiofilm activity against P. aeruginosa. After preparation of extracts by successive maceration in various solvents, their antibiofilm activity was evaluated on biofilm formation and on mature biofilms. Their inhibition and eradication abilities were determined using two complementary methods: crystal violet staining and quantification of adherent bacteria. The effect of active extracts on biofilm morphology was also investigated by epifluorescence microscopy. Results revealed a promising antibiofilm activity of two extracts (cyclohexane and ethyl acetate) derived from the green alga by exhibiting a distinct mechanism of action, which was supported by microscopic analyses. The ethyl acetate extract was further explored for its interaction with tobramycin and colistin. Interestingly, this extract showed a promising synergistic effect with tobramycin. First analyses of the chemical composition of extracts by GC-MS allowed for the identification of several molecules. Their implication in the interesting antibiofilm activity is discussed. These findings suggest the ability of the green alga U. lactuca to offer a promising source of bioactive candidates that could have both a preventive and a curative effect in the treatment of biofilms.

Ulva compressa from Copper-Polluted Sites Exhibits Intracellular Copper Accumulation, Increased Expression of Metallothioneins and Copper-Containing Nanoparticles in Chloroplasts

In order to analyze the mechanisms involved in copper accumulation in Ulva compressa, algae were collected at control sites of central and northern Chile, and at two copper-polluted sites of northern Chile. The level of intracellular copper, reduced glutathione (GSH), phytochelatins (PCs), PC2 and PC4, and transcripts encoding metallothioneins (MTs) of U. compressa, UcMT1, UcMT2 and UcMT3, were determined. Algae of control sites contained around 20 μg of copper g⁻¹ of dry tissue (DT) whereas algae of copper-polluted sites contained 260 and 272 μg of copper g⁻¹ of DT. Algae of control sites and copper-polluted sites did not show detectable amounts of GSH, the level of PC2 did not change among sites whereas PC4 was increased in one of the copper-polluted sites. The level of transcripts of UcMT1 and UcMT2 were increased in algae of copper-polluted sites, but the level of UcMT3 did not change. Algae of a control site and a copper-polluted site were visualized by transmission electron microscopy (TEM) and the existence of copper in electrodense particles was analyzed using energy dispersive x-ray spectroscopy (EDXS). Algae of copper-polluted sites showed electrodense nanoparticles containing copper in the chloroplasts, whereas algae of control sites did not. Algae of a control site, Cachagua, were cultivated without copper (control) and with 10 μM copper for 5 days and they were analyzed by TEM-EDXS. Algae cultivated with copper showed copper-containing nanoparticles in the chloroplast whereas control algae did not. Thus, U. compressa from copper-polluted sites exhibits intracellular copper accumulation, an increase in the level of PC4 and expression of UcMTs, and the accumulation of copper-containing particles in chloroplasts.

In vitro digestibility and Caco-2 cell bioavailability of sea lettuce (Ulva fenestrata) proteins extracted using pH-shift processing

Seaweed is a promising sustainable source of vegan protein as its farming does not require arable land, pesticides/insecticides, nor freshwater supply. However, to be explored as a novel protein source the content and nutritional quality of protein in seaweed need to be improved. We assessed the influence of pH-shift processing on protein degree of hydrolysis (%DH), protein/peptide size distribution, accessibility, and cell bioavailability of Ulva fenestrata proteins after in vitro gastrointestinal digestion. pH-shift processing of Ulva, which concentrated its proteins 3.5-times, significantly improved the %DH from 27.7±2.6% to 35.7±2.1% and the amino acid accessibility from 56.9±4.1% to 72.7±0.6%. Due to the higher amino acid accessibility, the amount of most amino acids transported across the cell monolayers was higher in the protein extracts. Regarding bioavailability, both Ulva and protein extracts were as bioavailable as casein. The protein/peptide molecular size distribution after digestion did not disclose a clear association with bioavailability.

24(R, S)-Saringosterol - From artefact to a biological medical agent

Enhancing the cholesterol turnover in the brain via activation of liver x receptors can restore memory in a mouse model for Alzheimer's disease. The edible Asian brown alga Sargassum fusiforme (Hijiki) contains high amounts of oxysterols such as (3β, 24ξ)-stigmasta-5, 28-dien-3, 24-diol (24[R, S]-saringosterol) that are a potent liver x receptor agonists. We aimed to find native European seaweed species with contents of 24(R, S)-saringosterol that are comparable to those found in Sargassum fusiforme. Additionally, we hypothesize that seasonal variations modify the amount of 24(R, S)-saringosterol in seaweeds. Sterols and oxysterols were extracted with chloroform/methanol from various seaweed species harvested in the Eastern Scheldt in different seasons between October 2016 and September 2017. Identification and quantification of the lipids was performed by gas chromatography- mass spectrometry and gas chromatography- flame ionization detection. We confirmed that brown algae Undaria pinnatifida harvested in February and Sargassum muticum harvested in October contained the highest amounts of 24(R, S)-saringosterol (32.4 ± 15.25 μg/g, mean ± S.D. and 32.95 ± 2.91 μg/g, respectively) and its precursor fucosterol (1.48 ± 0.11 mg/g), higher than Sargassum fusiforme (20.94 ± 3.00 μg/g, mean ± S.D.), while Ascophyllum nodosum and Fucus vesiculosus and Fucus serratus contained amounts of 24(R, S)-saringosterol (22.09 ± 3.45 μg/g, 18.04 ± 0.52 μg/g and 19.47 ± 9.01 μg/g, mean ± S.D., respectively) comparable to Sargassum fusiforme. In other algae only minor amounts of these sterols were observed. The green algae Ulva lactuca contained only 0.29 mg/g fucosterol and 10.3 μg/g 24 (R, S)-saringosterol, while all investigated red algae did not contain any 24(R, S)-saringosterol or fucosterol. In the Eastern Scheldt algae harvested in September/October delivered the highest yield for 24(R, S)-saringosterol, with the exception of Undaria pinnatifida that showed the highest levels in February. We showed that exposure of lipid extracts of Ulva lactuca to sunlight at room temperature or in the presence of oxygen to UV-C light lead to the quantitative conversion of fucosterol into 24(R, S)-saringosterol. Exposing pure fucosterol to UV-light did not convert any fucosterol into 24(R, S)-saringosterol underscoring the requirement of seaweed constituents in the conversion of fucosterol into 24(R, S)-saringosterol. In conclusion, we showed that brown seaweeds harvested from the Eastern Scheldt contain amounts of 24(R, S)-saringosterol comparable to Sargassum fusiforme, varying per season and showing the highest amounts in spring. In accordance with these observations the amount of 24(R, S)-saringosterol in the brown seaweeds can be modulated by light.

High external Na+, but not K+, stimulates the growth of Ulva lactuca (L.) via induction of the plasma membrane ATPases and achievement of K+/Na+ homeostasis

This study aims at investigating the specific ion effects of Na⁺ and K⁺ on Ulva lactuca (L.) growth. U. lactuca was grown in balanced nutrient solutions with 10, 100, 300 and 600 mM NaCl or KCl. The growth was significantly higher at 300 and 600 mM NaCl compared to KCl, with the highest growth rate at 300 mM NaCl. NaCl-treated alga showed increases in the photosynthetic pigments and Rubisco protein content. However, KCl treatments adversely affected these photosynthetic attributes. U. lactuca needs adjusted, but not high K⁺/Na⁺ ratio for a proper growth, since the high K⁺/Na⁺ ratio in KCl-treated alga was associated with growth retardation. The cell wall was more extensible at high concentrations of NaCl compared to KCl. Therefore, the deleterious effect of K⁺ could be mainly on the cell wall and hence inhibiting the growth and perhaps the vitality of the whole cell. The transcript of plasma membrane (PM) H⁺-ATPase was detected only at 300 and 600 mM NaCl, implying that this gene was specifically induced by high concentrations of Na⁺ but not K⁺. The transcript of PM-Na⁺/K⁺-ATPase-like exhibited no Na⁺ specificity and its induction alone could not improve the growth of KCl-treated U. lactuca. The simultaneous induction of the two PM-ATPases could positively affect the algal growth at high NaCl concentrations by maintaining the proper cellular K⁺/Na⁺ ratio. Also, both PM-ATPases might contribute to energizing the plasma membrane and thereby promoting the cellular growth of U. lactuca at high Na⁺, but not K⁺, concentrations.

How Ulva lactuca can influence the impacts induced by the rare earth element Gadolinium in Mytilus galloprovincialis? The role of macroalgae in water safety towards marine wildlife

Rare earth elements (REEs) are gaining growing attention in environmental and ecotoxicological studies due to their economic relevance, wide range of applications and increasing environmental concentrations. Among REEs, special consideration should be given to Gadolinium (Gd), whose wide exploitation as a magnetic resonance imaging (MRI) contrast agent is enhancing the risk of its occurrence in aquatic environments and impacts on aquatic organisms. A promising approach for water decontamination from REEs is sorption, namely through the use of macroalgae and in particular Ulva lactuca that already proved to be an efficient biosorbent for several chemical elements. Therefore, the present study aimed to evaluate the toxicity of Gd, comparing the biochemical effects induced by this element in the presence or absence of algae. Using the bivalve species Mytilus galloprovincialis, Gd toxicity was evaluated by assessing changes on mussels' metabolic capacity and oxidative status. Results clearly showed the toxicity of Gd but further revealed the capacity of U. lactuca to prevent injuries to M. galloprovincialis, mainly reducing the levels of Gd in water and thus the bioaccumulation and toxicity of this element by the mussels. The results will advance the state of the art not only regarding the effects of REEs but also with regard to the role of algae in accumulation of metals and protection of aquatic organisms, generating new insights on water safety towards aquatic wildlife and highlighting the possibility for resources recovery.

The effect of Ulva lactuca and Sargassum hemiphyllum var. chinense on arsenic metabolites and enzymes in broilers

This study investigated the effect of seaweed supplementation (Ulva lactuca (UL) or Sargassum hemiphyllum var. chinense (SHC)) on the distribution and metabolites of As in broiler breasts. Broilers fed 5% UL or 5% SHC ingested 1.4- or 78- fold greater total As than birds fed the control diet. The majority of As species were arsenate in the SHC feed and dimethylarsinic acid in breasts from chicks fed the SHC-containing diet. Arsenate and arsenobetaine were the dominant metabolites in the UL-containing feed, and arsenobetaine was the major metabolite in breasts from chicks fed the UL-containing diet. Feeding SHC enhanced hepatic S-adenosyl-methionine and arsenic methyltransferase, whereas feeding UL elevated renal arsenic methyltransferase. Taken together, considerable variation in the profiles of As species and As metabolites existed in broilers fed seaweed. The use of SHC-containing feeds in poultry production should be approached cautiously because of the potential accumulation of inorganic As species in chicken breasts.

Synthesis and release of fatty acids under the interaction of Ulva pertusa and Heterosigma akashiwo by stable isotope analysis

Symbiosis of marine algae is inevitable in the marine environment, and species may occur interaction on the growth. In this study, the macroalgae Ulva pertusa and marine microalgae Heterosigma akashiwo were selected as target species to study the interaction mechanism between them. After the 8 days of co-cultivation, the inhibition on growth was observed for both of U. pertusa and H. akashiwo. Eight fatty acids in U. pertusa was detected, with the significant decrease in contents of polyunsaturated fatty acids (PUFAs) especially for C18:2, C18:3n-3 and C18:3n-6. Twelve fatty acids in H. akashiwo was detected, with the significant change for PUFAs. PUFA concentrations in the co-culture group were less than those in the mono-culture. Meanwhile the principal component analysis was conducted to insight into the interaction between U. pertusa and H. akashiwo by fatty acids content and carbon stable isotope ratio of fatty acids (δ¹³C_FAs). Fatty acid content could not distinguish mono and co-culture. However, δ¹³C_FAs could distinguish not only the culture time of algae, but also the living environment of algae. In addition, this study combined fatty acids content and δ¹³C_FAs to explore the release of fatty acids by algae into the seawater. The C18:3n-3 was identified as the allelochemical released by U. pertusa to inhibit the growth of H. akashiwo. The ratio of δ¹³C_FAs in seawater decreased. This study provides a theoretical basis for the symbiosis of marine algae, and a new method of compound-specific stable carbon isotopes was used to better explore the metabolism of fatty acids in algae.

Effect of different cooking methods on sea lettuce (Ulva rigida) volatile compounds and sensory properties

BACKGROUND

The effect of different cooking methods (boiling, vacuum and steamed cooking) on the volatile compound content and sensory properties of sea lettuce (Ulva rigida) seaweed was assessed. Sea lettuce was cooked at three different temperatures (50, 70 and 100 °C) for three different lengths of time (5, 10 and 15 min). Various statistical techniques were employed in order to establish any possible changes.

RESULTS

The different cooking methods modified significantly both the volatile compound content and the sensory properties of sea lettuce seaweed. In general, the cooked samples had lower concentrations of several volatile compounds than the control sample, mainly aldehydes. Regarding sensory analysis, the cooked samples exhibited lower values for various aroma descriptors such as seaside and seaweed, whereas descriptor scores such as cooked fish, salty dry fish and crustacean increased. No clear statistical differences were found between different cooking lengths of time and temperature levels with regard to both volatile compounds and sensory properties.

CONCLUSIONS

In the cooking of sea lettuce seaweeds, the main sensory changes and modifications in their volatile content took place during the first minutes of cooking and at medium cooking temperatures. © 2020 Society of Chemical Industry.

Nephroprotective effect of ethanol extract and fractions of a sea lettuce, Ulva fasciata against cisplatin-induced kidney injury in rats

Cisplatin is widely used in anticancer therapy, but a substantial percentage of patients who receive the therapeutic dose of cisplatin develop nephrotoxicity. Hepatotoxicity may also develop after a single dose or low repeated doses of cisplatin. Ulva fasciata is an edible seaweed, commonly known as sea lettuces have also been shown various biological activities. In this study, ethanol extract and its solvent fractions (n-hexane and chloroform) of U. fasciata were given (orally) to different groups of rats for 10 days. Injury to the kidney was induced by administrating cisplatin, intraperitoneally (i.p.) to rats at a dose of 7 mg/kg body weight (b.w.) dissolved in 1 mL saline, at 5th day of the experiment. At 10th day rats were sacrificed and kidney parameters (creatinine, urea, and blood urea nitrogen (BUN)) and electrolyte balance (Ca⁺⁺, Mg⁺⁺, K+, and Na⁺) in serum were determined, while oxidative stress markers glutathione (GSH), catalase (CAT) and malondialdehyde (MDA), and inflammatory cytokines, tumor necrosis factor (TNF α), and interleukin (IL-6) were determined in kidney tissues. Histological examination of the kidney was also performed to examine the changes in kidney tissues. Cisplatin caused adverse effects on blood parameters, antioxidants, and inflammatory markers with severe renal tubular injury in kidney tissues. Ethanol extract of U. fasciata and its fractions effectively improved these disorders and diminished the renal dysfunction. However, ethanol extract was found more effective in attenuating the adverse effect of cisplatin than its fractions. n-Hexane-soluble fraction that was subjected to GC-FID and GC-MS analysis revealed the presence of several compounds and some of them are new from this source. It could be concluded that the U. fasciata possesses nephroprotective effect and can attenuate cisplatin-induced renal dysfunction. Since U. fasciata is an edible seaweed, it may be used as a diet supplement.

Photoprotection and antioxidative metabolism in Ulva lactuca exposed to coastal oceanic acidification scenarios in the presence of Irgarol

Anthropogenic changes such as ocean acidification, eutrophication, and the release of hazardous chemicals affect coastal environments and aquatic organisms. We investigated the effects of seawater pH (7.4 and 8.2) isolated and in combination with Irgarol on Ulva lactuca. Stress indicators such as membrane damage, lipid peroxidation, and hydrogen peroxide content were assessed. In addition, chlorophyll fluorescence and antioxidant enzyme activities were measured. The photosynthetic yield was affected by low pH in assays with and without Irgarol. However, the combination of low pH and Irgarol promoted photoinhibition, besides the induction of non-photochemical quenching (NPQ) and changes in photosynthetic pigment contents. The induction of NPQ was directly influenced by low pH. The membrane damage was increased in low pH with and without Irgarol exposure. Total soluble protein and carbohydrate contents decreased in low pH, and in presence of Irgarol. The H₂O₂ content and lipid peroxidation were not affected by low pH. In contrast, Irgarol exposure strongly increased lipid peroxidation in both pHs, suggesting a possible synergistic effect. To avoid the harmful effects of high H₂O₂, U. lactuca increased antioxidant enzyme activities in treatments under low pH and in presence of Irgarol. Our results indicate that U. lactuca is tolerant to low pH by inducing NPQ, changing pigment contents, and increasing antioxidant defenses. In contrast, these protective mechanisms could not avoid the harmful effects of the combination with Irgarol.

Bioprocessing strategies for cost-effective simultaneous removal of chromium and malachite green by marine alga Enteromorpha intestinalis

A large number of industries use heavy metal cations to fix dyes in fabrication processes. Malachite green (MG) is used in many factories and in aquaculture production to treat parasites, and it has genotoxic and carcinogenic effects. Chromium is used to fix the dyes and it is a global toxic heavy metal. Face centered central composite design (FCCCD) has been used to determine the most significant factors for enhanced simultaneous removal of MG and chromium ions from aqueous solutions using marine green alga Enteromorpha intestinalis biomass collected from Jeddah beach. The dry biomass of E. intestinalis samples were also examined using SEM and FTIR before and after MG and chromium biosoptions. The predicted results indicated that 4.3 g/L E. intestinalis biomass was simultaneously removed 99.63% of MG and 93.38% of chromium from aqueous solution using a MG concentration of 7.97 mg/L, the chromium concentration of 192.45 mg/L, pH 9.92, the contact time was 38.5 min with an agitation of 200 rpm. FTIR and SEM proved the change in characteristics of algal biomass after treatments. The dry biomass of E. intestinalis has the capacity to remove MG and chromium from aquatic effluents in a feasible and efficient manner.

Effect of allelochemicals on photosynthetic and antioxidant defense system of Ulva prolifera

Ulva prolifera is a macroalgae that forms massive blooms, negatively impacting natural communities, aquaculture operations and recreation. The effects of the natural products, eugenol, β-myrcene, citral and nonanoic acid on the growth rate, antioxidative defense system and photosynthesis of Ulva prolifera were investigated as a possible control strategy for this harmful taxon. Negative effects on growth were observed with all four chemicals, due to the excessive production of reactive oxygen species and oxidative damage to the thalli. However, the response of U. prolifera under the four chemicals stress was different at the cellular level. β-myrcene, the most effective compound in terms of growth inhibition, induced oxidative stress as shown by the damage of total antioxidant capacity (T-AOC) and the downregulation of the glutathione-ascorbate (GSH-ASA) cycle which inhibited the antioxidative system. This chemical also inhibited photosynthesis and photoprotection mechanisms in U. prolifera, resulting in growth limitation. In contrast, U. prolifera was less affected by the second tested chemical, eugenol, and showed no significant change on photosynthetic efficiency in the presence of the chemical. The inhibition effects of the third and fourth tested chemicals, nonanoic acid and citralon, on growth and on the antioxidant defense system in U. prolifera were inferior. These results provide a potential avenue for controlling green tides in the future.

The utilization of seawater for the hydrolysis of macroalgae and subsequent bioethanol fermentation

A novel seawater-based pretreatment process was developed to improve the hydrolysis yield of brown (Laminaria digitata), green (Ulva linza) and red (Porphyra umbilicalis) macroalgae. Pre-treated with 5% sulphuric acid at 121 °C, 15 minutes, L. digitata, U. linza and P. umbilicalis liberated 64.63 ± 0.30%, 69.19 ± 0.11% and 63.03 ± 0.04% sugar in seawater compared with 52.82 ± 0.16%, 45.93 ± 0.37% and 48.60 ± 0.07% in reverse-osmosis water, respectively. Low hydrolysis yields (2.6-11.7%) were observed in alkali and hydrothermal pretreatment of macroalgae, although seawater led to relatively higher yields. SEM images of hydrolyzed macroalgae showed that reverse-osmosis water caused contortions in the remaining cell walls following acid and hydrothermal pre-treatments in the L. digitata and U. linza samples. Fed-batch fermentations using concentrated green seaweed hydrolysates and seawater with marine yeast Wickerhamomyces anomalus M15 produced 48.24 ± 0.01 g/L ethanol with an overall yield of 0.329 g/g available sugars. Overall, using seawater in hydrolysis of seaweed increased sugar hydrolysis yield and subsequent bioethanol production.

Photosynthetic and biochemical traits change in the green-tide-forming macroalga Ulva pertusa during sporulation1

The physiological and biochemical changes in the green macroalga Ulva pertusa during the progression of sporulation have been characterized. The transition from the vegetative to the sporulation stage was accompanied by an increase in chlorophyll a (Chl a), chlorophyll b (Chl b), and carotenoid content, as well as an increase in DPPH scavenging and responsiveness to diphenylamine. However, oxygen evolution and maximum electron transport rate decreased. The discrepancy between photosynthetic performance and pigment content might relate to the self-shading of spores within a sporangium. Spore-forming U. pertusa thalli were low-light-adapted, due to an increase in the number of photosynthetic units. Decreased electron transport during sporulation might trigger sporulation, as for some cyanobacteria and other Ulva spp., via oxidization of the plastoquinone pool and cyclic phosphorylation, thus producing ATP to generate carbon and nitrogen skeletons required for spores. It is thus concluded that carotenoids function both in spore initiation and/or maturation and in their photoprotection.

Copper-induced concomitant increases in photosynthesis, respiration, and C, N and S assimilation revealed by transcriptomic analyses in Ulva compressa (Chlorophyta)

BACKGROUND

The marine alga Ulva compressa is the dominant species in copper-polluted coastal areas in northern Chile. It has been shown that the alga tolerates micromolar concentrations of copper and accumulates copper at the intracellular level. Transcriptomic analyses were performed using total RNA of the alga cultivated with 10 μ M copper for 0, 1, 3 and 5 days using RNA-seq in order to identify processes involved in copper tolerance.

RESULTS

The levels of transcripts encoding proteins belonging to Light Harvesting Complex II (LHCII), photosystem II (PSII), cytochrome b6f, PSI, LHCI, ATP synthase and proteins involved in repair of PSII and protection of PSI were increased in the alga cultivated with copper. In addition, the level of transcripts encoding proteins of mitochondrial electron transport chain, ATP synthase, and enzymes involved in C, N and S assimilation were also enhanced. The higher percentages of increase in the level of transcripts were mainly observed at days 3 and 5. In contrast, transcripts involved protein synthesis and degradation, signal transduction, and replication and DNA repair, were decreased. In addition, net photosynthesis and respiration increased in the alga cultivated with copper, mainly at days 1 to 3. Furthermore, the activities of enzymes involved in C, N and S assimilation, rubisco, glutamine synthase and cysteine synthase, respectively, were also increased, mainly at days 1 and 3.

CONCLUSIONS

The marine alga U. compressa tolerates copper excess through a concomitant increase in expression of proteins involved in photosynthesis, respiration, and C, N and S assimilation, which represents an exceptional mechanism of copper tolerance.

Bioprospecting of seaweeds (Ulva lactuca and Stoechospermum marginatum): The compound characterization and functional applications in medicine-a comparative study

Seaweeds are considered to be one of the richest bio-reserves, comprising of numerous bioactive compounds with versatile properties and multiple activities. The present study examined the antibacterial activity of two types of seaweeds, Ulva lactuca (green) and Stoechospermum marginatum (brown) collected from Oman Coastal region against five multidrug-resistant bacteria. The aqueous extracts of the seaweeds showed better antibacterial activity compared to methanol extracts. The results of the antibacterial assay revealed the excellent inhibitory effects of U.lactuca with the maximum activity against E.coli(8 mm) followed by K.pneumonia(4 mm) and S.typhi(2 mm). S.marginatum formed a clear zone of inhibition only against E.coli(3 mm).The major phytochemical constituents identified in both the types of seaweeds were Alkaloids, Terpenoids, Saponins, Flavonoids, and Steroids. Fourier transform infrared spectroscopy (FTIR) results confirmed the presence of alcoholic/phenolic groups, and amide groups in the seaweed extracts. Gas chromatography-mass spectrometry (GC-MS) results evidenced the presence of bioactive compounds such as 5-Octadecenal, 1-Tricosanol, Neophytadiene, Lactaropallidin, Phytol, Fenretinide, Lucenin, Vincadifformine in U.lactuca. Additionally, U.lactuca displayed better antioxidant activity (33.05%) in the DPPH free radical scavenging activity test compared to the S.marginatum (21.51%). Thus, the green seaweed U.lactuca could be considered as a potential source of natural antioxidant and antibacterial agents for food and pharmaceutical products.

Potential benefits of polysaccharides derived from marine alga Ulva lactuca against hepatotoxicity and nephrotoxicity induced by thiacloprid, an insecticide pollutant

The present study aimed to evaluate the potential protective and antioxidant effect of polysaccharides (PS) extracted from Ulva lactuca against thiacloprid (THC) induced nephrotoxicity and hepatotoxicity. The antioxidant capacity of PS was tested in vitro using ABTS radical scavenging activity and plasmid DNA cleavage assays andin vivo on adult male rats treated for 30 days. Animals were allocated into four groups: control; THC (22.5 mg/kg); THC (22.5 mg/kg) + PS1 (100 mg/kg diet); and THC (22.5 mg/kg) + PS2 (200 mg/kg diet). The structural features of PS were determined by Fourier transformed infrared (FT-IR), UV absorption peak detection, high performance liquid chromatography (HPLC) and gel permeation chromatography, and also functional properties were investigated. Overall, results indicated that THC increased significantly malondialdehyde, advanced oxidation protein products, glutathione levels, which is correlated with severe histological and plasmatic biochemical injuries in both liver and kidney tissues. However, cotreatment PS induced a significant protective and healing affects against the nephrotoxicity and hepatotoxcity induced by THC.

Cooking effects on bioaccessibility of chlorophyll pigments of the main edible seaweeds

Edible seaweeds are highly consumed food with a rich chlorophyll profile. Although seaweeds are mainly cooked ingested, the influence of cooking on the chlorophyll bioaccessibility remains unknown. In this research, cooked Nori, Sea Lettuce and Kombu were subjected to an in vitro digestion and following micellarization investigations. The processing of red seaweed does not affect the chlorophyll recovery, while cooking green and brown seaweeds implies an important increase in chlorophyll recovery after in vitro digestion. In this line, while cooking affects negatively the micellarization rate of chlorophyll derivatives in Nori and Kombu, it does not modify the micellarization in Sea Lettuce. Generally, the chlorophyll bioaccessibility of microwaved seaweeds is always higher than that of boiled ones. However, cooking improves the chlorophyll bioaccessibility in brown seaweeds, while decreases in red seaweeds. In conclusion, the characteristics of food matrix are the determinant factor on the chlorophyll bioaccessibility of cooked seaweeds.

The different responses of growth and photosynthesis to NH4+ enrichments between Gracilariopsis lemaneiformis and its epiphytic alga Ulva lactuca grown at elevated atmospheric CO2

We investigated how elevated CO₂ affects the responses of Gracilariopsis lemaneiformis and Ulva lactuca to NH₄⁺ enrichments. All algae were incubated under four nutritional conditions (zero addition, 100, 500, and 2500 μM NH₄⁺), and two CO₂ levels (390 ppm and 1000 ppm). The growth, photosynthesis, and soluble protein contents of both species increased under the eutrophication condition (100 μM NH₄⁺). However, the growth and carotenoid contents of the two species declined when NH₄⁺ concentration increased. Under the super eutrophication condition (2500 μM NH₄⁺), all indexes measured in G. lemaneiformis were suppressed, while the growth and photosynthesis in U. lactuca changed indistinctively, both compared with the control. Moreover, under the super eutrophication condition, elevated CO₂ reduced the suppression in the growth of G. lemaneiformis, but decreased the growth of U. lactuca. Nonetheless, G. lemaneiformis displayed much lower growth rates than U. lactuca under the super eutrophication and elevated CO₂ condition.

Chemical diversity and anti-proliferative activity of marine algae

The chemical diversity of three macroalgae (Ulva reticulata, Sargassum wightii, Gracilaria sp) were determined using the GC-MS method with principal component analysis (PCA) and their potential efficacy against human pathogens and cervical carcinoma cells evaluated using MTT bioassay method. Our results showed that >30 metabolites were detected in three seaweeds, among these, steroids and fatty acids are the most dominant chemical group that highly contributes to discriminate this species. The PCA of GC-MS mass spectral variables showed a clear discrimination between three different species based on the phytochemical diversity of seaweeds. The extracts of U. reticulata exhibited anti-microbial activity with Pseudomonas aeruginosa (6.00 mm) and showed potential anti-proliferative activity against the HeLa cells (IC50 37 µmol/L) at concentration 1-50 µM treatment. Results of this study concluded that PCA analysis of mass spectral variables could be utilized as a reliable tool for species discrimination and chemotaxonomic classification of seaweeds.

Phytoremediation potential of Ulva ohnoi (Chlorophyta): Influence of temperature and salinity on the uptake efficiency and toxicity of cadmium

Ulva ohnoi is a green macroalga with fast growth and high rates of nitrogen and phosphorus absorption. Recently, this species has been recorded in several places with record green tide formation in some of them. Using molecular tools, we herein report the first occurrence of this species in Brazil and demonstrate its potential for phytoremediation in typical environmental concentrations of Cd (0.625-15 µg L^-1). Similarly, the effects of physicochemical parameters (salinity and temperature) on the toxicity and uptake efficiency of this species were evaluated. Molecular analysis of two sequences (1141 bp) obtained corroborates another 34 sequences for U. ohnoi obtained from GenBank. The addition of Cd in the medium affected photosynthetic parameters and reduced growth rate. U. ohnoi showed resistance to Cd when cultivated at 18 °C, S15 and 18-25 °C, S35, at concentrations between 0.625 and 2.5 μg. L^-1 of Cd; yet, positive growth rate was maintained. Dose-dependent accumulation was observed in all combinations of factors used with a maximum value of 4.20 μg Cd per gram of dry seaweed at 15 μg. L^-1 of Cd at 18 °C and S35. Maximum value of the concentration factor was 81.3 ± 1.1% of Cd added at the concentration of 0.625 μg. L^-1 to S15 and 18 °C. Our results demonstrate the potential of using U. ohnoi in the phytoremediation of Cd in saltwater or brackish water.

Sequential bioprocessing of Ulva rigida to produce lignocellulolytic enzymes and to improve its nutritional value as aquaculture feed

The macroalgae aquaculture industry has grown up in the last years, and new applications for macroalgae should be considered. In this work, sequential biological treatments as solid-state fermentation (SSF) by Aspergillus ibericus and enzymatic hydrolysis (EH) were applied to washed and unwashed Ulva rigida. SSF of unwashed macroalgae showed higher xylanase (359.8 U/g), cellulase (73.07 U/g) and β-glucosidase (14.9 U/g) activities per dry mass of macroalgae. After SSF, two strategies to carry out EH were assayed. The best process was SSF followed by EH by simply adding a buffer. The non-starch polysaccharides content was reduced by 93.2%, achieving a glucan conversion of 98%. In addition, the antioxidant activity was improved 2.8-fold and the protein concentration of macroalgae extracts increased from 16.9% to 29.8% (w/w). These biological treatments allowed to increase macroalgae value as feedstuff with potential for use in aquafeeds.

Synergism of clay with zinc oxide as nanocatalyst for production of biodiesel from marine Ulva lactuca

In the present work, Ulva lactuca, a marine macroalgae was used for the production of biodiesel. The ultrasound assisted extraction of oil from autoclaved algal biomass was found effective with maximum yield. The maximum oil was extracted at optimal conditions of 5% moisture content of algal biomass, 0.15 mm size of biomass, 6:1 solvent: solid ratio, at 55 °C in 140 min. The n-hexane with co-solvent methyl tertbutyl ether has shown higher oil when compared to other co-solvents. The extracted oil was transesterified into biodiesel using silica doped with zinc oxide as novel heterogeneous nanocatalyst. The maximum biodiesel yield of 97.43% was obtained at optimized conditions of 800 °C calcination temperature, 8% catalyst concentration, 9:1 methanol to oil ratio, 55 °C reaction temperature and 50 min reaction time. The kinetics of the transesterification reaction was also studied. The Ulva lactuca was found as a potential source for biodiesel production.

The effect of salinity and alkalinity on growth and the accumulation of copper and zinc in the Chlorophyta Ulva fasciata

Copper and zinc accumulation in macroalgae is a complex issue. While these metals exist as micronutrients and can serve to add nutritional value to the macroalgae when consumed by both plants and animals, elevated levels of the metals can reduce growth or even kill the algae. Many water parameters can influence the toxicity of the metals, though past studies have rarely isolated individual water parameters. This study aimed to independently determine the effects that salinity and alkalinity have on the growth and accumulation of these two metals on the macroalgae Ulva fasciata, distinguishing the effects of salinity and alkalinity as whole parameters from the collective effects of the water different constituents. The effect of salinity was determined using sodium chloride additions rather than seawater dilution, as performed in past studies, while alkalinity was tested using sodium bicarbonate additions to artificial seawater. The results of the study reinforce previous findings that copper is very toxic to macroalgae, even at low concentrations (50 µg L^-1) though the effects of zinc remain inconclusive at 50 µg L^-1, since the experiment was conducted over only a two-week trial period. The research suggests that salinity and alkalinity have no significant effect on the toxicity of copper to the growth of the macroalgae, but alkalinity significantly reduced copper and increased zinc accumulation in U. fasciata. The results of this study warrant further research in the field to investigate which other components of seawater and macroalgae reduce metal toxicity in the macroalgae. Additionally, these findings suggest the need for further refinement of toxicity models when adapted to macroalgae.

Tracing nitrogen sources fueling coastal green tides off a volcanic island using radon and nitrogen isotopic tracers

The main sources of nutrients fueling coastal green tides off a volcanic island surrounded by an oligotrophic ocean are obscure, although they result in many societal and ecosystem problems. In this study, we attempted to trace the source inputs of nutrients in coastal waters off a volcanic island, Jeju, Korea, where the formation of green tides is perennial, using a radioisotope (²²²Rn) and stable isotopes (δ¹⁵N and δ¹⁸O) as tracers. Sampling of groundwater, seawater, fish-farm water, and Ulva spp. was performed during April and July 2015. The contribution of submarine fresh groundwater discharge (SFGD) to the dissolved inorganic nitrogen input was >70%, with additional inputs from aqua-cultural activities and bottom sediments. The δ¹⁵N-NO₃ and δ¹⁸O-NO₃ values in the coastal seawater and groundwater indicate that the main source of NO₃^- is fertilizer, rather than other potential sources, such as aquacultural wastewater, sewage/manure contamination, or precipitation, in this region. The δ¹⁵N value (+7.3-+7.7‰) in Ulva spp. also indicates the same source. Thus, our results suggest that the rapid infiltration of land N-fertilizer and subsequent leakage into the coastal ocean through submarine groundwater discharge (SGD) results in green tide massive occurrence in coastal waters off a high-permeability volcanic island.

Potential control of toxic cyanobacteria blooms with Moroccan seaweed extracts

Marine macroalgae are a promising source of diverse bioactive compounds with applications in the biocontrol of harmful cyanobacteria blooms (cyanoHABs). In this work, we evaluated the potential algicidal activities of 14 species of seaweed collected from the coast of Souiria Laqdima, Morocco. Methanol extracts were screened in solid and liquid medium against the growth of the toxic cyanobacteria Microcystis aeruginosa and the microalgae Chlorella sp. used as food supplement. The results in solid medium revealed that the algicidal activity was limited to M. aeruginosa with the extract of Bornetia secundiflora showing the highest growth inhibition activity against Microcystis (27.33 ± 0.33 mm), whereas the extracts of Laminaria digitata, Halopytis incurvus, Ulva lactuca, and Sargasum muticum showed no inhibition. In liquid medium, the results indicated that all methanolic extracts of different macroalgae tested have a significant inhibitory effect on M. aeruginosa compared with that of the negative control. The maximum inhibition rates of M. aeruginosa were produced by the extracts of Bifurcaria tuberculata, Codium elongatum, and B. secundiflora. Moreover, the extracts of B. secundiflora recorded the maximum inhibition rate of Chlorella sp. Overall, the results highlight the potential of the extracts from macroalgae to control toxic cyanobacteria species.

Extensive Variations in Diurnal Growth Patterns and Metabolism Among Ulva spp. Strains

Green macroalgae of the genus Ulva play a key role in coastal ecosystems and are of increasing commercial importance. However, physiological differences between strains and species have yet to be described in detail. Furthermore, the strains of Ulva used in aquaculture usually originate from opportunistic collection in the wild without prior selection of best performing strains. Hence, efforts are required to detect the potential variability in growth and metabolic accumulation between Ulva strains and ultimately select the best performing strains under given environmental conditions. Here, the growth, physiological, and metabolic characteristics of 49 laminar Ulva spp. strains were investigated using a custom-made high-throughput phenotyping platform, enzymatic assays, and gas chromatography-mass spectrometry. We found large natural variation for a wide range of growth and metabolic characteristics, with growth rates varying from 0.09 to 0.37 mg.mg-1d-1 among strains. Ulva spp. possess a unique diurnal growth pattern and primary metabolism compared with land plants, with higher growth rates during the night than during the light period. Starch and sucrose only contributed on average 35% of the carbon required to sustain Ulva's night growth. Nitrates accumulated during the night in Ulva tissues, and nitrate accumulation and consumption was positively correlated with growth. In addition, we identified six amino acids as possible biomarkers for high growth in Ulva The large variability in growth and metabolite accumulation recorded among morphologically similar Ulva strains justifies future efforts in strain selection for increasing biomass, metabolite yields, and nutrient removal in the growing aquaculture industry.

Phycoremediation of coastal waters contaminated with bisphenol A by green tidal algae Ulva prolifera

The phycoremediation of coastal water contaminated with bisphenol A (BPA) by Ulva prolifera (U. prolifera) during green tide blooming was investigated. The results demonstrated that BPA could be removed rapidly in the presence of U. prolifera. >94.3% of BPA was removed by live U. prolifera while <2.5% of BPA was removed by dead biomass. The accumulation of BPA in U. prolifera was confirmed by laser confocal scanning microscopy (LCSM). Uptake experiments under different conditions showed that the removal efficiency of BPA by U. prolifera had positive relationships with light, nutrient and temperature while the salinity had no effect. A linear relationship existed between the removal efficiency and the BPA initial concentration when the BPA initial concentration increased from 50 to1000 μg L^-1, indicating the high tolerance of the green-tidal algae to the toxic effect of BPA. High BPA removal efficiency (>94%) was achieved at the environmental relevant concentrations of BPA. The field investigation indicated that the BPA concentration in the coastal water in the green tide blooming area was much lower than that in the adjacent coastal water without green tide. The contribution of the green-tidal algae in the removal of BPA in the coastal waters was remarkable due to the high BPA removal efficiency, and high biomass & huge covered area of the U. prolifera during the outbreak of green tide. These findings demonstrate a new important phycoremediation process for coastal water containing typical endocrine-disrupting chemicals (EDCs) during the green tide blooming.

Efficient decolourization of malachite green with biosynthesized iron oxide nanoparticles loaded carbonated hydroxyapatite as a reusable heterogeneous Fenton-like catalyst

In this study, iron oxide nanoparticles (IO-NPs) with a mean diameter of 102.85 nm were firstly synthesized via a facile green route using Ulva spp. aqueous extract as a bioreductant agent. Then, IO-NPs were loaded into carbonated hydroxyapatite (c-Hap) and the final product was named as the iron oxide nanoparticles loaded carbonated hydroxyapatite (IO-NPs-Lc-Hap). Subsequently, IO-NPs-Lc-Hap was characterized by FT-IR, SEM, XRD and EDX analysis methods. MG colour removal efficiencies of Ulva spp., Hap, IO-NPs and IO-NPs-Lc-Hap materials were also evaluated by adsorption and/or Fenton-like reaction methods. IO-NPs-Lc-Hap with the highest decolourization capacity was chosen as a heterogeneous Fenton-like catalyst for Malachite Green (MG). For Fenton-like decolourization of MG, the optimum H₂O₂ concentration, initial dye concentration and catalyst concentration were determined to be 30 mM, 100 mg/L and 1.0 g/L, respectively. At these optimum conditions, 100% decolourization efficiency and 33.3% COD removal were obtained. On the other hand, 94% decolourization efficiency and 42% COD removal were achieved for the real textile wastewater at the obtained optimum conditions. The experimental decolourization reaction rate for MG was determined as -r_d = 0.0779 [(mg dye0^.3) (g cat^-0.3) (min^-1)] _× q_t0^.7. Also, the catalyst had high decolourization efficiencies at the end of six sequence usages.

In Vitro and In Silico Approaches to Generating and Identifying Angiotensin-Converting Enzyme I Inhibitory Peptides from Green Macroalga Ulva lactuca

A protein extract was generated from the macroalga Ulva lactuca, which was subsequently hydrolysed using the food-grade enzyme papain and angiotensin-converting Enzyme I and renin inhibitory peptides identified using a combination of enrichment strategies employing molecular weight cutoff filtration and mass spectrometry analysis. The generated hydrolysates with the most promising in vitro activity were further purified using preparative RP-HPLC and characterised. The 1 kDa hydrolysate (1 kDa-UFH), purified and collected by preparative RP-HPLC at minutes 41‒44 (Fr41‒44), displayed statistically higher ACE-I inhibitory activities ranging from 96.91% to 98.06%. A total of 48 novel peptides were identified from these four fractions by LC-MS/MS. A simulated gastrointestinal digestion of the identified peptide sequences was carried out using in silico enzyme cleavage simulation tools, resulting in 86 peptide sequences that were further assessed for their potential activity, toxicity and allergenicity using multiple predictive approaches. All the peptides obtained in this study were predicted to be non-toxic. However, 28 out of the 86 novel peptides released after the in silico gastrointestinal digestion were identified as potential allergens. The potential allergenicity of these peptides should be further explored to comply with the current labelling regulations in formulated food products containing U. lactuca protein hydrolysates.

Bioavailability of dissolved organic nitrogen and its uptake by Ulva prolifera: Implications in the outbreak of a green bloom off the coast of Qingdao, China

To investigate bioavailability of dissolved organic nitrogen (DON) and its contribution to nitrogen demand for Ulva prolifera, a cruise was conducted during a bloom of U. prolifera in Qingdao coastal waters, China, dissolved inorganic nitrogen (DIN) and DON components were investigated. Uptakes of both DIN and DON by U. prolifera were synchronously measured onboard using stable isotope techniques. The contribution of DON to total dissolved N (TDN) was >50% and that of labile components (urea and to amino acids, AA) to DON exceeded 30%. Both DIN and DON were utilized by U. prolifera, which uptake NH₄-N preferentially, then urea, NO₃-N and AA in turn; whereas the ranking of turnover times from short to long was AA, NH₄-N, urea and NO₃-N. The high uptake rates and short turnover time of AA and urea indicated that DON may play an important role in the nutrition of U. prolifera.

Marine vegetation analysis for the determination of volatile methylsiloxanes in coastal areas

Volatile methylsiloxanes (VMSs) are massively produced chemicals that comprise a wide range of industrial and household applications. The presence of cyclic and linear VMSs in several environmental matrices and ecosystems indicates persistence associated with a potential of (bio)accumulation and food web transfer with possible toxicological effects. Due to the high anthropogenic pressure in its vicinities particularly in summer, coastal areas in Southern European countries are potential hotspots for the presence of VMSs. The massive afflux of tourists and consequent increase of the use of personal care products (PCPs) with VMSs in their formulations highlight the importance of VMSs assessment in such areas. In this study, different species of marine vegetation (algae and seaweed) were collected in three different geographical areas, covering the Atlantic Ocean (North coast of Portugal), as well as the Mediterranean Sea (coasts of the Region of Murcia, Spain and of the city of Marseille, France). Samples were analysed for the determination of 4 cyclic (D3, D4, D5, D6) and 3 linear (L3, L4, L5) VMSs employing a QuEChERS extraction methodology, followed by gas chromatography/mass spectrometry (GC/MS) quantification. VMSs were detected in 92% of the 74 samples analysed, with the sum of the concentrations per sample ranging from below the limit of detection (LOD) to 458 ± 26 ng·g-1dw (dry weight). A strong predominance of cyclic VMSs over linear ones was verified in almost all samples studied, with D5 and D6 found at higher concentrations. Seasonal variation was also assessed and despite higher levels of VMSs being identified mostly in summer months, clear seasonal trends were not perceived. It was also noted that generally the higher incidence of VMSs occurred in samples from urban and industrialized areas or in the vicinities of WWTPs, suggesting a direct input from these sources in the levels of siloxanes observed.

Copper excess detoxification is mediated by a coordinated and complementary induction of glutathione, phytochelatins and metallothioneins in the green seaweed Ulva compressa

In order to analyze the involvement of intracellular thiol-chelators in the accumulation and detoxification of copper, the marine alga Ulva compressa was cultivated with increasing concentrations of copper such as 2.5, 5, 7.5 and 10 μM for up to 12 d, and the amount of intracellular copper, glutathione (GSH), phytochelatins (PCs) and transcripts encoding three metallothioneins (MTs) were determined. Over this exposure period and concentration range there was a linear correlation between intracellular copper and the copper concentration in the culture medium. Increases in GSH concentrations occurred mainly between days 1 and 3 and at lower concentrations of copper (2.5 and 5 μM). The level of PCs, and particularly PC2, increased from day 1 of exposure mainly at higher concentrations of copper (7.5 and 10 μM). The levels of transcripts encoding MT7 increased at day 3, whereas those of MT3 and MT6 increased between days 9-12, mainly at higher concentrations of copper. Thus in U. compressa, the initial responses to increasing intracellular copper concentrations are increases in GSH and PCs that are followed by higher levels of MTs expression, suggesting that thiol-containing peptides and proteins may participate in copper accumulation and detoxification responding in a coordinated and complementary manner. In addition, the alga was cultivated with 10 μM copper for 5 d and transferred to synthetic seawater with no copper and cultivated for 3 d. The release of copper from cells to culture medium was observed and accompanied by a similar nanomolar amount of GSH; no PCs or small proteins were detected. These results could suggest that a component of the detoxification mechanism also involves the release of copper and GSH to the extracellular medium.

A Supercomplex, of Approximately 720 kDa and Composed of Both Photosystem Reaction Centers, Dissipates Excess Energy by PSI in Green Macroalgae Under Salt Stress

The thylakoid membranes of plants play a critical role in electron transfer and energy fixation, and are highly dynamic. So far, studies on the thylakoid membranes have mainly focused on microalgae and higher plants, yet very little information is available on the macroalgal thylakoids. Here, we studied the structure and organization of the thylakoid membranes in Ulva prolifera, a representative species of the green macroalgae. We found that U. prolifera had few but long loosely stacked membranes which lack the conventional grana found in higher plants. However, the thylakoid membrane complexes demonstrate lateral heterogeneity. Moreover, we found a supercomplex composed of PSII, light-harvesting complex II (LHCII) and PSI from U. prolifera under salt stress. The supercomplex is approximately 720 kDa, and includes the two important photoprotection proteins, the PSII S subunit (PsbS) and the light-harvesting complex stress-related protein (LhcSR), as well as xanthophyll cycle pigments (violaxanthin, antheraxanthin and zeaxanthin). Time-resolved fluorescence analysis suggested that, in the supercomplex, excitation energy could efficiently be transferred from PSII to PSI, even when PSII was inhibited, a function which disappeared when the supercomplex was incubated in mild detergent. We suggest that the supercomplex might be an important mechanism to dissipate excess energy by PSI in green macroalgae under salt stress.

Fatty Acid Composition and Thermotropic Behavior of Glycolipids and Other Membrane Lipids of Ulva lactuca (Chlorophyta) Inhabiting Different Climatic Zones

Increasing global temperatures are expected to increase the risk of extinction of various species due to acceleration in the pace of shifting climate zones. Nevertheless, there is no information on the physicochemical properties of membrane lipids that enable the adaptation of the algae to different climatic zones. The present work aimed to compare fatty acid composition and thermal transitions of membrane lipids from green macroalgae Ulva lactuca harvested in the Sea of Japan and the Adriatic Sea in summer. U. lactuca inhabiting the Adriatic Sea had bleached parts of thalli which were completely devoid of chloroplast glycolipids. The adaptation to a warmer climatic zone was also accompanied by a significant decrease in the ratio between unsaturated and saturated fatty acids (UFA/SFA) of membrane lipids, especially in bleached thalli. Hence, bleaching of algae is probably associated with the significant decrease of the UFA/SFA ratio in glycolipids. The decreasing ratio of n-3/n-6 polyunsaturated fatty acids (PUFAs) was observed in extra-plastidial lipids and only in the major glycolipid, non-lamellar monogalactosyldiacylglycerol. The opposite thermotropic behavior of non-lamellar and lamellar glycolipids can contribute to maintenance of the highly dynamic structure of thylakoid membranes of algae in response to the increasing temperatures of climatic zones.

Introgression of UfCyt c6, a thylakoid lumen protein from a green seaweed Ulva fasciata Delile enhanced photosynthesis and growth in tobacco

Cytochromes are important components of photosynthetic electron transport chain. Here we report on genetic transformation of Cytochrome c6 (UfCyt c6) gene from Ulva fasciata Delile in tobacco for enhanced photosynthesis and growth. UfCyt c6 cDNA had an open reading frame of 330 bp encoding a polypeptide of 109 amino acids with a predicted molecular mass of 11.65 kDa and an isoelectric point of 5.21. UfCyt c6 gene along with a tobacco petE transit peptide sequence under control of CaMV35S promoter was transformed in tobacco through Agrobacterium mediated genetic transformation. Transgenic tobacco grew normal and exhibited enhanced growth as compared to wild type (WT) and vector control (VC) tobacco. Transgenic tobacco had higher contents of photosynthetic pigments and better ratios of photosynthetic pigments. The tobacco expressing UfCyt c6 gene exhibited higher photosynthetic rate and improved water use efficiency. Further activity of the water-splitting complex, photosystem II quantum yield, photochemical quenching, electron transfer rate, and photosynthetic yield were found comparatively higher in transgenic tobacco as compared to WT and VC tobacco. Alternatively basal quantum yield of non-photochemical processes in PSII and non-photochemical quenching were estimated lower in tobacco expressing UfCyt c6 gene. As a result of improved photosynthetic performance the transgenic tobacco had higher contents of sugar and starch, and exhibited comparatively better growth. To the best of our knowledge this is the first report on expression of UfCyt c6 gene from U. fasciata for improved photosynthesis and growth in tobacco.

Introgression of UfCyt c6, a thylakoid lumen protein from a green seaweed Ulva fasciata Delile enhanced photosynthesis and growth in tobacco

Cytochromes are important components of photosynthetic electron transport chain. Here we report on genetic transformation of Cytochrome c₆ (UfCyt c₆) gene from Ulva fasciata Delile in tobacco for enhanced photosynthesis and growth. UfCyt c₆ cDNA had an open reading frame of 330 bp encoding a polypeptide of 109 amino acids with a predicted molecular mass of 11.65 kDa and an isoelectric point of 5.21. UfCyt c₆ gene along with a tobacco petE transit peptide sequence under control of CaMV35S promoter was transformed in tobacco through Agrobacterium mediated genetic transformation. Transgenic tobacco grew normal and exhibited enhanced growth as compared to wild type (WT) and vector control (VC) tobacco. Transgenic tobacco had higher contents of photosynthetic pigments and better ratios of photosynthetic pigments. The tobacco expressing UfCyt c₆ gene exhibited higher photosynthetic rate and improved water use efficiency. Further activity of the water-splitting complex, photosystem II quantum yield, photochemical quenching, electron transfer rate, and photosynthetic yield were found comparatively higher in transgenic tobacco as compared to WT and VC tobacco. Alternatively basal quantum yield of non-photochemical processes in PSII and non-photochemical quenching were estimated lower in tobacco expressing UfCyt c₆ gene. As a result of improved photosynthetic performance the transgenic tobacco had higher contents of sugar and starch, and exhibited comparatively better growth. To the best of our knowledge this is the first report on expression of UfCyt c₆ gene from U. fasciata for improved photosynthesis and growth in tobacco.

Metabolic responses of Ulva compressa to single and combined heavy metals

Accumulation of metals and metabolic responses were studied for two Cd and Cu concentrations (1 and 10 μM) either alone or as a combination in marine macroalga after 7 days of exposure. Cd accumulated more at a low dose (115 μg of Cd/g DW) but Cu at a high dose (378 μg of Cu/g DW); Cu suppressed Cd accumulation (by 57%). Na and Zn levels were unaffected, but higher metal doses depleted K and Ca levels. Higher metal concentrations strongly stimulated reactive oxygen species and depleted nitric oxide (NO) formation, but differences between the action of Cd and Cu were not extensive. Higher metal doses increased cell wall thickness with a potential relation to NO signal that is visible mainly in the apoplast in those treatments. A higher Cu dose depleted proline, ascorbic acid, and phenol levels more than Cd, whereas Cd elevated nonprotein thiols and ascorbic acid in combined treatments. An eventual role of malic or citric acid in metal chelation was not evident: malic acid level decreased in all treatments. The total content of fatty acids reached 16.7 mg/g DW in control with the quantitative order of PUFAs > SFAs > MUFAs; palmitic, vaccenic, linoleic, and α-linolenic acids were the major compounds. Cu was more toxic for fatty acids than Cd (even at 1 μM); mainly, PUFA levels strongly decreased (from 43% of total acids in control to 28.9% and 5.4% at 1 and 10 μM Cu treatment, respectively). Results are precisely and critically discussed in relation to limited literature focused on macroalgae, and a comparison with microalgae is also provided.

Copper-induced increased expression of genes involved in photosynthesis, carotenoid synthesis and C assimilation in the marine alga Ulva compressa

BACKGROUND

The marine alga Ulva compressa is the dominant species in coastal areas receiving effluents from copper mines. The alga can accumulate high amounts of copper and possesses a strong antioxidant system. Here, we performed short-term transcriptomic analyses using total RNA of the alga cultivated with 10 μM of copper for 0, 3, 6, 12 and 24 h by RNA-seq.

RESULTS

De novo transcriptomes were assembled using the Trinity software, putative proteins were annotated and classified using Blast2GO. Differentially expressed transcripts were identified using edgeR. Transcript levels were compared by paired times 0 vs 3, 0 vs 6, 0 vs 12 and 0 vs 24 h at an FDR < 0.01 and Log2 Fold Change > 2. Up-regulated transcripts encode proteins belonging to photosystem II (PSII), Light Harvesting II Complex (LHCII), PSI and LHCI, proteins involved in assembly and repair of PSII, and assembly and protection of PSI. In addition, transcripts encoding enzymes leading to β-carotene synthesis and enzymes belonging to the Calvin-Benson cycle were also increased. We further analyzed photosynthesis and carotenoid levels in the alga cultivated with 10 μM of copper for 0 to 24 h. Photosynthesis was increased from 3 to 24 h as well as the level of total carotenoids. The increase in transcripts encoding enzymes of the Calvin-Benson cycle suggests that C assimilation may also be increased.

CONCLUSIONS

Thus, U. compressa displays a short-term response to copper stress enhancing the expression of genes encoding proteins involved in photosynthesis, enzymes involved carotenoids synthesis, as well as those belonging to the Calvin-Benson cycle, which may result in an increase in C assimilation.

Diet-dependent gene expression highlights the importance of Cytochrome P450 in detoxification of algal secondary metabolites in a marine isopod

Isopods of the genus Idotea have an unusual ability to feed on algae containing high amounts of chemical defense molecules, such as species of the genera Fucus and Ulva. In this study, we compared gene expression patterns of Idotea balthica individuals fed with Fucus vesiculosus to individuals fed with Ulva lactuca. We generated the first-ever transcriptome assembly for this species, and found 3,233 differentially expressed genes across feeding regimes. However, only a handful of biological functions were enriched with regard to differentially expressed genes, the most notable being "alkaloid metabolic process". Within this category, we found eight differentially expressed cytochrome P450 (CYP) unigenes, all of which had a higher expression in the U. lactuca diet treatment. A phylogenetic analysis showed that the differentially expressed CYP genes are closely related to a CYP gene described from the hepatopancreas of the spiny lobster Panulirus argus, and we hypothesize that these transcripts are involved in metabolite detoxification. This is a first step in the understanding of this algae-grazer interaction, and will form a basis for future work to characterize cytochrome P450 functioning in marine crustaceans.

Photoperiod mediates the effects of elevated CO2 on the growth and physiological performance in the green tide alga Ulva prolifera

Ulva spp., an increasingly important food, are the dominant species of the large-scale green tides. In this study, both the growth and the physiological responses of the Ulva prolifera were studied after cultured in three different light and dark regimes (12:12, 14:10 and 16:8-h light/dark) in combination with current (420 μatm; LC) and increased (1000 μatm; HC) levels of atmospheric CO₂. Grown rate of U. prolifera was significantly enhanced by increased CO₂ under the three light:dark regimes, especially under 16:8 h-light:dark, indicating that growth was C-unsaturated at present CO₂ levels. U. prolifera showed a significantly higher growth rate and lower dark respiration rate (R_d) at 16:8 h-light:dark treatment than at 12:12 h-light/dark treatment, regardless of the CO₂ treatment. The photochemical performance was largely unaffected by elevated CO₂ and daylength. These results suggest that U. prolifera in a future CO₂ enriched coastal water, seems to be resilient to higher CO₂ concentrations, and this could be enhanced by longer daylength.

Statistical optimization for cadmium removal using Ulva fasciata biomass: Characterization, immobilization and application for almost-complete cadmium removal from aqueous solutions

Cadmium is a global heavy metal pollutant. Marine green algae were used as efficient, low cost and eco-friendly biosorbent for cadmium ions removal from aqueous solutions. Plackett-Burman design was applied to determine the most significant factors for maximum cadmium removal from aqueous solutions using dry Ulva fasciata biomass. The most significant factors affecting cadmium removal process were further optimized by the face centered central composite design. The results indicated that 4 g of dry Ulva fasciata biomass was found to successfully remove 99.96% of cadmium from aqueous solution under the conditions of 200 mg/L of initial cadmium concentration at pH 5, 25 °C for 60 min of contact time with static condition. Dry Ulva fasciata biomass samples before and after cadmium biosorption were analyzed using SEM, EDS and FTIR. Furthermore, the immobilized biomass in sodium alginate-beads removed 99.98% of cadmium from aqueous solution at an initial concentration of 200 mg/L after 4 h which is significantly higher than that for control using sodium alginate beads without incorporation of the algal biomass (98.19%). Dry biomass of Ulva fasciata was proven to be cost-effective and efficient to eliminate heavy metals especially cadmium from aquatic effluents and the process is feasible, reliable and eco-friendly.